A few days ago dad and I were driving our 89 3.0 auto pickup to get her some new rear springs. We were on the interstate when I noticed the truck shaking when the trans went in to overdrive. We have 37s on it, so I thought that must have been the culprit. Well, I got off the exit ramp and while at the stop light the truck was still shaking at idle. When I took off, the thing shook BAD. It was obvious the engine was misfiring. It started just all of a sudden. So we pulled over and got out to have a look. Unfortunately, it had the same sound it had when we got it and it had a blown head gasket. You could clearly hear what seemed to be a dead cylinder. We decided it was best to try to make it the 45 or so miles back home and hope it held until we got there. It seemed to get worse on the way home, although it never really lost any power. The sputtering was definately the worst when the motor had a large strain on it (taking off/in overdrive). We got it home and the thing sounded horrible. But there were no signs of a blown head gasket. No water in the oil, it wasn't running hot, and the rad. was still full. There was white smoke coming out the tailpipe, but we think its always done that a little bit, especially when cold. We decided it had to be a head gasket anyway, and called it a night.

Today we ran a compression test on it, and here were the results:
1-160 2-150
3-180 4-162
5-165 6-162

As you can see, the number 2 cylinder is the lowest, but its still in spec., and clearly not blown.

So now we thought it was an electical problem. The wires and dist. cap were pretty old, so we got new wires, cap, rotor, and plugs (though the plugs only had about 5k on them). We thought for sure one of the above was the problem. No such luck. Still had a bad miss in it.

Well, a few days ago I had taken the manifold and downpipe apart because there was a bad exhaust leak there and sealed it. Dad thought maybe some of the sealer had gotten blown into the cat and clogged it up, causing it to not run right. So he pulled off the cat, and it wasn't the problem either.

So now we're pretty much stumped. I really don't think its the head gasket, because all the cylinders check out ok, and it woulda showed some other sign within the drive back home. All we've done to it in the past few days is fixed the exhaust leak and added some Lucas to the tranny. All vacuum lines are fine.

Any advice would be appreciated! We just finished the SAS, and now we can't even go play!

 

Have you had someone do a leakdown test on it? That would be more accurate than a simple compression test for identifying a bad headgasket.

Good luck. I'm having similar problems with mine, however the misfiring is only occurring (so far) at night??? and when doing highway speeds.

 

I would say that there is something worng in those compression numbers.....180 on num 3 down to 150 on num 2 there is not susposed to be more that 10% difference from highest to lowest cyl......if you are seeing a miss you can pull the plug wires one at a time to see if you can not tell which cyl is missing......

 

Yea we tried pulling the wires and everyone of them made a difference in the sound of the engine, meaning they were all firing. Have not had a leakdown test done. Thanks for the advice guys!