45 to 50mph Issue, Feels Like TC is locking and Unlocking

[Dashmaster]

Interesting Update

Ronnie, I unhooked the MAF, Car did not run as good. Drove it about a mile did not notice the issue but not running as good. Stopped and plugged in the MAF, Car Stalled, I turned off the key and restarted. Drove wonderfully, No issue at all, drove about 10 miles. On my way back I thought I should stop and turn it off for a minute or two and see if the problem is still solved, Nope Nada. Problem returned.

 

Here is some new information, The unplugged MAF did not set a code, I unplugged the EGR earlier today, Did not set a code and EGR light was flashing notmally in the ECM data screen.  The only think the ECM complain about is the Cruise, even though it plugged into a new unit.

 

I am starting to think the ECM may be bad. What do you think??

The ECM I have, I bought 2 years ago from the Reatta store when the original would not fire the injectors.

[Ronnie]

16 minutes ago, Dashmaster said:

I unhooked the MAF, Car did not run as good. Drove it about a mile did not notice the issue but not running as good. Stopped and plugged in the MAF, Car Stalled, I turned off the key and restarted. Drove wonderfully, No issue at all, drove about 10 miles. On my way back I thought I should stop and turn it off for a minute or two and see if the problem is still solved, Nope Nada. Problem returned.

 

I think the fact that unplugging the MAF made the problem go away for a while should be reason enough to try another MAF on it that is known to be good.

With the engine idling tap on the MAF and see if the engine stumbles. If it does the MAF is almost certain to be defective.  They are expensive new. I would get a couple from the junk yard and try them before spending a lot of money just to see if it corrects the problem.

 

It could be the ECM but I wouldn't spend the money on a ECM until you have eliminate all other possibilities - including re-seating the ECM connectors.. .

[Dashmaster]

I just rapped on it, No stumble or anything. Idle was steady.

[Dashmaster]

Since I was waiting for some parts last weekend, I decided to take a look at things I have not looked at yet. The Car was starting and idled fine I know the cam and crank sensors were working fine. I decided to remove the front cover and inspect everything. Timing chain had almost and inch of slack, tensioner was worn out Harmonic balancer was showing some dry rot cracks. I also have not changed anything on the cooling system. This weekend putting it back together, all new cooling system hoses including heater hoses, new thermostat. New Cloyes Timing set, New style timing tensioner also Cloyes 195, Fit fine in my 88, my block does not have counter bored hole, new oil pan gasket,new cam sensor magnet. Not sure this will resolve this problem but its going to help. Those heater hoses are a pain in the hands to put clamps on.

[Dashmaster]

Car back together,  No Leaks, The Dorman Balancer seems to wobble a little so I plan to put my original back on so I can have this one exchanged.

Test Drives, Had bad almost stalling taking off a couple of times, main issue is still present. I have tried another ECM so it is not an ECM problem.

unhooked the MAF and the stalling issue did not occur but the main issue was present. I am at a loss as what to check next. Its funny if you do wen searches for my issue and everything I have changed or checked is in those but I have not found one that ever posed a resolution.  

Any more suggestions???

[Dashmaster]

Put back on the original Harmonic balancer. Took it for another test drive. Still have the main issue. But did notice that when it happens the OX sensor reading goes to 0.

Now can anyone tell me if 0 is lean or rich?

I still see nothing from any of the ECM data items that change directly from this issue. 

[Ronnie]

Have you changed the O2 sensor?

[Dashmaster]

I did get a new one, installed it and ran like crap. I have not sent it back, Was supposed to be Delco but looked like a Bosch. The one it the car I got last year from the Reatta Store. I can try it again to see what it does. I am thinking the IAC may be at play here even though its rather new and been cleaned good. . Some think something is letting in to much OX when this happens since the reading goes to 0.

The OX sensor seem to be responding to the condition not the cause

Edited July 11, 2016 by Dashmaster (see edit history)

[padgett]

I do not think the original Delco O2 sensors are available and have been replaced by a AFS-21 or AFS-22. Key is you can remove the firewall side plugs with a Delco sensor in place but not a Bosch.

 

ps sensor that reads zero when warmed up is bad. I am more interested in transitions than values which is constantly varying from below .5 to above .5 (but never 1.0 or zero except when cold).

Edited July 11, 2016 by padgett (see edit history)

[Dashmaster]

I have no problem changing out OX sensor with plugs in. I have not tried to turn off any injectors and test. I had all of them out and cleaned them on my test bench. I know this does not test them in the car.

The OX reading only goes to 0 when this problem occurs, Readings look regular up and down 20's to 70's .

