1988 Chevrolet Truck

Electrical problem
1988 Chevy Truck V8 Two Wheel Drive Automatic 165000 miles

I have been having trouble with a friend's vehicle he needs for work. It had a bad fuel pump, so dropped the tank and replaced it thinking it would fix the no fuel problem.
Getting proper fuel pressure at the TBi assembly. Motor fires over with starter fluid. Heard on this site about changing the ignition module/pickup coil in the distributor to get the ecm to ground the fuel injector circuit.. changed out for a jy distributor assembly. Still no go.
Checked for voltage at injectors, 12v, and at the ECM's power out for them (A6 pin) 12v, and D14 and D16 I get 12v, so wiring is fine. After this in the circuit the computer grounds out the circuit, making it closed briefly and the fuel injectors fire.

Are there any other sensors/modules, when bad, will keep the ecm from grounding out the fuel injector circuit(s)? I haven't checked them with a noid light but pretty certain there isn't a circuit complete due to a bad sensor

attached wiring diagram schematic

also check the thread on page 2 I posted more info about the ignition module voltage at ignition on position, there was basically no voltage coming back to the ecm, but power in from the ignition coil to the module.

possible bad jy distributor? Any help appreciated, thanks!

March 27, 2008.

You need to check the TPS volts
make sure its not in a flood mode
if its in flood mode ECM will not fire the injector
so check the volts at the TPS and also give it a good look
check if its moving with the paddle
good luck

Mar 27, 2008.
Btw all fuses are fine (inj a + b, etc) and the ecu when tested gives 12 codes repeatedly when I jump the aldl connector

Mar 27, 2008.
Disconnect the tps and check if you dont have a way to test the volts
that will put the ECM in a limp mode

Mar 27, 2008.
Flood mode voltage would be 5v meaning maxed on that circuit meaning the tps isn't doing the proper resistance potentiometer it should be? Or do I have it backwards (maybe cause I work on Fords heh) btw here's a better diagram the other one I attached thru the site didn't show up right: so C13 blue wire should be power to tps, 5v, and the black wire should be the changed voltage so at closed throttle it would be 1v'ish back once it goes thru the coolant temp sensor that alters a bit too?

How does this go, thanks for any help here and for the help you've shown, it sound's like a possible bad tps

Mar 27, 2008.
Forgot to mention I have tried to put it in limp mode before by disconnecting the TPS plug on the otherside of the TBi opposite of the linkage and still no fire from injectors. But I think I had disconnected the MAP sensor at the same time but I don't think it should've had bearing on the injectors spraying.

Maybe I need to check the ignition module once more.

Mar 27, 2008.
If you can use a scanned it will be a plus
Tps is at the throttle body
flood mode will not allow injector to open unplug the injector and check it for pulse
ive seen it where the metal round that the air cleaner sits on cuts the injector wires you may wants to check that too
if wire good and TPS
far to do it but check the coolant sensor too
if all ok you may be dealing with a bad ECM

(flood 5 volts yes or over 3)

Mar 27, 2008.
Bmr thanks for all the help. Just got back to it since i've been off-on'ing this for a friend

checked tps voltage at the ecu pins and at idle it's.5ish v and it goes up to 4.5 or 4.8 I cant remember when I pushed on the throttle pedal so I know tps is good

swapped the ecu's and didnt do it. Possibly wrong ecu
gonna get the old ecu reflashed either tonight or tomorrow night (no charge, good to know old employees : )

i did test the old ignition module and it had a bad reference signal (the last test on the diagnostic machine)
tested the newer one and it passed all tests

also checked the ohms for the pickup coil and it is where it should be (800-1300ohms not magnified)

spin the shaft on the distributor manually, set to volt AC and it's where it should be (.2 to.7 volt ac)

so the new distributor setup is good and not causing the ecu to cutout the grounding part of the fuel injector circuit

anything else you think might be the culprit? I've pretty much covered everything I think

is there a wire that comes off the fuel pump to the ecu that tells the ecu the fuel pump is on and/or primed? I havent checked but I did have to repair the ground wire for hte fuel pump (it works fine just fixed the connector on top the tank, soldered it up then taped)

Apr 10, 2008.
All i add is check the wiring
check for battery power at the injectors with key on
and also check the wiring back to the ECM
let me know

Apr 10, 2008.
I did this a while ago, probably didnt catch it due to all the info I gave
it's fine it gets power (oh that diagram where it has D4 for inj should be D14 btw cause d4 is really for ign module) it's a typo on chilton's behalf (where autozone gets the diagram)

i'll let you know how the reflashed ecu does thanks for the help

Apr 11, 2008.
Ok went through all the steps you listed and then some, still no luck with my 88 c1500, after a frustrating day of messing with it a buddy comes over taps on the injector a couple times and what do you know spraying like a champ and it starts right up! Might be worth a shot! Good luck

Feb 22, 2011.