High NOX Smog 1977 Seville Ideas

[Bloo]

Historic plates or not, I think you will be able to solve this with the suggestions posted early in the thread, starting with EGR.

[MarkV]

3 hours ago, Pfeil said:

From the California Bureau of Automotive Repair;

Collector Cars

What is a collector car?

A collector car is used primarily in shows, parades, charitable functions, and historical exhibitions for display, maintenance, and preservation. It cannot be a vehicle used primarily for transportation. (Vehicle Code section 259)

Are there any requirements to qualify a vehicle as a collector car?

Yes. The vehicle must be insured as a collector car and must meet one of the following requirements:

• The vehicle is at least 35 model-years old. (Health and Safety Code section 44011)
• The vehicle is at least 25 model-years old with historical vehicle license plates. (Vehicle Code section 5004)
• The vehicle is classified as a special interest vehicle. (Vehicle Code section 5051(a-b))

What is a historical vehicle license plate?

A historical vehicle license plate is issued by the California Department of Motor Vehicles (DMV) to a vehicle of historic interest that was manufactured after 1922 and is at least 25 model-years old. (Vehicle Code section 5004)

What is a special interest vehicle?

A special interest vehicle is one that is collected, preserved, restored, or maintained by a hobbyist. The vehicle must not be altered from the manufacturer’s original specifications. (Vehicle Code section 5051(b))

Can a specially constructed vehicle qualify as a collector car?

No. A specially constructed vehicle (e.g., kit car) is built for private use, not for resale, and is not constructed by a licensed manufacturer or remanufacturer. (Vehicle Code section 580; Health and Safety Code section 44017.4)

Can a grey market vehicle qualify as a collector car?

No. A grey market (i.e., direct import) vehicle is not manufactured to meet U.S. federal motor vehicle safety standards and/or California emissions standards, and is not intended by the manufacturer to be used or sold in the U.S. For more information on grey market vehicles, visit the California Air Resources Board’s Frequently Asked Questions page.

Do collector cars require a Smog Check?

Collector cars that are model-year 1976 and newer require a Smog Check and are eligible for an abbreviated inspection performed by a state Referee. All vehicles that are model-year 1975 and older do not require a Smog Check. (Health and Safety Code sections 44011(c) and 44012(f))

 

they still do the tail pipe which doesn’t help me.

[MarkV]

23 minutes ago, Bloo said:

Historic plates or not, I think you will be able to solve this with the suggestions posted early in the thread, starting with EGR.

Which is what we did, as a result of the egr functioning we have high CO 

[nickelroadster]

I had problems on an early EGR valve on a 1978  Toyota pickup.  It was taken off twice and the second time I made sure all the passages leading to it were clean of any deposits and it wasn't hanging up while working.  It does sort of have moving parts without any lubrication.

[Pfeil]

4 hours ago, MarkV said:

they still do the tail pipe which doesn’t help me.

I know that's why I posted this,

Collector Cars

What is a collector car?

A collector car is used primarily in shows, parades, charitable functions, and historical exhibitions for display, maintenance, and preservation. It cannot be a vehicle used primarily for transportation. (Vehicle Code section 259)

Are there any requirements to qualify a vehicle as a collector car?

Yes. The vehicle must be insured as a collector car and must meet one of the following requirements:

• The vehicle is at least 35 model-years old. (Health and Safety Code section 44011)
• The vehicle is at least 25 model-years old with historical vehicle license plates. (Vehicle Code section 5004)
• The vehicle is classified as a special interest vehicle. (Vehicle Code section 5051(a-b))

What is a historical vehicle license plate?

A historical vehicle license plate is issued by the California Department of Motor Vehicles (DMV) to a vehicle of historic interest that was manufactured after 1922 and is at least 25 model-years old. (Vehicle Code section 5004)

What is a special interest vehicle?

A special interest vehicle is one that is collected, preserved, restored, or maintained by a hobbyist. The vehicle must not be altered from the manufacturer’s original specifications. (Vehicle Code section 5051(b))

Can a specially constructed vehicle qualify as a collector car?

No. A specially constructed vehicle (e.g., kit car) is built for private use, not for resale, and is not constructed by a licensed manufacturer or remanufacturer. (Vehicle Code section 580; Health and Safety Code section 44017.4)

Can a grey market vehicle qualify as a collector car?

