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7.4L tbi + fuel problems...injectors dump gas (full open delivery)

36718 Views 22 Replies 9 Participants Last post by  Napoleon Solo, 
8
7.4L 1992 GMC sierra 1ton
--Problems just started, i have to fully depress pedal to start
--injectors have been replaced, they pulse during ignition...when started, injectors spray constant, dumping fuel
--NO o2 sensors on the manifold

**NO engine codes, only code 12
**Can't figure out why injectors are not pulsing, idle revs up to 1,500
--ECM replacement? TPS and IAC need to be replaced?
--everything on the harness gets the correct Voltage.

I'm thinking that the ECM needs to be replaced, the IAC and possibly the fuel pressure regulator.
Very hard to maintain an idle now on the truck and the conical spray pattern is thick and constant when the truck is running.

No MAF sensor or O2 sensors on this TBI 454 engine...it's a 1ton.
again, i replaced the injectors but it's not fixed yet.
Played with the idle screw to no avail as well. :grrrrrr:
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Thanks guys!
Yes, i checked all the sensors but only a voltage check.
Haven't checked the distributor yet.
Stock everything. After i pulled the harnesses to the distributor from the ignition coil...truck wouldn't start. That's as much as i did with that yesterday.
Sounding like the ECM computer might need to be the last thing to replace...
I'm gonna recheck the harnesses....i only have a chilton's for this truck not the FSM and the voltage levels per harness aren't exactly listed well...
I'm gonna guess the usual 12v or 4.5-5v??? Sound about right or do i need to locate a more specific level and drop or variation under load for this harness?
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Solid! I'll post an update later today thanks again for the help so far.
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Replaced the Ignition module, Throttle position sensor, and the Idle Air Control valve.
No progress. Injectors still idle with steady stream of gas and idle holds around 1500 RPM.
Only thing left is MAF sensor (maybe called MAP?) and the ECM right?

Not sure what else would be signaling the injectors to pour gas.
Is there a relay or something else along the chain that might be stuck or not operating correctly?
I switch the under the dash relays around just for fun and that did nothing either.
Truck gets harder and harder to start through out the day and holding the accelerator to the floor is a must for the truck to start at least 98% of the time.

...hmmmmmm
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MAP sensor is next...if that's not it, then the ECM...

Crank pos sensor...Bigg Ron...where is that one...
--Front drive side of engine or back tucked up by the starter on the passenger side? Didn't see anything else. Haven't had or heard any problems with the flywheel or starter though...heard starts and idle can be rough though if the crank sens. is out...
After messing with the MAP sensor, unplugged and the engine light came on...ran better and raced up to 1500 when plugged back in...so makes me wanna rule out the ECM and crack sensor so far.
Thanks again guys...always helps.
First time i've ever worked on a TBI...
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Yeah, replaced the MAP sensor..problem persists.
The plugs keep getting really fouled out with gas and are black drippy messes.
I'm gonna clean the plugs again, check the timing again and go from there.
--CRANK sensor...couldn't find it yet....really hard to see around the starter motor...I don't have a lift and it's 4x4.
I'll do my best but my manual doesnt show a location so im going on past experience that it is located near the starter motor...anyone know where that is exactly?

This sure is one of the harder problem finds that i've had in a while...kinda funny because i know it's something easy.
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Ya, this 1-ton does not have an o2 sensor.
Blanks on the manifolds...no hole or sensor.
Been looking at that since the beginnning but there was never any sensor or hiring harness

---------- Post added at 03:30 PM ---------- Previous post was at 03:28 PM ----------

exhaust with straight pipes + H-pipe.
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Ya, it must have been deleted then...only an H pipe and flowmasters.
NO harness wire can be found though...dangling or otherwise...

Sure they had em on the 1tons?
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Yes, replaced the regulator, new Computer, New IAC, TPS, MAP...after the new computer, new plugs and wires...spray is finally a fine mist, truck starts right up...but now the idle RPM flutters from 800ish...holds then jets up to 1500 then back down...up and down up and down.
I'm gonna try the EGR vacuum and reseting the idle screw procedure again...
if that doesn't work...maybe try drilling in an O2 sensor and wiring it to the COMPUTER....just will need to find out what wires would hook into the computer to do that.
But that would be a long shot for sure esp when there wasn't an o2 on this truck.
Definitely have one of the weird ones im thinking...but its making progress at least.
ANy other thoughts?
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After the new computer went in...and new wires and plugs again...ran good. Still surged up on idle though...up and down. Turns out it was the thermo sensor on the front top of the block/head. Tellin' the computer that the temp was -30deg so it was attempting to warm up or something like that.
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