Re: 1989 325i issue...


"Psycho" <psycho@xxxxxxxxx> wrote in message news:hmmtq11t34ipb2agegf3mv8547sbec8hr0@xxxxxxxxxx 
First a little background on the problem. Car was running fine
until I was halfway to work the other morning. At that time, the
performance dropped off drastically and the engine no longer wants to
rev at all. Around 2500 is all she'll rev and it misses very bad at
that RPM. The plugs are also black suggesting a very rich mixture.


Black plugs also suggest oil in the mixture. Oil can mean worn valve guides/seals, and/or worn rings. I don't recall if you told us the mileage on the car, but an '89 suggests high mileage. My 325 ('94 with the M50 motor) was closing in on 220,000 miles without any sign of being worn out.



I 
have already changed the plugs and the fuel filter. I haven't pulled
the cap and rotor yet as I'm leaning more towards a sensor than a cap
and rotor problem.

Cap and Rotor AND wires. Don't forget the wires. I would be looking to these components before the sensors because the sensors typically result in a go-no-go scenario, not a goes-crappy-after-a-certain-point scenario.




I have substituted the airflow sensor from my other 
325i and ruled it out as the cause. My understanding is that the TPS
only tells the computer that the throttle is fully closed or fully
open, nothing in between so I'm not focusing much energy there. The
places I'm looking now are the O2 sensor (car has a 1221 code in the
computer) and the coolant temperature sensor. The O2 code has been
there for a while and the check engine light comes and goes so unless
something really went south I'm unsure as the O2 sensor would have
this negative of an effect. Could this or the coolant sensor cause the
car to run this bad? Any input will be happily accepted and
considered.


A bad O2 Sensor can cause the motor to run rich. The coolant temp sensor can also make the car run rich too. These two sensors adjust the fuel mixture, and if they are telling the computer that the car is cold, then the computer will set the fuel mixture as if the Choke (this is a part that carburetors have, but fuel injection accomplishes by changing the injector timing) is on. The choke is on when the engine is cold, and it causes a rich mixture until the engine warms up.

I wouldn't place these two sensors at the top of the list for the trouble you are complaining of, but they can certainly feed into the black condition of your plugs. Assuming the plugs are fouled and you replace them and do nothing else, the car should run reasonably well again until the conditions caused by the O2 and Coolant Sensors to foul the plugs again. That is, if the sensors are bad and they cause the plugs to foul, replacing the plugs should immediately restore the engine again until the sensors foul the new plugs.

If you had bad sensors AND trouble with the cap, rotor, and wires, then you would still have a crappy running motor even if you replace the plugs and sensors.

My Jeep recently began to run like shit, and two plugs had fouled. I have converted my Jeep from a carb to fuel injection, but I still have a distributor and plug wires. Anyway, I put in new plugs and the trouble immediately went away, but looking at the plugs I can see that I'll be needing valve guides and seals soon. My point is, you can have underlying problems that won't have any day to day effect on the running of the engine, but will manifest themselves over time. The time it takes decreases as the problems go unattended. The point is, you can correct the affects of the underlying problems and restore a semblance of normalcy. I think you probably do need an O2 Sensor and a Coolant Temp Sensor, but these parts are not part of the crappy running that you are chasing down.





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