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93 Grand Cherokee Shaking & Shuddering

edited February 2012 in Repair and Maintenance
I'm having an issue with my 93 Grand Cherokee with 193k miles.

The RPMs will fluxuate and even drop to 0 at times and the whole Jeep with shudder and shake and then the RPMs will return back to normal. It could just drop down once, or several times in a row. I've even had it completely die a few times and I'll have to restart it. It's the worst when idling or driving slowly, like through a drive through or a parking lot, but the Jeep will still give a small jerk at times during acceleration as if it's trying to do it but can't completely.

I know next to nothing about cars but I have a friend who has helped me with a few things. We changed the fuel filter which he said looked like it may have been the stock fuel filter. He hooked up his compressor and blew all kinds of black garbage out of it and concluded it definitely needed a new one. He told me just to run it and see how it did, which it did fine for awhile but today it seemed to be acting the worst ever with it shaking and shuddering and trying to die but it didn't. He also looked at the spark plugs and told me that while they were aged they didn't look bad enough to be worth the money replacing.

I tried to get a recording of it doing it while idling but of course as soon as I pulled out my phone and started the video recorder it stopped misbehaving. It also wouldn't do it while I had it with my friend. Funny how that works...

I thought I'd see if anyone has any suggestions or thoughts.

Thank you very much for everyones time.
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Comments

  • Sorry guys. I clicked the post button and it looked like nothing happened. So I hit it again... still looked like nothing happened. Changed the title and hit it again and it tells me it's been posted :/ Most forums it takes you to your thread that you just created.

    Sorry for the spam >_<
  • Pull the fuel filter again. If there was a lot of crud in the tank, the new filter may be clogged. Is the "Check Engine" light on?
  • If this problem came from a fuel pressure issue (such as you might get from a clogged fuel filter), it would probably be ok at idle/low speed and get worse with load.

    Forgetting about the guy eyeballing the plugs and wires, how old are they?

    Idle/low speed dropping/surging is what happens if you have a vacuum leak. If your friend has a vacuum gauge and knows anything about using it, he could tell you whether this is plausible within about 10 minutes or less.
  • I feel for you. I have the same problem and I have replaced the crank sensor twice, and the engine computer. In the meantime my catalytic converter melted and I blew out the muffler backfiring because fuel was igniting int he wrong place. Still happening!!! I am desperate for a solution.
  • Mine is a 1997 Grand Cherokee Laredo. V6. Automatic.
  • It is more likely to backfire if I give gas too soon when the problem occurs.
  • Also it is more likely to happen first thing in the morning when the engine is cold.
  • SpankN, your problem is typical of a fuel deliver or metering problem caused by insufficient fuel delivery or a vacuum leak. If I blew that much black crud out of the line filter, I'd be concerened about the sock filter on the end of the fuel pickup tube in the tank. It may be a good idea to look further, as well as to test the fuel pump.

    Vacuum lines do get old an crack. And leak. Bought by the foot, the rubber line is dirt cheap. I'd sugtgest buying some and replacing the lines...ONE BY ONE to be sure you route them correctly and don't leave any off. They're all pushin' 20 years old.

    An erratic ignition pulse can also act like a vacuum leak. Can you tell us a bit about the maintenance history? When was the last time you changed the basics, the ignition components and the filters other than the fuel filter?

    NanHam, you have an entirely different problem. You have a cylinder or more not firing, or perhaps even an injector not closing. Another much lower probability possibility is a fuel pressure regulator not working, allowing too much squirt.....but I consider that a very low probability cause. You have raw vaporized gas blowing up everywhere. I'd start by checking the ignition of each cylinder. Until you get all cylinders firing reliably, you'll not make any progress.

    Let's try not to get these two problems mixed up. Perhaps a new thread would have been a better approach.
  • As far as the wires/plugs go I haven't replaced them in the roughly four years I've had the Jeep.

    This is just a random problem that comes and goes along with its severity. Sometimes it will do it once, twice, and be done. Other times it's so bad it's nearly undrivable. Today I was driving it around town and didn't have the first issue in a roughly 20 mile journey. Would this be so random with a vacuum leak?

    Also no there check engine light isn't on. The last time it came on was when my alternator died around 4 months ago. I replaced that and the battery (bad cells) no engine light since then.

  • Really? That too can cause your symptoms. And probably is. In my response I assumed you'd looked at the basics first. That's what happens when I assume.

    That vehicle has an OBDI system. If you had an OBDII system you'd have a light for sure.
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