special tool

I can't believe noone has told you to put in a new fuel pressure regulator. If that doesn't fix it, I am buying everyone in this post before me a round of drinks.

streckfu's

Any changes?

Danton

LOL!!! Is there a way to check the FPR? The one I have is the Bosch adjustable which runs like $130 or so. I'd hate to buy a new one without knowing for sure. Too bad I threw away the stock one! Well at least the car decided not to start in my garage and not leave me stranded...

Regards,
Danton

Bri Bro

Connect a fuel pressure gauge to the front of the rail on the test connector. Pull the DME relay and connect 30 to 87b, that will make the fuel pump run constantly. Measure pressure.

The Injectors are connected to +12VDC on one side and the DME on the other. Without cranking, and the LED connected to the DME side, you should see a constant LED light because the DME isn't pulling the injector to ground. With it cranking, the DME pulses the injector to ground. This also pulses the LED on and off. The amount of time it is on vs off (duty cycle) will change the intensity of the LED.

Danton

I'm getting a fuel pressure reading of 37 with the pump running. When I shut it off it goes down to 30-32psi. I'm still wondering if the LED test light is supposed to be so dim while cranking. It's less then an 1/8th of the brightness it is when the ignition is in the on position. And I don't see any fuel in the chamber after cranking. Is my fuel pressure in the normal range? It's the Bosch adjustable unit....

Thanks,
Danton

Bri Bro

The reading should be between 2.3 and 2.7 bar with he jumper in and the engine not running. 14.7 Bar= 1 PSI so 37 PSI = 2.5 bar.

Attached is what the injector pulse should look like. You will need a scope to see this waveform correctly. The LED tester has it limitations. The waveform starts at around 12VDC, then is driven to around 1VDC, this sets the injector open. The oscillation after the first pulse holds the injector open. The spike at the end is generated by the injectors magnetic field collapsing after the injector pulse is turned off.

Injector Waveform

Have you checked the TPS?

Danton

I did check to see if it clicks when I open and close the throttle but I haven't put a meter on it. It's pretty new that's why I didn't bother. Could a faulty TPS keep the injectors from opening which I think is the case? A local shop said it could also be the KLR. Any thoughts?

Thanks.
Danton

theedge

Stop worrying about the LED, its supposed to be dim when the injector is firing. Its the principal of waves, waveforms, averages, etc.

Give it 12 volts 100 % of the time. You get full bright

Now form that constant signal into the wave caused by turning it on and off at a set frequency. For the purpose of this example, give it 12 volts half the time, zero the other half, pulsed in a steady wave, many times a second. What does this work out to? Half the power of 12 volts 100% of the time. Thats why the the LED is dim, because of the nature of how the injectors are controlled, by being turned on and off quickly.

Danton

Ok...... I tested the TPS and it seems to be bad. I did it the way the Haynes manual says and how Clarks Garage recommends. I'll pick up a new one tomorrow and see if it helps.

Thanks,
Danton

Danton

Well I went to pick up the TPS and the way my lucks been going ofcourse they have the TPS for NA 944. So now I have to go back tommorow to get the right one. Also the head guy there says there's no way the TPS can be causing my problem. Whatever, it needs to be replaced anyways....

Regards,
Danton

Waterguy

It is possible for a failed TPS to keep yiur car from running, just not the most common failure mode. If the full throttle switch fails it can prevent the car from starting.

I assume that, from the fact that your car starts with starter fluid, you have spark. Good fuel pressure and apparently signal to the injectors. It would be worth verifying that your injectors spray fuel as Danno(?) suggested. One other failure mode I can think of is the AFM. I believe that if you disconnect the AFM plug that your car should start and idle, but stall if the throttle is open. There are full diagnostic procedures available for the AFM availbe somewhere around here (Clark's Garage? FRWilk?)

Danton

I'm using a HR MAF kit so it can't be the stock AFM. I did hook up the stock unit just to see if it was possibly the MAF and still nothing. I wish I could pull the injector rail out and crank it but I know the larger injectors will fall out under the pressure as they don't have the same mounting as the stock injectors. I did check for fuel in the chamber after cranking and I couldn't see or smell any. If it ends up not being the TPS then I'll have to find a DME and KLR to swap out...

Thanks,
Danton
87' 951
03' 325i

Danno

How long did it run when you sprayed starter-fluid in?

"One other failure mode I can think of is the AFM. I believe that if you disconnect the AFM plug that your car should start and idle, but stall if the throttle is open. "

"I'm using a HR MAF kit so it can't be the stock AFM. I did hook up the stock unit just to see if it was possibly the MAF and still nothing. "

There's some clues here. Waterguy is right on, you can actually have the AFM/MAF completely disconnected and the car would start up. But it will die within a second or two. Someone posted earlier about hooking up a toggle-switch to the power-line of the GURU MAP-computer to use as an anti-theft measure. In this case, with no air-flow signal going to the DME, the car would still start, then the DME will look for an air-flow signal to figure out how much fuel to injecto, then not seeing one, it will turn off the car.

So here's another test: find out what your idle-voltage is going to the DME. The MAF should be putting out a signal that's massaged to be compatible with the DME; that is, the pure output of the MAF has been modified to look like an AFM signal. To measure this voltage, hook up a voltmeter + probe to the DME #7 wire (green/red-stripe) and see what voltage is generated by the MAF. It very well could be that the air-flow signal of the MAF is hooked up to the incorrect wire going to the DME.

Bri Bro

It is possible for a failed TPS to keep yiur car from running

It did on mine. I had a car that would not even try to start. Went though all the tests and the last one was the TPS... it didn't pass. Went to Autozone with the part, they crossed it using the Bosch number on the part, and the car started right up. I am at a loss to explain why the TPS did this but it was the only part replaced.

Danton

OK... I installed the new TPS and it still didn't start. But at least I'm getting the proper readings from it now so maybe it will have better driveability. So then I decided to take the hose that goes to the fuel pressure damper and check the flow and for possible dirty gas. Well the flow was fine and the fuel looked clean. Now after I hooked this hose back up, IT STARTED! Please explain this. I don't believe the damper had anything to do with it not starting. Maybe the FPR was stuck and messing with the fuel rail unstuck it? I don't know......

Thanks,
Danton
87' 951
03' 325i