I love my '90 Majestic, but I have one nagging problem; hot fuel fuel pump vapor lock and stalling. On hot Tampa Bay days after a hot shutdown and then hot restart my car will stall.
The fuel pump, O2 sensor and ignition are all new. I have a new fuel pressure regulator ready to go in. What about adding a fuel cooler to the return line. I'm thinking about mounting it
in front of the radiator with a length of hose connecting to the hard fuel line.

Any thoughts/advice?
Thanks,
Roger

 

What about making sure the fuel pressure does not fall (functioning check valve) when the pump is shut down???
New does not mean $h!t. New parts can be faulty.

Have you checked the fuel pressure at the rail to determine the fuel pressure at time intervals after shutdown??
There should be a period of positive pressure for a certain length of time after shutdown. Low pressure after shutdown will encourage vapor lock due to engine bay temperatures.

More diagnosis will determine if the injectors are leaking, the pressure regulator leaks or the pump check valve functions. Many things can leak and cause a pressure drop to cause a 'vapor lock'.

Keep looking!!!!!!!!!

bob

 

Hi, thanks. I have a new FPR that I'll intall in the next few days, the fuel pump and check valve are both new.
Good point about checking system pressure during/before a hot start. I haven't been too concerned with fuel pressure because my car fires up instantly,
doesn't even rotate on the starter on a "cold start". A "hot start" after a half hour or so of sitting is different. The engine will
turn over several times on the starter, fire up on a "weak start" stumble and burp, sometimes stall out and then run fine. I also intend to go through the
EVAP system to be sure all is well.

 

Im curious as to what you find here. Mine has done the same thing for as long as Ive had it. Just a longer crank and a mild stutter after a hot soak. Ive never bothered to chase it down as I chalked it up to oldercaritus

When I first got the car I noticed it and when I checked the pressure I saw it bleed off. I assumed fuel pump/check valve and forgot that even after I replaced my fuel pump it still did it. (the pump housing broke in the tank) and I haven't rechecked it since. I wouldn't recommend a cooler. To me thats just asking for an issue with extra failure points.

Its always run very well from the heat of the summer 105+ to the cold of the winter 0-10 so I've suspected possible injector bleeding off vs the regulator because it never seemed to have a running issue.

 

I changed the FPR this AM and the situation is better. The first hot start was instant though it did stall. Second hot start was instant and it didn't stall and it didn't throw a Fuel Fail 44 which it always did so...?

 

Thats nice to hear. Like I said on mine its never been an issue other than that hot soak stumble but Im going to look into that. Thanks for the update.

 

Mine does the same,, but i chalked it up to the fuel pump module. Lots of little parts that can fail,,,including the check valve. Mine is a 91 XJ6,, replaced the pump twice,,, the hot start problem hasn't gone away. One day,,, if I win the Lotto,, ill get a new module. Ive seen them for upwards of $500....

 

Is your fuel pump in the tank? $500.00 for a "fuel pump module"? Please, what "module"?
I have the external fuel pump and replaced the original Bosch with a Denso and a new check valve for little more than $100.00.

Thanks,
Roger

 

Yes it is in the tank. Basically the module is a cylindrical plastic container that the pump is enclosed in. So there are connections inside the module that the pump physically attaches to. Those are then connected to a couple internal components which connects with other fittings. Hope the attach pic helps.