Zero10

Don't worry about it so much. Is this car your daily driver?
No offense, but it's just not worth getting stressed out over.
Just follow through with checking the speed sensor signal, it should give you an indication of where to start. I think that's where you will find the problem, given your low tach reading as well as the fact that only #1 and #4 get spark. If the speed sensor checks out, let us know, and I'm sure everybody here will help you continue to troubleshoot it.

Buying parts just to swap out and see if they are the problem is near the bottom of the list of good troubleshooting methods. There is usually a way to test just about anything. If the speed sensor output is low, you need to re-gap the bracket, which really isn't as hard as it sounds. If the sensors are stuck, there is sort of a trial and error method that can be done with the sensors still in the bracket. It's how I've done 2 944's now, and both worked great. It's especially easy if you have an oscilloscope.

tomrc

Thanks, a good night sleep chilled me out a bit. I'm suspecting the harness is bad, luckily myself and some friends coop a shop with lifts, an extremely good set of tools, a pretty good Knowledge base although 80% are Honda guys (I'm the only kraut), and beer in the fridge.

I'll try aligning the sensors today or tonight, the next step maybe to cut into the harness and jumper the speed sensor wires right before they go into the DME connector. What do you think? The thought of cutting into the harness doesn't make me too happy though.

No luckily I don't depend on this to get me back and forth from work.

Thanks for all your help,

Zero10

Only cut into the wiring harness as an absolute last resort. It's a very difficult thing to change if any damage is done, so I try to leave it for absolutely last. That said, since you don't need it to get to/from work, that gives you an advantage, time. So, if you have access to a nicely equipped shop, that is a good place to start. I wish I had access to such. Just start with checking the speed sensor output at the sensor, if good, check at DME, if good, then consider the DME as the culprit. If it's weak at the sensor, re-gap the sensors, if it's only weak at the DME, then look into wiring. Hopefully following this train of thought will lead you to the solution to this problem.

Best of luck!

tomrc

Here we go, still no joy BTW. I checked the signal at the sensors with them disconnected from the harness. Then I compared them to the signal with it the sensors connected but not connected to the DME, same thing, then with the DME connected, no change. So I'm thinking it's not the harness anymore. I re- adjusted the sensors (what a pain in the a$$ that is) and I got a stronger signal out of the sensors but the car still insists on running on 2 cylinders. So, I'm also thinking it's not the sensors or the harness anymore.

Also I checked the injectors at the non-working cylinders and there is a nice strong square wave, sort of what I was expecting.

So anything else? I'm at a loss now, I'm going to check the coil tomorrow and see if that's bad, the cap was replaced, I'll get a rotor on Monday if I can't get anything going by then.

Anyone, have a spare early DME I can borrow to try out? Is the coil neg the output of the DME? Should there be some sort of waveform or pulse there that I can check? I'd like to make sure before I go buying a DME.

Thanks all for your help, hopefully we'll get her running right again.

Zero10

Okie dokie, you didn't mention what the output voltage of the speed sensor was.

It does sound more like a spark problem now, but I am not certain why the tach reads so low. I was thinking it was related to the fact that there was weak spark on #2 and #3.

It's possible it's the DME, the way to check the output of the DME is as follows:
The DME grounds the -'ve lead of the coil. So, attach your oscilloscope to the negative lead of the coil, and it will hover at +12V, then drop to 0V for a brief second, then return to +12V. the brief 0V reading is the DME grounding the coil. Check if it is consistent. That's a good next guess.

Do you have a spare set of plug wires to swap out for testing?
I know around here a lot of parts stores just have an entire rack of them, and if you're on good terms with them, you might be able to borrow 2 wires for troubleshooting.
I've had wires break inside before, and it caused some strange problems. If throwing your oscilloscope on the coil doesn't yield any results (i.e. it is getting proper pulses) then that is good news at this point.

tomrc

Ya, know I'm not sure what the voltage is either. Today before I do anything, I'm going to put a known voltage through that scope and try to decipher the voltage readings (I probably should of done that from the start). That will give me some idea of what we're dealing with. I'll check the voltage to the coil also on the scope.

tomrc

OK, I went and re-aligned the sensors, now I'm getting like maximum P-P Voltage, I don't think I'm hitting bottom. Anyway we now have different symptoms. The car starts right up now and idles OK, the tach is working but once I step on the gas the car bogs, sputters and backfires. I think at idle I'm running on 3 or 4 cylinders now but cannot give it gas. Also now if I hook up the scope to any of the sensors the car won't start (WTF?) though I still get a good signal.

I may of had or I may have more than one problem here. The coil to the distributor cable is not tight, it seems to be only held onto the coil by the rubber boot. I can't tell if it's the cable or the coil that is to blame, though it looks like the coil only has a contact at the bottom of the connector not the sides like I would expect. I need to look further into this but I don't have another cable or coil to test with. I might need to run to pick and pull and find a suitable cable to test with.

I'm still open to suggestions, I'll let you all know what I find out.

PorscheDoc

I had the same problem when my harness crumbled apart at the reference/speed sensors. I tried cutting and splicing in new connectors, along with some new wire, but that made it run like you describe. Ended up putting in a used harness and it took care of the problem. Problem is now, the used harness is starting to give me the same symptoms of not starting until i wiggle the wires on occasion.

So my next solution is to buy some shielded wire and rewire them all the way back to the DME. I have been told the shielded wire is available, just havent found it yet....

Zero10

Shielded wire is not necessary, simple twisted pair wire should be adequate. The reason the wiring on the speed/reference sensors is shielded, is because it is not twisted. Honestly, I'd bet you could run a piece of cat 5 wire to the sensors, and use 1 pair for each sensor, and it would work just great. Although the wiring size may be a bit on the small side, but there is virtually no current, so it shouldn't matter.

Otherwise, try some electronics stores for some outdoor rated 2 conductor #18 shielded wiring. They will probably have something that will work.

Just a thought on the shielding...

Anyhoo, it's good to hear that it gave you a step in the right direction. With what you are at now, what is the voltage that the speed and reference sensors puts out?

tomrc

OK, I am totally convinced it's the harness, so I'm going to try to splice new wires into the harness but ultimately I'd like to get a new(used) harness and new(used) sensors. Does anyone have these for an early 944 that they'd want to donate? Sell real cheap? Barter? .

Not having a car particularly, the 944 sucks.