TBI 350 hesitation

[crashandburn]

I've got a pretty mean little S10 Blazer. It's on solid axles, triangulated 4 link suspension and 40" Swampers.
Recently I swapped in a TBI 350. Nothing crazy, totally stock except for a throttle body spacer. Huge upgrade from the tired smokey 4.3 that it had.
Only problem is that I have a stumble especially coming off idle.

- Important part- For the first maybe 10 seconds after a cold start, it runs absolutely perfect. Then it idles a little rough, not terrible, and the hesitation starts.

I'm wondering if it is the EGR. I'll try to be both thorough and concise. Here goes:
The truck is a 91 and the motor is a 94. Some things were a little different but I swapped them all over.
I did swap the 350 EPROM chips into the computer.
I tried scanning for codes (SES light is on) but the truck would not communicate.
I tried jumping out the OBD port to read the codes. That didn't work either.
I tried the 350 TB (has different TPS. I wired the connector to adapt it)
I tried the 4.3 TB and swapped in the 350 injectors
If i stick my fingers in the EGR valve and depress the diaphragm, the engine does stumble, so I know the passages are not clogged.
I do have vacuum at the input of the EGR acuator
When my new vacuum gauge shows up in the mail I will test the EGR valve and see if it holds vacuum.

Aside from throwing parts at it, is there anything else I can try?

 

[1-ton]

sounds like a rich fuel condition to me. Your ECM could be in "limp mode" (i.e. full rich fuel) because it does not know what to do with the Frankenstein list of parts you have thrown at this swap. If you have an improper combination of EPROM's, injectors, sensors, and wire harnesses...who knows what could be going on with your engine.

 

[crashandburn]

Well, it is a 350 with 350 injectors and 350 EPROMS. There is no black smoke, so I'm not thinking it is a rich condition. Momentarily lean, maybe. Also really the only sensor that is pertinent to this problem that had to be adapted is the TPS. And that's only because the truck is pre 92 and the engine is post 92. I used the one that goes with the truck.

 

[jekquistk5]

Well, it is a 350 with 350 injectors and 350 EPROMS. There is no black smoke, so I'm not thinking it is a rich condition. Momentarily lean, maybe. Also really the only sensor that is pertinent to this problem that had to be adapted is the TPS. And that's only because the truck is pre 92 and the engine is post 92. I used the one that goes with the truck.

Was just gonna say tps. I had one that you had to wallow out the holes to get it at .47v. It was at .6 and causing all sorts of issues.

 

[crashandburn]

Was just gonna say tps. I had one that you had to wallow out the holes to get it at .47v. It was at .6 and causing all sorts of issues.

Interesting...
When you say wallow out the holes, I assume you mean you had to rotate the TPS some to get it to push the lever the correct amount?

Tell me more about the voltage...
Which wire do you test?
You mentioned .47v, is that my target? Is that with the throttle closed or at wot?
You also said that .6 gave you trouble. Does the voltage drop as throttle increase, or the other way around?
Did you have to rotate the TPS clockwise or counterclockwise?

 

[jekquistk5]

~ .5 volts is idle(blades closed). I used an Aldl cable and tuner pro to see the tps voltage but you can measure with a good set of needle probes and a multi meter. The tps voltage goes up with increased throttle. I believe I had to rotate mine clockwise.

 

[bp71k5]

~ .5 volts is idle(blades closed). I used an Aldl cable and tuner pro to see the tps voltage but you can measure with a good set of needle probes and a multi meter. The tps voltage goes up with increased throttle. I believe I had to rotate mine clockwise.

If you get a scanner/tuner pro, you can see the voltage as you press the gas pedal. Make sure the voltage changes smoothly as the pedal moves.

 

[1-ton]

~ .5 volts is idle(blades closed). I used an Aldl cable and tuner pro to see the tps voltage but you can measure with a good set of needle probes and a multi meter. The tps voltage goes up with increased throttle. I believe I had to rotate mine clockwise.

The problem with using Tuner Pro is that the EPROM has been swapped from one ECM to another ECM. You need to know the proper "broadcast code" in order to get the correct .BIN file, and the getting the correct .ADX, .XDF files could be an issue too with a swapped out EPROM. Without the correct files Tuner Pro will not communicate.

 

[jekquistk5]

The problem with using Tuner Pro is that the EPROM has been swapped from one ECM to another ECM. You need to know the proper "broadcast code" in order to get the correct .BIN file, and the getting the correct .ADX, .DFX files could be an issue too with a swapped out EPROM. Without the correct files Tuner Pro will not communicate.

Yes that is true. If you feel that's complicated you can always use winaldl