Shuts off after warmed up

WHOTFDUNIT

MEMBER
1994 MERCURY COUGAR
4.6L
V8
2WD
AUTOMATIC
200 MILES

Stalls out after running for a few. Idles fine until car warms up then acts like it gets choked out, eventually stalling. Very bad hesitation and misfiring while accelerating when it starts doing this. As well as a spike and erratic voltage jump when this starts happening. It seems like it only starts after the car has warmed up to regular temp. Have replaced MAF, TPS, plugs, wires, PCV valve.

1 Reply

HARRY P

MECHANIC
2,292 POSTS

Hello. Have you checked your fuel pressure? To me it sounds like the fuel pump is warming up and losing pressure as it does so. With the key on, and engine off, it should put out from 35-45 PSI. While idling, it should be in the 30-40 PSI range. In particular, you need to know what the pressure is when it is acting up. I would get that the pressure is dropping closer to 20 PSI once it has run for a few minutes. I'm including a link to our general guide on fuel pressure testing. You can borrow the fuel pressure test kit from the local auto parts stores loan-a-tool program with a deposit.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Run that test and let us know what you get. We'll go from there.