Thread: TBI problems we think

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howdy Gang,
My friends 5.7L 1988 GMC pickup is running pretty rough. We did a compression test and all cylinder came out pretty even, less than 5 psi difference on one cylinder than the rest.

It had what looked like the original spark plug wires so we changed them.
New plugs, cap , rotor and fuel filter and oxygen sensor.
I aimed the timing light at the TBI injectors with the air filter off and saw the spray wasn't much of a spray more like a drizzle. So I replaced both injectors.

Now with the engine running and using the timing light there is a spray but it seems like there is alot of fuel. It still runs rough. If I disconnect one of the electrical plugs to the injectors it runs sort of better.
I don't have the timing specs but the painted mark on the vibration damper is right on.

Can we disconnect the battery to reset the computer?
Any ideas?
cheers
hank

the first thing I would do check for any codes that are stored in the computer then check fuel pressure and yes if you unhook the batt. it will erase the codes .....ted

thanks Ted
not to be a dim wit but how do we check the codes --my reader is for 97 and newer rigs

Google is my friend
I see that I need to jump A&B and write down the flashing light code
thanks
I'll report back when I get the codes
cheers
hank

Louey wins by 2 minutes over Google---is this a record setting performance ??? Yea Louey

Nice work Louey

Ok we got the 12 code then 31 or 13 (I'm pretty sure it was 31)
I looked it up and 31 can be the
canister purge solenoid
camshaft sensor or circuit
EGR circuit
shorted MAP
and
turbo over boost( no turbo)
park neutral switch(3.3L)
MAT (Cadillac only)

that flashing light sure is fast compaired to other makes I've seen

any idea what to do next
thanks
hank

Sounds like good advise to me Louey!!!
I was gonna say I don't believe it's the fuel pressure because it will usally quit running if the fuel pressure ain't right.
Kurt

Originally Posted by TOW'D

Nice work Louey

Ok we got the 12 code then 31 or 13 (I'm pretty sure it was 31)
I looked it up and 31 can be the
canister purge solenoid
camshaft sensor or circuit
EGR circuit
shorted MAP
and
turbo over boost( no turbo)
park neutral switch(3.3L)
MAT (Cadillac only)

that flashing light sure is fast compaired to other makes I've seen

any idea what to do next
thanks
hank

Three of those codes stand out.The canister purge could be as simple as a cracked vac line which is pretty common.EGR is a simple as taking off the EGR and cleaning the carbon chunks out of it and replacing the gasket with a screen gasket from the help section of your local auto parts store to prevent it from happening again.A EGR would act like a vac leak and would effect the idle making it a rough idle.The MAP sensor would effect the fuel curve,But as stated,the codes has to be seen at a temp of 195.Fuel curves "could be" effect by the following senors:Map,Temp sensors,throttle position sensor,air idle sensor,O2 sensor.If it where me,I would get the engine to 195 and take a hard look at the very first code displayed because the other codes could be a result of the fault of the first one.The values of the first sensor to test confirm it is defective can be had on the Autozone web site.

I'd heat it up to 195 so it would go into closed loop--then disconnect battery to clear computer--then restart --that way, you will by pass all the cold start stuff and get rite to where its supposed to run

good stuff guys
I'll try it as Jerry suggested
thanks
hank

Please make sure to give us a update.

We warmed the engine( it stayed at 50*C) then disconnected the battery and took it for a drive but it seems I didn't drive enough, had to get to work.
The check engine light was lit solid but I could not get any codes.
So I'll get up a little early tomorrow and do it again but with more driving
it runs crappy and will not idle---I have to mash the gas to the floor to get it to start.

I'm looking for a good place to find out about all the gadgets(EGR and what ever all the rest is) near the TBI on the intake manifold.

How to test the water temp sender and EGR?

Is there a good port to hook up a vacuum gauge on these engines?

thanks for the spiritual advice.

cheers
hank

you may have a cloged converter

the most common problem on these tbi units is the gasket under the tbi unit is a vary thin paper and it blows out if you pull the bolts that hold it to manifold you can raise it enough to replace it when that gasket blows it allows air into the iacv passage (idle air control valve ) and they run like crap.......ted

Today I pulled the throttle body off and found the gasket cracked and crumbling. So I replaced it . Still ran crappy.
So I tried to take the EGR valve off but the throttle body was in the way so I pulled the TB off and was able to undo the two rusted nuts.
I cleaned the EGR and put it back on.
When I was putting the throttle body back on I noticed the IAC was finger loose on the TB.
I pulled it off and cleaned it and reinstalled. I waited a few hours for the silicone on the base gasket to cure.
When we started the engine it idled smooth and feels like it has good power.
Not too sure just which one of the problems we fixed after finding the many possiblities

Thanks for all the help guys
cheers
hank