diagnosing engine vibration

So uh....Torque converter.....I said it first! Glad you found the problem.

It's hard to say what's causing/caused it.... Ishould have it back together soon...hopefully by this weekend. But the top two bolts on the tranny weren't just loose, they were backed out almost a 1/4 inch, so the tranny may have been flopping around. As the tranny moved around, since the TC was bolted to the flex plate, it became the pivot point, which is what caused the grooving and funky wear on the bushing. If that's the case it didn't cause the vibe, it was just destroyed because of it.

Hurry up and get it back together! I've had the same problem for a while. Vibration at 1750. Nothing at highway speed. I had issues with trans bolts missing and the starter falling off. Then it would die when I shifted into reverse. Bad / weak CPS as the trans was twisting when I put it in reverse and the bolts were missing on the trans to engine.

I did the same stuff you did with injectors, plugs, wires etc. Haven't indexes the distributor (that was my next thing).

Good luck.

" But the top two bolts on the tranny weren't just loose, they were backed out almost a 1/4 inch, so the tranny may have been flopping around. As the tranny moved around, since the TC was bolted to the flex plate, it became the pivot point, which is what caused the grooving and funky wear on the bushing. If that's the case it didn't cause the vibe, it was just destroyed because of it."

I am going to disagree with that. It is an obvious place and source for vibration in the driveline, and the CPS is mounted to the Trans bell housing, so if the flex plate is moving and vibrating the CPS sensor may not see the flex plate teeth all the time causing a partially defective CPS timing signal causing an engine vibration from poor ignition timing that comes and goes at a high frequency.

Ecomike said:

I am going to disagree with that. It is an obvious place and source for vibration in the driveline, and the CPS is mounted to the Trans bell housing, so if the flex plate is moving and vibrating the CPS sensor may not see the flex plate teeth all the time causing a partially defective CPS timing signal causing an engine vibration from poor ignition timing that comes and goes at a high frequency.

Click to expand...

Hmm, not sure if we're saying the same thing different ways or different things altogether...

What I was implying was that the torque converter didn't cause the vibe, the loose tranny bolts did. The damage done to the torque converter snout and bushing was then caused by the tranny vibration...

Anywho, it's all back together, but it' ain't running at all now. =(

It started up, ran like hell for a couple secodns...

Pulled the distributor, tried to reseat it a tooth back, and now no spark at all. =(


Not sure if the cps just went kaput or what. Is there a way to test those?

Yes and no. The test is not always conclusive. The flex plate may be bent now, and that would affect the CPS signal, as looks for the holes in the ring next to the gear teeth that starter runs on. I would replace the TC and flex plate.

But I am not clear on which bolts, part was loose, was the flex plate loose or the just the TC? Is the flex plate bent or damaged?

Well I had to replace the front tranny seal anyway, so when I pulled the the tranny, I checked the TC and it was grooved about an inch up the snout and the bushing in the pump was bad. So I pulled the oil pump to replace the bushing, but couldn't get it out, and rather than buy the tools to do it, I just bought a rebuilt pump and stator with all new bushings and seals. However, when I looked at the flex plate once it was exposed, , the wear patter on the back of the flex plate didn't look totally symmetrical, which made me think the same thing a bent plate, so I got a new ATP flex plate and a rebuilt Pro King TC. and put it all back together.

I loaded it up with fluids but spilled a heap over the funnel that leaked down by the distributor...and perhaps coil. I added 5 quarts of tranny fluid plus one in the TC (everyone said expect to use 8-12). Filled up the transfercase, installed new stock header to replace Borla header and new downpipe/cat/muffler/tailpipe.

I really expect this to fire right up.

Instead, I put in the key and the batter was dead, I hooked up jumper cables and cranked it and turned over two or three times and died very rough, tried it again and it cranked a little bit longer. Again, very rough with a fluctuation in the idle almost like it was 180 out. Tried again and gave it a little gas, and it actually sounded ok at slightly higher rev, but when I let off the gas it backfired and died.

With the backfire, I figured my timing was off. I pulled off the distributor, found top dead center and tried to stab it one tooth back. I got in the car, tried to crank it and it just kept turning over and over and over. I pulled the #1 plug and it was brownish.

