88 f150 4.9 straight 6 stalling when engine warm


Asked by May 20, 2015 at 05:09 PM about the 1988 Ford F-150 XLT Standard Cab LB

Question type: Maintenance & Repair

I start the truck runs okay then when it gets warmed up the rpms start bouncing around give it gas to try to save it and it ends up sputtering out. fuel pumps are engaging already drained tank completely and filled with brand new gas and used STP fuel cleaner, PCV is not clogged, cant find any cracks in Vacuum lines, getting good pressure from tail pipe. sometimes it will be fine put it in gear to take off and it will sputter out have to do it quite a few times just to get it back into garage. I am completely stumped.

5 Answers


If the truck idles good, Then it is put into drive and given gas but wants to go dead. Sounds like the fuel pump. It should do this regardless of engine temperature. If it is hard to start after driving and the engine temperature is high, And you do not have this problem when the engine temperature is cold. Sounds like the engine timing could be set several degrees to high. If you think there could still be rust and grit in the gas tank that is causing this, Then put a inline a see through fuel filter in the gas line under the hood.

1 of 1 people found this helpful.

I have two 1985 F150 with the 300, 4.9. One needs a power brake booster and attempts to go dead when I have the vacuum line plug into the brake booster. When the vacuum line is stopped off it idles great, But then I do not have power brakes.


Check the idle air control, my truck had similar probs until I replaced the iac......

2 of 2 people found this helpful.

i got a 86 f150 302 auto. practically does the same thing but if the truck is moving enough to get air flow it runs great. if i start going slow and stopping more often in town the it will backfire, spit and sputter, die out completly then has to cool down(not all the time but most the time). i replaced the inline fuel pump and it does fine but it makes a wierd whining sould like its struggling thats when it starts running irratically. read alot about this but cant seem to find anyone who has fixed it.

I've got the same problem, everything tests fine, I've even remotely the ignition module to the wheel well of the drivers side. Still, once it warms up it stops pulling and starts sputtering out until it dies. Crank it 30 min later it's like nothings wrong til you hit operating temperature again, then same vicious cycle.

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