miller313

Hi,

I have browsed these forums for the last couple years as I have been rebuilding my dads Porsche 944. Long story short, I pulled the motor and installed a new oil pump as the old one was bad.

current situation:

The car has spark and fuel, and also the correct timing but will not start. I have double checked the timing several times, made sure the spark plug wires are correct. inspected the DME along with the DME relay for any signs of bad solder joints etc.

Recently I inspected the reference sensor along with the speed sensor, they both hovered around 900ohms when tested. The problem is I can not get any voltage out of the sensors. I understand that I needed a Oscilloscope but for a quick check i used a multimeter and could not for the life of me get a voltage reading.

From what I have read, wouldn't having these sensors go bad cause a no spark situation? I never took off the bracket when I pulled the motor so I am doubtful that I need to readjust the bracket to be within the right spec.


What is even more weird about this car is that I can get it to start and run very ruff if I switch the spark plug wires around in a weird configuration. I am leaning that the reference sensor is bad and is not telling the DME when to spark.

I have spent far to much money on this car already and would like to start making sure something is wrong before I replace it. Clark's garage and this forum have already been a huge help for trying to locate problems and for that I appreciate all the advice and tips everyone has listed.

Thanks,
Lance Miller

**Side note the compression is consistent with all cylinders 145-155 psi. Fuel pressure is good, voltage is good to injectors, on the safe side I removed and cleaned the injectors, I have bypassed the DME relay, along with the alarm**

pnbell

Check the Rotor inside the Cap.. It sounds like it might have come loose, and is causing spark at the wrong time.

miller313

Thanks for the reply,

I have inspected the rotor and it appears to be in good condition. I used a bit of sandpaper and a wire brush to clean the posts up, having only one way to put the rotor on, I don't think I installed this the wrong way. While I was at it I also cleaned up all the grounds on the car.

I have been out in the garage a bit more today and still can't get a voltage signal from the sensors. On a side note the Tach does jump a mm or so when cranking.

To me it appears as if the car seems to be firing and trying to start but the car is just firing at the wrong time which would lead me to believe it is a timing problem. I have sanded down the tdc mark on the flywheel to also better see the hash mark. I also made sure that I was at tdc by putting a wooden dowel in #1 cylinder. The cam gear is aligned at the hash mark also. I have inspected and realigned this several times already and have had no success.

This is why I believe it could be the Reference sensor not telling the DME when it is at TDC and then the DME failing to send the spark signal to the coil at the right time. Would I be onto the right assumption?

I just question that these sensors both went bad considering I had the right ohm readings and I never moved the bracket.

fwb42

Did you remove or unplug the sensors? Bad or wrong connections??

whalebird

Are the two sensors (ref/speed) connected to their appropriate plugs in the harness. They can be reversed at the plugs(rear of motor bracket at the intake).

miller313

I have double checked that the sensors are plugged in correctly, Yes I did remove the sensors to inspect them after I found that I had no voltage. I did not remove the bracket so I don't think that the gap should be an issue.

On a side note this car only has 40,000 miles so many of the parts I would think would still be good, this was kept inside in a heated garage for the last 10 years unused.

944Ross

The tach would jump more than a mm while cranking if everything was right with the speed/ref sensors. I'd bet you've got them switched as Whalebird says.

whalebird

[QUOTE=miller313;8458555]Hi,

I pulled the motor and installed a new oil pump as the old one was bad.


What is even more weird about this car is that I can get it to start and run very ruff if I switch the spark plug wires around in a weird configuration. I am leaning that the reference sensor is bad and is not telling the DME when to spark.

Both of these statements make me wonder.
Personally, I've never seen an oil pump failure. A little background on the original problem you're chasing might help.
As for ignition timing, it is pretty easy to get it right unless the cam is not set at TDC.
I want to help(a 40K original mile 944 needs to be kept alive for sure), but...what year is this car? and, any background on it's condition would be helpful. Why was it parked for so long(oil pump failure?)? Do you have workshop manuals, Haynes manual, etc? What did you "attack" upon this repair;i.e. what all did you disassemble?
Let us know...we'll get this sorted out.

miller313

Thanks for the replies so far,

The sensors are in the correct place and plugged in correctly, This problem has persisted before I took these sensors out.