No. A grey market (i.e., direct import) vehicle is not manufactured to meet U.S. federal motor vehicle safety standards and/or California emissions standards, and is not intended by the manufacturer to be used or sold in the U.S. For more information on grey market vehicles, visit the California Air Resources Board’s Frequently Asked Questions page.

Do collector cars require a Smog Check?

Collector cars that are model-year 1976 and newer require a Smog Check and are eligible for an abbreviated inspection performed by a state Referee. All vehicles that are model-year 1975 and older do not require a Smog Check. (Health and Safety Code sections 44011(c) and 44012(f))

[Pfeil]

4 hours ago, MarkV said:

Which is what we did, as a result of the egr functioning we have high CO 

Get the car on the FWY for about an hour at about 70-75mph, take it back to the shop immediately and run the test immediately!

[EmTee]

4 minutes ago, Pfeil said:

Get the car on the FWY for about an hour at about 70-75mph, take it back to the shop immediately and run the test immediately!

What's the rationale for this recommendation?  EGR is now presumed functional.  Why didn't it pass the retest?

[MarkV]

13 minutes ago, EmTee said:

What's the rationale for this recommendation?  EGR is now presumed functional.  Why didn't it pass the retest?

Now with the egr functional the CO went up to 2.0 it has to be .8. 

[EmTee]

So now the engine is running too rich?

[John348]

Could that be something as simple as a dirty air filter?

[Pfeil]

47 minutes ago, EmTee said:

What's the rationale for this recommendation?  EGR is now presumed functional.  Why didn't it pass the retest?

Converter loaded up- CO too high, let it get good and hot on the FWY to clear it out.

[Pfeil]

36 minutes ago, MarkV said:

Now with the egr functional the CO went up to 2.0 it has to be .8. 

It should be lower even though they give you .8 %

[MarkV]

10 minutes ago, Pfeil said:

Converter loaded up- CO too high, let it get good and hot on the FWY to clear it out.

do you think it’s because the EGR has been non functional for a while? 

[Bloo]

5 hours ago, MarkV said:

6 hours ago, Bloo said:

 

Which is what we did, as a result of the egr functioning we have high CO 

That just isn't how that works. EGR is inert, more or less. It does take up space in the cylinder, so in theory it should get slightly richer, but in practice the difference is negligible. While I believe pfeils idea of cleaning the cat out might get it to pass, I don't believe it should be 2.0 going INTO the cat let alone coming out. 0.7 going into the cat is more like it, and less at the tailpipe. You have a fuel mixture problem to troubleshoot now. It is a little bit too rich.

 

Is the NOx number OK now?

 

Which test did it fail CO in? Both?

 

 

[pfloro]

Unfortunately, this ancient analog FI system is going to be difficult to troubleshoot.  

 

It was standard equipment on only 1 expensive model from 1 division from 1 manufacturer for 4 years. The Seville used it from 1976 - 1979 for all 50 states. It was also standard for CA Sevilles in 1980.  GM did offer it as an option in '75 & '76 models with the 500 cu. in. engines and through 1979 with the 425. 

 

A few years back, I read that GM did publish a supplemental service manual for this analog FI system.  I have not been able to find anymore information about it.  Getting your hands on this manual would be very helpful.

 

Specialized test equipment was made to service this system.  I'm sure it's as rare as hen's teeth.

 

I suspect that many of the system's key parts are difficult to obtain. 

 

GM completely abandoned this system in 1980 when their throttle body DFI came into use.  By 1981, CCC (Computer Command Control) was standard on almost the entire GM line (both carbureted or TBI). 

 

***

 

I really hate to cast a dark shadow over this situation and I hope that I'm wrong...  

 

Paul

 

Helpful Links:   GM Analog FI

                          Info 01

                          Info 02

                          Info 03

                          Info 04

 

 

Edited April 17, 2022 by pfloro (see edit history)

[Pfeil]

2 hours ago, MarkV said:

do you think it’s because the EGR has been non functional for a while? 

Nope.

