Hi,
I have started to look and chase my Code 44 Lean Condition on my 1984 Trans Am STOCK LG4 Auto AC car. It seems to have gotten worse. I am at the point now where, in closed loop, at idle in Drive, the car will set the check engine light within a minute and the exhaust is awful smelling. While driving it is perfectly fine and responsive. This is really just an issue at idle..... I have done testing with my SNAP ON MT2500.

I have changed out the O2 sensor multiple times...some BOSCH, some AC Delco. The result is the same. I have traced the O2 wire to ECM and it is good (no shorts or open).

The Dwell at idle in closed loop is 6 which is full rich. I have the factory service manual and I followed the below sheet (I circled in RED where my results lead me). It says if all else fails, i.e. you have replaced the O2's and traced the wires for bad connections replace the ECM. I am looking for advice from anyone who may think to look in a different direction. I have no vacuum leaks (I smoke tested the car). I know the MC solenoid is working as if I choke the engine at part throttle ) I see the values changing on the snap on reader for the solenoid.. I also see the O2 varying the voltage at different throttle positions.

Any other thoughts or is replacing the ECM the way to go? I just hate swapping something unless its known bad and today I have no idea if what I get from any parts store will be any good..... also what makes me think it is not the ECM is that I see the values change when I choke the engine or increase the throttle......Thanks.

 

Very low dwell = the ECM thinks it's WWWAAAAAAAAYYYYYY lean

Question then is, is it REALLY lean, or is the ECM just out to lunch.

Changing the O2 sensors with no noticeable effect says it's probably FOR REAL lean. IOW, time to stop efffing with the ECM, and start troubleshooting a lean (no fuel) condition.

When you manually "choke" the carb, either by manually closing the blades or by just covering the throttles up with your hand, the dwell reading should increase somewhat. No guarantees one way or the other on how the engine will run, but, restricting the air, should allow however much (little) fuel is being fed, to more nearly equalize with the air.

Try backing your IAB out a turn and see what happens.

Of course, this is all going to be, assuming your fuel system is in good proper working order. Great place to start on that would be, the fuel filter. That would be PARTICULARLY suspect if it has the problem where when you floor it from a stop and just let it eat (get on a long uphill freeway ramp for example), it runs somewhat OK through 1st gear, struggles a bit through 2nd, then falls flat on its face near the top of 2nd or at the 2-3 shift or partway through 3rd. Somewhere in that range is about how long it usually takes for the engine to drain the fuel bowl, and if the fuel system can't keep up, that'll be about when it shows up.

It would not surprise me if your problem turns out to be the fuel filter.

 

I would add also, the troubleshooting charts in the FSM, while not "wrong" or anything even remotely close to that, are NOT meant for near 40-yr-old hoopties with a half-million miles on them, like ... us.

They are meant for BRAND NEW cars, right straight off the showroom floor, UNDER WARRANTY or close to it, wherein some ONE random thing has FAILED. The ARE NOT meant for a car where every gasket, every seal, every wire, every EVERYTHING, is ancient and decrepit and used-up and suspect. They are NOT meant to cover every possible thing that could ever go wrong, LONG AFTER the car is out of warranty. They are therefore not particularly useful in situations like this. They DO NOT for example allow for the possibility that the car has sat around for a decade with old gasoline in the tank, and the ENTIRE fuel system is plugged up with that viscous insoluble GUNK that gas turns into; they DO NOT take into account that all manner of mechanical problems may have set in that generally don't show up until acoupla decades and a hundred thousand miles have passed by; they DO NOT have visibility into the changes in fuel that have occurred since 1980; in a word, they are LIMITED. Again, they are not "wrong", they are simply, ... ,,, ... not fully applicable. Which is to say, you can go through EVERY SINGLE step that it tells you to go through, and get no closer to a solution, simply because in the context they were written for, such a thing as whatever YOU have going on, would NEVER have occurred. Geriatric problems just weren't an issue yet as far as the FSM writers were concerned.

Think of it as, the FSM consists of instructions for babies in a neonatal ward, whereas YOUR problems are more like, somebody in an assisted-living home. Not "wrong", just, not really right either. They're both "human", but the things that a newborn baby might have trouble with, are FAR different from what you'll encounter in a 90-yr-old.

At a certain level you have to use basic Stone Age techniques. All that stuff that people (like me, one of the last of the Neanderthals) used to have to do, before things like ... scan tools, affordable DMMs, and so forth, even existed. Gonna have to get personal with it.

 

what kinda fuel are you running?

my 83 does the same thing if it idles for more than 2 minutes or so then goes away once you start driving.

 

Thanks for the replies. ... The fuel Filter and pump are new.....so that is not issue and it did occur with previous fuel pump and filter....

Yes the car is showrrom condition with 90K original miles and stock but I do agree, the car is close to 40 years old and the books are not meant for something that old.....

Perhaps changing the type of gas and octane may do something...I generally just put in 87 octane from the local MOBIL station......

Again, this is just at IDLE. Everything else is 100%...plenty of power (well for an LG4) and no other issues other than the CE light at idle after a minute when in closed loop....Thanks.

 

Just wondering aloud here;

Have you checked the EGR valve for a slight leak (carbon buildup causing it to not fully close) ? A slightly leaking EGR valve will cause a lean condition that will be most noticeable at idle.

 

Yes EGR is new and solenoid (which I just found after a long search) is new. Both are in working condition.....Thanks

 

vacuum leak is going to affect idle more than any other operating range.

I'd plug every vacuum port on the carb and manifold, booster, choke pull off, everything... then try it at idle. If you notice a difference, plug them back in one by one and note which causes it.