ihrinko

Howdy y'all. First post here...

I have a 1991 4wd pickup with the 3vze and M/T. The truck is in great shape. I got it for a steal because the previous owner couldn't figure out what's wrong with it. Here's the run down...

Before it gets to operating temp it runs great. No CEL, snappy throttle, no miss, runs smooth as silk.

As soon as it gets to operating temp (I mean immediately) the CEL light comes on and it surges and runs rough.

Here's the kicker though. There are no stored codes no matter how many times I start it and let it warm up to turn on the CEL and the CEL doesn't come on for the self check with key on engine off.

Also no constant flash of the CEL when the Te1 and E1 pins are jumped.

I have confirmed that the wiring from the TE1 connector to the ECU is good and I have a good ground at E1. TPS idle circuit is closed with the throttle closed. All accessories turned off. I know that I'm getting a good connection with my jumper at the TE1 and E1 pins.

All the wiring looks good and has not been messed with. Everything is connected.

I've checked everything I know to check.
No codes stored and no CEL with KOEO plus I know that the truck sat with a dead battery for 11 months.
I'm starting to lean towards the ECU.
Has anyone else had this issue or anything similar?

Benji19912wdsr5

WOW! A month later and no help? Check your EGR setup and all vacuum lines. Also, be sure you have your diagnostic jumpers connected correctly. I found my simple rough idle was caused by the knock sensor. I hope that's not your problem.

scope103

The lack of self-check is a big problem, particularly combined with an intermittent flash of the CEL (the flash should rule out the simplest explanation; burned out bulb).

The W pin of the diagnostic connector is the CEL. I'd check for voltage to ground there (you might need a test light; you're looking for the flash that you're not getting on the CEL). Since you've already checked the wiring from TE1 back to the ECU, you might as well try it with W as well. The wire color should be V (violet).

ihrinko

Thanks for the replies. I actually got it figured out, it ended up being a combination of things.

Eventually after messing around with it for a while it finally stored codes for the IAT and AFM. I took the top off the AFM and the solder joints for the IAT and AFM wiper resistor doodad were broken at the board and the leads were touching each other. Repaired that and the surging and rough running at operating temp issue went away.

However, I still had other problems

The tell tale was that it would run fine on the first start after unhooking the battery for a while. Then, on the second start it would have no Key On Engine Off CEL and it would run like ˟˟˟˟. Unhook the battery and the process would repeat.

I got a "remanufactured" ECU off ebay and it runs like a top now.

I'm not sure if the shorted leads in the AFM wiped out the ECU or if the ECU's ROM, RAM, or EEPROM was damaged or lost it's "programming" from sitting with a dead battery for so long.

Sorry if this is kinda hard to follow, as y'all know sometimes it's difficult to describe these types of things. Words R hard.

Question, is there a way for me to edit the thread title so I can add "SOLVED" in case anyone else has this same issue?