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Intermittent Ignition fault.


Bones_inst

Member
Joined
May 1, 2011
Messages
5
Vehicle Year
1992
Transmission
Automatic
Truck has no power and misses badly at idle. If it idles for a long time it will clean itself up, but seems to be overfueling. Check engine light is on, very hard starting.

Engine is a 4.0 l V6.

The truck wouldn't start at all this morning, so I tried to pull the engine codes.

I put the jumper in to to pull the engine codes with the key on but not running and waited 5 min without having the system enter into the test mode. I took the cover off of the ecm and bumped it with a pair of pliers, 30 seconds later the truck would go into test mode and give all engine codes. Shows 185 and 186 code, performed clean on mass air sensor with electrical mass air sensor cleaner.

Tested the vacume, and it is within spec, the compression is from 120 to 150, the fuel pressure is operating as per manual.

The truck fired right up. No codes no issues. I turned it off, and attempted a restart, same issue. I tried to run a diagnostic on it again and would not initialize, after a few min I bumped the ecm with a pair of pliers again and like before it went into test mode again and gave the same errors, I assume because they have not yet been cleared, and after test, truck would fire up again.

Cleared codes, road tested, engine runs well until put under load.... 1/2 throttle, then throws more codes, 181, 185, 186. Book says 181 - fuel system at lean adaptive limit at part throttle, system lean. 185 mass air flow lower than expected. 186 injector pulse width higher than expected.

On the bright side, the engine is now running better at an idle, but i suspect that a cold start might be bad again will find out tomorrow morning, will post update. Started good this morning but no power under load and throws engine codes.

Won't start after work, won't recognize that the jumper is installed on the ECM, I suspect that the ECM is failed and that the MAS is damaged too.


Is the ecm failing? Do I need to change the MASS air sensor and O2 sensor? Am I missing something??
 
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In my limited experience, I would recommend cleaning up all grounds first. A bad ground can make any component seem bad. Having to tap the ECM worries me a little bit though..

84BB2
 
I've taken apart all of the ground wires and scraped the paint around them, then re-torqued them down.

I think that I am getting a little further with it, I've definitly spent some more money on it.

I've found that if the truck won't fire, and won't go into program mode, my fuel pump runs continuosly. If I disconnect the ECM for the day, it seems to repair this issue, again making me suspect of the ECM. I've ordered one from a wrecker, so heres to hoping it is in better shape the the one that I had.

I also remedied the engine code issues by changing the MAF sensor and O2 sensor. But now have a new code after a couple of miles of driving. A 172 code which says "Lack of oxygen sensor indicated lean." This was done with the key on and engine on. No codes were present with the key on engine off.

So it looks like I have some more work to do, I tested for vacume leaks again, can't seem to find any. It isnt an exhaust leak as I've tested the manifolds and put new gaskets in, as well changed the entire exhaust system from the y pipe back.

The truck does,'t have alot of power and has a serious lack of power around 2000 rpm. I am going to look around this forum for any info on this but do appreciate the help.
 
Ok, I've changed the ECM and now have one problem repaired. The truck consistantly starts, and runs. The fuel pump no longer continuosly runs and I can pull engine codes at will. Thank goodness for lifes little miracles. Now the truck comes up with the original 185 and 186 codes, even after a new mass air sensor and o2 sensor, the original sensor was white when I pulled it, and my plugs are white, which makes me believe that it is lean. The only thing I have a problem with is how much gas it is using and how little power it has, as well as how bad the exhaust smells like gas especially at low idle.

I would have thought injectors, but they are new. The fuel rail pressure is at spec. I'm at a loss. :icon_confused:

Is it possible that I've wrecked the new O2 sensor?????
 
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Check the pressure regulator on the fuel rail. Pull the vac line and see if its wet.
Check your CAT to see if its clogged, Check your intake for a leaky gasket, clean you IAC.
 
Thanks for the help, I've taken your advice and checked the torque on my lower intake bolts. I started by tightening the closest to the front intake which caused the truck to run worse. So, I loosened all of the lowest bolts and re torqued following the torque pattern and specs in the chilton manual. It seems to have helped, the truck began running rough when I first started it, I took it for a little burn and it cleaned right up. It now runs well and seems to be running smooth at an idle. It did throw the 172 code though which is disturbing.

Thanks for the help.
 
If it cleaned up with torque on the lower plenum bolts I would say its time for a new gasket :) Retorquing them is just a band aid fix. It will eventually blow out or suck in leaving you stranded some where if you don't replace it. Its not to terribly hard to do, but it is time consuming and tedious.
 

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