[Pfeil]

2 hours ago, Bloo said:

That just isn't how that works. EGR is inert, more or less. It does take up space in the cylinder, so in theory it should get slightly richer, but in practice the difference is negligible. While I believe pfeils idea of cleaning the cat out might get it to pass, I don't believe it should be 2.0 going INTO the cat let alone coming out. 0.7 going into the cat is more like it, and less at the tailpipe. You have a fuel mixture problem to troubleshoot now. It is a little bit too rich.

 

Is the NOx number OK now?

 

Which test did it fail CO in? Both?

 

 

Just seems ironic EGR is fixed and now we have a CO problem. Also, a little ironic the hoses on EGR were crossed. Who crossed them? This is why I do everything myself because that way I know no one has been messing about. A tech could screw up a car on a guy and all he would have to do is turn around for a few seconds. I smell a mystery here; sure, it could be the FI and it probably is, but I have my doubts what happened and how it got that way especially looking at those numbers from the first test.

Edited April 17, 2022 by Pfeil (see edit history)

[Pfeil]

1 hour ago, pfloro said:

Unfortunately, this ancient analog FI system is going to be difficult to troubleshoot.  

 

It was standard equipment on only 1 expensive model from 1 division from 1 manufacturer for 4 years. The Seville used it from 1976 - 1979 for all 50 states. It was also standard for CA Sevilles in 1980.  GM did offer it as an option in '75 & '76 models with the 500 cu. in. engines and through 1979 with the 425. 

 

A few years back, I read that GM did publish a supplemental service manual for this analog FI system.  I have not been able to find anymore information about it.  Getting your hands on this manual would be very helpful.

 

Specialized test equipment was made to service this system.  I'm sure it's as rare as hen's teeth.

 

I suspect that many of the system's key parts are difficult to obtain. 

 

GM completely abandoned this system in 1980 when their throttle body DFI came into use.  By 1981, CCC (Computer Command Control) was standard on almost the entire GM line (both carbureted or TBI). 

 

***

 

I really hate to cast a dark shadow over this situation and I hope that I'm wrong...  

 

Paul

 

Helpful Links:   GM Analog FI

                          Info 01

                          Info 02

                          Info 03

                          Info 04

 

 

Illegally but, I have seen a few Q jet's Olds 4bbl. manifolds on Seville's. Always thought it was an easy way out of a problem but n/a FI parts availability explains some of it I suppose. I believe manufacturers are only required to have parts on hand for eight years. It used to be ten but manufacturers lobbied the gov. for eight because the gov started taxing them on inventory. In the end it's always us that get it in the end. 

[Bloo]

High CO is just too much fuel. There is no other explanation. I would start by being sure the MAP or vacuum sensor is plumbed to the manifold via hoses that FIT TIGHT, do NOT LEAK, and show no signs of sucking flat. I would check fuel pressure. I would pull the rubber hose (which also must be tight and not leak) off the fuel regulator and make sure that the pressure gauge rises, and also that it is not leaking fuel into the rubber hose. Good luck and let us know how it goes.

 

 

[EmTee]

6 hours ago, Bloo said:

I would start by being sure the MAP or vacuum sensor is plumbed to the manifold via hoses that FIT TIGHT, do NOT LEAK, and show no signs of sucking flat.

Agree - I fixed a rich condition years ago on my father's '83 Eldorado that turned out to be a deteriorated vacuum hose to the MAP sensor.  Computer thought manifold vacuum was low, so it added more fuel...

[pfloro]

Yes... as both Bloo and Emtee stated, a leaking vacuum hose connected to the MAP sensor will fool the ECU into thinking that the engine is under more load and requires more fuel (low vacuum = high manifold pressure). 

 

On this analog FI system, the MAP sensor is part of the ECU which is inside behind the center of the dash.  This sensor was made by Bosch (I believe) and is not a stand alone service item.  The MAP's vacuum hose runs from the throttle body through the firewall to the ECU.  It's bundled with the ECU's wiring harness. There is also a short "jumper" vacuum hose within the ECU which connects to the actual MAP sensor.  I would replace every inch of this critically important hose.  Hey, your Seville is 45 years old...! 

 

As was stated, measure the fuel pressure at the rail.  It should be ~39 psi. Higher pressure will cause more fuel to be metered into the cylinders during the injector's pulse.  

