1999 Dodge Caravan low compression

Which engine do you have? My 3.0L in a 1988 Grand Caravan has 378,000 miles. I have no idea what the compression is, and I don't care to know. Same goes for my '95 3.3L with 130,000 miles.

The next step is to perform a cylinder leakage test. That forces compressed air into each cylinder, one at a time, then you run around looking for the results of the leak. Possibilities include:

1. exhaust valve - tail pipe
2. intake valve - air intake
3. piston ring - oil fill cap
4. head gasket / cracked head - bubbles in radiator

Low compresion doesn't happen instantly like you described except for some catastrophic event, and it won't cause stalling. You should feel it too. Not to second guess your mechanic, but is it possible the tester hose wasn't sealing perfectly? If he did the test by only testing one cylinder, then comparing them by viewing a waveform of starter current, I never actually did that, so I don't know how accurate it is.

caradiodoc

thanks for the reply,
It's a 3.3

he did a compression on 3 and 5 - 3 was good at about 145 and 5 was about 50-60 - it was a few months ago he performed the test.

when it happened it was immediate, no notice at all. you said that was not normal. it drives as long as I'm on the gas - stalls when I come to a stop and runs really really rough and backfires a bit.

when computer said piston 5 and 6 had problems and he checked compression on 5 he made it sound like motor was done, but I am having different feelings now and trying to educate myself so I can get the problem solved

I am speaking with a different mechanic over the weekend and going to ask him to perform the test you mentioned. and someone else said to put oil in the spark pug before doing compression to see if its the valves sticking or rings (does that sound right?)

I appreciate the help

inafix - but hopefully not for long

Yup, adding oil is a common next step. If the reading goes up significantly, it's seaaling the rings, but that's only one out of four possibilities. The cylinder leakage test will instantly reveal what is causing the low compression.

Used to be common for all cylinders to develop low compression equally as the piston rings wore due to high mileage. Burned valves typically affected individual cylinders. Today it is a little more common to have worn piston rings in just one cylinder due to a leaking fuel injector causing excessive fuel to wash the lubricating oil off the cylinder wall. Chrysler, in general, has very little trouble with injectors, especially when compared to other manufacturers.

Still, low compression itself should not cause stalling. The Engine Computer controls idle speed by opening an air passage aound the throttle blade with the Automatic Idle Speed (AIS) motor, and increasing the length of time the injectors are held open. To show how much control the computer has, a Chrysler trainer demonstated unplugging an injector on a running V-8 engine on a Jeep. The computer overcame the misfire. One by one he unplugged six injectors. The engine still maintained proper idle speed with only two working cylinders. Obviously it ran extremely roughly, . . . but it ran.

You appear to have only one or two affected cylinders, but they aren't totally dead, just not up to full power. You might be able to feel the misfire, but I suspect the stalling is not related.

If no problem shows up during the cylinder leakage test, suspect a worn lobe on the camshaft preventing an intake valve from opening. That can cause a low compression reading due to the inability of sufficient air to enter the cylinder. Worn lobes are caused by insufficient oiling, which is something else Chrysler has little trouble with.

caradiodoc

Thank You again for sharing in such detail -

This is extremely helpful. I will post results of tests in a few days when my van gets checked out again.


inafix

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