What's shaking in my car...

I just got my 2000 Mitsubishi Pajero IO 4x4 (automatic transmission) back from the mechanic after a complete engine change*. And now it has a nasty vibration, but only at certain engine rpms (around 900 or 1800rpm) and only once warmed up (engine running for 15-20 minutes before the shake starts). Vibration is bad enough I pull over and sometimes the check engine light comes on.

I have been disengaging the overdrive to force the engine to rev higher. No shake at higher revs that way. Is this going to damage the engine?

I could see a bad or loose engine mount causing a vibration only at certain rpms, but why would it not shake when the engine is cold?

I feel the vibration particularly through the transfer case shift lever. But I can’t think of a reason an engine swap would unbalance a drive shaft. Maybe it is engine shaking and I’m feeling it there due to the mechanical connections to the transmission and then transfer case?

Maybe it is dumb luck and now is the time something else decided to break on my car?

So, Dopers, what else should I check. Anything this modestly mechanically inclined guy should do before just taking it back to the mechanic for a ride along?

I have checked the engine oil and transmission fluid and levels are ok.
*Check your damn oil. Even if you got back from your vacation five hours late due to a cancelled flight and change of airlines. Even if it’s almost midnight and you are only putting $5 of gas in the car to get home and are going to fill it up and check the fluids tomorrow. Yeah. Especially then. Ouch.

I’d say you’ve checked what’s reasonable for you to check, and it’s time to get it back to the shop.

Make sure all tires are properly inflated. Check to see if you have any wheel weights missing. Check to see if any of the steering or suspension parts are excessively worn. Check to see if you can find any vacuum leaks near the intake.

Your mechanic will do this anyway, but it’s better to know that all that stuff is OK than to take it to the guy and have him say “well, your right front tire was a bit low and I didn’t see any wheel weights on it, so maybe that’s your problem”. Go to your tire shop and have them rotate and balance your tires first and tell the mechanic that you did that before bringing it in. It will get him to try and find the real problem a bit faster.

If you have determined that it is rpm related and not speed related I would take it back to the mechanic immediately. It sounds to me ike an engine miss, maybe a bad spark plug or coil pack. If the check engine light is comming on it shoul be easy to diagnose once he hooks up the diagnostic tool.

What’s shaking in my car…



You should take it back to the people who changed your engine. It could be something unrelated to the engine swap or they may have done something while doing the change, maybe not plugging some connection in fully. Broke something, didn’t tighten something.

Your description does sound to me like it could be a faulty coil or plug, as HoneyBadgerDC has already said. Was this a newly rebuilt engine that was put in? A junkyard engine that has been gone through with new plugs, coils, injectors etc.? Or just an engine swap with another engine of unknown maintenance history?

Don’t throw time and money at the problem, make them do it. The swap was apparently only partially successful.

When your engine light is on, a code is usually stored that can be read with an OBD II reader. Sometimes the code can direct you to the problem like “misfire on cylinder #7” and sometimes the code message is something that you will need a mechanic to decipher anyway. These codes can send you on a safari looking for zebras when the problem is just a horse.

Call it an unfinished swap and take it back to the people who did the engine swap, or if you don’t think they are the best option, take it somewhere else.

This would be my first guess as well. An engine missing badly enough can cause the oil light to come on even if there is plenty of oil in the engine.

Go to Advance Auto or Auto Zone or another place and have the codes read for free so that you will be fore armed before you go to your mechanic.

Broken or unsecured motor mount? Especially after a complete engine transplant.

Get thee back to the shop. Whatever it is should be covered under warranty. It does sound like a loose motor or transmission mount.

Not in my experience. Why do you say that?

Gary, he may be talking about a situation at idle whjere it is barely running at enough rpm’s not to stall, or in kind of a half stalled half running condition. Chugging we call it.

When it shakes at low rpms there is a bit of chugging.

And it is definitely rpm related and not speed. 80kph in top gear at 1800rpm and it shakes. 80kph in top gear with overdrive off and engine at 3000rpm and no shake.

Just seems weird that it is not doing this when the engine is cold. Go figure.
And I didn’t mention my location in this thread… but I’m in the Cayman Islands. Warm climate so oil flows quickly. Maybe the Napa Auto parts store can pull codes for me. The closest AutoZone is a long boat ride away.

Not sure if they put in new spark plugs. Doubt it. I can pull a plug and see and swap those on my own.

Shade tree mechanic job with a junkyard engine. Mechanic is a good guy. He welded my leaking exhaust while he had the car in for the engine job and just charged the rate he quoted for the engine work.

Uneducated guess: they damaged one of the mounts installing the new engine. Or it was already damaged and they loosened it up or something.

I had a Mazda 626 that did it. I thought I had an oil pump issue because the oil pressure light would come on at idle. I also needed plugs and wires. Turned out the tune up solved the oil pressure issue. I thought that was odd and had it checked out at my local mechanic’s shop and he verified that he had seen it happen as well. The skip was causing the vehicle to idle too low to maintain sufficient oil pressure. May be unusual, but it was a cheap fix.

If the Mitsubishi has the wrong transmission fluid it can also shake violently when driving. I fought this problem for two years on my Diamonte before I discovered what the problem was.

Does the vibration happen if you rev the engine up to 1800 RPM in neutral?

I think HoneyBadgerDC might be onto something. IIRC Mitsubishis do take some sort of special ATF. I’m not sure if they’d have needed to drain it for the engine overhaul or not, but it’d be worth calling and asking if maybe they changed it or topped it off.

Does the engine have a harmonic balancer? I had similar issues with my 4 L Jeep a long time ago…
No matter, sounds like a trip to the garage is in order, and sooner than later.

No idea if it has a harmonic balancer. Not sure if they drained ATF fluid. Should be able to go talk to the mechanic in the morning.

If I put it in neutral and carefully hit the exact rpms it does shake.

And it is the check engine light that comes on. Apparently there is a separate low oil light that does work! If the low oil light worked then I wouldn’t be in this mess to begin with.

Not the trans if it shakes in neutral.