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Gran Turismologist
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35 Posts
Discussion Starter #1 (Edited)
I have a good friend with a 2001 Silverado with a 4.3L V6, 153,XXX miles. It's a basic truck; 2wd shortbed, automatic transmission, A/C, and manual everything else. He recently bought it and it has an unusual starting problem. If you turn the key to start it, sometimes it cranks right up and runs like a top. Other times, when you crank it, it acts like it's starved for fuel. It just doesn't start. However, if you turn the key off, then try to start it again, it will crank right over, no problem, and run like a top. I have spent a great deal of time checking this thing over, but I am lost. I have virtually no experience with GM's CFI/CMFI setup, and I feel like there's something I am missing here.

What I have checked:

I have tested the fuel pump relay, and I have even substituted it with a known good relay for comparison. The relay is OK.

I do not have a pressure gauge that will work with this system, so I do not have fuel pressure readings, but I do know that the system will drive the O2 sensors rich at WOT from 0-100+ MPH according to my Genysis (that was on a long stretch of road with another set of eyes on the O2 sensors while I ran it down the road). I would think that under such conditions, a fuel problem might surface and cause a lean out, especially with such a long sustained heavy load.

I have no current or pending DTCs, and all OBDII monitors have run and passed.

I have witnessed IAC counts fluctuating all over the map from a low of 23 to a high of (NOT kidding) 47,351. Yet there is no DTC.

I have witnessed intake air temperature readings fluctuate from ambient (80-95*F range) to -38*F and then swing as high as 348*F then back to ambient in under 10 seconds, yet there is no DTC, nor a pending DTC.

I have extensively monitored all other sensors at length and they are reading normal.

I have managed to inspect MOST of the PCM grounds. There are a few I have yet to reach. All grounds I have located are in good order.

Needless to say, this is a bit frustrating. I am sure I'll get it at some point, but this is a very foreign set up for me. Leave it to automotive engineers to take a relatively simple Idea like Port Fuel Injection and make it more complicated than needed for no good reason.
 

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Pardue the Traveler
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4,023 Posts
Kind of sounds like the VATS (Vehicle Anti-Theft System) acting up. I had an '04 alero that would do the same kind of thing, where it would start fine but some times it would only turn over and not start. I had to turn the key off pull it out and then reinsert the key to get the vats to recognize the key. It wouldn't set off the Security light.
 
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