Voltage @ Injectors?

sneed21 · 05-04-2004, 03:42 AM

I need some help. I've been checking through my factory manual and can't find it. Should I have 12v on both leads of my injector clips? I thought one side should be 0v and the other 12v. I couldn't find an answer in the manual.....only the ohms value between the two. The DME relay has been changed as well.

Reference the latest 9magazine Q&A section of the 924/944/968 section.

Thanks.

FLA944 · 05-04-2004, 03:44 AM

Yes, should have 12vdc. Pick up a Noid light for Bosch injectors at Advance,Discount or Auto Zone to check the pulse

sneed21 · 05-04-2004, 03:55 AM

You got it. That's my plan. Should I pick up an oscilliscope (sp?) while I'm there?

SoCal Driver · SoCal Driver's Garage

An o-silly-scope is a good item to have when you need it and if you can set it up and read it. Think Fluke and a few other meter makers have a digital graphic display that will go the necessary settings to read and show the pulses.

As to the injector voltage; 12 vdc on one side (think it's the rear pin) and about 10 vdc on the front (other pin) if the injectors are still connected. The windings of the injectors reduce the voltage. If you disconnect all of the injectors then there shouldn't be any voltage on one side. Note this is with the key on.

sneed21 · 05-04-2004, 06:56 AM

Thanks SoCal. I can borrow a Digital Fluke from here at work, but it will probably take me a while to get through the instructions. In the meantime, I'm running to PepBoys on the way home to pic up the Noid light. Hopefully they will have the Bosch connection I need.

sneed21 · 05-05-2004, 04:14 AM

Bought the Noid light yesterday. (Had to go 3 places before anyone knew what I was talking about)....I actually had a girl behind the counter at Advance Auto Parts ask me "Now who makes Porsche?" Unbelievable. Anyway, I checked the injectors, and each ones firing. I also re-wired the DME to bypass the extra Motronic Box (as recommended by FR Wilk), and it still will run for two seconds, then cut off. See previous thread:

Sudden loss of pwr, then no start

I need to add an avatar showing a guy pulling his hair out....that would be me....

SoCal Driver · SoCal Driver's Garage

I have an avatar for you. It's a digital snap of the reference pulse that another board member took. Seems fitting.

sneed21 · 05-05-2004, 08:02 AM

I don't know whether to laugh or cry

I need another set of eyes to look this one over before I get it towed to the shop. There's got to be someone in the Jacksonville, FL area that can lend a critical eye. I've reached my tech/mech limits. After running through all the manual's tests, everything checking out, and still no go?? Whatever happened to the good old days where gas + air + spark = vroom!?!?!

ae1969 · 05-05-2004, 10:28 AM

Try jumpering on the test plug B and C, disabling the idle stabilizer valve first....... just for kicks

BUT after that.... give us this info

1. Fuel Pressure readings: WHAT are they while cranking and when it stall out.
2. Voltage at the injectors: What did you get. Give us the readings. Ignition on and off.
3. Voltage at the Coil: Tell us what you got. Ignition on/off
4. Spark: Yes/No
5. Reference sensors: Your readings of both sensors. Also check the reading at the dme connector. Make sure something isnt out of wack in the harness.
6. Timing. Your belt lines up?

sneed21 · 05-05-2004, 10:46 AM

I'll try jumpering the test plug when I get home, thanks,

1. I will have to re-run the FP readings. It stalls as soon as it starts.
2. 11.89v +/- .03v @ all injectors w/ the switch on, will have to check when off
3. Yes V @ the coil, will re-run readings
4. Yes Spark @ all 4
5. Ref sensor readings were w/in spec via the factory manual (don't remember what they were though) The reading off the dme connector was the same.
6. Timing is OK, no missing teeth, and it all lines up. I initially thought timing, but after breaking down, and not being able to rev over 2K, then mysteriously everything was fine until 3 miles down the road, and it happened all over again.

I'll follow up tomorrow.
Thanks!

SoCal Driver · SoCal Driver's Garage

Need to jump the DME relay pins to run the fuel pump. If the fuel pump runs then start thinking FPR. Could have a vacuum line off.

Let me add to this: If the fuel pump runs then also suspect the DME relay. The fuel pump should run for a half second or so after you stop cranking.

sneed21 · 05-06-2004, 04:49 AM

Jumpered, FP runs. Also runs while starting (new DME Relay installed just in case).

I checked some values last night.

I have 27 to 29 fuel psi while it runs for 1 second.
I do not have voltage on the injectors with the ignition off. I don't have voltage on the injectors with the ignition off on my other 944 and it runs great.
I tested DME pins 35 and 18 to 5, and there was battery voltage at each.
I jumpered to bypass the aux air reg and there was no change. Checked the resistance and voltage, they were w/in spec.

sneed21 · 05-06-2004, 04:55 AM

I did find this. It goes to a 3 prong test point, and was just laying underneath the intake. What is this?

SoCal Driver · SoCal Driver's Garage

Later 944's (post 85.0) have a third sensor. That is the plug for the dealer to use when diagnosing. You can take the sensor off if you want.

Voltage to the injectors is only there with the key on. The first set of contacts in the DME relay have to close. This provides voltage to the DME and to the injectors. But you did use a noid light and it indicated that the injectors are getting a pulse.

How about fuel delivery. Need to pull the fuel rail with the injectors and lay the whole thing on some rags. Have someone crank the car while you watch the injector tips. These may be clogged.

sneed21 · 05-06-2004, 08:51 AM

Good point, I'll check the injectors. I'm hoping they're trickling, instead of spraying.....fingers crossed. I'll see if I can't grab some new seals on the way home....might as well change them while the injectors are out.

ae1969 · 05-06-2004, 11:10 AM

....and if the spray pattern looks good.........

Throw a match on it and be done with it.

sneed21 · 05-06-2004, 11:20 AM

I AGREE!!!!

Wait, better put the insurance back on her first.....

adrian jaye · 05-06-2004, 02:33 PM

sneed,
have fukk photo layout on testing injectors go to my website

www.playback.demon.co.uk
then Porsche then technical FAQ

sneed21 · 05-07-2004, 02:03 AM

OK, to add to the laundry list of things I've checked/changed out. Last night I checked the injectors....each was spraying a wide fan pattern...very pretty... Anyhow, I went ahead and changed them, along w/ the fuel rail, FPR and Damper. Add that to the other things I"ve changed:

Plugs
Plug Wires
DME Relay
Temp Switch
AFM
Coil
Dist Cap
Dist Rotor
TPS
DME

I've run through the 13 or 14 step factory manual DME check, and all came out clear. I ran another compression test last night and came up with:
Cyl 1 - 176 (at front)
Cyl 2 - 178
Cyl 3 - 176
Cyl 4 - 175 (at back)

Not too bad, car has <80K miles.

Timing lines up, have hot spark, fuel pressure......just no go.....

sneed21 · 05-07-2004, 05:40 AM

BTW: I've found out just how difficult it is to work on the 944's while the wife is breathing down your neck saying "Sell both together for $3800 on eBay and be done with it"......... I thought I had broken her in to classic car repair woes with my past MG and XKE........but no.....