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Shaking, knocking, vibrating van!

We have a '95 GMC Vandura G2500 and today when we took off from a stoplight the van suddenly started vibrating like crazy and running rough. It was making a knocking noise and the van kept shaking the whole way home. The shaking was worse both coming to a stop and accelerating. We could also smell gas when we stuck our heads out the window. Any ideas?

There’s any number of possibilities. First guess would be some kind of ignition system failure. A shop’s igntion analyzer gadget could say one way or the other. Second at bat would be something in the fuel system, fuel pump or fuel pressure regulator. Has the car had the recommended routine maintenace suggested in the owner’s manual? It may just need a tune-up.

We’ve only had the van a year now, we gave it a tune up right after we bought it and replaced the egr valve and throttle pos sensor.

EGR? A faulty EGR valve (or the various stuff that controls the activation) can cause this problem. Maybe something has gone haywire with that again.

Hmmm, could be…We replaced it the first time b/c it was running funny and hesitating. Hafta check that out, sounds a lot better than it if was something in the fuel system ($$$)!

Could it be the o2 sensor?

I had an EGR problem with my 70’s Ford truck one time. I diagnosed it by connecting a hand held vacuuum pump to the EGR control port. At idle, when the EGR is activated this by vaccuum, there should be a noticeable decrease in RPM and/or rough idling. Often the engine stops completely. That means the EGR is working. If there’s no change, it means there is something wrong.

In use, the EGR isn’t supposed to open at idle. It is connected to a vacuum source that only allows it to open in conditions where performance loss isn’t easily noticed. But it can stick open and will then yield a rough idle, stalling,etc.

You are right, the EGR is usually easier to fix than a fuel system problem. If you are looking for something easy to fix, a general check of the vacuum hoses and devices they control might be worthwhile. A vacuum leak can cause this kind of symptom. Best of luck.

I had similar symptoms when my crank position sensor went. That should cause the Check Engine Light to light up though-is yours on?