Odd "vapor lock" ?

[Thawk97]

I'm having a symptom in my '96 GTS (all stock) that I can't figure out - it seems like vapor lock, but I haven't been able to find much info on it with Vipers (doesn't seem common).

After driving, if it's warm out (~80 degrees and up maybe?) and I park the car for an extended period (more than 30-60 minutes), it will struggle to start. It will always turn over eventually and if I give it some gas it will fire more quickly after a few cranks & sputters. It's definitely temperature sensitive as it doesn't happen in cool weather or in the garage no matter how long it sits. And, if I park to briefly run into a store or something, it'll fire fine - it's only after sitting for 30+ minutes when it's warm/hot outside.

I don't think it's a check valve issue because if the temp outside is low, it doesn't happen (and it didn't happen after sitting over the winter or when I have it parked in the garage for any length of time - fires right up immediately after sitting for a week or 3 months).

Car runs great otherwise. Anyone else have similar symptoms/experience?

[bluesrt]

try to cycle the key on/off 3 or 4 times before cranking it up, see if maybe you have a weak pump in the tank when warm. prolly not but worth a try./ also check for codes/ possible faulty crank sensor when it gets heat soaked

[Miviper]

I have a 96 rt/10 and had the same issue a few weeks ago. Took the car to the track on a 90 deg day. Car had the same trouble starting after sitting for 60 mins. Hopefully someone can help both of us.

[plumcrazy]

i seem to recall a gen1 issue tom figured out with the pump. didnt he add a check valve to the system to solve this problem ? anyone remember this ?

[Matt M, Pa]

Yes, Tom designed a "primer timer" that lets the pump run for more time with the key on cycle. I built and installed one in my '96...

[Coloviper]

Mine does the same thing if hot and left outside for an hour after running. If cold, after one hour, it will turn over right away but if mine is cold, left over night, I have to cycle the key 5 times to get it to start in the morning.

It is the cheap check valve issue. I lucked out (really lucked out on my 96 RT/10) and found a complete NOS replacement fuel pump assembly to install. Just need time to get to it, drill out the trunk rivets and all that crap. I may do a "how to" if I get it tackled myself. I did build a primer timer but never hooked it up and embarked on replacing the problem at the source. If it works, I will sell my unused primer timer.

Dodge, Carter and others do not build the fuel pump assembly so it is obsolete. Unless you can find a good used or a new pump, you will need to primer time it or just cycle the key before starting. Sucks and what a cheap fricken' pump assembly.

[Thawk97]

Thanks for the replies - I was under the impression the check valve issue would manifest regardless of temp. What about that system would make it fail only when it was warm outside? I have tried the key cycle thing a couple times (thinking it was the check valve) and that didn't seem to make any difference to mine.

I don't have any codes at the moment.

[Matt M, Pa]

Thawk97.....I would agree that it should do it all the time if it's the check valve...