No Fuel, No Spark

[beaugranbois]

So I decided to save a 95 Sierra standard cab short box 4x4 5.7L auto truck from the crusher at our local salvage yard. When I got it, it was in pretty rough shape but the body was good and I was told that it ran when it was brought in. I guess this is all a story for another post so I'll get to the point. It had been picked through and it had a propane conversion on it. I removed the propane conversion and started working on getting it started. Now it didn't have and battery cables, all of the fuses and relays had been pulled out, I have to remove the ignition and replace it but the big thing was that someone had grabbed the ecm. I found one in the salvage yard but it didn't work. I had replaced as many fuses and relays, the ignition. I was still getting no spark no fuel.So I assumed the ecm was bad and I ordered another one off of ebay. While waiting for it to arrive I went through and did some tests and rebuild the tbi and replaced the spark plugs and coil. The new ecm showed up today and I'll been waiting for it with excitement. I was hoping that I would be able to put it in and atleast get some spark or fuel but nothing. I checked the fuel pump relay and it isn't getting power on pin 85 or 86 which would mean the relay is not engaging. When I put the tbi off to rebuild it there was no fuel in the lines. I'm not too sure where to go from here. The first ecm was questionable but the second one was pulled off of a running truck. I'm thinking the next step from here was going to be looking into the crankshaft position sensor(if I can find it). Any help would be greatly appreciated. Thank you

 

[PlayingWithTBI]

Check all of your ground connections 1st. Battery to engine and fender, engine to frame, back of head to fire wall, there should be 2 grounds on, or next to, the T-Stat housing (these are for the PCM). Then you need to ensure your sensors are all working properly like the TPS, MAP, CTS, etc. For this it's best to use a scanner that will get direct feedback from the PCM. Very rarely does the PCM go out. BTW, the 95 TBI doesn't have a crank position sensor. Do you have an electrical manual for your 95? Here's some courtesy @hatzie

https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[beaugranbois]

I have the Haines/Chiltons manual but the wiring diagrams in it ain’t the best. I know the grounds going from the engine to the frame and to the body are all there. I’ll take a look when I get back and check the others. I know there’s one next to the battery that isn’t hooked up but I thought that was for the front lights. Thank you for the reply.

 

[beaugranbois]

Could I actually have two failures at once? I guess since it was setup for propane it could have been running with a bad fuel pump but as far as I know the PO was running gasoline. What controls both the fuel pump and the ignition? Does the ICM? I'm gonna do a node test today to see if its getting a signal at the injectors. What would cause there to be no signal voltage at the fuel pump relay? I've also tested the coil and ignition power to the coil. I guess the next step is it start going after fuel or spark. I guess the node test will be a start on going after fuel so I guess ill go that way first. Plus its easy to run a jumper at the fuel pump relay and get power to the pump. Does anyone know or have a diagram of the electrical/fuse panel that is under the dash? Not the one in the side of the dash, the one under the dash by the drivers left foot? Thanks again.

 

[PlayingWithTBI]

Could I actually have two failures at once?

Yep!
Look at the link I posted and open "GMT_95_CK-2_1995_GM_CK_TRUCK_DRIVABILITY_EMISSIONS_AND_WIRING_DIAGRAMS, go to page 80/1384 where you can start checking point-point wiring. You should have an oil pressure switch on the back of the block near the distributor that will also turn on the fuel pump when cranking.

What controls both the fuel pump and the ignition? Does the ICM?

Nope, you can disconnect the black/tan EST wire which will take the PCM out of the equation as far as spark then, once you get the engine running, you set the base timing.

 

[beaugranbois]

Nothing on the noid test.

 

[beaugranbois]

I found my problem. I started testing the connectors on the ecm and had 12v on battery feed but only 2v on the ignition feed. I’d noticed the ecm 1 fuse was dim when I previously tested it for power and guess which fuse supplies power to the feed line. I jumped 12v to the bus in the fuse box and I could hear everything kick on. Now my question is where where does the pink 439 wire come from? I was hoping Playingwithtbi or someone else would know that info. I also wanted to thank playingwithtbi for the info and guidance.

 

[PlayingWithTBI]

Now my question is where where does the pink 439 wire come from?

It looks like the Pink wire $439 originates from the ignition switch (I don't know if it changes color or not on that side of the ECM-1 fuse) but it goes to a lot of places - it goes from the ignition switch through ECM-1 20A fuse to the PCM pin E15 and the brake switch.

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The same Pink wire #439 goes from the ignition switch through ECM-1 20A fuse to the injectors. This is from the manual, I suggested you open, starting on page 149/1384. These pages, from 143 on, show all of your PCM connections starting with the 4L60E trans and the 4L80E.

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It also goes to the EGR system

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There may be others too, enjoy!

 

[beaugranbois]

Yea. I have a bad ignition switch. I’m only getting about 2v from it and as far as I can see that where the voltage originates. Thanks again.

 

[98_4x4_Xcab_dream]

Yea. I have a bad ignition switch. I’m only getting about 2v from it and as far as I can see that where the voltage originates. Thanks again.

I did an ignition switch repair on a '97 Jimmy. and I believe the under dash wiring is similar. FYI the ignition Switch in these models have actually 2 part numbers, there's the actual key-ignition switch, and there's a wiring harness 'Ignition switch" that runs down the steering column. This harness replacement is an easy-peasy swap--if you have to go that route. Hope that helps!