engine suddenly only works on 5 cyl

Asked by Jul 27, 2016 at 10:07 PM about the 1990 Ford F-150 XLT Lariat LB

Question type: Maintenance & Repair

My truck was running rough on
excelleration at times. Then suddenly on 5
cyl instead of 6. Friend said he did
compression test then no compression on
#1 cylinder.  Said it might have a bent valve.
Could that be so? Lariat but unsure SB or LB

2 Answers

113,815

Bent or burnt, put compressed air in the cylinder with the piston at TDC and listen where the air blow out from, out the tailpipe the exhaust valve, the intake and intake valve is bad, in the oil pan piston damage.

26,785

Doesn't this up a lot of extra pressure on the remaining cylinders that are firing? The best thing is to restore the 6th cylinder to normal service as soon as possible to avoid further damaging the engine.

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