Mechanics

CRANKS ATTEMPTS TO BUT NO START

1998 GMC Sierra

Engine Mechanical problem
1998 GMC Sierra V8 Four Wheel Drive Automatic 120000 miles

I have a 98 Z71. Cranks attempts to start but does not start. Have an Actron 9180 scan tool. Initially gave me a p1345 code, but after clearing it, the code never reappeared. Compression at 150-160 psi, so I don't think the chain jumped time. Not sure about the distributor though. Once again 1345 code never came back. Have spark and fuel pressure. Fuel pressure I have is 63 psi when you turn key on engine off and after pump shuts off it drops to and holds at 56 psi. Is this normal? Should I be looking at replacing pump? Don't know what else I should be checking. Any help would be greatly appreciated.
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Jak1973
January 3, 2009.




Yes the fuel pressure is normal, should be 60-66psi. It is normal for the pressure to hold with the key off. A rule of thumb is it should not bleed down any more than 5psi every 20 min. So this is normal and it shows the injectors are not bleeding down. As far as checking things these are some things to check: A loose CMP sensor causing a variance in the sensor signal

" Excessive free play in the timing chain and gear assembly

" Incorrectly installed distributor - 1 tooth off in either advance or retard positions

" A loose distributor rotor on the distributor shaft

" A loose or missing distributor hold down bolt

was the distrubutor ever taken out? A bad crankshaft pos sensor can cause this. I've also had a few with the distributor broken and loose inside the shaft. Might want to pull the cap and move the rotor back/fourth and see if the dis moves excessively. Found a couple broken distributors. Post back with what you find and will advise from there.

Brian 1
Jan 3, 2009.
Replaced CMP sensor with no luck. Would a bad crank pos sensor still allow spark and not throw a trouble code? Never had the distributor out since I've owned the truck. Also, rotor does seem to have some rotational freeplay appx 1/4 inch. Put fresh set of plugs in it and noticed a metallic sound when first cranked it over, after that flooded out and sound went away.

Tiny
Jak1973
Jan 3, 2009.
Yes a bad crank pos sensor would cause no spark, it might not throw a code. Looking at the scematic the crank pos sensor, it gets battery voltage from the pink wire at the under hood fuse block and goes directly to the crank sensor. The crank sen is a hall effect sensor which means it has an internal ground if there is a problem and the crank pos sensor dosen't close to complete the circuit it will not run, also battery voltage runs through the crank pos sensor and then to the cam pos sensor then to the ICM, which would cause a no spark condition. Also you can monitor crank rpm's with a scan tool, when you crank it see if you have any RPM's on either sensor, might tell you if there is a problem. Follow this first and post back with what you find and will help.
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Brian 1
Jan 3, 2009.
Well just for kicks I pulled the distributor to find half of the teeth worn pretty good but none of them were broken. Tried to find just a gear to replace it but everyone said they had to order one, so bit the bullet and bought a reman. Installed new distributor and am guessing the old distributor jumped time because I had to turn the oil pump shaft to get the rotor and timing mark on distributor to line up. Truck fired up and ran. Only thing now is it shows a misfire on cylinder 6. Will try replacing cap and rotor and warrantying out the wires and hope for the best. Thanks for your help.

Tiny
Jak1973
Jan 5, 2009.

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