What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Fixed my hesitation problem... Well kind of...

crashandburn

crashandburn

1/2 ton status
Joined
Dec 6, 2007
Posts
334
Reaction score
10
Location
Colorado Springs, CO
Earlier this year I dropped a 94 TBI 350 into my 91 SAS'd S10 Bazer. The tired old 4.3 just wasn't very happy about 40" Swampers. But I had a hell of a stumble off idle, so bad that I could stall the engine if I hit it right.

On a hunch, I suspected the EGR was the source of the problem, since I had ruled out the TPS previously. Today I hooked up a vacuum hand pump to a tee running to the EGR and to a vacuum gauge. It would not hold vacuum. Tried it while running and while shut off. So I'm thinking I'm on the right track now.

Just for S&G's I pulled the vacuum line and ran it directly into the EGR, bypassing the EGR control solenoid. Now the truck runs damn near perfect. The stumble off idle is almost completely gone, in fact it is so minor that I could even live with it if I had to.

So, the EGR tested bad, but bypassing its control solenoid took away the symptom. Which do I swap out? I think the solenoid came from the 4.3, since the 91 and 94 motors had some minor differences and some things had to be transferred over. I'm not totally sure on that. The 4.3 did not have a hesitation problem. It had about every other problem, but responded off idle fine.

Also the check engine light is on. My OBD1 port does not work. It won't communicate with a scan tool, and even jumping terminals with a paper clip does not work, any ideas?
 
Does the check engine light flash when you turn the key on, or does it just come on and stay on?

I'd not worry about other problems until I fixed that, since the port not working can be an indicator of ECM, PROM or related wiring problems.
 
I'd say fix the cel as well. It's on because a signal is lost somewhere. The ecm hopefully isn't dead. Did you flash it for any new components you have now that weren't on the donor truck?
 
It does not flash, just comes on and stays on. I did not have the ECM flashed. I swapped EPROMs from a 1990 350 powered pickup into the 4.3 computer because that's how I was told to do it. The 1994 computer that came with the engine was totally different.

If the ECM was dead, wouldn't the truck just not run at all?

What would cause my OBD port to not work?
 
No, they will run without the PROM, if the tune is "close enough".

I don't think you can swap any PROM's between ECM's, if they are different ECM part numbers, except for one exception I can think of, and that was a waterproof ECM used in Corvettes. The PROM from a 1227747 ECM will not work in a 1227165 ECM, etc. even though the ECM's are physically the same size and shape, and may share the same connectors.

If both ECM's are the same GM part number (again, normally a 122-something number, but I believe some start with 16?) then a PROM swap shouldn't be an issue.

The OBD terminal might not work because the PROM is wrong for the ECM. The non-flash of the check engine light is an indication of this as well, but it can indicate other things as well. Need to narrow it down.
 
Ok, so it sounds like my first step might be to grab a complete ECM with EPROMs from a 350 truck in the junkyard and swap the whole thing in. That way I know they match, and maybe if I'm lucky it will fix the non-communication problem.

As far as the CEL, it does idle a little bit goofy, not really bad, but kind of like the O2 sensor is bad (it's not,i put a new one in for good measure during the engine swap). I figured the light was on because of whatever was causing that. But if I can get it to communicate, at least I can read the codes and go from there.

This is an off road only truck, so as long as it runs good, I'm not terribly concerned about it. But I would like it to all work for future troubleshooting.
 
Did you have the ECM numbers? If they re the same youre good. Otherwise the ECM usually isnt terrible expensive from a junk yard
 
You need to be careful swapping ECM's. I have a hard time keeping facts in threads like this straight, but the wiring harness/engine displacement (to put it broadly) need to match whatever ECM is put in. Even with the same plugs, different ECM's have different pinouts.
 
Interesting. Is that what the numbers on the ECM refer to?

That being said, if I have the ECM that is original to the S10 body (in pretty sure that's how I did it), then why would my obd port not work?
And also we never got to talking about my EGR problem


dyeager535 said:
You need to be careful swapping ECM's. I have a hard time keeping facts in threads like this straight, but the wiring harness/engine displacement (to put it broadly) need to match whatever ECM is put in. Even with the same plugs, different ECM's have different pinouts.
Click to expand...
 
Ignore the EGR problem. You don't know what is wrong with it, the ECM is telling you it has a problem. ECM controls nearly everything, fix it before trying to do any further diagnosis.

Is the original S10 ECM the same ECM part number as whatever you used? (part number is what the 122x number is)
 
No idea. I might have tossed the junkyard ECM after I grabbed the EPROMs. Or I might have let my brother in law try it for his Howell injection in his jeep. I'll ask him.

dyeager535 said:
Ignore the EGR problem. You don't know what is wrong with it, the ECM is telling you it has a problem. ECM controls nearly everything, fix it before trying to do any further diagnosis.

Is the original S10 ECM the same ECM part number as whatever you used? (part number is what the 122x number is)
Click to expand...
 
You must log in or register to reply here.

Latest Posts

Top Bottom