1984 Lesabre Runs Fine Until it Doesn't

[Roger Frazee]

I am trying to get a barn-stored '84 Lesabre back on the road and have run into a snag.  After cleaning the fuel system and having a pro rebuild the carb, I finally got everything back together and started the car.

 

The engine starts right up and runs smoothly for about two minutes, at which time the idle becomes rough, the mixture control solenoid clicks rapidly and the check engine light flickers in sync with the mixture control solenoid.

 

This is my first go-around with a computer controlled engine, so I don't know where to start looking.

 

Any help and advice is appreciated.

[Frank DuVal]

Two minutes sounds like when the computer goes into closed loop. Until then it is playing the engine with a record of approximations. Now it is looking for data from the sensors. Have you read codes with the check engine light or scanner? Should be a Google search for how to do it. I think the ODB 1 saves codes that are not set quite yet.

 

Does it have a MAP sensor?

[NailheadBob]

I would check computer for trouble codes first, you have OBD1 system, if you have Autozone parts store in your area, they do free diagnostic code checks, not sure if they do OBD1 systems.

another thing to look at, is all your ground wires in engine compartment, including battery and chassis grounds for being loose or corroded.

 

Bob

[EmTee]

You should be able to read OBD-1 codes by putting the ECM in diagnostic mode and counting check-engine light flashes.  Again, the ALDL connector pins to to jump together are "A" and "B" as identified in the video below.

 

Ref: https://www.youtube.com/watch?v=vgXSXCRyw2w

[60FlatTop]

ALDL diagnostic tools have been pretty cheap on Ebay over the years. I have an OTC 4000 that I don't think I paid much more than $100 for.

 

It is hard to work without the tools.

[Smartin]

You mentioned that you cleaned the fuel system.  Did you drop the tank and have it cleaned out?

[NTX5467]

When the carb rebuilder took off the air horn of the carb, were ANY little red silicone-type rubber (usually circular, or a part thereof) slivers in the bottom of the float bowl?  IF so, then a new metering solenoid is needed.

 

In code reading, you will need the SPECIFIC codes for that model year and BRAND of vehicle.  NO universal codes as with OBD-2.

 

You can troubleshoot the mixture control solenoid with a simple dwell meter.  The mixture control solenoid took the place of the prior "power valve" and spring under it to run the metering rods up and down.

 

Compared to more modern vehicles, those old OBD-1 systems are very crude when compared to current model year vehicles.

 

Keep us posted on your progress,

NTX5467

[Roger Frazee]

Thanks to all for your help.  I should have mentioned that I did check for codes and there were none.  

 

Frank, yes there is a map sensor.  What are the symptoms of a bad MAP?

 

Smartin, yes, I dropped the tank and inspected it.  There is no rust or crud in the tank.  While I had it out, I replaced the fuel pickup.  

[Roger Frazee]

7 minutes ago, NTX5467 said:

When the carb rebuilder took off the air horn of the carb, were ANY little red silicone-type rubber (usually circular, or a part thereof) slivers in the bottom of the float bowl?  IF so, then a new metering solenoid is needed.

Thanks.  I will check with the carb guy and find out if there were any red slivers in the bowl.  I will also look up the procedure for checking the solenoid dwell.  

[EmTee]

18 hours ago, Roger Frazee said:

What are the symptoms of a bad MAP?

My father had an '83 Eldorado that was dumping fuel like no tomorrow - black exhaust smoke and about 7 mpg.  Found a rotten vacuum hose to the MAP sensor.  Make sure all of the the vacuum hoses are sound.  I had an '85 Delta 88 with the same type of Quadrajet.  I had to replace the intake manifold gasket due to a coolant leak and that car had miles of vacuum hose running all over the top of the engine.  Upon closer inspection most were cracked or hard.  I replaced them all.

 

Your issue may not be due to a bad hose, but unless they have been replaced, your next problem likely will be... 

[avgwarhawk]

As usual with these as well as other vehicles,  check every ground wire you can find.  And as mentioned, the issue starts when the computer goes into closed loop.  In short, running the show as best they can with the technology at the time.  Check for vacuum leaks.  

 

Edited July 25, 2022 by avgwarhawk (see edit history)

[Roger Frazee]

Update:  I made the decision to install a non-electronic Quadrajet carburetor and a vacuum-advance distributor, so I can eliminate the ECM and all the headaches that go with it.  My questions for today are:  What is the black box with the X pained on it, to the right of my distributor wrench?  Will I need that box once the ECM goes away?
 

[avgwarhawk]

What do the vacuum lines from the black box run to?

 

[Roger Frazee]

13 minutes ago, avgwarhawk said:

What do the vacuum lines from the black box run to?

 

Literally, they go nowhere.  The previous owner disconnected them and left them scattered on top of the engine.  

[avgwarhawk]

2 hours ago, Roger Frazee said:

Literally, they go nowhere.  The previous owner disconnected them and left them scattered on top of the engine.  

Well then, remove it!