Vapor lock 5.3L

[Jkb242]

A few times I have encountered what someone suggested as vapor lock issues with this engine. What I have experienced is when in hot weather heavy traffic AC on then stopping to shop, then restarting the crank speed is noticeably faster similar to loss of compression followed by no start. Then after a few minutes it might start then immediately back to fast crank.

Waiting much longer, a few hours, it starts and runs normally. Could this be a vapor lock issue? The fast crank no start is really puzzling and only when outside air is >85 engine at normal temp after being in slow traffic for extended time after shutting it off then the no start fast crank.

Much thanks

 

[Mooseman]

Vapour lock hasn't been an issue since the 90's when return fuel systems were introduced and pumps put in the tank. They went back to returnless systems as higher fuel pressure prevents vapour lock. I haven't seen or heard about it in decades.

No idea what would be causing your fast crank though. You should diagnose it as a crank no start when it happens. It might not be fuel related, maybe spark. Check for spark when it happens. Also check fuel pressure. Maybe a failing pump doesn't work when hot. Listen for it to prime when you turn the key to RUN. It would be a bit hot to try and do a compression test when it happens so I'd leave that as a last test.

 

[Jkb242]

A few times I have encountered what someone suggested as vapor lock issues with this engine. What I have experienced is when in hot weather heavy traffic AC on then stopping to shop, then restarting the crank speed is noticeably faster similar to loss of compression followed by no start. Then after a few minutes it might start then immediately back to fast crank.

Waiting much longer, a few hours, it starts and runs normally. Could this be a vapor lock issue? The fast crank no start is really puzzling and only when outside air is >85 engine at normal temp after being in slow traffic for extended time after shutting it off then the no start fast crank.

Much thanks

Vapour lock hasn't been an issue since the 90's when return fuel systems were introduced and pumps put in the tank. They went back to returnless systems as higher fuel pressure prevents vapour lock. I haven't seen or heard about it in decades.

No idea what would be causing your fast crank though. You should diagnose it as a crank no start when it happens. It might not be fuel related, maybe spark. Check for spark when it happens. Also check fuel pressure. Maybe a failing pump doesn't work when hot. Listen for it to prime when you turn the key to RUN. It would be a bit hot to try and do a compression test when it happens so I'd leave that as a last test.

Thanks Mooseman, the fast crank is the most baffling issue as I am unaware of anything other than a mechanical engine issue as the culprit yet the engine performance being normal, idle and lack of misfire detection seems to suggest no engine issues. I learned today from the shop who will be replacing the original struts, the crankshaft position sensor code was detected after it failed to start yesterday. Is it possible for this sensor to prevent a no start but would allow cranking? Also in the works here is the doorman ignition switch which has been replaced twice. Granted they have been reported as problematic but two within a year? Is it likely the ignition cylinder could become improperly aligning with the tooth gear on the ignition switch which would also cause all sorts of start issue hot or cold. Not sure if it has ever been changed. Has ignition cylinder wear been a known issue?

Much thanks!!

 

[Mooseman]

Is it possible for this sensor to prevent a no start but would allow cranking?

Yes.

Also in the works here is the doorman ignition switch which has been replaced twice. Granted they have been reported as problematic but two within a year?

Known fact, anything electrical from Dorman is junk. ACDelco are no longer available. I think people have been using Standard with success.

Has ignition cylinder wear been a known issue?

It's been known to happen but it's usually problems with the key not able to turn it.

 

[TJBaker57]

May want to consider the somewhat common issue of cracked copper traces in the underhood fuse block.

 

[Jkb242]

May want to consider the somewhat common issue of cracked copper traces in the underhood fuse block.

Thanks TJ, it was originally the very issue causing the car to die while driving which was indeed caused by this and it was corrected. Now the possibility of other hairline cracks in the fuse box, God I hope not.

 

[Jkb242]

Thanks Mooseman I wasn’t sure about the crank position sensor being suspect. Without a lift this could be a very difficult for me to fix. The shop says the starter needs to be removed for access, true?

 

[Mooseman]

According to this, yes, and it's a biatch of a job to get it out on this platform because it's so tight in there. A lift is almost a necessity to do it but I've done it without one.

That's why it's important to actually diagnose it before replacing it. If it isn't the CKP, then