'95 5.7 TBI Starting Issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**special-K** · 01-24-2023, 01:48 PM

Twice before my '95 K2500 Suburban has failed to start. Both times it was wet out, so I suspected it was time for a new cap and rotor.

I had noticed it was cranking longer, especially when cold, and take a while to smooth out. The first time it didn't start I had just reached inside and didn't crank it quite long enough to catch. I climbed in and it just cranked. The next day was dry and it started. Weeks later it happened again, and it was wet again, started once the weather dried up again.

Yesterday it had rained overnight and half way through the day. I went to start the truck and it tried but didn't fire up. Really seemed like it was moisture in the cap so I put the new cap and rotor in. and they both looked good and ready. No carbon tracks but plenty of sooty stuff inside the cap and the rotor as well as contacts being very played out. Now with new cap and rotor it only cranks, never tries to fire at all. Now I'm not sure if moisture wasn't just a coincidence.

I checked spark from the coil and nothing, so I assume I do have fuel but no spark. I've never had to service a TBI with EFI. In an older truck I'd be putting a new coil in, but I know there is more to it on these. There is power to the coil at the fat pink wire. Is the small pink wire connection going out of the coil also a constant 12v with key turned on? I get nothing there (with 'in' plug connected). Does that mean the coil is bad or is there more to it?

Just call me Sean · 01-24-2023, 03:56 PM

It could be the ignition coil, the ignition control module, or the pickup coil. I like this place for testing instructions:

https://easyautodiagnostics.com/gm/4...ed-icm-tests-1

Most likely ICM though.

ChevyTech · 01-24-2023, 05:46 PM

The small pink wire at the coil brings power from the coil to the ignition module in the distributor. So with everything connected and the key turned on the small pink wire should have 12 volts on it. If you unplugged it off the distributor module that end should have power with the key on. If you unplug the coil end it will have no power.

If a test light is put on the small white wire (with everything connected) or the tachometer lead the test light should flicker when the engine is cranking.

You can look at the injectors and see if they are spraying fuel when the engine cranks. If the injectors spray fuel you know that the pick-up coil inside the distributor is triggering the module. The computer will not pulse the injectors unless it gets a reference pulse from the distributor module.

**special-K** · 01-24-2023, 08:38 PM

Thank you. This explanation/rundown is exactly what I was after. I want to understand how the system works, not just get the truck running. I decided to replace the coil since I got no light at the pink wire contact on the coil with the 'in' side connected. It fired up just fine. The contact at the coil end of the coil to the distributor cap wire was really crusty with buildup. It was a coincidence that the coil let go 100% at the time of new cap and rotor

ChevyTech · 01-24-2023, 09:58 PM

You're welcome!

Glad you got it running.

01-24-2023, 01:48 PM	#1
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	'95 5.7 TBI Starting Issue Twice before my '95 K2500 Suburban has failed to start. Both times it was wet out, so I suspected it was time for a new cap and rotor. I had noticed it was cranking longer, especially when cold, and take a while to smooth out. The first time it didn't start I had just reached inside and didn't crank it quite long enough to catch. I climbed in and it just cranked. The next day was dry and it started. Weeks later it happened again, and it was wet again, started once the weather dried up again. Yesterday it had rained overnight and half way through the day. I went to start the truck and it tried but didn't fire up. Really seemed like it was moisture in the cap so I put the new cap and rotor in. and they both looked good and ready. No carbon tracks but plenty of sooty stuff inside the cap and the rotor as well as contacts being very played out. Now with new cap and rotor it only cranks, never tries to fire at all. Now I'm not sure if moisture wasn't just a coincidence. I checked spark from the coil and nothing, so I assume I do have fuel but no spark. I've never had to service a TBI with EFI. In an older truck I'd be putting a new coil in, but I know there is more to it on these. There is power to the coil at the fat pink wire. Is the small pink wire connection going out of the coil also a constant 12v with key turned on? I get nothing there (with 'in' plug connected). Does that mean the coil is bad or is there more to it? __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

01-24-2023, 05:46 PM	#3
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: '95 5.7 TBI Starting Issue The small pink wire at the coil brings power from the coil to the ignition module in the distributor. So with everything connected and the key turned on the small pink wire should have 12 volts on it. If you unplugged it off the distributor module that end should have power with the key on. If you unplug the coil end it will have no power. If a test light is put on the small white wire (with everything connected) or the tachometer lead the test light should flicker when the engine is cranking. You can look at the injectors and see if they are spraying fuel when the engine cranks. If the injectors spray fuel you know that the pick-up coil inside the distributor is triggering the module. The computer will not pulse the injectors unless it gets a reference pulse from the distributor module. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 01-24-2023 at 05:55 PM. Reason: Add more wording

01-24-2023, 08:38 PM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: '95 5.7 TBI Starting Issue Thank you. This explanation/rundown is exactly what I was after. I want to understand how the system works, not just get the truck running. I decided to replace the coil since I got no light at the pink wire contact on the coil with the 'in' side connected. It fired up just fine. The contact at the coil end of the coil to the distributor cap wire was really crusty with buildup. It was a coincidence that the coil let go 100% at the time of new cap and rotor __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

01-24-2023, 09:58 PM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: '95 5.7 TBI Starting Issue You're welcome! Glad you got it running. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.



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