I put a screw driver in the plug wire and laid it across the valve cover and cranked it and nothing, then I put a plug in it and tried again, thinking maybe just not enough juice to jump from the screwdriver. Again, nothing. It doesn't look like I'm getting any spark at all.

oh, and it was those damn E12 bolts on top that were loose. Everyone complains about how hard the are to get to, but I stuck my hand up there, gave it a couple twists and out it dropped. You could also see where oil had been leaking into the top of it from an apparent valve cover leak....new gasket for that too.

Well paint my neck red!

I guess it helps if you plug the distributor back in. Now it fires up right off the first crank, but still runs rough. I'll mess with it tomorrow.

Any suggestions? Think the computer is still just trying to relearn itself after being powered down for so long?

So jeep starts, runs rough, has a very mild backfire...but basically, it just feels like it isn't running on all the cylinders. I pulled the plugs and they were all just black. The next question is, is it running poorly because the plugs are fouled or are the plugs fouled because it's running poorly?

I should add that the end of the plugs smell quite strongly of gas.

Found of set of autolite plugs and tossed those in, the jeep still ran the same. I moved the distributor one tooth forward so it was pointing at where it was originally...the backfiring went away.

Now the engine barely runs like it isn't getting gas. It starts but just rattles and dies. If I give it a little gas, it picks up the revs, but it the revs increase and decrease harmonically by about 500 RPM.

If I let off the gas it just dies.

Poor grounds?

Battery voltage too low, corroded posts, clamps, bad grounds at the battery.

Loose or damaged sensor or sensor wires from the recent work.

Vacuum to the MAP sensor leak,

TPS connections,

Worn cap and rotor,

bad plug wires,

Leaking fuel pressure regulator leaking into the vacuum line (if there is one in 94? I forget).

Bad CPS

checked most of the grounds and they seem fine.
battery was pretty much dead, but I've never had a problem with the alternator, and it is charging the battery, so I don't think that's it.
TPS, hard to say...is there a way to check that?
brand new cap/rotor from Summit.
brand new Accel 8mm spiral core plug wires
tried unplugging the vacuum regulator so it had more pressure, didn't seem to make a difference
CPS is so finicky, it's hard to say..that and the O2 sensor are my most likely culprits for damage, just don't know how to check them, and I don't want to just go out and buy stuff.

This sounds like a cam synch problem to me.
Maybe the distributor is off a tooth or two, or
maybe it was installed 360 degrees out? (On the
exhaust stroke, since the distributor turns once
for every two crankshaft revolutions.)

I'd verify TDC on the compression stroke, then see
if the cam sensor is indexed properly to give a
signal, at the same time the rotor is pointing at
the #1 terminal on the distributor cap...

And double-check the firing order and plug wire
routing. Then check it again. This is basic stuff but
sometimes your brain and eyes will disconnect when
checking something so simple. I know mine does.

LOL, I chased one for months that was a new, but loose plug wire. Drove me nuts.

Disconnect the O2 sensor, as one way to test. Check the cranking voltage of the battery, the battery may be about to die.

Search Naxja advanced for "Ecomike Oxygen sensor test" for my old how to thread here

I'm sure it's at top dead center, I've reset it like 10 times.

I've checked the resistance in the new wires, they all are 0.

I've swapped the O2 sensor with a spare unit I had, no difference.

I'm getting pretty confident it's a bad flexplate.

Gonna pull the tranny again next weekend and match it up with the original...checking the holes on the outer band was the one thing I didn't verify. I've seen too many threads lately where the holes were off just slightly from stock.

New CPS showed up and it's back running.

Doesn't seem to be a vibe at any particular rpm either.

Still think the flexplate is a little out of round, and I suspect when this cps reaches an older age, it's going to start giving me issue too.

Next major tune up I'll probably get one from Jeep.

Anyway, I still haven't gotten it out on the road, but at least it fires up and runs.

Yippie! Glad you got it running again.

If you still suspect a warped flexplate, I'd check
it with a dial indicator mounted at the starter
opening. (Before tearing it all down again) You could
turn the engine at 90* intervals and take readings.
Don't know what the allowable run-out is, maybe
3-4 thousands...?

Let us know how it drives.

Great idea!!!!