Engine shake

[talon2swords]

Hello,

I have a secondary vehicle, a 99 3.1l Lumina. The car still has under 100k, and the engine and tranny appear to be ok. Right now, it only has a possible leaky fuel injector issue and it makes a "whirring" noise which may be the power stearing or an exhaust leak.

Anyhow, I put an aux tranny cooler and hitch on it with the intention of towing a trailer for camping gear, etc. on 3-5 hour trips.

My wife used it for a two hour drive (one way) and I told her to take the trailer to test it. She came back with some furniture on it, and I lifted the hood to check the engine, and the engine had a sporadic idle and then had a violent shake. I turned the engine off, and restarted it and the problem never returned.

I would like to use it again for towing under 1K lbs of gear, but I can't replicate the engine shake in normal driving. I have seen a 3100 engine do something similar at a used car lot before (the shakes).

My question is, other than vacuum leak, what could be most common cause of this (sensor, etc)? Thanks.

[60dgrzbelow0]

These four videos may touch base with this problem...either in regards to a stuck EFI or with the DIS Ignition system. Don't worry too much about all the fancy equipment involved in the first two videos... the third video shows the means to do ignition testing with fairly inexpensive equipment. All of the videos are very interesting for anyone concerned with getting a "One Over The World" view of the GM Waste Spark systems on our cars. Best of luck with your diagnosis:


Stuck Closed Fuel Injector

http://www.youtube.com/watch?v=NXrd1fYwj1o

DIS Waste Spark Diagnosis

http://www.youtube.com/watch?NR=1&v=9TqB76mZzhM

Wells Training Video on GM DIS System Diagnosis

http://www.youtube.com/watch?v=2woQT1eOy8U&feature=relmfu

Ignition Wiring Diagnosis (The Problem of Secondary Resistance)

http://www.youtube.com/watch?v=OKCQPlr2k6c&feature=relmfu

[talon2swords]

Thanks for the links. I broke out the Haynes manual and only checked the secondary resistance on the coils. They were all in spec. However, when I purchased the car 2-3 yrs ago, I found corrosion (rust) on some of the terminals and tried to clean it off as much as possible before installing new wires. I think one of the vids mentioned this as a sign of trouble.

Btw, I installed new Autolite wires, and the restraining clips inside the female plugs are kinda weak and seem to wear out quickly. I don't think I'll buy any more of that brand.