GM TBI Fuel problem

i wish you were up here and not down in cincy, i have all the tbi diagnosis tools and factory service manuals for an 89 pickup that would get you through the flow charts.

i'm going to say ignition module is the culprit, as it can fail to where it'll spark but not tell the computer to fire the injectors. unfortunately, i have one of those laying around too, would be simple to swap out and check but would be nice to not throw parts at it from the store.

patgizz wrote: i wish you were up here and not down in cincy, i have all the tbi diagnosis tools and factory service manuals for an 89 pickup that would get you through the flow charts. i'm going to say ignition module is the culprit, as it can fail to where it'll spark but not tell the computer to fire the injectors. unfortunately, i have one of those laying around too, would be simple to swap out and check but would be nice to not throw parts at it from the store.

Would the 4.3 out of the S10 be likely to use the same ignition module?

Should be able to swap them. May have slightly different spark offsets and such, but it should work.

Noid light flashes for both injectors. I also watched the throttle body while my wife turned the key to start. Did not see any fuel at all. At this point, is it reasonable to asssume no or little fuel pressure, or is there something else I should check first?

I'm guessing injectors could be faulty, but don't they usually leak when they fail?

In reply to eastsidemav: You should have seen fuel spray from the injectors when the engine cranked. If you heard the fuel pump turn on for at least two seconds after you turned the ignition switch on (prior to cranking), then your fuel rails should have had enough fuel to fire the engine. This leads me to believe that your fuel pressure wasn't within the 9-12 psi range, or worse, no fuel was reaching the injectors.

I recommend tapping into the fuel lines to determine your fuel pressure while the fuel pump is running. Worse case would be no fuel is making it through to the injectors. (If the injectors were leaking, you would have noticed a strong gasoline smell prior to cranking the engine.)

I don't think that you have a bad ignition module as you can fire the engine on starter fluid. If you need confirmation that the ignition module is firing, just pull #1 or #3 spark plug wire (whichever is easiest), place a metal conductor in the spark plug boot, and use an insulated pair of pliers to hold the metal conductor about 1/4" away from the spark plug's end terminal while an assistant cranks the engine. You should see a bright, white spark jump the gap. If the spark doesn't jump the gap (typically a bad module) or is yellowish and small, a tune up is in order. (Could be cap, rotor, and/or wires.)

Hope this helps!

It's pretty redneck but effective to just crack a fuel line somewhere and see if you've got fuel at all. For a no start you don't really need a gauge. I'd start right at the throttle body since it's probably not rusted there and then work my way back to the tank. Wear safety glasses.

i cant remember exactly what the root cause was but my buddy had a TBI 4.3 and sometimes it wouldnt start and he had to wiggle the connections real good on the injectors then it would fire up, probably worth a shot if you havent tried it yet

I have a fuel pressure gauge with a TBI adapter on its way to me. I should have it tomorrow, just in time for the snow to hit, so I may not be able to test it for a while. It looks like the adapter connects to the hose between the chassis and the hardliners under the hood. If I get no (or little) pressure, do these sound like smart next steps?

Disconnect the fuel line under the hood and run some hose from it into an empty gas can.

1. If it flows well here, assume the fuel filter (back by the gas tank) is fine, and something may be wrong with the pressure regulator in the TBI, since this will take the regulator and return line out of the loop?
2. If I get no, or almost no fuel, assume the filter is clogged, or there is something wrong with the fuel line from the tank to the front?

eastsidemav wrote: I have a fuel pressure gauge with a TBI adapter on its way to me. I should have it tomorrow, just in time for the snow to hit, so I may not be able to test it for a while. It looks like the adapter connects to the hose between the chassis and the hardliners under the hood. If I get no (or little) pressure, do these sound like smart next steps? Disconnect the fuel line under the hood and run some hose from it into an empty gas can. 1. If it flows well here, assume the fuel filter (back by the gas tank) is fine, and something may be wrong with the pressure regulator in the TBI, since this will take the regulator and return line out of the loop? 2. If I get no, or almost no fuel, assume the filter is clogged, or there is something wrong with the fuel line from the tank to the front?

Yup. At the risk of getting a reputation for specializing in redneck diagnostic approaches I'll add that a quick test of the regulator on cars that have rubber return lines is to pinch the return line off.

Temps got up above the teens today, so I attached the fuel pressure adapter to the lines, and tested the fireturd's fuel pressure. 13.5 psi according to the gauge. I'm assuming that is well within "acceptable" parameters?

I'm now pretty much stymied. Good fuel pressure, but nothing out of the injectors. Completely clogged fuel injectors, maybe? Maybe they're okay, and I'm just not seeing (or smelling) the fuel coming out of them? Any other possibilities?

All this is generic:

If you have fuel pressure and nothing out of the injectors, you have likely got no injector pulse. There will be an ignition pulse signal from the ignition module back to the ecu, and the ecu will wash the signal and send the required properly timed and duration trigger out to the injectors.

So, if you have spark, your crank and cam signals are fine. If you have a pump relay trigger, that means the ecu is seeing a spark signal. There should be 12 volts at one pin of each injector while cranking. If you have a self powered LED test light, you can also check for triggered ground while cranking.

