97 Olds Bravada

I have a hard starting problem that is progressively getting worse. Initially the truck would just idle rough for a few seconds if you turned it off and then turned it back on again before it reached full operating temperature. Now if you turn it off, even if its only been running for about 10 seconds, it won't turn back on again. Also, while coasting down a hill when the engine isn't fully warmed up the rpm's will jump around as if the pcm is turning the fuel injectors on and off. It will also idle too high when in the warm up period. I feel like this is a bad TPS except I was under the impression that a bad TPS wouldn't keep the truck from starting.

I'm pretty sure this must be related to a bad sensor. What sensors, if not working, will completely keep the truck from starting?

The truck runs fine once it reaches full operating temperature and it is not setting off any codes.

Thanks

 

i would not start guessing A bad TPS would trigger a code

Id start diagnosing the fuel system
96+ Fuel System Diagnosis - Blazer Forum - Chevy Blazer Forums

 

I'm not guessing, I'm looking for insight into what sensors would keep the truck from running. A problem within the fuel system does not explain any of the problems. Once started the truck will run forever. It starts fine when cold just not if you turn it off and then start it again. This is the second time I've encountered a completely perplexing problem. About two years ago this truck would stall randomly at any given moment. You could be idling or you could be driving down the freeway at 70mph. I took it to the dealer who spent all day with it, charged me $380 in labor and told me it was stalling because of carbon build up. Complete BS since I pulled a spark plug and it looked perfectly clean. I ended up converting the fuel injectors from CSFI to MPFI on a whim and that completely solved the problem. I have searched and searched and there is no reference anywhere to the CSFI injectors all failing at once and causing a stall. I'm not going to just throw parts at the truck I just want to narrow down what sensors could prevent it from starting.

 

Check your fuel pressure, the specs say 55 to 65 PSI. I had the SAME thing on 97 Blazer when my fuel pump was going, it was about 45 PSI when trying to start, and wouldn't. The CSFI have poppet valves that essentially create a minimum pressure to work, so they can all fail at once, or really close to each other. It seemed as though once it would eventually fire sometimes, the engine vacuum helped the pressure, it would go to 50 when finally running, still below spec. After it really didn't want to start all, it helped to diagnose by putting starting fluid in the intake, started right up. New pump and pressure is 55 at idle, no problems.

 

Pulled up a No-Start Diagnosis, skipping codes related, some important looking things are :

* TPS, Throttle Closed, should be less than 2.5V
* Ignition Off for 10 seconds, turn on, should hear fuel pump run for 2 seconds, check relay inside glove box.
* Injector Test - with tester light?
* Fuel Pressure 55-61 (oops, not 65, makes me feel better about seeing 55)
* Disconnect a spark plug, use a light or old spark plug to verify spark. IF NO spark, you're looking into other sensors.

There is a crankshaft sensor I had to clean once, before all that, but it was throwing codes.

 

checking the fuel pressure is an insight

weak fuel pressure can cause an hard start even leaky injectors could

you wanna start messing around changing random parts have fun with it
its going to be harsh on your wallet