 

I have been trying to think what would make an OX senor read 0

 

[Ronnie]

If you suspect the O2 sensor is causing your problem you can unplug the electrical connector going to it and see if the problem goes away. Unplugging it will cause the engine to run in open loop just like it does when the engine is cold. You will probably get a code E013 set and maybe a message will be displayed but the engine should run just fine - assuming the O2 sensor is the problem.

 

If the engine runs good with the sensor disconnected either the sensor is bad or there is a problem with the connection between the sensor and the ECM. OR there could be a problem with the  ground for the O2 sensor at ECM terminal YD3. The FSM says the ground is via circuit 413, a TAN wire. Have you checked all ground connections?

[Dashmaster]

I have not tested it with it unplugged, will try tonight. I have the ECM down so I can easily get to the plugs. I have cleaned all grounds from under hood. I have not seen or done any inside the car. I will have to see which of the 3 plugs the Tan ground wire is in.

[2seater]

2 hours ago, Dashmaster said:

I have no problem changing out OX sensor with plugs in. I have not tried to turn off any injectors and test. I had all of them out and cleaned them on my test bench. I know this does not test them in the car.

The OX reading only goes to 0 when this problem occurs, Readings look regular up and down 20's to 70's .

 

I have been trying to think what would make an OX senor read 0

 

Zero is dead lean. In ordinary operation it should not get to that level. That said, I have seen momentary zero readings on my own, (primarily on coast down), although most of the chips I have been running are modified to some extent, so it may not be totally representative  Are there any exhaust leaks anywhere near the O2 sensor, or upstream? It sounds like you are correct that it is reacting rather than the cause. By the way, Bosch developed and brought the first automotive O2 sensor to market a long time ago. Just my own personal experience but have found little difference in operation between good quality, name brand,  sensors.

[padgett]

I once had an O2 sensor that would drop out at speed. When it did the TCC would unlock.

[Dashmaster]

TC unlocks like it should when you lift the throttle, problem starts after its in an unlocked state. I have verified TC  lockup with DVM.

Give it gas, TC locks up, problem stops car accelerates fine, Touch break to slow down problem stops. Its only when lifting the throttle to slow down to adjust speed. 

 

[Ronnie]

What does the Tach read when the problem is happening? Is it really low? I had a Fiero with similar symptoms. The torque converter clutch was mechanically sticking in the locked position even though the ECM was commanding it off. The problem started out with the the engine jerking some when I let off the gas like a straight shift car would when slowing down without downshifting. I finally figured out what was going on when the converter clutch failed to unlocked at all at a stop light and stalled the engine. Luckily I wasn't far from home. When I started it and jerked the shiftier in gear it unlocked it to get me home. I put in a can of transmission additive that cured the problem but I can't remember what it was. This was about 10 years ago.

 

This is a fairly common problem with the GM 3 speed automatics. I'm not sure about the 4 speed automatic like the Reatta has. You can do a search about it on the Internet if you want to read more about it..

 

You could test to see if that is your problem by unplugging the electrical connector going into the transmission so the converter never locks to begin with. Maybe the computer will pop up a warning but the transmission will still shift just fine. If the problem goes away you might have found your problem.

 

This may not be your problem, and I admit it is a long shot, but I'm just trying to think of anything I can to  help you solve your problem.

[Dashmaster]

Yes I did consider this very hard and I do appreciate all suggestions. I did a meter test from ADL connector in the car. and it confirms the operation with ECM. I can feel when it unlocks and locks The Brake switch provided a better ground reading than the ECM does when it unlocks. I will give this a test, I already know how to wire in my own lockup switch if needed.

If I don't get this solved the car may not make it to Allentown. 

[Ronnie]

I have a switch under the dash to break the circuit going to the converter to prevent it from locking. I prefer the torque converter to stay unlocked on curvy back roads. It makes the car feel more responsive in my opinion. I turn it on when I'm on fast 4 lane highways and Interstates to get better gas mileage.

[ChrisWhewell]

Try driving it in regular D (drive gear, NOT overdrive) ?   What does it do then ?   My first thought was TPS but you already have that handled.   It sounds like cruise control circuit, obviously, maybe, since its apparently been halfway on the fritz anyhow.   Is there such a thing as a cruise control module somewhere ?  Wish I could help more

[Dashmaster]

Tonight's Tests

1. OX sensor unplugged, Problem still exists!! So the OX sensor is reading the condition not causing it.

2. Trans electrical unplugged, Problem still the same, so the TC is not involved.

 

Since OX is reporting lean, The only other thing that can adjust fuel mixture is the MAF

The MAF sensor on the car I will assume is original or at least 10 years old, I do get readings for it in the ECM, tonight the reading were about 6.8 at idle into the 20's driving.

I did reset the IAC and its set at 79 with no throttle.

 

I guess I will order a MAF, I am thinking of trying the Walker.

Edited July 12, 2016 by Dashmaster (see edit history)

[Ronnie]

If it is the MAF is seems like the problem should go away when you unplug it. I thought I remembered you saying it didn't make a difference?

