Questions and Answers
Comanche Running Very Rich
Q. Mr. Ciulla, I understand you are only picking and choosing e-mails because of the overload of questions sent to you, but you are my last hope. I have a 1990 Jeep Comanche Eliminator, 4x4, 4.0 liter, 5 speed manual transmission. I rebuilt the engine in 1999.
The cylinders were so badly egged shaped I had to buy another block. I bored and installed 40 thousands over pistons, new oil pump, new crank and bearings, new timing gears and chain, new push rods; well everything is new in the engine to include the valves, springs and so on. I installed an oversized cam and bearings, headers, and cold air intake tube, All sensors have been replaced, distributor has not been replaced.
Now to the question: I go through spark plugs faster then most people change underwear. About every three months I am replacing spark plugs due to them fouling out because the engine runs so rich. I am now replacing the Catalytic Converter because of the excess gas that has been run through it. What do I need to do to this engine to get it to stop running so rich??
The engine has a good lope to it @ 400- 600 rpms. It back-fires through the muffler when I shift from first to second and sometimes from second to third. I have been using the Bosch 4 platinum plugs but at $50.00 for six plugs it gets expensive. I am now using the cheapest I can find and I still only get about three months out of them. I use 93 octanes fuel, truck will not run on cheap fuel. Please help with this problem before I set the truck on fire and roast hot dogs over it.
Thank You For Your Time.
WilliamA. I do not pick and choose the questions I answer like all the other guys. I answer them all. Sometimes, well, quite often I get backed up and it takes three or four days to answer, but I do answer them all. This is why I encourage people to look through these Q&As. Someone somewhere probably had the same problem.
Now, with that said, the first thing I would have to look at is the fuel pressure. If the fuel pressure regulator is bad (blocked, not opening), the fuel pump can hit it's maximum pressure of about 100 psi. This will push so much fuel through the injectors you could run two engines with it. So check that first.
Another possibility is a bad O2 sensor. There are a number of other things that could cause a rich condition. Connecting a scan tool to the system will pull codes and allow you to see what is going on and pinpoint the problem.
The backfiring is probably related to the rich condition, but I would check the camshaft and valve train components to be sure they are correct for this engine.
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