Wiring\Fuel Woes

[rmac]

I posted this in the wrong forum. Hopefully you 2.5 guys can troubleshoot it.

I have a 90 2.5, 5sp, tbi. Spun a bearing and bought a 2.5 engine from a 90, auto, tbi. Popped in the engine using the wiring harness from the auto.

Everything works. Runs great when you prime the tbi, but will not start\run on its own.

No fuel, or power at injector. Checked it with a noid light.

Fuel pump runs when you jump the relay, or power the test wire. But it doesn't stir on its own via the ignition. Not even the 2sec burst. It does have power into the relay. Have tried 3 relays.

Have swapped out ECMs and proms. Still, no dice.

What activates the signal to the relay? What sends the signal to the injector? Just the ECM, or ignition module?

Appreciate any help. I’m almost ready to replace the harness. Just don’t see why the auto harness wouldn’t work. I find no loose wires. I did adapt one tranny plug to work on the 5sp.


Thanks,

Rob

[blackhawkbill]

Rob
Try a seperate ground to the fuel pump. I had similar problems and it worked for me

[lesterl]

Could put a meter across the wires at the pump and see what the voltage drop is also to make sure it is ground issue, sometimes the ground to the frame isnt so good, sometimes the pump is bad. I am sure there have been cases reported of both.

[rmac]

Thanks for the replies.

I'll check the ground, but the pump does run when I put 12v to the test wire.

Thanks,

Rob

[lesterl]

It may still run, but it may not develop enough pressure because of low voltage to pump, I PM'ed ya also.

[rmac]

I'm still neck deep in this wiring thing. lesterl and blackhawkbill have been helping. Here are a few emails:

Quote: Originally Posted by lesterl

Quote: Originally Posted by rmac

Quote: Originally Posted by lesterl

Quote: Originally Posted by rmac

Quote: Originally Posted by lesterl

Quote: Originally Posted by rmac

Quote: Originally Posted by lesterl

Yeah, if the noid is not flashing, check the pickup coil and stator, try changing the IGN modules first, then if you still have a NG on fuel/ Noid Flash, we need to take voltage from injector (12v fed from fuse on fuse block to injector, ECM grounds the other side of the injector to fire it.) If the module still dosent fix it, check with a Voltmeter from ground to injector (ignition on) and it should read 12v, if no 12v then you need to check fuse/ wiring.

Thanks for the help Lester.

I have a couple of days of work to do, but when I get back I'll start with the module.

Appreciate your time on this.

Rob

NO Problemo, just let us know what U find out.

Hey Lester,

I swapped out the distributor since the ecm plugs were different. Still no fire to the noid light. Still runs when I prime the tbi. Used an alternate ground for the fuel pump. no diff. I did pull the injector and I have fuel coming through when cranking. I don't have my voltmeter here (I'll get it tomorrow), but I checked the red wire into the injector and it is grounded. No 12v pos signal with key off or on.

Any ideas?

Thanks,

Rob

The Injector should have 12v on the red wire side? fused off a fuse in the fusebox thru the ignition switch, the white wire should pulse to ground when cranking (use a test light to go from battery + to white wire and crank ---- you should see the testlight flash, if you do then you know to track down the loss of 12v supply to the injector and you should be in business.) If the red wire is grounded you have a short and your fuse will be blown, Just start tracking you will find your problem sooner or later. Good Luck!

Hey man, thanks for the help. Color probably makes no diff, but my injector wires are red and blue. I checked it tonight and the red one is definitely grounded and the blue gets no testlight flash when attatched to a 12v supply. The fuse was blown a couple weeks ago, but I replaced it and it's held.

I have a hard time getting to it during the work week.


Appreciate it.

Rob

Its been 3 months since I have seen my 89 2.5l, so sorry about the color code, almost always red wires on GM products will be a 12v wire either ignition on or sometimes ignition off, but almost always will be a 12v wire, since it is grounded (I assume that you GROUNDED the testlight to the BATTERY + and went to the red one and your light lit indicating that it was shorted to ground?

