Hey, i'm a newbie here. i have 2 suburbans with TBI. a 93 and a 90. i know those aren't camaros but many other sites list this place as the best source for efi tech so here i am.

my 90 i just aquired and is a high milage rig- 160k. compression is 90-100 accross the board. it is starting hard and seems to hesitate if not bog just off idle then pick up and run great at higher rpm. another strange thing is when i hit the throttle once quick then back off the engine runs on for a couple seconds before coming down. so first off do you think these are all related or different problems? i tested the tps and it was around .6 volts closed throttle. the cst was only .1 so i replaced it. still kinda new at the electronic game so bear with me. the plugs are ok but not great and i have not done the standerd wires cap and rotor routine yet. let the newbie bashing begin!

 

Looks like you are in the same boat with me. Let's see what happens after plugs+wires+cap/rotor. Check for vacuum leaks, you might be running slightly too rich (you know the drill, carb spray, blahblah).. Check for leaky injectors (remove air filter, look at the spray... drippage = trouble).. Make sure that throttle plate is at 90 degrees when you mash the pedal -- if not, adjust it.

The engine running on sounds like ignition trouble. Happens to me sometimes, too. Do you see the tach needle getting bouncy?

 

didn't check for leaky injectors. pulled 15 inches at the manifold. if i remember right, when i pulled the plugs to do a compession test they looked like they were burning normal. thanks for the help,

jason

 

Ignition voltage could drop suddenly above certain RPM, I think... which means if it's above 3000 RPM, it's not somewhere where you rev the car all the time, so your plugs don't show the signs of abuse... I might be wrong, but seems like a sound theory to me. Does the tach needle bounce around when you let off throttle?

 

don't have a tach. what will i mean if it's bounceing when i let off the gas?

 

I have a 91 camaro TBI that runs great. I also have an 87 chevy pick up with TBI that doesn't.

I'd check out the Idle Air Control (IAC)- it may not be functioning properly. This helped my truck.

Also may check to be sure that EGR is working properly (not stuck wide open).

Also check the basic stuff, like ensuring vacuum lines are in good shape.


Here is just one thread on IACs:
https://www.thirdgen.org/techbb2/sho...&highlight=IAC


May also use the search function to check other threads. There is so much good info on this board it is amazing.

Keep trying and good luck-
S-D

 

It also looks as though the compression redings are kinda low. Did you do those with the engine warm and the throttle fully open? Just a few things to throw out... hope they help you in some way. Take your vacuum gauge and watch it as you snap the throttle open. I have a good chart here somewhere on vacuum gauges and ill see if i can post it.

edit: opps, being unobservant again...

 

engine pulled a steady 15 inches at idle. as i gave it gas it would drop only an inch or 2 then go back up . seems just as i crack the throttle is when it stumbles. wouldn't this be TPS? the compression is low. as i said, 160k. still should run a bit better then this. on the top end it runs great. engine was warm for the compression test.

also thinking about fuel filter as a possibility or part of the problem.

thanks all

jason

 

hmm... you could try the general tech board. Alot of knowlege and more traffic there. If youve done a full tune up then it should give semi-decent throttle response unless the valves are all coked up and the compression is shot and what not.

 

I would replace fuel filter since its cheap and easy. Look for leaky injectors. I have someone turn the ignition key on and off (don't engage starter)while I look at the injectors. If they drip or spray any fuel during the 10 secs of pump priming when the key is turned on then that injector is bad. I have seen some really bad ones. Your vac seems a little low. My 130k mile car will still pull over 20 inches. You PVC, IAC or EGR valve could be stuck open causing the low vac and that makes the computer think there is more load on the engine than is really there and tries to give it more fuel than it really needs. The TPS sensor usually gives a jerky cruise on the highway when they get flakey.