[padgett]

IAC should be .38-.42 at idle. I shoot for .39.   

.79 at idle will make it think the throttle is depressed slightly and may foul up the DFCO (Deceleration Fuel Cut Off).

[Dashmaster]

I did the IAC reset before test drive to make sure it was set by the ECM. My TPS is 3.8 at Idle.

The IAC was reading 79 off throttle and stays there off throttle.Car Idles fine at 750 RPM and varies very little. IAC steps up during driving. from 79. 

[Dashmaster]

Coolant Temperature was from cold 60 to 96 during these test. The system never went into closed loop during the OX test.

[2seater]

I make the assumption the decimal is in the wrong place on that tps setting? Is it .38?  The IAC counts can be any number really, but as long as they keep the rpm where needed, and increase with increased throttle, that all sounds normal. I am not certain the lack of O2 signal would prevent closed loop but it would be logical that it would, since the fuel mixture reference active in closed loop would be missing. So is that surging still present when in open loop? Do the IAC counts wobble around when the surging is happening? I need to take mine out for a spin after relocating the IAT sensor and some shrouding for the air filter, so I can see what mine does.

[Dashmaster]

TPS .38 not 3.8.  Yes ECM showed open loop, with OX unplugged, Car was up to 96 degrees shown from ECM. Problem still

occurred,  IAC was stable at 79 , did not budge during the problem, only changes when I open the throttle.

[2seater]

It sounds pretty much like mine. IAC counts are stable at any steady throttle opening, but will drop to a new stable reading on coast. Something like 92 counts running steady 60'ish mph, let off throttle to coast, IAC counts decrease rapidly and steady out at 68. Just for reference, my IAC counts are in the forties at warm idle in gear, but they do move around a bit trying to maintain idle speed. If your IAC counts are stable, the ECM doesn't see a problem with the rpm fluctuation so it isn't trying to compensate? Not sure what that means? Mine will do the rpm drop cycle on extended coast down, but there is a time and speed delay for the DFCO in the chip to prevent it going into that mode immediately upon releasing the throttle, or at least there is supposed to be.

[Dashmaster]

My IAC count was reset with engine warm so I am sure it will be lower when started and cold, In gear with load could go lower a little. I have ordered a new MAF. Since it is old and has a affect on fuel mixture, Not sure if it could activate the DFCO. I read an article that was talking about MAT and MAF cars late OB1 and some early OB2. He stated the in some of these cars the MAT maintained the

timing and MAF controlled the Fuel. Some were a mixture of the 2 sensors.  I am not sure what the relationship is on our cars

between the MAT and MAF. 

 

 

[Dashmaster]

One other question. The ECM shows coolant temp at usually 94 to 96 degrees. Yet if you are looking at Gauges it shows almost 200.

What is the normal reading for coolant temp in the ECM Data screen. I am  thinking these 2 reading are coming from different

sensors, Are my data numbers way off?  Or is this normal?

[Ronnie]

96 degrees Celsius (in diagnostics) = 204 degrees Fahrenheit . Mighty close if you ask me.

[Dashmaster]

Thank You!! I forgot it was in Celsius.Had so many things going in my mind is becoming mush. 

[2seater]

Padgett could probably explain better, but there is a MAT chart in the program that will modify timing based on rather large steps in the incoming air temperature. Really cold, say -20F will add a few degrees, really hot, say 230F, will pull a little timing, also has an rpm relationship, but it really is just a modifier of the actual timing map. It does have an effect, but is not the main timing control. I have heard, or read, somewhere that the MAT information is used by the MAF for a baseline temperature reference, but I do not know this for sure. The MAF uses a heated wire and a thermistor to measure the temperature. The ECM uses a frequency to measure the amount of energy needed to maintain that target temperature and infers the actual air mass with this information.

 

The actual timing map has a lot of cells, over 100 but I don't have it in front of me, so don't quote me on that. The X axis is rpm and the Y is engine load (LV8), which is a calculated value based on several factors. There are many maps, or charts that all interact. One that may be of interest is the BLM map, which has 16 cells, 0-15, which contain information on fueling, one axis is MAF and the other is rpm. IF you are at a point just over the line in one cell, and then drop rpm or air flow, to switch to a different cell, it may be wanting to add or subtract fuel based on the last number in that cell (this changes with the interaction of the integrator and block learn). I can't imagine that this is the case with yours as it apparently does it at different points in rpm or air flow and probably shouldn't have mentioned it. I am an absolute neophyte when it comes to the information in the chip, but am trying to learn and burn a few of my own.

[Dashmaster]

It was just an interesting read I found,  and you are way ahead of me on this and the chips. I do have an electronic and computer related background. But I have never tried to decipher any thing like this. You and Padgett are why ahead. Thank You for your

suggestions. 

