ECU Problem?

[josehuerta]

First, I'm not the mechanic many of you are here but here is what I got.  I have a '91 with 4.0. It started slow for about a week but I hoped it was just the ethanol gas Now it starts hard or not at all, then sputters, stalls  if I try to drive it. First I had a new crank sensor installed at a shop  (blown back means I can't do the stoop, shimmy, twist under the truck anymore).Process of elimination the cam sensor, distributor cap, rotor have all  been replaced. Disconnecting the MAP sensor lets it idle but not run correctly. I had the instrument cluster out chasing a short and wonder if that could have caused the problem. What am I missing? Is my ECU likely the problem? If so, smarter to have my original rebuilt or just do the exchange and any recommendations for a quality rebuilder would be appreciated. If I need another ECU will it learn the truck or do I have to take it to a shop for programming? Lots of questions but would appreciate any advice.

[Pete M]

has the the idle sensor or tps been tested yet?   

[gogmorgo]

Have you checked for trouble codes?

 

[Minuit]

25 minutes ago, gogmorgo said:

Have you checked for trouble codes?

 

Do this. The OBD1 system is pretty limited but sometimes it can point you in the right direction.

 

The ECU is about the last thing I'd suspect. I generally don't hear about them failing often - almost always it's one sensor or another.

[Green Mesa XJ]

Wait the MAP disconnected let’s it idle correctly ? Maybe I’m missing something but that seems backwards.

 

 

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[Jeep Driver]

ECM is not your problem. 

[gogmorgo]

36 minutes ago, Jeep Driver said:

ECM is not your problem. 

The earth isn't flat, either. Care to elaborate?

[Green Mesa XJ]

I have two spare ecu for our XJ when I did swap out to Test they never were the problem. These computers are usually pretty reliable even 26 years on. If you want to test it just pick up a cheap junk yard ecu, match the year and ecu number to be sure of interchange. I wouldn’t bother with rebuilt or trying to find a pricy ecu specialist, a plane old used ecu with a guaranteed to be good warranty is enough to test and use if it’s the problem.

But check the codes see if anything is being flagged.

 

Sadly wiring can be a problem, don’t know where to describe the trouble shooting for that.

 

To me I’m thinking fuel pressure test, hard starting is normally a bad check valve in the fuel pump, one trick is to prime the pump by turning the ignition to on but not starting the engine. Do this three times you should hear the fuel pump prime.

Bad fuel pump or injectors would keep it running like it’s not getting enough gas.

 

oxygen sensor and maybe MAP sensor because every time my MAP sensor vacuum line was disconnected the jeep ran like crap can’t figure out why yours would run better with it disconnected.

 

Even alternators can cause weird issues.

 

These are a few ideas that may be way off for your symptoms.

 

 

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[Jeep Driver]

10 hours ago, gogmorgo said:

The earth isn't flat, either. Care to elaborate?

99.9% of the time.................

 

It's wiring, vacuum, sensors.TB cleaning, general maintenance.......always. 

 

OP needs to begin the process, after 30 years, everyone does. 

 

Rinse, repeat.........gets old repeating myself............shorthand. 

[HOrnbrod]

OP, ignore the guessing game above and check the codes. That's always the first step with OBD1.

 

A bad ECU is possible but unlikely. But do disconnect it's 60-pin connector and check for any bent or recessed pins, then clean both the male and female connectors with a good electrical contact cleaner then reseat.

[yxmj]

I will agree with getting the codes..... Do you need guidance with that......

Pete already said it but my first guess is tps....

 

And if you have the electrical cleaner spray out....spray all the sensor plugs...(tps first)....sometimes a slight bit of green corrosion will cause head scratching for days 

[josehuerta]

 My old friend is back on the road. My inexperience with these problems is apparent (I bent nails for a living - construction) but this has been a frustrating yet challenging and rewarding experience. Apparently it was the perfect storm. Crank sensor and fuel pump (10 lbs.) were dropping out at the same time. Along the way my distributor had seen better days. All have been replaced and I -and my dogs - are happy to be back in the Comanche. Advice given here was of tremendous help. I assumed I needed a scanner to read the trouble codes but this forum has saved my butt. Many thanks to all for your input..

[Pete M]

  we're happy to help.  too bad I can't seem to fix the ones and zeros that are messing up your old screen name.   I thought about merging them, but hesitate til the original issue is resolved.