tbi issues, on my 88 gmt400

[Swims350]

how would I check the vss? the speedo does work. nothing else does though, like the trip or odo, but speedo does. Last time I was under it everything was ok but maybe I should recheck.

 

[Jims86]

how would I check the vss? the speedo does work. nothing else does though, like the trip or odo, but speedo does. Last time I was under it everything was ok but maybe I should recheck.

Yeah, the VSS is an important part of the Idle strategy, which if messed up somehow, could cause the shift stall. It is a brown wire in cavity A10 of the small ECM plug, and it goes to the DRAC unit under the dash...not sure exactly where in the gmt400....Retro?

 

[RetroC10Sport]

1988-91 did not use a DRAC module. It was contained within the cluster.

 

[Jims86]

1988-91 did not use a DRAC module. It was contained within the cluster.

Ahhhh... Okie doke. Chris, unplug the ecm(might not hurt to peep at the pins while your there) and the other end at the speedo, and check for continuity and ground.

 

[RetroC10Sport]

You have any ideas as to why mine is in open loop at 190F? Bad CTS? Bad ECM?

 

[Jims86]

You have any ideas as to why mine is in open loop at 190F? Bad CTS? Bad ECM?

Whats the o2 doing, and whats TPS volts? If the o2 cools too much at idle, it will go OL, regardless of coolant temp. Pig rich will cool the **** outta the o2.

 

[RetroC10Sport]

TPS is 0.00% at idle. o2 seems to be doing its thing, about the same as my Blazer which doesn't run rich. I'll see if I can get a good datalog tomorrow.

 

[Jims86]

TPS is 0.00% at idle. o2 seems to be doing its thing, about the same as my Blazer which doesn't run rich. I'll see if I can get a good datalog tomorrow.

Ok, while your at it, go ahead and see if you can get the min air idle re set at about 450rpm, and see what the MAP voltage is...should be around 1.21-1.23
Also, check ground for the O2, Cavity D6 on the large ecm connector.

Chris, Pin cavity D on your ESC, check for good ground...goes to the thermostat housing, but could be internally jacked up.

Another thing for both of ya's. The sensor ground and MAP ground were swapped on my 88 harness. I swapped them per the diagrams, and it seemed to run a little better. the pins in question on the ECM are: Pin A11 SHOULD have a black wire from the TPS, and CTS.
pin D2 Should have a purple wire from the MAP sensor.
Both the TPS and MAP share the 5v reference, but for some reason, have their own grounds.
Chassis grounds are specifically A12 and D1, check those...I am hoping your next posts will be in a positive direction....this is kicking the **** outta me, and makes me wish I could be there to join in the fun.

 

[RetroC10Sport]

Got it. Will do that tomorrow or Tuesday, depends on the weather, I don't drive it in the rain.

 

[Jims86]

Lets clean the o2 sensors too...with the engine running, up to temp, ground a and b and run her at 2k for about 3 minutes. CEL will flash like a ************. slow flash(1 per second)=closed loop
Fast(1every 1/2 second)= open loop

 

[Jims86]

Got it. Will do that tomorrow or Tuesday, depends on the weather, I don't drive it in the rain.

Sweet.

 

[RetroC10Sport]

Okay, had to set the TPS to .55 because it skips odd numbers. No datalog but screenshotted TunerPro. Still runs pig rich and the BLMS and INT drops like a rock when idling.

 

[Swims350]

well mine I thought I had figured out something and it was the esc module, but I forgot I had advanced it back so most of the idle and hammer down bog sitting in park went away, which it always does when I advance it.

I also noticed it was shaking bad and missing, uuumm well when I tried pawpaws icm and switched mine back in it's place, I got 7 and 6 wires mixed up lol.

got that straight, ran to lowes and hauled some vinyl flooring to my mom's, ran fine.

it usually runs fine advanced however, just increases the chances of stallin changing between D and R.

Now another thing I noticed... with either ecm or ecu, which is it?... anyways...

when it first fires, connector hooked up, check the timing and my balancer groove its pointing almost straight up at 12 o clock position, as it warms up it slowly drops back down towards the timing tab, with the timing connector unhooked it's set to zero(or was) now I said that to say this....

when I advance my distributor, when it runs great, no miss or bog and will roast them 33's, the timing is running about the 12 o clock position again. I can run it that way without the timing connector plugged in, and then with it hooked up, hooked up requires less physical advancing done by me, and seems to run better, but unhooked requires me to advance it more and maybe a tad worse on running.

neither seem to have an effect good or bad towards the gear change stall or hot refire.


my plans as of now, once I get the old 305 truck motor back that was once in my dad's 84 c10 and is now in my old monte carlo ss my brother in law has, swap those 305 heads, and the dist. and intake onto my 350. I may get an aftermarket intake though, as it's a stock q jet type, and would require me to use an adapter IF I can find asquarebore carb, plus block off the egr and that crap. I may also port and polish the heads to help them flow, but undecided on that. I want to try it since I never have, but it seems my swirl port tbi's run outta steam around the same rpms as most say the 305's would. It has enough rpm's for me now, runs good and all so who knows.

 

[Jims86]

Okay, had to set the TPS to .55 because it skips odd numbers. No datalog but screenshotted TunerPro. Still runs pig rich and the BLMS and INT drops like a rock when idling.

MAP volts perfect. At normal op tem, go ahead and decrease the Throttle blade angle slowly....about 1/4 turn, and see if the IAC counts start to climb. see if you can get it around 30, and then reset the TPS.
I have seen Factory non adjustable TPS at .70v just as an fyi.

well mine I thought I had figured out something and it was the esc module, but I forgot I had advanced it back so most of the idle and hammer down bog sitting in park went away, which it always does when I advance it.

I also noticed it was shaking bad and missing, uuumm well when I tried pawpaws icm and switched mine back in it's place, I got 7 and 6 wires mixed up lol.

got that straight, ran to lowes and hauled some vinyl flooring to my mom's, ran fine.

it usually runs fine advanced however, just increases the chances of stallin changing between D and R.

Now another thing I noticed... with either ecm or ecu, which is it?... anyways...

when it first fires, connector hooked up, check the timing and my balancer groove its pointing almost straight up at 12 o clock position, as it warms up it slowly drops back down towards the timing tab, with the timing connector unhooked it's set to zero(or was) now I said that to say this....

when I advance my distributor, when it runs great, no miss or bog and will roast them 33's, the timing is running about the 12 o clock position again. I can run it that way without the timing connector plugged in, and then with it hooked up, hooked up requires less physical advancing done by me, and seems to run better, but unhooked requires me to advance it more and maybe a tad worse on running.

neither seem to have an effect good or bad towards the gear change stall or hot refire.


my plans as of now, once I get the old 305 truck motor back that was once in my dad's 84 c10 and is now in my old monte carlo ss my brother in law has, swap those 305 heads, and the dist. and intake onto my 350. I may get an aftermarket intake though, as it's a stock q jet type, and would require me to use an adapter IF I can find asquarebore carb, plus block off the egr and that crap. I may also port and polish the heads to help them flow, but undecided on that. I want to try it since I never have, but it seems my swirl port tbi's run outta steam around the same rpms as most say the 305's would. It has enough rpm's for me now, runs good and all so who knows.

I wonder if your balancer slipped?...have we covered that already? Dunno, too lazy to go back and look...lol
Timing always advances on cold start.

 

[RetroC10Sport]

I will likely get to that this weekend and try it. Got too much to do this week and no way I am taking it out right now. Even though San Marcos is almost an hour away, had fukin APD shine their spotlight on me last night while going around the block...