[Dashmaster]

I will take another  look at IAC. I was not sure what direction the count should go, My mind thinks closed should be zero, and any opening a count up. Car was warm when I did a reset on it. I will try again tonight and see what it reads. 

[Ronnie]

28 minutes ago, Guest of you all here said:

While warming up (fast idle, IAC uses data from ATS and CTS to increase)

 

 

30 minutes ago, Guest of you all here said:

MAF controls the pulse width of the injector duty cycle (like a needle jet in a carburetor)

 

Well, this just is not correct. The IAC is a stepper motor that is controlled by the ECM. The IAC doesn't use any data at all from any source. The MAF and other sensors simply supply information to the ECM so it can determine the correct pulse width to the Injectors. You can usually unplug a sensor and the engine will still run to get you back home. Maybe not as well as it should but it will run. When you unplug the O2 sensor for example, the ECM never goes into closed loop and it relies on data tables (in memory) to control the engine. I will stop here because I don't want to piss anyone off -that is NOT my intent at all - but some of the information being provided here just isn't correct for the 3800 engine with the OBD-I computers.

 

BTW, I think it would be a mistake to push too hard on the pintle of the IAC. You could do damage to it. It is better to clean the pintle and the passageway and let the ECM determine where the pintle needs to be. IF the IAC is bad replace it. Don't try to adjust it. Just my opinion.

 

I don't think the throttle plate can be closed too much unless it is sticking in the throttle bore. It is not intended to be used to adjust the idle. If you adjust the stop (screw) for the throttle plate in an effort to change the idle, the ECM will command the IAC to compensate for it the next time you start the engine. Again - just my opinion based on my experience.

 

[Ronnie]

12 minutes ago, Guest of you all here said:

No one is pissed off

 

That's good to hear. I'm just here to try to help out when I can. I don't want to make anyone mad. I have to be careful because my writing style in my posts seems to come across that way sometimes. It usually causes me to have to do a lot of apologizing after the fact. 

 

 

Edited July 12, 2016 by Ronnie (see edit history)

[2seater]

Whoa boys. I got a couple of things wrong in what I said previously, (imagine that). The spark timing map has 255 cells, which I should have known (doh!) and the Y axis is rpm with the X being LV8. Doesn't make much difference I guess.

 

I have always seen the IAC counts follow the throttle upwards with increased throttle, never have seen it static. My ASSumption is it increases to let the engine slow down under a semblance of control, for many reasons. Sort of like the dashpot used on carbs to keep the throttle from slamming shut. The IAC bypass air is still measured by the MAF as it is downstream. The throttle blade really only limits the air flow rate, nothing else. Everything else is calculated.

 

I posted a few weeks ago about finding a broken IAC pintle. It may have been my fault from pressing too hard although have done that before? My idle IAC counts were over 100 so I knew something was wrong. I found it easier, and perhaps safer, to remove it, connect the wiring and run it in and out with the override controls. Pretty easy to see it if propped where visible through the windshield. Leave it fully retracted before installation and it will adjust.

 

 

[Ronnie]

Just as info.

 

According to the FSM - the IAC should  only be disconnected when the engine is OFF - and it should not be moved by overrides when it is removed from the throttle body

 

If you want to reset the IAC the FSM says it is reset "when the engine is started, RPM exceeds 800 and then turned OFF". No mention of pushing in on the pintle. I've always heard it shouldn't be moved by hand but I can't find that addressed in the FSM

 

To be honest I don't think a problem that occurs when you let off the throttle at higher speeds is going to be the IAC but it could be something telling the ECM to control it incorrectly..

[2seater]

Good call Ronnie   I was theorizing prior to this by looking at the construction of the disconnected parts that the stepper motor spins on a threaded shaft which has the actual pintle on the end. I don't see any issue with electrically powering it back in, but if true, I could see where it may "unscrew" in the extended direction. I have the broken one, which may actually have just over-extended, although I don't know how that could have happened since it was installed at the time? I suspect the shaft may have a broken end and somehow that caused a loss of reference position?

 

I agree it isn't likely the IAC, but I started down that path to see if it was giving any indication that the ECM saw a fault and was perhaps trying to keep the rpms up. Upon reflection, the ECM probably wouldn't care as the engine is running at elevated rpm and the IAC would have little effect? I noticed a previous post that mentioned the EPROM and /or possibly the ECM causing this. Could be. I have witnessed this behavior on extended coast down  but it shouldn't engage immediately. I'll sneak back to my cave now.

[Dashmaster]

I took it out for a drive when I got home, Started it then brought up the ECM data screen, Looked at the IAC from cold. It readjusted down to 20  after about a five mile drive with several stop lights. Car ran fine with except for problem.