Nissan Xterra random misfire

We recently replaced the engine in my 2003 Nissan Xterra and since then we have had a problem with misfires. When accelerating it will periodically.bog dow and the car runs so rough the whole thing shakes. Then it rapidly accelerates and smooths out. Then the check engine light flashes. We have replaced everything not nailed down-plugs, wires, knock, crankshaft and mass flow sensors and on and on. Anyone have any ideas?

When a Check Engine light flashes it indicates a major misfire. And a major misfire can damage the catalytic converter if you continue to drive the vehicle.

Why was the original engine replaced?


Is it a general misfire, or a misfire associated with a particular cylinder? Suggest you post the actual diagnostic codes here. Misfires on a specific cylinder are usually debugged by moving stuff around, to see if the misfire follows what’s been moved. If your car uses coil packs, those seem to be a frequent cause.

Have you checked compression yet? Posting the codes will help. Are all the grounds hooked up properly and all wire harness connections correct? Where did you get the new engine from, I have seen used motors that have water damage from being stored outside and rain getting into the cylinders. What parts did you have to swap?

Major oil leaks and some other minor issues

umm . . . if you have oil leaks, isn’t it cheaper to just fix the leaks, versus replacing the engine?

Did you install a new/remanufactured engine, or a used engine?

I didn’t have a say in replacing the engine and it is already done so it is irrelevant. The engine is used with 80000 miles.
We were able to get a code this time: P0172.

your mechanic needs to start looking for a rich condition

For that matter, I would advise him to look at the fuel trims on both banks. Even though the fault is for bank 1 only, bank 2 might also be close to setting a code

Also have the fuel pressure checked. It may be too high.

fyi to the OP, the code means the car’s computer (ECM) is not able to figure out how much gasoline to inject by its normal method of monitoring the O2 sensors and the air flow sensors. It is saying if it follows the normal calculations – which assume at a minimum the O2 sensors and the MAF are all working — it results in too much unburned gasoline going out the tailpipe.

A misfire can cause that symptom & code, as a misfire means the gas/air mixture in the cylinder which should have exploded due to a spark plug firing, didn’t explode for some reason, and the gas just went out the tailpipe instead.

But it isn’t necessarily due to a misfire. A leaky injector for example could cause this. Edit: Or a faulty O2 sensor, or faulty MAF, bad compression, valve problems, etc. Lots of things could cause it actually.

The Nissan shop manual will have a flow chart which tells the mechanic which steps to follow to get to the bottom of it. If the mechanic follows that chart, the problem will be found. Eventually.

If I had this problem on my Corolla the first thing I’d do is visibly check to make sure all the spark plugs are getting a good healthy spark. If that didn’t show anything, probably next I’d swap the banks for all the spark plugs and coil packs and see if the problem moves to bank 2.

“Also have the fuel pressure checked. It may be too high.”

Exactly. That is a perfect example of a rich condition