snipsa

Hi everyone, I was hoping you could help with this problem. Hopefully I have enough info here.

My 83 944 suddenly started running and ideling roughly in the middle of a drive. I was just around the corner from my house and was able to get it home even though power was greatly reduced.

The car will start right up and idle(roughly) both hot and cold.

Because it will start and run, I assume that the DME relay is not to blame. Correct?

I pulled the spark plug wires from the plugs one by one and ultimately discovered that my #2 AND #3 cylinders were not firing! (with both wires removed, the engine behaved exactly the same as with them connected)

I then pulled the 2 spark plugs from the head and with them connected to the wires, laid each one on the intake manifold.
when I cranked the engine, I was able to clearly see that they were both creating a strong spark.

So now I assume that I can eliminate the plugs, wires, cap, and rotor from the list of suspects. Correct?

Next, I checked the injectors. I pulled both connectors from the problem cylinders and, as expected, noticed no change.

I thought that if the 2 injectors were in fact firing that I would probably smell unburnt fuel in the exhaust. I did not notice anything unusual.

I then consulted the haynes manual for some injector troubleshooting tips. First, I checked the resistance on each suspect injector and they were within spec.

Then, I checked for voltage from the injector connectors and found:

From the 2 pins in each connector, With the ignition "ON", BOTH showed 12+ volts when checked from ground.

If I am reading the haynes correctly, only one pin should have voltage and the other should be ground from the ECU.

OK, I am thinking that I am on to something here...

Does this mean that the ECU could bad or perhaps I have a wiring fault somewhere?

Something seems a little strange though.

I am sure that the front cylinder is firing because when I pull its injector harness, the engine immediatly dies. BUT, when I test the connector for voltage, I get exactly the same results from when I test the 2 bad cylinders. Voltage on both pins when tested from ground. (I have not checked #4 yet)

How could this be?

I do have an 84 that I could borrow the ECU for a bit but I am worried that if this is a wiring issue I might just be sacrificing it to the almighty porsche gods.

Anybody know what the next step is? I was thinking about getting one of those injector test lights.

Thanks in advance!

Ben

944_S_TYPE

I would take the injectors and switch them around. See if the fault follows.

tod84944

Sounds like you have 2 clogged injectors, or the needle is stuck in both. Try this.... with the car running, try to see if you can hear the injectors on the bad cylinders clicking. If you can, they are firing and moving. If not, try this..... with the car still running, lightly, notice I said LIGHTLY, tap on the sides of the injectors. Sometimes if the needle is sticking some, you can free it up by lightly tapping on them.
To listen to the injectors, put a long screw driver on the suspect ones, put you ear to the other end of the screw driver, if no loud click, bad injector.

Zero10

The injectors are wired in pairs, and all fire together. 1 and 3 are wired together, along with 2 and 4 (Or so I have been told)). It sounds like if it is a wiring problem, that it is localized to a very small segment of wiring.
How do the other injectors check out at the plugs?

83na944

Like 944_S_type said, swap them, that'll tell you if it's an injector problem.

snipsa

Thanks for the input everyone.

After work I picked up on injector plug test light apparently called a NOID. (why is it called a NOID?)

After hooking it up, it looks like I am getting an equal pulse at all of the connectors.
So I guess this rules out ECU problems or injector wiring issues.

I will try to listen with a screwdriver and if no clicking I will try to lightly tap them.

I guess if that fails I will pull the rail and swap the injectors around.

It seems unusual to me that the two injectors would stop working at the same time. The car had been sitting for several weeks and I was deliberately taking an easy drive so maybe it was running on three and I didnt notice until the other one stopped and I was running on 2.

Thanks again, I am crossing my fingers that a little tapping on the injectors to get them running and healthy dose of techron will have me back on the road.

I'll keep you posted.

Thanks!

Ben
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83 944
84 944
81 300D
81 300TD
85 300D

tod84944

After sitting for a few weeks, and if you already had some old fuel in it, you probley have some stuck injectors. Gas like to varnish up in injectors.

Danno

NOID = solenoid tester. For ON/OFF type things like injectors.

i think you have bad wiring on the #2 & #3 injector connectors. All the rearward pins on each connector should read +12 and all the forward pins should be 0-volts. If you get ANY voltage on the front-pins, you've got a short somewhere. Most likely it's in the spot where the wire goes into the hard-plastic body of the connector; a stress-riser. Slice the rubber-boot up and down and peel it off the connector and see what you have. This is a sign of trouble:



The power to the injectors are are fed from the same power-source at the 14-pin plug. I don't see why Porsche ran four separate power-wires from the same source to all four injectors, bizzare. At least in the later cars, they ran only one big wire. The grounds connected in pairs 1&2 and 3&4 to the DME. However, internally, they all run to to the same driver injector.

snipsa

It has been a while, but I finally got some time to work on the 944's again.
I am happy to report that all is running well again although I don't really know what actually fixed it. I installed some new plugs, plug wires, cleaned/wiggled all of the connections and put everything back together and it fired up on all cylinders.

Now i'm trying to get the 84 back on the road by replacing the fuel pressure regulator. Can't seem to get it off of the rail. But thats a different thread.

Thanks to everyone for there help!

Ben

83 944
84 944
82 240D
85 300D

Mighty Shilling

good work Ben! glad to hear she's running!

carsonmx114

the reason you had voltage on both wires is because when the plug is on the injector the voltage goes in on one side passes through the injector coil and comes back out of the other side. the voltage is seeking a ground, as soon as the ground comes from the dme the voltage your seeing on the ground side of the plug will be gone.

caster951

I originally had trouble getting my FPR off of the rail, then tried air tools to get it spinning quickly, BINGO. Give it a try and good luck...................