 

The coolant temperature sensor or it's wiring could be messed up. This sensor has no moving parts and is a thermister. It changes resistance based upon temperature. If the ECU thinks the engine is not fully warmed up, It will add more fuel (longer injector pulses).

 

The ambient air temperature sensor functions like the coolant temperature sensor. 

 

The throttle position sensor (Bendix made) could also be creating the rich running situation. If the ECU thinks the throttle is opened more than it actually is, additional fuel will be metered into the cylinders.

 

***

 

In many ways, this is a simple FI system.  There is no O2 sensor which means there is no feedback loop.  The fuel delivery is based upon sensor input and "look up" tables burned into the ECUs chips.

 

Try to source that supplemental FI service manual...!

 

Paul

 

 

 

Edited April 17, 2022 by pfloro (see edit history)

[John348]

 Why was the CO reading lower prior to the EGR repair? That is what is confusing me 

Edited April 17, 2022 by John348 (see edit history)

[pfloro]

3 hours ago, John348 said:

Why was the CO reading lower prior to the EGR repair? That is what is confusing me

My gut tells me that these 2 abnormally high emissions are unrelated. Other posters have said the same thing.

 

Introducing a small amount of non-combustible exhaust will dilute the air/fuel charge and lower the flame temperature. It won't cause the raw hydrocarbons to burn less completely and generate CO.  I believe this only happens when all the O2 is consumed during the combustion event while partially burned HCs are still present. In this situation, CO is formed instead of CO2. 

 

I suspect that the sensors, the wiring/electrical connections/vacuum hoses, and maybe the ECU are marginal.  Perhaps the fuel pressure is spiking on occasion.  Things are getting randomly flaky.  I bet that most or all of the components of this FI system are 45 years old. 

 

I would like to see the printout from the 2nd test (normal NOx & high CO).  I'd also like to know when the car last passed smog.  Present odometer reading...?

 

MarkV:  Can you provide more information...?

 

Thanks,

 

Paul

 

 

Edited April 17, 2022 by pfloro (see edit history)

[Bloo]

3 hours ago, pfloro said:

My gut tells me that these 2 abnormally high emissions are unrelated. Other posters have said the same thing.

 

Introducing a small amount of non-combustible exhaust will dilute the air/fuel charge and lower the flame temperature. It won't cause the raw hydrocarbons to burn less completely and generate CO.  I believe this only happens when all the O2 is consumed during the combustion event while partially burned HCs are still present. In this situation, CO is formed instead of CO2. 

This exactly.^^

 

 

Edited April 18, 2022 by Bloo (see edit history)

[MarkV]

3 hours ago, pfloro said:

My gut tells me that these 2 abnormally high emissions are unrelated. Other posters have said the same thing.

 

Introducing a small amount of non-combustible exhaust will dilute the air/fuel charge and lower the flame temperature. It won't cause the raw hydrocarbons to burn less completely and generate CO.  I believe this only happens when all the O2 is consumed during the combustion event while partially burned HCs are still present. In this situation, CO is formed instead of CO2. 

 

I suspect that the sensors, the wiring/electrical connections/vacuum hoses, and maybe the ECU are marginal.  Perhaps the fuel pressure is spiking on occasion.  Things are getting randomly flaky.  I bet that most or all of the components of this FI system are 45 years old. 

 

I would like to see the printout from the 2nd test (normal NOx & high CO).  I'd also like to know when the car last passed smog.  Present odometer reading...?

 

MarkV:  Can you provide more information...?

 

Thanks,

 

Paul

 

 

ECU was rebuilt two years ago

It passed two years ago and two years before that 

it’s not all 45 years old I’ve replaced most everything through the years.

 

im thinking it could be a vacuum leak to the ecu map. Car runs flawless. 

[MarkV]

Odometer- 39000. I had the camshaft and lifters replaced with stock ones many years ago (lobe was flattened). All the seals were replaced when this was done. 

