Missing badly

[o. l. t.]

I have low pressure coming out of the right exhaust. The service engine soon light flashes constantly while driving but not while sitting still at idle. The engine is missing and loping badly. The only real code is an oxygen sensor code and I put a new oxygen sensor on it.

There's a small exhaust leak at the pipe that goes into the passenger side manifold where the metal pipe clicks in but that's the only thing

[andrewwynn]

the low output has nothing to do with exhaust, everything to do with cylinder not firing.

no spark or weak spark or no fuel will be the cause, almost certain.

a previous car of mine (z28 camaro) had the same problem you describe twice.

1st time was a shorted spark plug wire (shorted against the heat shield designed to protect from the exhaust manifold)

2nd time was a defect in the distributor

I would check for spark at the plug; in the old days we'd do this by pulling each plug while running (thick rubber gloves or 1000v pliers is good; it was bad enough when cars used 15-20kv spark but new cars with 30-45kv really sucks). when you pull a plug and the engine doesn't change it's tune you've found the misfiring cylinder. Not sure how a new engine deals with this method of diagnostics but it should work.

If not the spark, most likely a fuel injection problem. injector not getting signal or gummed up or just plain broken.

ps when i read the title i thought you were coming back to say you missed your X5 and came back for company.

[o. l. t.]

Actually I thought the low output and other issues could be a clogged cat. Didn't take the thought further. I'm not getting a specific misfire code and this truck will throw it if it does hence why I figured a cat when I was getting an o2 sensor code but have all new sensors.

[andrewwynn]

unless there is a cross-over pipe between the outlet of the exhaust manifolds, there is nothing that will stop the output volume of air if the cylinders are firing, only the pressure at certain places will change. The internal pressures of the cylinders after combustion is so much higher than exhaust back pressure it's not very consequential.

Check out this web page. It gives some good advice about backpressure and how to measure using the O2 sensor port.

If the engine 'runs smoothly' no 'ch chugga cchu ugga' just low performance than I would guess more likely to be backpressure problem, but if all 4 cylinders firing and no cross-over pre-cat than if not even volume out both pipes not even volume being created from burning, so previous line of reasoning prevails.

[bcredliner]

Originally Posted by o. l. t.

I have low pressure coming out of the right exhaust. The service engine soon light flashes constantly while driving but not while sitting still at idle. The engine is missing and loping badly. The only real code is an oxygen sensor code and I put a new oxygen sensor on it.

There's a small exhaust leak at the pipe that goes into the passenger side manifold where the metal pipe clicks in but that's the only thing

Pre cat or post cat 02 sensor code?

[o. l. t.]

Bad #6 coil pack. Runs like a top now

[andrewwynn]

:-)

Follow up: I was "missing badly" my x5 the past ten days when I went on a trip to Arizona.