I'd bet there is a fuse or two somewhere to power the injectors, too.

I'd pull the assembly loose and check the regulator. If it's sat with ethanol it's possible it's just clogged the E36 M3 outta that thing.

In reply to Streetwiseguy:

I checked for an injector signal with a noid light sometime in the last week or so, and there is an electrical signal going to the injectors. Before that, I did check the two injector fuses, and they were good.

In reply to Bobzilla:

Wouldn't the regulator be after the injectors in the flow path? If it was before, you'd be getting whatever pressure is going down the return line? Also, if it's showing good pressure on the feed line, I'd hope that means the regulator is doing its job.

So, noid light flashes, fuel pump makes proper pressure? It should have flow from the injectors. Maybe the wiring has a bad connection somewhere that only gives you enough power to light an led, not enough amperage to lift the pintle. Test for power with a real incandescent bulb that will need an amp or two to light it properly.

Or, something has gone out of range, like the coolant temp sensor thinks its running at 240, so its too lean to start.

I think the noid light set I have is an older style, with incandescent lights. I'm headed to the junkyard on Saturday anyway, so at this point, it's getting tempting to just grab a whole throttle body, and see what happens when I replace it.

In reply to eastsidemav:

There are little passages in that aluminum housing that can clog. I would take it apart and get the rebuilt gasket kit for $9.

Your inlet fuel pressure of 13.5 pis is very good (9-12 psi is acceptable according to GM). The fuel pressure regulator is located before the injectors so as to vary the fuel pressure according to engine load (vacuum). These units are notorious for weak springs that allow the fuel pressure to bleed off below the acceptable psi level. A complete throttle body rebuild isn't that hard and will correct a lots of little problems that can crop up later in daily use. Here a link to a YouTube video. (You don't need the adjustable fuel pressure regulator shown in the video unless you're trying to fine tune a TBI unit.)

Before you do the rebuild, measure the resistance between each injector's firing terminals. If all is okay, you should see 1.2-1.3 Ohms (find your vehicle's resistance value in this PDF table). If the solenoid is burnt out, you should see an open circuit. If both injectors test okay, go ahead with the rebuild. Clean out all the TBI's electrical connectors both male and female with a good electrical cleaner. (I use CRC products exclusively because they do the job the first application.)

Good Luck!

Thank you. I will have to see about pulling it all apart to rebuild. A little tired now from pulling the drivetrain from the s10, but will look into that in a bit more detail tomorrow, when my brain is working again.

Was at the junkyard on the weekend, so I grabbed a fuel injection assembly from a wrecked GMC Sierra with a 305. Installed it this evening, wrapping up just as it started to rain, so I pretty much had one chance. The car fired up pretty much immediately, but wanted to idle pretty low, would rev though if I pressed the gas. I let it idle, and eventually, it chugged and died. Tried to fire it up again, starter turned it a bit, then hard stop I hopped out of the car, and pulled the air cleaner lid in time to see pooled gasoline draining down the throttle body.

So, it looks like I've traded one problem for another. Clogged up system at the beginning, now, presumably a leaky injector. I do not have the time or inclination to pull the plugs tonight to deal with this. Since it hydrolocked while I was using the starter, rather than while it was being driven, is the engine probably okay, or am I looking at the possibility of a bent rod?

This is getting really annoying - I'dve been willing to just pull the engine to put in the truck, and switched it to a carb, but I still want to see if the transmission is any good, which pretty much means I need the engine to be running in the firebird.

It should be fine. And usually not an injector, but the o ring that seals them to the fuel pod.

Agree with Dusterbd13. Leaking injectors make for hard starting and rough idle. If the engine was flooded with excess fuel, o-rings would be my first guess. Sorry that you're having such a miserable time getting the TBI to work. I think your best bet is to rebuild the TBI unit and get the engine running to check out the transmission.

If you do switch to a carburetor later on, at least you would have a functioning TBI setup to sell to offset the cost.

Good Luck!

In reply to Dusterbd13 and MrBeachcomber:

Thank you. I've got a TBI rebuild kit on order from Amazon, so should get it in a few days. Before then, I'm going to recheck the fuel pressure, and just see if I can see where fuel is flowing from with the pump running. Once I've rebuilt it, I'm thinking it would be wise to pull the spark plugs to get any gas out of the cylinders, and change the oil, since the I'm sure its pretty contaminated at this point. May not get to any of this until the weekend - I can just switch my attention to the S10 for the next few evenings.

If I can get it working right, I'll be happy with the TBI, at least unless I can put together a considerably more powerful engine for the challenge.

This morning, I planned on rebuilding the TBI unit, and seeing what happens. First, I asked my wife to hit the fuel pump switch, so I could check pressure on the junkyard TBI, and get a good look at where it was leaking. Well, pressure was good, and there were no leaks anywhere, so I tried to fire it up, and other than blowing out a lot of condensation, it ran fine.

I did a very quick (and somewhat incomplete) change of the oil in order to get some of the gas out of it, and fired it up again. Still running fine. My best guess is an injector stuck open, but who knows, hopefully whatever happened won't happen again.