QuestionQUESTION: Van with 134K miles runs very rough and stalls when put in gear (auto). Pulling plug wire off #1 cylinder has no effect on rough idle, #2-4 pulled wires make the van die. Compression on #1 is 112 psi with no leakage. #1 has good spark and plug dark, but not heavily fouled. Ruling out bad rings/valves. The van will rev 4k in nuetral. What else would only effect #1 cylinder at idle? Thanks in advance.
ANSWER: 112 psi cpmpression on the #1 cylinder is too low, it should be at least 150 psi, what are the readings on the other cylinders?
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QUESTION: If I turn it over more than 4 seconds the pressure #1 is 134 psi, with the engine running on the other 3 cylinders, #1 rises to 170 psi. The other cylinders are 150-170 range. At any psi, the leak-down is very slow, an hour for any noticeable drop. I heard sucking on EGR vacuum hose while van is idling should kill engine, that doesn't happen.
AnswerThe compression needs to be tested with the gauge on each cylinder by cranking the engine over with all the spark plugs out, checking one cylinder with the engine running will give a false reading. Applying vacuum to the egr valve directly should make the engine idle rough and even stall, if that doesn't happen then the most common cause is that either the egr valve is stuck of clogged up or that the egr passage in the manifold is clogged with carbon. This will not cause a misfire condition it just makes the egr system inop. There is a problem with the #1 cylinder, if the compression is good then I would look at things like an inoperative fuel injector or possibly an intake manifold leak, most other malfunctions will affect all of the cylinders so ypu need to check what is specific to the #1 cylinder.
