Misfire Diagnosis - PLEASE HELP

[erikjlokensgard]

Just bought a 1992 Ram 50 2.6 2WD.

I've recently noticed a random misfire at idle along with some white/grey smoke from the exhaust. This hasn't affected performance much.

The larger issue is a random loss of power: after truck is warmed up, at completely random times (highway speed, stop lights, etc) This will happen for 30 seconds or 20 minutes.

symptoms:


loss of 80% power
sputtering
backfire
strong gas odor
check engine light
large clouds of white smoke from exhaust
oil or gas dripping from exhaust manifold gasket


Other than this random, short lived, total system meltdown the truck drives like new. No coolant loss. No oil loss.

Replaced:


spark plugs
wires
fuel injectors


Possible issues:

injector coil
distributor cap and rotor (rotor shows signs of wear)


I am NOT a mechanic and have brought it to many mechanics with no help!!

[camoit]

I would start with the ignition coil. Then look at the fuel system. It's the smoke that bothers me.

[geezer101]

Hi and welcome to mightyram. Being a 92' truck it won't be a 2.6 so unless it's a V6 it'll be a 4G64 (2.4 L) Check engine light could be a number of things but you can get error codes off the ECU by plugging in an OBD 1 scanner and it will reveal all. The oil leak is probably something as minor as a bad rocker cover gasket.

[pennyman1]

Since it is a 92, it has an ECM - the issues you are having is classic signs of bad capacitors in the ECM. There are threads on here that talk about the cap issue and even instructions to repair it yourself if you can work on circuit boards, or where to send it to have it fixed. Check them out.

[erikjlokensgard]

Thanks everyone. I'm going to check fuses and ignition wires as well as check the caps in the ECM. Found a new ignition coil at autozone for $50 might give that a shot.

[erikjlokensgard]

Does the ignition coil cause intermittent problems or is it more regular? I'll check the fuel system but don't know much about it. Another system to learn I suppose.

[erikjlokensgard]

Unfortunately the CEL is so random its difficult to bring it somewhere to check the codes. When the misfire starts its nearly un-driveable until it resets itself. I changed that gasket a few weeks back.

[geezer101]

This might be a wiring fault. A lot of DSM guys have issues with wiring harnesses deteriorating and causing similar faults. If you have a multimeter use it to go through the backs of all the harness plugs and check for continuity. Don't need an uber buck meter, a little pocket meter will do the job.

[erikjlokensgard]

Had a misfire diagnstics done and mechanic told me I have a sticky valve issue. (+$1000 issue.) Every mehanic has said something different. Would a sticking valve or valve guide cause a intermittent misfire? When the misfire happens there is oil mixture squirting out where the exhaust manifold connects to the exhaust pipe.

Nightmare.

[Giovanni89]

I would pull the valve cover off and spin it over slowly by hand. See if you see anything strange happening near the valve in question. That oil mixture has to be coming from somewhere. i think it would take a really worn out valve guide if it wasn't a head gasket or crack. I had a minor crack in the head on my G54B. It would only act up at sustained high speed (75mph plus) or sitting in a lot of traffic, both only on a hot day.

[royster]

My gut feeling was that it might be the EGR...don't know why I feel that way, but it somehow made sense. A malfunctioning EGR could cause hesitation, and if the passages are blocked...???

I agree with Giovanni - see what's going on with the valve train. Be sure to get a new valve cover gaskets.

[geezer101]

A bad EGR will cause rough idle and leave the engine feeling hesitant and down on power (but don't disregard it - this could be a combination of issues) I'll throw this out there - a bad valve guide. If it moves/dislodges it can hold the valve partially open (there's your intermittent 'sticking' valve) and also draw oil into an intake/exhaust gallery (there's your mystery oil leak). This is a PITA but you'll have to take off the exhaust manifold and physically see into the exhaust gallery in the proximity of the oil leak. You find one that is particularly fouled up - you're on the right trail

[joshuaholland]

Mine is doing the same thing but its like clockwork. First 15 minutes cold after that a lot of sputtering and backfire like too much fuel. Follow for sure

[joshuaholland]

Edit* first 15 minutes of cold run is a hard misfire

[geezer101]

^possible bad engine temperature sensor. It will send false readings to the ECM making it run rich and altering the ignition timing. It won't necessarily detect it as a 'fault' as it's only reading whatever value the sensor is sending the ECM.
(https://www.youtube.com/watch?v=8X2kIfS6fb8)

[erikjlokensgard]

Since it is a 92, it has an ECM - the issues you are having is classic signs of bad capacitors in the ECM. There are threads on here that talk about the cap issue and even instructions to repair it yourself if you can work on circuit boards, or where to send it to have it fixed. Check them out.

****SOLVED****

pennyman1 found the problem! thank you everyone for helping find this misfire. I took out the ECM and found that 2 caps had been replaced by the previous owner so I decided to order a new ECM for $200 on Ebay and the truck now runs beautifully. No more misfire! only a high idle at cold start for about 1 minute - but i'm sure there's another post about that in here somewhere.

[Giovanni89]

Every fuel injected vehicle I've seen has a high idle for the first minute or so on a cold start. It's the ECM putting on the "choke". Someone correct me if its different for these early EFI trucks, but I think you're good to go!

[geezer101]

The ECM waits for a temp sender signal to disengage the IAC solenoid (idle air circuit). Had one go bad in a GM family II 1.8 - it sounded like a jet engine...