The car has 209k miles. The check engine light came on. I opened the "A" cover of the OBD in the engine compartment. Put probe in #2 got 121 for a code. Which has to do with the AMM. This explains my bad gas milage (~20 mpg lately). I then put the probe in #6 and got 214. Which is an RPM sensor signal absent intermittently. Huh?
Where is the AMM? I unplugged the electrical connector at the intake manifold. It had little effect on the idle, there was a difference though. I unplugged the electrical connector on top of the air filter housing. The car stumbled and died. I figured that would happen. What does all this mean. Do I have to replace the AMM?

Chris
Buffalo, NY

a bad fuel pump relay can cause the 121, if it cuts power to the control unit, it throws a code for that. Myself, I'd clean the throttle plate and adjust the associated stuff, TPS, kickdown cable. Clean the manifold grounds and install star-washers, this is all preventative stuff, but can cause those problems. Dirty t-plates usually cause a fuel trim code instead of a 121, but both can be a bad air mass meter. Clear the code, see what comes back, if anything.

I'll try that. Funny because the car does not startup or drive or idle any differently that it normally does. i've owned it for the last 4+ years.

Chris

Dear Chris,

Good p.m. and may this find you well. I'm a little puzzled by your question, "Where is the AMM?" While I don't have a 940 with a turbo, I believe the AMM is next to the air intake box, connected to the throttle body by a 3"/75mm diameter corrugated rubber/plastic hose.

Before replacing the AMM:
(a) clean the electrical connectors
(b) clean the AMM itself.

In regard to (b) do NOT try to clean the filament with anything, other than a spray (pump or aerosol). That is, do NOT use a cotton swab or anything solid, that will make contact with the filament. This hair fine filament is easily broken. Clean the AMM filament with carb cleaner. Removal of dirt/carbon might restore it to smooth operation.

In regard to Code 214, if the RPM/Crank sensor signal goes away, your car will stop. The sensor's signal tells the fuel pump to continue working. If the sensor does not signal that the flywheel/flexplate is turning, the fuel pump shuts down. This is a safety feature: it keeps the fuel pump from sending fuel into an engine bay, wherein the engine is not turning (perhaps because of accident damage).

The RPM/Crank sensor sits atop the transmission bell housing, at the 10 o'clock position, as you face the engine (passenger side, US/Canada models). There is a procedure in the FAQs, under FEATURES, above, for chaning the RPM/Crank sensor.

If this sensor is the original, it does not owe you a nickel. They usually fail because the wiring harness deteriorates with time/heat, causing the wires the break and/or to short.

Hope this helps.

Yours faithfully,

spook

I was under the impression that the RPM/Crank Sensor, which I've also seen called a Crank Positition Sensor, had something to do with spark timing. Of course, if this was the case, it begs the question of what the rotational position of the distributor rotor means then.

Is it true that the output signal from this device merely enables/disables the fuel pump?

--
David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto

no, it is a crank position sensor, and tells the ECM the positsion of the crank and where the cam "should" be. turning the distributor changes timing relative to the cam posion not to the crank. The old ones with the hall sensor you could adjust the timing because there was no crank sensor, just a cam sensor. If the engine stops, then there's no fuel. I've seen 240s mis-diagnosed as having a fuel problem, because the pump isnt coming on, only because the ECM isn't getting a signal from the EZK module telling it that it's ok to send fuel to the engine.
--
cjregensurger@yahoo.com '86, '88 740 GLE; '88, 89 740 Turbo, '88 760 Ti