misfire on acceleration.


Asked by Jun 07, 2013 at 06:07 PM about the 1990 Ford F-150 XLT Lariat 4WD LB

Question type: Maintenance & Repair

i have a 1990 f150 larait 300 6cyl. i recently did a tune up and got cyl 4 and 2 reversed on the cap.. i feel dumb but now it runs alright at idle. took it for a test drive and i made it about a block and it started to misfire badly and stumble. it would accelerate but not at the rate it should. i think i need to adjust timing? also there is an intake gasket leak and a friend told me that the leak may be causing it because there is too much air getting into the cylinders. any possibility that could cause it? i appreicate any help because this is stumping me. the fuel pump is only a couple years old. i just replaced the fuel filter.

3 Answers


An intake leak will cause all kinds of issues, I would have that fixed before tackling anything else, make sure that the manifold assembly is flat, you might need to have it machined as they do warp. Might check the distributor cap for carbon tracking, it only takes a few arcs across the electrodes to etch a cap.


While the 300 is a great workhorse - it is prone to warping the exhaust manifold and taking the intake with it. When you do address the concern, don't try to fudge it - you'll only have to do it again. Gaskets help but they aren't the fix. Tennisshoes knows what he's talking about here - vacuum leaks cause all kinds of drivability concerns as well as the carbon tracking issue)


thank you for your answers. i did get it fixed, the timing was badly off. runs much better now.

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