edzdallas79

so i decided to swap the bosch plugs i had in the car for motorcraft copper because it seems like that's what everyone recommends. while i was doing this, i decided to do a compression test and am a little worried about the results:

cyl 1 - 170
cyl 2 - 120
cyl 3 - 120
cyl 4 - 150

the car seems to be running a little rough and when i've got a vacuum gauge on it, it still bounces back and forth very quickly and roughly between 17" and 18". the new plugs seem to have corrected the lack of power problem i was having. it seems to be much more powerful even though it still takes a second or 2 for it to kick in after i really give it some gas.

the tach still isn't working, so i'm wondering if the ICM is bad even though it's less than a year old and the tach didn't work even after i swapped the ICM. when you turn the key, it just jumps up to 4k and stays there.

any ideas guys?

sleeper_inc

Do a leak down test.

Do you have oil in the radiator? or water in the oil?

I would suspect a HG but the only way to tell is to pull the head off or do a leak down test

edzdallas79

no, no oil in the radiator or coolant in the oil. and it's not burning or losing any oil or coolant.

edzdallas79

swapped the ICM out since it was under a lifetime warranty. the tach still isn't working. anyone have any ideas what else might be causing the problem other than a bad tach?

U S Marine

I would be a bit more concerned about those compression readings. Differences of 10% is the most you would want between cylinders.

edzdallas79

yeah. i'm going to do another compression test this week. last time i did it with all of the plugs out on one side of the engine, the engine was cold, and i didn't put any oil in the cylinders. i think that maybe that screwed up the results. i really don't think there is anything major wrong with the engine though. there's no oil in the coolant or coolant in the oil, there's no loss of coolant or oil due to a leak or burning. the spark plugs looked good when i swapped them out.

but does anyone have any ideas what might be causing the problem with the tach other than the tach itself?

sleeper_inc

I would change the ICM with a cheap JY one

edzdallas79

why's that sleeper? are the aftermarket ones that prone to failure? or partial failure?

sleeper_inc

The Junk Yard will have a return policy of some sort.

If you do buy a new one, motorcraft ONLY!

Aftermarket ones are known to fail or nearly fail very soon

edzdallas79

is it normal to have oil in the vacuum hose that connects to the middle nipple of the pcv valve? it's not the big hose that the pcv valve sticks into that goes to the crankcase, and it's not the top hose..... don't know where that one goes to. but it's the middle hose that i believe goes to the intake manifold.