1990 2.9L V6 - Randomly Getting Missfires - No CEL - Not Sure How To Troubleshoot

[rusty ol ranger]

I wanted to touch on the check engine light - so the truck does actually have a check engine light. When the engine is running its off. Is it still possible there are some codes to read? I have an OBDII scanner, but I think this is too old for that. Should I just take it somewhere to read codes? Or will there definately not be anything to read because the light is off when engine is running?

I took a photo of my dash below to show:

View attachment 94279

That was why I was hesitant taking it somewhere, and thought maybe the shotgun approach to just throwing parts at it would work - because I'm worried the mechanic might not be able to find something wrong. Unless I'm lucky enough for it to be running bad at the same time they are looking - its so random though.

Im not sure if memory codes will trigger a check engine or not.

Also no its not OBD II, its EEC IV (OBD I, basically).

You can pull codes by blinking the check engine (the procedure is in the tech library) or you can save yourself the hassle, spend 30 bucks, and get the digital innova EEC IV reader.

 

[franklin2]

Here's a link. If you plan on keeping this truck, I would bone up on how to read the codes.

Testing EEC-IV Equipped Engines - The Ranger Station

The EEC-IV equipped engines use an older diagnostic system to monitor and report engine related malfunctions. This system is known as On Board Diagnostics (OBD-I). The Diagnostic Trouble Codes (DTC’s) are two or three digit numbers and can be … Continued

www.therangerstation.com

 

[Mahonroy]

UPDATE:
I ended up figuring out what the problem is - I will explain below.

So I initially got the distributor replaced, along with the TFI ignition module, and it did not solve the problem. No change there.

The battery cable (negative) was heavily corroded, exposed freyed and oxidized wires, etc. It was in bad shape. So I replaced that. No change yet.

Next I did the MAP sensor - still no change.

Next I did all 6 spark plugs, and new spark plug wires. When I was replacing the 7th wire that leads from the center of the distributor to a module mounted to the fender well, I noticed that the terminal had some black charring/soot on it. This led me to believe that it was not making a good electrical connection, and very well might be what the problem was:

So I replaced that wire too.

Fired it back up and its now running perfect! So it could of been due to the spark plugs, the wires, or the 7th distributor wire, but I have a feeling it was probably that 7th distributor wire that was causing the problem all this time.

Thanks again for all of the help!

 

[franklin2]

Just for your info, that module on the fenderwell is actually the ignition coil. That is where the high voltage spark is generated from, the top of the distributor "distributes" the spark to the proper sparkplug. That was a good find.

 

[Cees Klumper]

Just goes to show, diagnosing is 90% of the solution and the hardest part ...