Strange Engine Problem

lstuckey1 · 06-11-2008, 06:35 AM

My '90 2.5 is acting up. I normally drive my jeep locally and it doesn't see the open road very often. A few days ago I had to drive it to the next town and had about 15 miles at highway speeds. I noticed after a short while that the engine seemed to be losing power and seemed sluggish, almost as if something was physically slowing the jeep. Then I started to hear a sound that was kind if like detonation but not quite the same. I seemed more like a rattle than a knock. I backed off the pedal and slowed down and it seemed to subside. When I sped back up it seemed fine then started the noise again. Suddenly the engine shuddered once very hard (shook the whole jeep) and returned to normal. I pulled over, shut it off and looked under the hood for anything obvious. Nothing. When I started it back up it ran fine and I drove it the rest of the way. On the way back it did the same thing.
Since then it has been running great but I only drive it locally and have not stretched its legs much.
This morning I was driving to work (about 3 miles on country roads) and it did exactly the same thing again.
Does this sound familiar to anyone? Sorry for the long story.

EABiker · 06-11-2008, 06:53 AM

A couple things to check; fuel system, when was the last time you changed the filter? Detonation is either caused by too much timing, too little fuel, (lean), or higher compression, (carbon build-up). Also, there is a chance the cat is going bad; it may be falling apart internally and causing exhaust blockage.

lstuckey1 · 06-11-2008, 07:20 AM

Thanks for the reply. I’m ashamed to say I have not checked the fuel filter. I bought the Jeep in December and have been doing maintenance since but never changed the fuel filter. Is there another one besides the in-tank filter?
The P/O removed the cat so that would not be the problem. Is there a way to remove carbon build-up? Sea foam?

EABiker · 06-11-2008, 07:39 AM

The fuel filter should be external, behind the driver's rear wheel. Seafoam is a good bet to clean the carbon, Another thought I had though was your coil may be having issues when it heats up.

All that should keep you busy for a while!

lstuckey1 · 06-11-2008, 08:14 AM

Just one more question on the sea foam topic. I've read that you can disconnect a hose or vacuum line and pour this stuff very slowly through the fuel injector. Is this wise? And exactly what hose/vacuum line would one use for this?

Thanks for everything, you've been a big help!

EABiker · 06-11-2008, 09:18 AM

I use the brake booster line pinched over a smaller diameter tube that goes into the bottle; that makes it easy to squeeze the tube a bit to slowly add the liquid into the intake, (too much and it will stall out). I also let it sit overnight and do it's magic for the early morning smoke show!

**laybackman** · 06-11-2008, 06:53 PM

Either you have a clogged fuel filter orrrr a clogged cat converter. Highway speeds bring out the problems in both of them. Do the FF first since it is cheap $$ then road test it.

Fastbeeatch · 06-11-2008, 07:50 PM

I had same thing happen to me I ended up using dry gas took care of my problem. I knew my filter was good and filled it up the morning the problem happened, so it was easy to figure out I got bad gas. Before you change the filter unplug the out line, put a bucket under it and prime it a few times. Water settles to the bottom of the gas tank so it will be the first out, so if that is your problem you'll get a mixture of the two. If it's only gas then you know you can change the filter without worrying about ruining it by running water trough it.