engine suddenly only works on 5 cyl

Asked by StarF150 Jul 15, 2016 at 03:46 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

1 Answer
34,765

lrodri911 answered 7 years ago

If there's no compression, try squirting about a spoonful of engine oil in the spark plug hole and recheck compression, if still no compression, u have a bad valve, if compression goes up with oil, u have a bad ring or cylinder

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