aaron7

iTrader: (7)

1991 TBI, stock except with headers.

Problem was gradual. Sometimes would hesitate lately, and has always had a high idle.

Then one day it started to choke out when giving it gas, like when you are almost out!

Now it runs fine if you dump gas down the TB, but will only start and run very bad off the tank. If you give it gas when running off the tank; it dies.

We tried all sorts of stuff... a new TPS, new MAP, new fuel lines... no difference. The tank and fuel pump are almost 2 years old and are Delco GM replacements.


What can I check? Do they make TBI rebuild kits? Help!!!

This is my friend's description (his project!):

It will not stay running. It has 10 psi of fuel pressure at the filter, the egr is fairly new and doesn't seem to be sticking, I tried a replacement module under the distributor cap, cleaned the IAC with carb cleaner, and tried a replacement TPS.
It cranks much longer before firing before all this started. When it does fire, it stumbles and dies. If I give it some gas, it will load up, bog down, and die.
I unplugged the map sensor, and now the truck still cranks for a long time, but idles smoothly, at a high rpm. If I put it into gear, it dies immediately. Also, if I blip the throttle, the rpm's come down slowly. New map sensor did not help.

New fuel filter as I just replaced some fuel line, maybe I'll try running it wothout one for a minute.

z71stroker

you cleaned the IAC, but does it work? sounds like it's seized.
I'd go through and check all vac hoses and for vac leaks, get some new tb gaskets, then run some gunk (that's the brand) or equivalent through the motor to clean up any deposits on the intake valves/fuel system. maybe it needs a tps adjustment too?

Benm109

I second checking for vacuum leaks and the IAC. Did you happen to check or clean out the IAC passages when the IAC was out? Sometimes the IAC passages in the TBI unit get clogged up with carbon and won't allow the IAC to move freely. Another suggestion would be to watch the fuel spray out of the injectors while it's running, just to make sure the injectors aren't clogged or sticking. The fuel should spray out in a conical shape with an occasional drip.

They sure do. Most auto parts stores list them as "TBI Tune-up Kits". They cost around $40. An example of one of these rebuild kits is GP-Sorensen part number 97-724.

aaron7

iTrader: (7)

Ok, rebuilt the TBI, replaced the oil sending unit and switch, still a no go!!

Now it doesn't even run if you pour gas into the TB. It just cranks and spits back at you, never catching.

The injectors do drip, and there is plenty of fuel at the lines at the throttle body.

We took the TB all apart and cleaned every inch of it, so no clogs there.

We checked the distributor, and it is where it was before, so I am at a total loss.

dimented24x7

iTrader: (2)

Have you checked the P/U coil, ign. coil? All grounds in good shape? Also dont forget to make sure the dist. base, clamp, and area on the intake the clamp contacts are as clean as possible. This is the ground path for the dist. and it must make good contact for everything to work. How did the exhaust smell when it was running?

I was thinking egr, but that would only be a problem at idle. It would clear up when you gave it moderate throttle. Vac leaks could also be an issue, but any leaks around the tbi will just cause a high idle for the most part.

Hmmmm... Definatly an interesting problem.

steve8586iroc

How many miles are on the engine itself? Have you checked the timing to see if the it might be fluxuating( i.e. bad timing chain and or sprockets )? You mentioned it would spit back through the tb so something is causing the ignition to fire while the intake valve is still open.

Hope you find the problem.

Steve

aaron7

iTrader: (7)

About 90,000 miles. It isn't igniting at all, just spitting a cloud of raw fuel out the TB.

dimented24x7

iTrader: (2)

It could be, and probably is, flooded. Disconnect the injectors and crank the engine to clear it out first. Also consider new plugs.

Teh fact that it has fuel means that the ecm is at least sort of injecting fuel. Have you tried another ign. coil?

aaron7

iTrader: (7)

Ok, the initial problem turned out to be the oil pressure switch... guess the computer was messing with the gas because it thought there was no oil...

and then the timing was 180 off, due to taking the intake off.

Anyway, it runs great now... and idles much better thanks to the TB rebuild. Thanks for all the help!