[Pfeil]

On 4/15/2022 at 1:08 PM, MarkV said:

Good news looks like the hoses were routed wrong to the EGR. So no vacuum was going there at all! I’m taking it back later to be smogged

The first thing you said was " So I took my 77 in which passed smog fine two years ago, any ideas as to what could be wrong? The smog tech mentioned EGR"

 

So, the question I have is. Who has touched this engine from two years ago until the smog people ran the test????? Who crossed the hoses? Who may have played with the engine on the retest?????? Did you watch these guys perform the two test????

I'm telling you (especially for a collector car) you've got to watch your peas and cues all the time! 

[MarkV]

54 minutes ago, Pfeil said:

The first thing you said was " So I took my 77 in which passed smog fine two years ago, any ideas as to what could be wrong? The smog tech mentioned EGR"

 

So, the question I have is. Who has touched this engine from two years ago until the smog people ran the test????? Who crossed the hoses? Who may have played with the engine on the retest?????? Did you watch these guys perform the two test????

I'm telling you (especially for a collector car) you've got to watch your peas and cues all the time! 

The only things I had done was the ac had to be sealed and refilled and that was it. I was not there the last time I had it tested as it was at a repair shop. I’ll bet they did some voodoo to get it passed. But two years before it passed fine. It’s strange 

[Pfeil]

3 minutes ago, MarkV said:

The only things I had done was the ac had to be sealed and refilled and that was it. I was not there the last time I had it tested as it was at a repair shop. I’ll bet they did some voodoo to get it passed. But two years before it passed fine. It’s strange 

So let me get this straight.

No one touched the car except the AC people in between the test two years ago and the first of the recent test?

You take the car in for smog this time and the EGR hoses are mysteriously crossed so that the EGR will not function-but they test the car anyway, The CO and HC are perfect but NOX is off the chart, fail.

You bring the car back to them and they connect the EGR vacuum hoses properly and it passes NOX but fails CO.

You just drop your car off and don't observe them working on your car?

[EmTee]

Maybe the shop owner has a boat payment coming up?

[60FlatTop]

I was thinking about this NOX problem during some windshield time. The report shows the air injection pump passed inspection. I wonder if that means it was there visually but not checked functionally. If I wanted to get high NOX numbers I would block the A. I. R. diverter valve to constantly flow through the manifold ports. This may be what is happening. Things get stuck on collector cars.

 

Having an inspector tell you to go through some gyrations under the full moon is pretty crappy advice. Something is broken and it needs to be fixed. One of my frequent troubleshooting techniques is to ask myself how I could create this condition if I wanted to. It works quite well.

[John348]

I was thinking that one of the brittle plastic ports broke of a sensor causing a leak when someone was poking around with the EGR faking out the ECU causing a lean condition. It just seems too coincidental/accidental  

[MarkV]

12 hours ago, Pfeil said:

So let me get this straight.

No one touched the car except the AC people in between the test two years ago and the first of the recent test?

You take the car in for smog this time and the EGR hoses are mysteriously crossed so that the EGR will not function-but they test the car anyway, The CO and HC are perfect but NOX is off the chart, fail.

You bring the car back to them and they connect the EGR vacuum hoses properly and it passes NOX but fails CO.

You just drop your car off and don't observe them working on your car?

There are four shops at play here 

shop 1: doesn’t do smog just repairs, they found the egr vacuum hose fixed for free they did the ac too.

shop 2: smog only he did the retest for free and told me to drive it around. 
shop 3: sent it out to be smogged at another shop, two years ago, they had to adjust the timing that was it. I have a feeling they crossed something.

 

I replaced the air pump about 4 years ago 

egr was also replaced. 
 

im thinking it’s a bad injector or a vacuum issue.

[Pfeil]

2 hours ago, 60FlatTop said:

I was thinking about this NOX problem during some windshield time. The report shows the air injection pump passed inspection. I wonder if that means it was there visually but not checked functionally. If I wanted to get high NOX numbers I would block the A. I. R. diverter valve to constantly flow through the manifold ports. This may be what is happening. Things get stuck on collector cars.

 

Having an inspector tell you to go through some gyrations under the full moon is pretty crappy advice. Something is broken and it needs to be fixed. One of my frequent troubleshooting techniques is to ask myself how I could create this condition if I wanted to. It works quite well.

