2001 Sierra 8.1 crank no start then start

C

Cougar281

Well-known member
Sep 11, 2006
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St Louis, MO
My Step Father has a 2001 Sierra with the 8.1/Allison that has only like 80k on it, lived in a garage most of its life with trips to Vermont and Florida mostly. A few years ago, IIRC, it started throwing a crankshaft sensor code, and I replaced the sensor for him. Everything had been fine since then until probably three or four years ago. It started doing a crank no start, followed by starting no problem. On first attempt, you could hold it on start for however long you want, and it'll just crank, but if you return the key to run and then immediately try to start it, it fires right up like normal.

It's had me scratching my head because there are not DTCs and nothing has stood out. I know the fuel pump has been replaced, but I'm not sure offhand if anything else has been replaced.

Does anyone have any ideas? It's so odd that it's not just a long crank, it simply won't start on the first crank, but will just start like nothing on the second attempt, and there are no codes like crank or cam sensor issues.
 
Pure Diesel

Pure Diesel

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Apr 22, 2008
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If I remember they don't make the crank sensor for the 2001 anymore but one for a 2002 works. I had the same problem when my 2001 was about two years old. The AC Delco were the only ones that would work on the truck. Make sure you clean the hole out really good and no fine metal particles. This I believe is a Hall effect sensor and works off of magnetic pulse pick up. The mechanic said any debris in the hole and it won't seat properly and be to far out and not register.
 
NC-smokinlmm

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
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It’s got low voltage, they throw a crank position code if it gets too low while trying to crank it. My regular cab used to do it, it drove me nuts. Load test your battery at the starter and see what it reads.
 
C

Cougar281

Well-known member
Sep 11, 2006
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St Louis, MO
N2BRK said:
I'd check fuel pressure. Suspect FPR, but that's my unprofessional SWAG :)
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I wouldn't think it would be the FPR - if there was a bad regulator that didn't allow pressure to built fast enough, I'd expect an extended crank, not a crank no start on the first try. He had taken it to one of the local dealers and I guess they thought it was the fuel pump and replaced it, but no change.

Chevy1925 said:
What brand sensor was used for the crank sensor?
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I'm told it was an AC Delco
NC-smokinlmm said:
It’s got low voltage, they throw a crank position code if it gets too low while trying to crank it. My regular cab used to do it, it drove me nuts. Load test your battery at the starter and see what it reads.
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No codes whatsoever. That's the headscratcher.


Apparently I had also replaced the cam sensor in the last few years (I don't really recall doing it lol), but I don't recall why. It may have been in response to this issue, not sure.
 
Chevy1925

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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Phoenix Az
Sounds like you need to watch some scan data and see what it does while cranking that first time
 
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