GM 2.5 TBI fuel troubleshooting

Project S-10 has come to a grinding halt.

It was running poorly. I replaced plugs, air filter, pcv, and O2 sensor (which subsequently required exhaust manifold replacement).

Now it's a no fuel no-start. Verified with spray down the TB, and it runs for a second. Jumped fuel pump relay and I can hear the pump running, still no start.

Factory wiring diagram is useless. It says that the ECM output pulses the injector, but it doesn't tell me what inputs cause that.

I am very frustrated. I know I can beat this, but I really need help.

Thanks.

get a noid light to verify injector pulse. they're cheap at the parts store or really cheap to buy a whole set online if you have a little while to wait. your profile doesn't say where you are, but if you're around me you are welcome to borrow mine.

pump on does not mean adequate pressure either. i had a 3.1 tbi running very poorly on 2psi of pressure from a dying pump. when the pump finally dropped to 1psi it would not start.

what year? i have 88 or 89 3 book factory service manual set if anything inside them could help.

Rented the noid light at AZ. Injector pulse verified.

Removed filter to TB connection. Jumped fuel pump. Gas is coming out the outlet side of the filter. Hard to determine pressure without tester. Hmmm.

Noid light flashes, pump delivers fuel, but no spray from injector? That seems a bit wrong, I'd say. Its either got very low fuel pressure, totally clogged or electrically open injector, or the noid light is picking up a pulse, but there isn't enough amperage to actually open the injector. Do you have an ohm meter to test the coil of the injector? Can you use a stethescope to hear whether its clicking as the engine cranks?

my fuel pump worked just fine... but wouldn't start... talking to my grand-mother-in-law it started where the truck would just randomly cut out... let it sit and it would start up again after a bit...

but anyway when I pulled the pump to inspect/replace this is what I found...

also if you don't have a mechanics 'scope you can jut touch a flat head screw driver to the injector and put your ear to it... if the injector is pulsing you'll hear it

oh also from what i've read/seen about 100% of the s10 duke engines EGR's fail... and from what I understand the 'O'vanced-zone replacments are trash

Well, I discovered a horrendous, PO-hacked fuel pump ground - hoped that might help solve. Made a better ground. No luck.

I can hear the injector clicking as I crank.

I'm quickly running out of ideas.

The filter sock on the fuel pump is famous for clogging up if the car has been sitting a while too. That might be holding up your fuel pressure.

It seems like a fuel pressure gauge would be very useful, I assume there's a test port near the injector?

pres589 wrote: It seems like a fuel pressure gauge would be very useful, I assume there's a test port near the injector?

generally on gm TBI stuff - no - there is no test port. you need a gauge that tees in the line.

In reply to patgizz:

How nice of GM!

pres589 wrote: In reply to patgizz: How nice of GM!

it's one notch above a carb.. .runs at about 12psi... (about 5 or 6 for carbs is normal)

If it is anything like the V8 TBI system, you should also be able to take the dizzy out and turn it by hand to get the injectors to fire. Take off the air filter to see the pattern. Make sure the fuel pump is on.

Rob R.