Here is what happens when the AI pump is diverted or disconnected or removed on a two way catalytic converter car. CO and HC become richer for two reasons. 1. injecting air into the exhaust manifold helps combustion after the fact (what happens in the combustion chamber) because we all know combustion in the combustion chamber does not combust all the mixture. 2. the air pump supplies enough O2 to help the catalytic converter light off ( like when you blow on coal in the fire place you make them glow red hot).

 

I must say something about AIR or Air Injection Reactor. There are two types. The first type pointed an air nozzle from an air manifold directly into the combustion chamber pointed at the exhaust valve. We first saw this in 1966 and this type decreased the life expectancy of exhaust valves. The second type ( like my 76 Olds) just injects air in the exhaust manifold. AIR is crucial to the life of the catalytic converter.

[edinmass]

 

Back in the day, we just replaced all the hoses every few years, as most of the hoses were of very poor quality and just didn't hold up well. Seems like the new stuff today is much better. We only installed Goodyear rubber in the shop at that time. Also the vacuum T's are subject to crack and leak........so a hose that looks fine must still be checked for the entire length. Today, I would use a smoke machine to test the entire system. (Check the brake booster for leaks also.)The old chase the numbers emission game was classic........fix one, and another goes out of range. Brings back my early days of fixing cars when I didn't know much........and needed assistance for almost every job. Remember punching out the plugs on the GM carbs so you could adjust them? I expect today on the show field 99 percent of the carbs have been modified. I still have the Snap On J shaped mixture adjustment tool somewhere..........haven't laid hands on it since the early 90's. 

Edited April 18, 2022 by edinmass (see edit history)

[Pfeil]

13 minutes ago, MarkV said:

There are four shops at play here 

shop 1: doesn’t do smog just repairs, they found the egr vacuum hose fixed for free they did the ac too.

shop 2: smog only he did the retest for free and told me to drive it around. 
shop 3: sent it out to be smogged at another shop, two years ago, they had to adjust the timing that was it. I have a feeling they crossed something.

 

I replaced the air pump about 4 years ago 

egr was also replaced. 
 

im thinking it’s a bad injector or a vacuum issue.

Bad injector. are you dropping cylinders? A non functioning injector won't give you a high CO number. a open injector will flood you out.

Vacuum leak= High HC lean misfire.

[MarkV]

HC are low even on the retest

so possibly a bad injector? 

[Bloo]

8 hours ago, Pfeil said:

Here is what happens when the AI pump is diverted or disconnected or removed on a two way catalytic converter car. CO and HC become richer for two reasons. 1. injecting air into the exhaust manifold helps combustion after the fact (what happens in the combustion chamber) because we all know combustion in the combustion chamber does not combust all the mixture. 2. the air pump supplies enough O2 to help the catalytic converter light off ( like when you blow on coal in the fire place you make them glow red hot).

 

Exactly. You can also temporarily disable it in the shop to get a better idea of what is going IN to the converter. It will eventually light off without the AIR system probably but you can get an idea.

 

8 hours ago, Pfeil said:

Bad injector. are you dropping cylinders? A non functioning injector won't give you a high CO number. a open injector will flood you out.

Vacuum leak= High HC lean misfire.

 

Exactly right. The exception would be if the leak is in the line to the vacuum sensor, which would cause the system to richen the mixture.

 

11 hours ago, 60FlatTop said:

I wonder if that means it was there visually but not checked functionally. If I wanted to get high NOX numbers I would block the A. I. R. diverter valve to constantly flow through the manifold ports. This may be what is happening.

I don't believe this has a dual bed converter. Can anyone confirm or deny? I believe it is too old. Cars of this vintage normally dump air in the manifold ports most of the time.

 

8 hours ago, edinmass said:

Back in the day, we just replaced all the hoses every few years, as most of the hoses were of very poor quality and just didn't hold up well. Seems like the new stuff today is much better. We only installed Goodyear rubber in the shop at that time. Also the vacuum T's are subject to crack and leak........so a hose that looks fine must still be checked for the entire length.

 

I went through an unbelieveable amount of hose. So.... much..... hose.... I don't know if it was Goodyear or not but I was keeping some rubber company in business. I haven't really found the new stuff to be better, and vacuum caps are horrible. You don't get 6 months out of those sometimes. The old bolt in the end of a piece of hose trick, once a pet peeve of mine, doesn't look so crazy now (but I will still go out of my way to NOT do that).

