Oil in upper intake and misfire.
 

I have a 1995 GMC Jimmy 4.3L. While driving home form work it developed a misfire. I bought new plugs. I have not replaced them yet because i wanted to try to find out why the misfire happened. I pulled the plenum off today and could smell gas. I do not see any fuel leaks and fuel pressure is fine. There is oil under the plenum on both sides. Would the oil leak down to the cylinders and foul the plugs? I know the transfer case switch needs to be replaced, so could the oil be transmission fluid? It is black in color. Could it be transmission fluid mixed with the carbon build up in the intake?

This is what I have replaced in the past year:
spark plugs
wires
distributor cap
Rotor button
fuel injectors (spider injectors)
fuel tank
fuel pump
sending unit
fuel tank
fuel filter

Any help would be appreciated. Thank you.

Update: Changed the plugs. Changed the fuel lines inside the intake. Cleaned the carbon buildup I could get out of intake. Still has misfire. Any suggestions?

Any codes? You can try to clean the EGR valve and see if that fixes your issue.

What brands did you use for all of your parts. These things are picky

Thanks richphotos, The Check engine light is flashing. I have tried to get the codes but I can't find anyone with a reader that will read the codes. I forgot to put it in the list above that I have changed the EGR valve and the O2 sensor also. I did pull the EGR valve and check it the other day when I had the intake apart. As far as the brands, the only one I am sure about are the plugs. I had put Champion plugs in and I put AC Delco in last week because i kept reading on here about how bad Champions are.

Flashing CEL is indicating the active misfire. Check your ignition coil and check distributor for wear/play.

You can get an OBD1 code reader online pretty inexpensively. Just make sure you get one that is set up or has the adapter for GM.

Thanks Pepsibottle1, I had thought about the coil but i did not know if the coil would just stop firing to all the plugs or just 1. So if it is the coil could it cause random misfire on different cylinders?

Thanks rockp2, I will check those out.

Just saw one at the auto parts store also. Didn't take notice to how how much it was.

start it up tonight, in the dark, underhood light off. Look at all the spark plug wires for arcing/sparks. could be bad wires

how to check codes for free :

a little oil in the manifold is normal. How clean was carbon build up? its normal for it to be black is nasty. If there is a fuel leak then you will have cleaned washed areas since gas is a solvent.

Thanks everyone. I checked the distributor, changed the coil, and checked for arcing on the wires and everywhere else. Still no change. Could it be a sensor or maybe the cat is clogged?

I also wondered if it could have jumped time. I don't know if it would even start if that happened?

Thanks Chris015, I just changed the nut fuel lines and it was black and oily in there. I disconnected the battery while i was working on it. The battery won't hold a charge now. Now I can't get the check engine light to come back on. I let it run for over an hour,it is still running rough and no check engine light. I wonder how likely it would be the CAT clogged? If it is a clogged CAT wouldn't the check engine still come on and would it happen suddenly or gradually?

Update: I had to buy a new battery because the one i had would not hold a charge. I replaced it tonight. When i started the engine it is still jerking. I tried to put it in reverse, drive, and turned on the AC compressor. In all three instances the engine jerked even worse than before and stalled in less than 30 sec. When i would try and restart the engine it had a very long start time.

Hello everyone, I am still trying to get the codes off my Jimmy. I read in another thread on here that you can bridge pins 3 & 4 on an OBD2 connector to get the codes. I am attaching some pics of what I have. There is no pin 3. Everywhere i have taken my Jimmy, nobody's scan tool can communicate with my vehicle. Can someone help me figure this out, please?


This is the OBD plug:
https://2.bp.blogspot.com/-TZpxV8XIv...or%2BJimmy.jpg

This is the computer:
https://1.bp.blogspot.com/-NMbqHZlrb...or%2BJimmy.jpg

I have this little cheap scan tool.
https://www.amazon.com/Oxgord-Scanne...d2+code+reader
It works well for getting codes, but I have the same issue as you and my valve stem seals along with head gaskets have gone bad.

I wonder if a oil catch can like the ls1 and all ls motors use would be beneficial to these vortex motors.

Flashing eng light
 

check or a intake leek replace gaskets to stop the vacume leek and water from going in to your exhaust if allowed to continue the cat will clog and you will be stranded

intake is leaking will clog cat