Today I did get the car to start for a minute or so. It was shaking and misfiring bad and was slow to rev up. To put this into better perspective, I have actually had this car running before, the problem is that it will misfire and shake violently. Usually this car simply refuses to start.

If someone could tell me a definitive answer- would a bad reference sensor automatically cause a no spark? or could a bad sensor still allow the computer to send a signal to spark?

I did inspect the rotor again today after the initial comment was posted above and it does seem to have a tad bit of wear on the posts. I have a new distributor cap on order along with a rotor.

944Ross- the Tach jumps just a little bit when cranking, I actually just tried to see what it jumps to on the Tach but ironically it started every time, although it had a horrible miss and shaking every time it starts. I did notice for a few cranks it jumps very little and a 1mm or 2mm would be fairly accurate on how it jumps.

This is a 1984 944 N/A for better reference

Thanks for the help thus far
Lance

miller313

A little background on the car-

The car was parked due to a ticking noise in the head, and a 0 oil pressure on the gauge according to my father. I am not really sure if this is true or not but he had another oil pump laying in the shop so I went ahead and proceeded to pull the motor out and replace the oil pump. The motor came out with ease and went in without any major problem.

It appears that I hooked up all the connections right and have checked several times and crawled underneath the car to make sure everything seemed in order. The car does have oil pressure now and it see's around 4 psi or so on the gauge. I have never seen less but have read that it will go down a tad when the engine is warm. I have yet to have the car started long enough for this to happen.

miller313

on the oil pump replacement I was pretty straight forward on the repair, I did go ahead and install new belts while I was there as I have read it is wise to do so.

I do have many memories of being in this car when I was young and would love to get this car on the road again.

whalebird

Did you have the motor in a stand? or was this done "on the bench"? Reason I ask is that you may have had to remove the cluch housing etc. Upon reassembly, finding TDC is pretty easy with the clutch housing assembled. A wooden dowl is frought with danger compared to the TDC mark found on the rear flywheel when aligned with it's mark on the cluch housing. All this being done while installing the cam belt(was the motor in or out of the car when all this was done?).
Long story short...set the crank on TDC using the mark on the flywheel. Make sure the cam is at TDC through the inspection hole just above the distributor cap while insuring that the dist. rotor is pointing at the #1 output on the dist. cap.

Tom M'Guinn

Do you actually have spark and fuel? How did you confirm you had spark? How did you confirm you had fuel? If you have both, then chances are pretty high that your speed and ref sensors are giving you the signals you need. no? Have you checked to see what voltage your AFM is sending to your DME? Sitting for years, the variable resistors in the AFM can go bad. Have you tried starting the car at part or full throttle?

miller313

The engine was indeed on a stand when I installed the timing belt and oil pump.I did not remove the clutch housing when I installed the new timing belt. I lined up the marks actually how clarks garage listed, I put a wooden dowel in #1 cylinder just to verify that I was indeed at tdc.

I verified I had spark to all cylinders by using a test light, I also got gusty and removed my spark plug and grounded it.

I checked the fuel pressure on the fuel rail and If i remember right it was around 30ish psi, I did this awhile ago and my memory is foggy as to what psi it was. Although I do remember it was accurate to what clarks garage listed.

The next stage was to see if my injectors had voltage to them, I check with a multimeter and they came out fine. I figured that possibly the fuel injectors could have been clogged. I removed the injectors and curiosity got the best of me so i turned over the car and sure enough fuel sprayed out. On the safe side I went ahead and cleaned the fuel injectors individually.

I did pump out all the fuel and refill the car with 93 octane when I tried starting the car. Although I'm sure some bad gas was left I would assume that the 10 gallons or so I poured into the car would help out.

I have not checked out the voltage from the AFM to my DME, could you possibly tell me what voltage I should have. starting the car usually involves me having the peddle half to full throttle for it to start. It rarely ever starts without using some throttle. When Idling I also have to usually keep some throttle applied as it will stall out.

V2Rocket

are you sure the plug wires are in the right locations...?

also, how does the throttle position switch feel?