 

8 hours ago, MarkV said:

im thinking it’s a bad injector or a vacuum issue.

 

I doubt the injector thing for reasons others have pointed out. Injectors can be sent out for ultrasonic cleaning and bench testing, and it is a good thing to do on older cars, or anything over 90k miles in my opinion. Most on-the-car options are snake oil, and even when they are not snake oil, there is no way to verify the effect of such a treatment. That said, do NOT do any of this expecting it to fix the problem you are having now. There is about a 99.993% chance it is NOT the issue. One way an injector could raise CO is if it were leaking. That should show up in the leakdown time when you check FUEL PRESSURE, and then could be verified by pulling the fuel rail and eyeballing it, probably, depending on how the injectors are attached to the rail.

 

There can be no vacuum leaks. Zero tolerance is appropriate here. This is the reason edinmass and I kept the American rubber industry in business. If there are leaks, you will be playing whack-a-mole with the emissions and also the driveability forever. Get one fixed and something else will pop up. This cannot be overstated. It doesn't go directly at your current problem though.

 

If I am remembering it correctly this is speed density system with NO CLOSED LOOP. Speed density means it calculates how much fuel to inject based on RPM, and intake manifold pressure (or vacuum). Like all cars there is some sort of a cold enrichment system for starting and warmup. No closed loop means there is no oxygen sensor, and the system will inject what is programmed, period. There is no self-correction.

 

So things to check, roughly in order of importance...

 

1) MAP, or vacuum sensor line. This cannot leak. Were these in the ECM? Check entire line with a vacuum pump. If it leaks down, find the leak and fix it.

 

2) Fuel regulator. Test fuel pressure. The service manual should have a value, Pull vacuum hose off regulator. Pressure should rise. Usually about 5psi, but whatever. There can be no gas in the vacuum hose, if there is gas, it is leaking through the regulator diaphragm and dumping gas directly in the intake manifold(!). It is a super common problem on EFI cars. Shut the car off. Most cars will drop pressure slightly, and then hold for a long time. Check the service manual to see what is appropriate here. Off the top of my head I would expect it to drop about 5 pounds when the engine shuts off and then hold for a long time. Leaks could be the fuel regulator, a leaky injector, or a worn out fuel pump. Mainly what you are looking for here is the simple part of pulling the vacuum hose and seeing the pressure rise and no gas in the vacuum hose, but since you have a gauge hooked up, check it all and write down what you find.

 

3) Coolant temperature sensor. You can probably find specifications for this in the service manual. Check ohms vs. ambient temperature, and check with a fully warm engine. This controls the cold enrichment. If you have the wrong resistance with the engine warmed up, either the sensor is bad or the coolant temperature is wrong. A bad thermostat or one of too low opening temperature could be to blame. I believe the system has an intake air temperature sensor, check it too.

 

4) Throttle position sensor. I imagine if it were bad you would have driveability issues, but make sure it is set correctly per the manual.

 

Edited April 19, 2022 by Bloo (see edit history)

[edinmass]

Bloo………this is bringing up fondly forgotten memories………..those early systems were a pain in the ass……but at least components were available back then for replacements. Today I avoid the 1975-1985 years like the plague. Sourcing stuff is just too time consuming. Worst part……almost no one wants to pay for your time…..and the actual time VS what you can bill still leaves you working cheap. All with the possibility’s of comebacks……..not related to any repairs done. Been there, done that. I rather spend 45 hours adjusting the valves on a Model J.

Edited April 18, 2022 by edinmass (see edit history)

[EmTee]

14 hours ago, Bloo said:

3) Coolant temperature sensor.

Yes, I've seen this problem also.  One hint I had in the past was that my '89 Silverado (TBI system) 'lost' its cold fast idle.  The sensor was always telling the ECU that the engine was warm.  It ran fine when hot, but I had to feather the throttle until the engine warmed-up, since the mixture was too lean.  Also, since this was happening during the 'open-loop' portion of the ECU program (and the sensor output was within the normal range) there was no MIL indication.  Maybe MarkV can think about this for a minute and let us know whether he's noticed any such subtle performance issues recently.