voltage to both sides of injector!?#$%

[earlr85944]

Im trying to get this car running that I never heard run, PO says it purrs like a kitten, we'll see!
I got the car with no keys, clean title. First it had a viper alarm which I removed. The factory alarm is in but I am able to shut it off. These issues were resolved here: http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/388958-bypass-viper-alarm.html#post3727856

Now following the SOCAL tried and true 5 minute no spark test I get stumped at the test for voltage at one side of the injector- I have voltage to both sides so obviously they will not fire, any advice?

[hpservertech]

what do you mean voltage to both sides?

disconnect the connector on the injector. put 12+ to one of the terminals and ground to the other. Using a battery from a cordless drill is perfect for doing this. if you hear it click it works. No click it doesn't.

Another test is to take the fuel rail off the engine. Keeping everything attached to it. put bottles under each injector and try to start the car. if a bottle doesn't have fuel, then either the injector is bad or the wiring is bad.

You can test to see if power is getting to the injector by using a noid tester.

Use 2 people for these tests though.

[earlr85944]

that will only show if the injector works when disconnected from the car, it does.The problem is that the harness is delivering 12Volts to both terminals, one side should be 12v the other should not.

[legoland951]

You cannot check injector pulse with a voltmeter as it "pulses" faster than your voltmeter can pick up. You need a "noid" light also known as injector pulse light. It plugs into the harness and you can see it flash as you crank the car.

[earlr85944]

ok, maybe im not explaining it right, there is no pulse. with the key on there should be 12v at the coil and 1 side of the injector, i have 12v at both sides....
even with the harness disconnected from the injector

[88BlueTSiQuest]

Shouldn't that be normal until the car is running? Wouldn't the DME send a pulsating negative pulse to fire the injectors based off of a rotating signal from the flywheel or something?

[ae1969]

More than likely you have shorted injector wire. I would venture a guess that the short is at one of the connectors itself.

Go and disconnect the dme.

Unplug all the injectors....and check resistance/continuity at all the injector plugs. You will probably find that it is shorted.

The injectors are wired in pairs and if you find a short you will probably have to clean up all the connectors.

[Razorback1980]

The red/blk wires should have the power from the DME. The green (cyl 1 and 2) and green/blk (cyl 3/4) should not have power.

[earlr85944]

Now we are getting somewhere, I did disconnect the dme and found power to the 2 pins, injector1-2 and 3-4, I believe it was pin 14 and 15. ( the red and black as razor mentioned)
which pins coincide with the grn grn\blk

since I have power at all injector pins, it maybe 2 shorts or 1 common to all the ground side.

I cant rule out a hack splice by the po (found 1 already) either or an alarm issue yet.......

Thanks for all the help!

[hpservertech]

I had the exact same issue and it was the injector connectors. Noid light is all you can use to check this. It's easy to replace the connectors and they are pretty cheap. Less then $5 each from what I remember from napa.

[earlr85944]

could it be that easy? I have repalcement connectores, Ill check to see if they are shorted but all 4 at once?....

hpservertech, I have 12v to both sides of the connector, no ground. One side should be 12v the other ground to complete the circuit. did you have the exact same problem, 12v volts to both pins on all 4 injectors........

Maybe things are looking up, if only 2 connectors are bad (hence the short ae1969 mentioned, all 4 injectors can be shorted as they are banked in 2's. I dont have my shematics avail, can someone verify the pinout of the green green \blk wires to the dme?

On another note after reviewing old threads I see a reference that the factory alarm grounds the coil negative wire to prevent ignition, can someone verify this?

[marky522]

You wont have ground on one side of the connector becasue the DME sends a ground signal to fire the injector.

My suggestion would be:

-Unplug the DME
-test resistance across a inector connector

There are 2 possible outcomes:
OFL (infinate resistance) harness is fine
A resistance reading- you need to inspect your harness

Its that simple.
If you harness is fine you have a shorted injector driver in the DME
Mark

[Razorback1980]

Here you go....

[earlr85944]

Thanks for the info, I really had the diag procedure screwed up! I decided to play "lets remove the dme harness" and I did find some things which were uncovered by the harness removal like a missing screw on the speed sensor but after looking at the schematics, thx razor and verifying on another car, 88bluetsi and marky you hit it on the head! I was going by this previous posts that suggested that there should be power to one pin on the injector and not the other, but after looking further there should be battery power to one side and a little less to the other because it has to go thru all the injectors. So it looks like the harness is fine and I will now check the sensor condition and gap as the PO said he installed a 968 flywheel.

[earlr85944]

the latest on my parts\driver car no start is that I found a set of new sensors at ********.com for $75 shipped, yes thats for 2 so I decided to just yank out the old and go with new, they are the BMW versions which have a longer lead but hey the price is right! Should be running withen 2 weeks, thanks for all the help!
In the meantime I will continue to ring out the harness and ensure all wires are good as well as go over the car grounds, she should be a runner, hate to see her on the chop block!

[legoland951]

The noid light would have indicated whether you have injector pulse or not and its the ONLY way I know other than an oscilloscope. DID YOU SAY A 968 FLYWHEEL? The crank and reference sensor pick up metal tabs on the flywheel and count the teeth of the starter ring gear. I am almost sure that the 968 is NOT the same as a 944 as it has a completely different clutch so there may be the answer to your no start problem if that is the case.

[earlr85944]

Yeah I did worry about the 968 flywheel comment but he did say the car was running, he also mentioned a 968 AFM with the "restrictor plate" removed and a $600 power chip installed and that the flywheel and 968 sensors really woke the car up. I will drill him again on the flywheel and "yeah it ran great" again. If its the flywheel then it will be a parts car!

[earlr85944]

Well shes a runner! Finally hooked up with the PO today to pick up the viper key fob and grilled him on the "968" flywheel and afm comments. Turns out they were 89 944 parts not 968, cool now were making sense. So, new sensors are in and gapped, spark but no start, drained fuel and put fresh fresh stuff in, no start but a nice 2.5 bar on the fuel pressure, rerouted spark plug wires which were on wrong (PO had them routed as #1 at the back of the motor, now shes sounding like she wants to kick over but no start. Last the timing looks to be 1 tooth off at the cam so I check compression and all cyls are over 170#'s, cool no bent valves.
For the life of me I couldn't get the belt to align dead on so I changed the belt thinking the old one was stretched and what do you know, liftoff! What a strange cluster of unrelated problems and each one would prevent a no start so I went from "just get a new key made and she will fire up" to a major project. To the PO's credit, the motor does sound good and strong, no strange noises. Thanks for all the comments and advice.
Regards,
Rich

[hpservertech]

That's a lot of things for the PO to mess up to go to a no start. Glad to see it's running now though.