Crank no Start

[hlhneast]

Hey fellers, got a weird problem with my 1997 4 door Tahoe 2wd. It cranks but will not run. I replaced the ICM and after the composite base of the distributor cracked, replaced that. It has a new cap, rotor and cam sensor with it. I changed the plugs because it was time for them anyway. Crank sensor tests ok. Plugs are getting fire, injector pulse at all eight pins at the connector. I have not gauged the fuel pressure but the plugs are getting wet and you smell gas when cranking. If you depress the schrader on the fuel line it shoots up and splashes off the hood.' As far as I can tell it has everything it needs to run except the command to do so.

All this evidence and diagnostics lead me to the ignition switch. My original switch went bad about a year ago during Hurricane Matthew and when I got home I replaced it with a junk yard switch because I wasnt sure if it was the issue at the time so it is a used switch with unknown mileage. So far I have probed the biggest (12ga) red wire and do have power to it. Key on, two pink smaller wires have power. What I do not have at the switch and before the switch connector is a ground at the large gauge black wire, the one next to the large 12+ red wire at the top of the connector. Thats as far as I have gotten with tracing the black wire back to its origin. More tracing to proceed today.

What is missing from my ignition system or elsewhere that tells the truck to run? Am I on the right track with tracing the black wire ground that seems to be missing? Is this actually a ground wire? Where does it terminate? Does it actually have a screwed to body or frame connection, if so where? Or does this ground come from the ECM and I am looking to replace the brain? I did spot one grounding point on the large metal underdash tube which I cleaned and reconnected with no change.

Thanks for any input, this thing has me stumped at the moment, especially the no ground at the ignition switch. I am hoping that is the issue. I am tempted to make a jumper just to see if it will run. Not having a wiring harness or any idea where it comes from I dont want to possibly back feed something and burn my truck down.

:waytogo:

 

[east302]

Is it cranking at normal speed? If so, I’d say your ignition switch and starter are fine. Here is the pinout and diagram for the ignition switch connector. It doesn’t look like it grounds through the circuit that you reference. Rather, it’s going back to fuse #8 and then to the starter relay.

I don’t remember if 97 had the Passlock system, but is the “Security†light staying on or flashing in the instrument cluster?

If you have spark at all eight cylinders and the VCM is pulsing the injectors, then a fuel pressure test may be in order. With ignition on/engine off, 60-66 psi is spec and it should hold for a few minutes with ignition off.

Also, check the four connections at the VCM, make sure they are clean and tight...someone else had a similar issue a while back and it was a bad ground at the computer.



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[hlhneast]

Thanks very much for your response and the wiring diagram. All the research I have done says the 1997 did not have security and there is no security light. The starter does turn at a normal pace. I can follow the 150 ground circuit from the crank fuse thru the starter relay to the G105 point and the Ground Cell 14. Any idea where these are on the truck? I see one point underneath the air cleaner but havent cleaned that one yet.

I see where the path goes thru the #8 crank fuse at the IP fuse block. It may be related, I am having problems with my turn signal relay buzzing and messing with the IP fuse block fuse occasionally gets them to work without the turn relay buzzing.

This Tahoe sat for 3 years, closed up with a water leak in the hot summer FL sun so a lot of the electronics are shot. Ive managed to revive a bunch of it, sprayed contact cleaner in the IP fuse block but there is still a lot of corrosion all over the inside of the truck.

I guess the first step is to verify fuel pressure. The fuel pump/sock/filter is new but FPR is not. If those check out I will trace out 150 today, clean the frame ground under the air cleaner and check grounds at the VCM. I will also check the starter relay's grounds, maybe swap it around with another if one matches the pin out.

Thanks again for your help. Please stick with me as I report back my results. I gotta get this solved as quickly as possible. I am not a mechanic by trade but am pretty good with the mechanical end and decent with electrical. I will eventually figure it out with folks that have more experience helping me follow the right paths.

 

[east302]

Ground 150 is near the thermostat elbow...

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[hlhneast]

Ground 150 is near the thermostat elbow...

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Thanks East. Can you tell me where G105 is located? I think thats the one I need. I cleaned and tightened braided ground connections at the Rside firewall and frame and at the front of the engine near the crank sensor with no change. Is there a ground connection thru an oil pressure switch that would stop the engine running? If so, where on the engine is it located? A friends 454 RV dumped on us on a road trip that ended up being the OP switch. I dont remember exactly what the symptoms were other than it wouldnt run either.

 

[hlhneast]

Definitely not fuel pressure. It bangs 60 psi and drops to about 55 and holds for a couple of minutes. Maintains the 60 psi durinf cranking. It has to be electrical.

I am sorely tempted to bring a ground jumper to the large black wire of the ignition switch. Anyone think this could be disastrous like fry my computer or other systems?