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92 ford thunderbird random cel

hi everyone and thanks for the help in advance, i have a 92 ford thunderbird 3.8l v6 lx naturally aspirated. 88,000 miles. the car has gotten gradually worse over time and no one can figure it out. the car has a hesitation (stumble) at idle no steady cel light on. when i take off from a stop car acts like its not getting gas for a few seconds then starts to speed up but the cel light pops on for a few secs then turns itself off but it randomly turns on and off (not flashing) at any speed or rpms constantly. sometimes it will come on and stay on till i bring the car to a full stop. i pulled codes and im getting engine lean on both sides bank 1 left and right, car never shuts off at all, ive replaced the following-spark plugs, wires, dizzy cap, iac, maf, throttle body gasket, checked all hoses for leaks, new gas cap. any ideas i am down to o2 sensors EGR components and the computer (hope its not that). please all help is great

What are the code numbers you pulled?


Try cleaning the throttle body and plate because there might be carbon deposits there.

Overly lean is caused by either too much air getting into the engine, or not enough gasoline. Presuming you’ve already ruled out the too much air theory (which can be quite an involved task), the cause must be not enough gas. The computer assumes a certain amount of gas is injected for each msec of injector pulse time. If that much gas doesn’t actually come out, it will cause this problem. Time to check for low fuel pressure or clogged injectors.

A clue can sometimes be obtained if there’s a difference in performance or symptoms when the engine is cold vs warm. Is there?

Misfires, O2 sensor , EGR, and PCV system problems are also possibilities, but less likely.

I’d suggest the strangeness of your problems and the age of the car may, indeed, suggest that the computer is at fault. Electronics have capacitors and capacitors age out. Since your ECU is now 26 years old, that may be your problem. Not sure what the availability of remanufactured ECU’s are, but any “new-old-stock” ECU’s will have the exact same problem due to the age of the caps. Sorry

Apologize for extremely late reply ive had a heck of a end year but I’m back and on the Thunderbird again. Tester- the codes I have pulled is 172, 176, 186, 189. It’s weird some times the cel light just pops on and off in few seconds and sometimes it stays on for a minute or two, I’m leaning towards fuel I started it the other day and it started but stumbled really bad for few secons, once I hit the gas it stopped stumbling. Bad pump, injectors or would that be caused (stumbling) by throttle body or both maybe?

The problem is likely from among: fuel injectors, HEGO sensor, thermactor, pcv, vacuum leaks, CANP, MAP, contaminated engine oil, throttle position sensor, throttle body, ACT sensor, fuel pressure, injector balance, canister purge valve, egr, ignition system, cylinder compression, exhaust leak.

Since one of the most noticeable symptoms is a stumble when accelerating, I’d probably start with testing the throttle position sensor. After that, since you believe it may have to do with the fuel system, next up if I had that problem would be a fuel pressure and injector balance test.

I replaced the iac, tps, sparks, wires, dizzy, fuel filter, air filter, maf, cleaned throttle body, throttle body gasket, with no change so I’ll check fuel pressure, cannister, how do I tell if the Purge canister valve is bad

I noticed you said you had lean codes on both banks

But you didn’t mention fuel pressure

Have you hooked up a fuel pressure gauge?

fuel pressure below spec can generate lean codes and drivability problems

I’m assuming this car has a mass air flow sensor

If it’s bad, that can generate lean codes on both banks and also cause drivability problems. In fact, a bad mass airflow sensor can cause an engine to pretty much fall flat on its face when accelerating

Do you have a scanner that is capable of displaying useful live data on this OBD1 vehicle?

You said you “checked all hoses for leaks” . . . exactly how did you go about doing that?

Checking the fuel pressure is the next step, no doubt about it. If that’s ok I’m leaning to an ignition system problem. If the spark doesn’t ignite the mixture a lot of O2 (which should have burned up) is then pushed into the exhaust system and makes the o2 sensor think it is too lean (too much o2). Given it is happening on both banks, ignition module is one possibility. I’m guessing however it is the distributor. On a 92 with quite a few miles on it, good chance the distributor bushing is wearing and allowing too much run-out on the ignition rotor, and making a bad connection for the high voltage spark signal inside the distributor cap. oh, I see you’ve already replaced the dizzy, scratch that last idea … what about the ignition module? have you replaced it yet? If not, suggest to have the ignition signals checked by a shop using their specialized ignition testing equipment. If they find something wrong, you can let them fix it, or you can fix it yourself if you like. After all this replacing, once it is working again, you will practically have a new car … :slight_smile:

Another idea, Fords of that era have a complicated egr gadget that controls how much vacuum is applied to the egr valve depending on certain other vacuum signals. That gadget tends to cause weird symptoms like this when it fails. Use the forum seach feature here, “ford egr” for examples. If you can figure out how to prevent the egr from opening (as a test), that might provide a clue.