Check the wiring harness off the injector and back to the ECM and back to the fuse block. Your harness may have shifted against something hot and melted/ welded itself to the block somewhere, that will kill the injector from spraying. Also, if the testlight (ground the light to battery+ and probe the blue wire when cranking if that does not flash or stays lit up you may have an ECM issue. The ECM takes the blue wire to ground completing the electrical circuit thru the coil in the injector causing it to open and spray fuel, like pressing the brake pedal causes a piston in the master cylinder to compress (the brake fluid doesnt compress) the fluid against all the slave cylinders and braking the vehicle.

So after probing the Red and Blue wires with the test light grounded to the Positive post of the battery and cranking (for normal operation) you should have no light on the red wire and it should flash when cranking to the blue wire. If the ECM is shorted it will stay lit up to the blue wire, if the ECM is open or the wiring to the ECM it wont light up. The Red wire if it is shorted will light the test light, if it has 12v on it (like it should with ignition on) or is open wont light the test light. All these tests in this paragraph are done with the testlight GROUNDED TO BATTERY + and one with engine cranking.

If you use a Meter instead of a test light you should get 12v for a light condition or 0v for no light condition. You can also unhook the ECM and pull the fuse for the injector to make sure you still have the short/ open after that, if the ECM is shorted unplugging it will remove the short :-) Check everything out real good, if you dont see something, dont spend all day trying to find it, go watch a show, get a beer, give it a while and rest your mind, then go back and try again with a rested mind.

DONT FORGET when you find out what is wrong post it, and post your doings as you go along in your thread, you never know when it will help someone else in the same situation.

So now it's... STAR TRUCK: THE SEARCH FOR SPARK.

[rmac]

Just thought of another question. Is there any kind of inertia switch that cuts off fuel on S10's? I did get the engine from a crashed truck.

Best,

Rob

[lesterl]

No inertia switch I know of, you say no spark? You said it runs great if you prime the TBI, is this a new symptom? Did you figure out the voltages on the injector yet?

[wi11ie]

distributor makes it all work
willie

[rmac]

Quote: Originally Posted by lesterl

No inertia switch I know of, you say no spark? You said it runs great if you prime the TBI, is this a new symptom? Did you figure out the voltages on the injector yet?

Yeah, we have good spark... that was just a weak attempt at humor. Still only dealing with the injector voltage problem. Runs perfect when primed.

Will dive back into it on Sunday (it's been along week of drywall!).

Best,

Rob

[grillen85]

how many relays do you have on your firewall ? I know 5 spd trucks have 1 an auto trucks sometimes have 2-3 . Above to the right of the brake booster.

[rmac]

Quote: Originally Posted by grillen85

how many relays do you have on your firewall ? I know 5 spd trucks have 1 an auto trucks sometimes have 2-3 . Above to the right of the brake booster.

Just the 1. I have swapped out 3 to see if the made any difference though. Nothing.

Best,

Rob

[rmac]

Success!

Sorta. I have a running truck, that’s kickass. But, not sure how all of this is going to add to the knowledgebase.

I traced the red wire back from the injector. It mated up with the pink\black wire from the alternator as well as with the pin\black wire from the EGR on the breather (I believe).

All three wires were joined to a single pink\black wire that went to the bottom, center terminal on the fuse block, next to the starter solenoid wire.

These wires were always grounded.

The blue wire on the injector went to the ECM.

I pulled out the old manual trans harness and tracked the injector wires. Both went to the ECM

So, I decided to put the manual harness back on the truck. Several wires\connectors were crushed, or thrashed in some way. Just made sure everything was taped. Robbed some connectors off the other harness.

Connected the ECM and battery. It fired right off. Purred like a 2.5l kitten (missing a donut gasket).

Thanks again for all the help.

Best,

Rob

[SLAMnoma95]

this is the same problem im having now, thanks for posting the progress on this.

So you're saying that the ECM sends the GROUND signal to the injector via the blue wire, and that the red wire is always hot via an ignition on power wire?

I traced the blue wire back to the ECM, and i tried the positive testlight trick on the blue wire- it didnt flash nor turn on for that matter.

I also grounded the test light and hooked the other end to the red wire of the injector and turned the ignition on... no light.

So, now im thorougly confused.

Does the ECM itself need to be negatively grounded to work properly? And where does the red wire from the injector get its power from... i lost it in the loom.

FYI- i have an 88 w/ 5 spd.