Maikelo

1990 5.7 c1500

I got this weird issue where it sometimes won't start because it sprays no fuel in the TBI. It can run fine for weeks and then at random it won't start... Doesn't matter if cold or hot.

I checked the fuel pump and the pressure is fine.

Any clues or people who are familiar with these symptoms?

Maikelo

So I pulled the fuel pump relais and the truck still starts up? Could it be the oil pressure sensor bypassing it?

kevinkpk

I would think if that were the case, you would get an oil pressure light. I don't understand it starting, and stays running with the pump relay out, does it stay running?

Sabino56

I’d suspect ICM or pickup, wiring in that area. ECM has to have reference pulse from ICM to turn on fuel pump. ICMs can be intermittent. I’ve never debugged one but plenty of threads on the topic around.

Chris94

How's the spray pattern look normally? I'm just tossing out ideas, but faulty injector, weak fuel pump or regulator?

Rednucleus

ICM fits these symptoms.

Maikelo

Thx for the reactions.

I did some better testing what and when it actually happens and try to describe it:

When cold it starts immediately and runs great.
After warming up the idle gets a bit rough and sometimes even stalls when waiting for traffic light, it will start again but not at the first turn but after it starts it runs great no stutter or loss off power.
After a longer drive and it gets parked for some shopping it wont start again and when i remove the air filter i do not see the fuel getting sprayed in when trying to start.

So it looks like it only happens when the engine is hot.
I have heard some story's about ICM acting weird because of heat and also saw Sabino56 and rednucleus writing about it above.

So my guess would be just replace the icm? Any thought you guys might have?

kevinkpk

Intermittent as you describe, to me, electronic issue.