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1999 trooper severe misfire

10-28-2008, 10:33 AM
Iím having a persistent problem with my 1999 Trooper that has been running perfectly for years until now. It idles a little rough, but revs nicely with no engine load. It barely gets down the road, however. A real dog. Like running on three or four cylinders. Codes are p1171, P0030, P0301, and various O2 sensor codes at times, like low voltage. I replaced the fuel filter. Fuel pressure is being regulated at about 37 pounds. Remove vacuum from regulator, pressure goes past 40. Replaced oxygen sensors (that one on the passenger side was a bear; had to remove front drive shaft to get to it). Replaced all six fuel injectors. Did the usual EGR cleaning, also removed the TB to clean the weird EGR passage molded into the intake manifold which was plugged with carbon. I have an OBDII reader that interfaces the ECM to a laptop. Long term fuel trim on bank one runs into the negative, while bank two runs far positive, into the twenties at times. I tried the trick of spraying carb cleaner around the manifold to check for leaks, but nothing happened. Never did hear a leak anyway.
About two and a half months ago the check engine light came on, flashing. Ended up being the no. 3 cylinder misfiring. Coil pack was bad. I replaced the pack and bought a spare. I tried the spare on various cylinders, but no joy. No surprise since the truck was running better before on 5 cylinders than it is now. Difficult to get up to 50 mph, have to go very easy on the accelerator or I get a lot of knocking and pinging like the engine is under great load.
Can anybody give me any ideas? Thanks //

10-28-2008, 04:23 PM
I've read somewhere about guidlines as to how long the engine can be run while in mode A before damage to CAT will result, but I don't remember what the limits were.
I'll post the concluding info and my fix here; maybe others can benefit from my experiences.

My trooper indeed had a bad catalytic converter. I came to the conclusion after examining the scanned results; the passenger side was out of kilter. Of course that by itself isn't enough, but what really got me to suspect the cat was the trouble (besides the little incident of driving back home on a trip from a neighboring state, with over an hour drive time left, when #3 coil pack died) was the lack of response on the right side. If I removed a coil plug or injector connector on the left side, it made major difference in the running of the engine. However, it made little difference on the right (passenger) side. And there was the clattering of the valves on that side, too. I got under the vehicle and drilled a few 1/4" holes in the engine side of the cat, and Man! did the gas shoot outta them holes. And the engine started to run properly. Case closed. Just got back from a muffler shop downtown that replaced the cat for 180 bucks.

11-10-2008, 07:20 AM
Glad you got it figured out. I'll file this away in case my 2000 Trooper ever has a similar problem.

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