4.3 TBI timing not advancing

[Micah Rutschmann]

At the end of my rope with this engine, it's a 93 4.3 pulled from a 4x4 manual S10 and transplanted into a Jeep Wrangler YJ. Still running a simplified harness and TBI from the S10.
The main issue I'm facing is I can't get the computer to control the timing advance. I've set the baseline to 6 degrees, but when I plug the EST wire back in, it makes no difference in advance. It stays at the baseline, and doesn't budge with rpm change, except at high rpm, it'll advance a few degrees. I'm told that is a built in advance in the distributer module. It's a new computer, with the PROM from the old one. I could barely get it to run on the old computer. It idles great and runs OK to get me to work, but you stab the throttle and it just bogs down. I've replaced almost all the sensors except for knock sensors, but I'm pretty sure its computer related as the timing doesn't budge at all.
I'm desperate! Any help at all will be greatly appreciated!

 

[Schurkey]

Wiring harness from distributor to ECM damaged or disconnected?

Anything else in the data stream that seems unusual? Knock sensor activity? Fuel trims OK? Commanded idle speed and actual idle speed similar? Failure to go into closed-loop operation?

 

[someotherguy]

Wiring harness from distributor to ECM damaged or disconnected?

Beat me to it. The little harness to the module can get quite brittle after all these years.

Richard

 

[PlayingWithTBI]

Or your ICM is shot.

 

[Micah Rutschmann]

Wiring harness from distributor to ECM damaged or disconnected?

Anything else in the data stream that seems unusual? Knock sensor activity? Fuel trims OK? Commanded idle speed and actual idle speed similar? Failure to go into closed-loop operation?

The tricky part is, I dont have any OBD ports anymore, so I really can't figure out any of that jazz. I did check for continuity from the dizzy plug to each pin on the computer and that checked out.

 

[Micah Rutschmann]

Or your ICM is shot.

It's a new distributer and ICM, though that's never been a guarantee that they actually work.

 

[Schurkey]

The tricky part is, I dont have any OBD ports anymore

No OBD port? How screwed-up is the wiring? You still have a MIL on the dash that works?

Sounds like you're in full limp-home mode due to the computer sensing a number of problems.

 

[Micah Rutschmann]

No OBD port? How screwed-up is the wiring? You still have a MIL on the dash that works?

Sounds like you're in full limp-home mode due to the computer sensing a number of problems.

That's the thing, when we stripped down the wiring, we pulled out everything aside from engine specific sensors, obvious stuff like distributer wiring, and power/ground leads and such for the computer. It was the 3 plug type, so lots to pull out. Didnt figure we needed diagnostics ports as I didnt even know at the time that OBD1 type software was still available. Probably shot myself in the foot by doing that, as I've gotta do everything the hard way now. That being said, it seemed to work just fine before, it's only since the last computer gave up the ghost that I've run into trouble.

 

[PlayingWithTBI]

Sounds like you're in full limp-home mode due to the computer sensing a number of problems.

X2 - you need to redo the wiring harnesses AND the OBDI connector. There's something you missed in the wiring to cause the PCM to default to limp mode. On a conversion like this you can't cut corners.

 

[MIHELA]

You really, really need that OBD port and a serial cable to datalog that thing or you will never know what is going on.