healey1968

Hi all,

I've now been chasing down a PSM + ABS lights issue for way too long. Originally started about a month ago after the car sat for winter and I replaced the water pump & spark plugs. I've cleaned my MAF in the past due to PSM+ABS lights, so I figured the quick fix was to order a new MAF.

Put the new MAF in the car and the PSM+ABS lights did not go away. Ugh.

I connected durametric to the car, my MAF reading looks ok, ~25 kg/h @ idle; ~70 kg/h @ 2500 rpm.

I looked at the 'Hot film MAF' voltage reading via Durametric and I get 0.03V, where I think the spec calls for 1.2V to 1.4V.

To double check this bad voltage reading I pulled out the power probe and connected to pin 5 (from this thread), put the key in - read 0.0V, start the car - read 0.0V. It sure looks like I have a voltage problem.

I see a procedure to check the wiring harness, but it requires 'Special Tool 9616' - which I don't have, nor do I know what it does.

Can anybody help me diagnosis this further? I've already thrown a new MAF sensor at the problem, I'd like to understand it better before throwing the next part at it.

Thanks!

kromdom

stock air filter/intake? or aftermarket? check out this link: http://www.6speedonline.com/forums/9...2-problem.html

healey1968

krom,

Stock air filter (replaced about a year ago). I did read that link before - another special tool

I'll try disconnecting the battery.

I also saw the 'bad throttle body' comment, but no data to backup why. Not interested in buying a new throttlebody if I can get away from it. Anyway to test them?

Ahsai

Everything you tested indicate you have a MAF problem.
MAF reading should be between 15 to 20kg/hr @idle, warmed engine, not ~25kg/hr

Hot film MAF should be close to 1.3V @idle.

Please remove the MAF and check the following pins on the MAF connector carefully, with key in the last position before cranking:

Pin 2 : ~12v
Pin 4 : ~5v

You have a wiring problem if those don't check out. Pin 5 is the signal GENERATED by the MAF so with it removed, you would get 0v.

healey1968

Hi Ahsai, thanks for the help - this is exactly what I was looking for.

I put the key in and got these readings:

Pin 2: 12.3V
Pin 4: infinite

The power probe didn't recognize any connection at all to pin 4 (it reads 0 on pin 5). Think I have a broken wire somewhere?

Thanks

Ahsai

What year and model is your car? Need to check the correct wiring diagram. Sounds like you have an open wire from the DME to the MAF. The DME supplies the 5v (reference voltage) to pin 4. You're supposed to get 0 from pin 5 as it's connected as an INPUT to the DME.

BTW, those measurements were done with the MAF removed and not back probed with it connected, right?

Ahsai

Actually, which version of power probe you're using? Does it display the actual voltage measured? If not, you need to use a regular multimeter. A regular power probe may be confused by 5v since it's not close to 12v or ground.

healey1968

Correct, MAF removed - not backside probing.

Understand the pin 5 = input, I poorly said that the Power probe is showing pin 4 as a complete 'no connect'.

I have a 2002 C2 Cab.

Ahsai

Please check post #7. Pin 4 (Violet/Red) connects to plug B pin 22 on the DME. If you still can't get 5v on pin 4 using a multimeter, you need to check continuity between pin 4 and B22.

healey1968

Ah - I missed post 7.

It's a Power probe 3 - shows real voltage

I took out a regular multimeter and it showed identical results (12V on pin 2, 0V on pin 4).

I'll have to pull out the WSM to figure out where plug B is on the DME, I've never mucked with it.

healey1968

I'll use this procedure to find the ECU. Still not sure how to get the correct bundle after I get that far.

Ahsai

Our 7.8 DME has 5 plugs (A to E, or sometimes labelled as I, II, to V) so B is the second one. The way the cables bend, usually it's easiest to disconnect them one by one in order (plug A first).

And no you don't need that special Porsche tool. Just make sure you disconnect the battery first before unplugging the DME connectors.

Are you a tech? PP3 is pretty advanced

Ahsai

You can see the plugs labelled #1 to #5 in the photos. B is #2.

Ahsai

And use this DME pinout diagram
http://www.6speedonline.com/forums/9...ml#post3152221

healey1968

Hmm, can you double check that B is correctly labeled '2' in the sharkwerks page? That connector is a 40 pole bundle.

The 6speedonline pin out you linked has bundle '2' (aka 'B') as a 24 pole group.

I'm a tech enemy - an engineer . Plenty of theoretical knowledge, minimal hands on experience. Very dangerous