88 gmc won't start

[roscoe73]

I have a 1988 gmc k1500 with a 5.7 v-8.

Problem is it's not running, again. I've got no pulse to the injectors, I am getting fuel to the throttle body, but it's not shooting any into the engine.

Here's whats been replaced, this year:

fuel pump and filter
O2 sensor
MAP sensor
Coolant sensor
EGR control valve
ESC
Dist cap & rotor
Ign module
Knock sensor
ECM with the old PROM and CALPAK being used.

The truck was running fine, then just shut off like it was out of gas. The only other thing it did was stopped displaying codes, check engine light does'nt come on eitehr when I turn the key on or when I plug in the diagnostic tool.


The only things left to replace are the distributor, oil pressure switch and the PROM. Is there anything else I'm missing that would cause the injectors to shut down? And would it also be related to the OBDI system not working?

Fuses are all good, and replaced them just to be double sure, I'm stumped I've never run into a problem this challenging before.

Thanks for any help.

[2000CAYukon]

The check engine light could be burned out and should come on with ignition on and engine off.

Could be a bad pickup coil (need to remove dist to replace it). The signal from the pickup coil is converted from AC to DC in the ignition module and it passes the DC signal to the ECM and that signal is used to trigger/pulse the injectors.

Are you getting spark? If you put a little gas or starter fluid in the TBI, does it start?

//2000CAYukon

[roscoe73]

yep, has good spark, i can get it to fire by dumping a little gas in the tbi. I just find it odd the check engine light would burn out the exact same time another issue pops up.

[2000CAYukon]

That is odd timing. Do you have a scan tool or access to one? That should tell you if the ECM is talking to the diag port.

I have the factory manuals for my 90 K1500 5.7 Auto and I will take a look at the diags for no pulse at the injectors. Will post later tonight or in the morning.

//2000CAYukon

[dfrfsucks]

dose stay runnig on sarter fluid or dose die. yourr TBI has to have 13 volts going to it to make it work. if you dont get this it wont give the primeing pulse to sart the engine and if you have no fuel flow this is more than likely the promblem. you can check this be finding the pink wire in the main engine harness this is ac wire to the injectors check the voltage see what you have.

[roscoe73]

if i manually prime the motor by pouring gas down the tbi it will run, then die. i'll check the voltage anyway just to make sure. i do have a haynes manual for it so i should be able to figure out which wire it is.

the only scan tool i have is the one you plug in to make the check engine light flash. it's OBDI on this thing, i can get ahold of a ODBII scanner if that's what i need to use as well.

[2000CAYukon]

Diags for no injector pulse (from 90 FSM)

- Disc dist 4-way connector, turn ignition on
Touch the purple/white wire using a test light connected to 12 volts. Each time you remove the test light from the wire, the injector light should blink.

If the injector light blinks, problem is faulty ignition module, pickup coil or connection

If no blinking, the purple/white circuit is open or grounded. Could also be connector at ECM.

Also check for 12 volts at the pink/black wire at the injectors. Fuse for this is ECM 1 (10A).

I would also check the engine ground straps near the heater core.

//2000CAYukon

[roscoe73]

i'll check that tomorrow since i'm off work anyway. thanks for all the help, i'll share what it is when i figure it out.

hopefully in the future i can help somebody else out as much as you've helped me.

[roscoe73]

OK got it solved.
First i feel kinda dumb, not thinking of the ground strap, had a similar problem on a chrysler.

1. ground strap was connceted, but just for giggles i added a second one and i got my check engine light back on and was able to do the other testes properly.

2. i replaced the distributor after doing the described tests. when i removed current fromthe purple/white wire the light flashed.


thanks for the help guys.