ECM question

[Hoodbj]

I recently replaced my 87 tbi 305 to a 91 350 tbi from a suburban (with lots of help from this forum). The issue I'm having is I used the engine from the suburban but not the tranny which is not a 700r (4160e? Possibly) I used the 700r that was in the pickup since the tranny in the burb didn't shift right. The problem is if I use the ECM and prom from the suburban my tranny shifts at the wrong points and does not lockup. If I use the original 305 ECM the engine is sluggish at low-speeds. Would a prom from a 87-91 with a 350 and 700r work if I could find one or do I need one programmed? Thanks again fellas

 

[RetroC10Sport]

If the Suburban was a 1/2 ton, it would be a 700r4 as well. Where are you in Texas? I have an extra couple of ECMs for my 1989 350/700r4 Sierra.

 

[Hoodbj]

Near Dallas Fort Worth area. I think you may be correct on the other tranny being a 700r also after checking the casting numbers. I wonder why no lockup on the 87 700r with the burb ECM? Thanks for the response

 

[RetroC10Sport]

Darnit. If you were closer, I'd hook it up to my computer and run a diagnostic.

It should be the same 7747 ECM. Perhaps you can find a 1987-88 PROM for a 350/700r4 and try that.

 

[Hoodbj]

I have a buddy with a 87 350 700r r10. I may try to coax him to let me try it. I am a little curious why the burb ECM would act this way. Are there different variations of 700r transmissions between 86 and 91, assuming both were factory

 

[RetroC10Sport]

I don't think so as far as the PROM goes. I am running a 1991 PROM in my 1989 with no problems. Someone could have put in a 3 speed or a 4L60E or 4L80E PROM in that computer and that's why the trans wasn't working right in the Burb.

 

[Hoodbj]

The tranny shifted ok in the burb, the only bad thing was it built high rpms between 1st and 2nd before shifting. After that it was good. The 700 r from the pickup ran fine so that's why I used it. The burb did lockup fine though. I will see if I can get my hands on that ECM. My pops has a 89 350 700rsetup also. Would that ECM fit or was there a difference between the squares and the next body style?

 

[RetroC10Sport]

Shouldn't be a difference. The ECMs are all the same, just different PROMs for different engine/trans combos. They all use the 7747 ECM.

 

[Hoodbj]

Thanks retro, will check into that this weekend

 

[RetroC10Sport]

Let us know.

 

[Hoodbj]

Just for the hell of it I pulled the prom from the burb ECM. It reads jt8(g)/j6/p. lfivz348. Ab04. I am trying to research this to see if it went to another style tranny

 

[RetroC10Sport]

Should be ASDU.

 

[Hoodbj]

Just for gits and shiggles I replaced the prom in the burb ECM. Put in pickup and whalaah. Shifting and locking up in overdrive. I'm not sure what was going on before but for now working good. The only thing that seems a little off is it may be going into overdrive a bit early, around 35-40mph. If you keep the rpms up in drive without letting off I can get it to shift later. A little more tinkering and it may become a daily driver yet. Hard to beat a square.

 

[shortboxchevy77]

Just for gits and shiggles I replaced the prom in the burb ECM. Put in pickup and whalaah. Shifting and locking up in overdrive. I'm not sure what was going on before but for now working good. The only thing that seems a little off is it may be going into overdrive a bit early, around 35-40mph. If you keep the rpms up in drive without letting off I can get it to shift later. A little more tinkering and it may become a daily driver yet. Hard to beat a square.

That's the same speed my 87 ECM goes into OD. I was having problems with keeping the truck at 75mph and keeping the converter locked. I finally just jumped the wiring to the trans so it goes into full lockup as soon as it hits OD, much better. I drive around town in drive only anyways so its not a big deal to me.

 

[Hoodbj]

That's the same speed my 87 ECM goes into OD. I was having problems with keeping the truck at 75mph and keeping the converter locked. I finally just jumped the wiring to the trans so it goes into full lockup as soon as it hits OD, much better. I drive around town in drive only anyways so its not a big deal to me.

What wires did you jump?