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. 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. 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
89 325i / 87 325is
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.
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
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
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
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.
On Sun, 25 Dec 2005 12:07:59 -0800, "Jeff Strickland"
Sorry, didn't mention the mileage. It's around 210,000 or so.
However, head was redone a little over a year ago.
Wires are only a year or so old as well. Cap and rotor are an
The new plugs turned black and sooty quite quickly after they were
installed. Definitely a rich condition or severe misfire problem. Just
have to get the time to sort it out.
Had the thought of fuel pressure regulator as mentioned in another
Easy way to check this is with the engine idling. Remove the vacuum pipe
feeding it and cover with a finger. If working, the engine should slow
down, stall or run roughly due to the mixture going rich.
*In "Casablanca", Humphrey Bogart never said "Play it again, Sam" *
Dave Plowman email@example.com London SW
On Mon, 26 Dec 2005 09:06:04 +0000 (GMT), "Dave Plowman (News)"
Just out of curiosity, why would it go rich at that point?
My 87 325is was idling very eratic until I disconnected the Idle
Control Valve. Now it idles fine. By eratic I mean surge and almost
die then surge again. Surely there's a problem there to chase down...
Finally got the transmission back in and the tires on the ground
again. Will adjust the valves and chase down the idle issue real soon.
Got to figure out why the 89 doesn't run worth a shit first though...
The fuel pressure regulator is there to keep the fuel flow through the
injectors independant of manifold depression. If the fuel rail runs at say
40 psi applying a vacuum of say 20 psi to an injector will obviously
effect the flow. So the regulator varies the fuel pressure in direct
relation to the vacuum in the inlet manifold. At idle the vacuum is high,
so disconnecting the vacuum pipe will increase the flow above the correct
value and make the mixture rich. On early EFI systems the actual fuel
pressure can vary by approximately 1/3rd under the control of the
regulator, and the wrong pressure can have a big effect on the running and
fuel consumption. I'm not so sure about current systems with a rather
higher fuel rail pressure.
*Do they ever shut up on your planet?
Dave Plowman firstname.lastname@example.org London SW
Fuel Pressure Regulator fits the scenerio of instant rich mixture. The fuel
pressure regulator really works as a pressure relief valve so when they fail
the pressure goes way up - maybe close to 100 psi depending on the condition
of your fuel pump. Sometimes they can fail in a mode where it will
temporarily fix itself if the engine is turned off for a couple of minutes
to let the pressure bleed down so that might be another symtom.
I'll say a fuel pressure regulator also, check it first and see what
the PSI is, should be 3bar or 43 PSI+-0.9. You'll need a pressure
gauge and a 'T' fitting. Autohaus has FPR for about $53.00
Bently or Chilton has the test procedure. Test first, might not be it
Here's where I stand... The issue with the 89 still persists but I
haven't been able to get to it. The 87 has a broken connection inside
the shell of the crankshaft position sensor. When it made good
contact, the engine ran. When it made s-so contact, the engine BARELY
ran. Obviously, when it made no contact it didn't run at all.
Needless to say, I'll be checking the sensor on the 89 tomorrow
while I'm looking for eratic spark as a cause of the poor running.
Also on the list is the fuel pressure. The O2 sensor was changed and
the car now idles much better. Also, DME no longer reports and fault
codes. I'm thinking there's a chance the sensor on mine isn't making
real good connection and causing the problem. Real easy to check as
I'll have a new sensor in my hand...
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