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Very interesting difference between FAE sensors & Bosch
Here's the new Bosch sensors:
For reference (pun intended), here's the FAE sensors again. Note that I didn't move the bracket when installing the Bosch ones above (bracket was gapped with washer on FAE sensor)
I seem to be getting slightly weaker speed signal (top) now--probably because the Bosch appear a teeny bit shorter--but the reference signal is.. stronger? Weird. [EDIT: on second look, the reference signal is weaker on the Bosch too; it's just properly full sine]
[EDIT: The scope is showing 5V / div; both signals are well in excess of the required 2.5V (speed--full sine) and 2V (reference--top half of sine only)]
And... a simple LED lights on the injector harness! Funny though; I did this test after a bit of cranking with the oscilloscope test above. Removed the fuel pump fuse 34 for both tests. Yet, the motor fired and ran during this one (?) .. freaked me out!
Now that's a ref sensor waveform! I'm still wondering if all FAE sensors are made to the wrong specs or if they just have a quality control problem leaving some up a creek. Seems like they'd have figured it out by now if everyone they sell doesn't work, but I dunno... (As for the test, your fuel lines probably had some left over pressure.) So are you back on the road and driving the car? You certainly earned that...
Way to go Dan!!! That is bloody awesome!!. So glad you got it going again. Your adventure reminds me of an old Beetles song (are there any others) "long and winding road". Great job.
Have a beer, then go polish the wheels or something simple. Good work. Think of all that you have learned though working thru to the conclusion.
Thanks guys! I would like to think that I am now qualified to install these things as per the warning on the label... lol
I haven't started driving it yet; turns out we had this ice storm this week, and I was going to put on the winter tires and go, then I realized "Oh Cr*p! Winter is over!" so I'll put the summers on today or tomorrow and just forget the whole thing ever happened
But yes, though I missed some really nice driving in March especially, I'm glad I got to learn a couple of new things
I just read this entire thing post by post from the very first post. All I can say is WOW... I'm glad you got your car back on the road. And to think all this started with a search for "tach not working" I'm a soon to be 944 owner and the cars tach doesnt work, Does that mean I have a bad ref. sensor? And I would buy that shirt too!
I just read this entire thing post by post from the very first post. All I can say is WOW... I'm glad you got your car back on the road. And to think all this started with a search for "tach not working" I'm a soon to be 944 owner and the cars tach doesnt work, Does that mean I have a bad ref. sensor? And I would buy that shirt too!
That's some commitment! Glad you enjoyed it
If your car starts and runs, I don't think it's a reference sensor; from my experience, I think they both need to be operating properly to even start the car. So, if it's running, you will need to look elsewhere. Check if there's a separate fuse for the tach. There's also a pin on the DME connector that feeds the tach (if I remember correctly)
If your car won't start at all, and there's no tach movement, well then, you've got quite a bit in this thread you can try (I would start with getting a simple little 12V LED and testing both the ignition coil and a fuel injector plug to see if it flashes while cranking. These two tests are super simple and quick. You can pick up a 12V LED for peanuts at an electronics supply)
If your car starts and runs, I don't think it's a reference sensor; from my experience, I think they both need to be operating properly to even start the car. So, if it's running, you will need to look elsewhere. Check if there's a separate fuse for the tach. There's also a pin on the DME connector that feeds the tach (if I remember correctly)
If your car won't start at all, and there's no tach movement, well then, you've got quite a bit in this thread you can try (I would start with getting a simple little 12V LED and testing both the ignition coil and a fuel injector plug to see if it flashes while cranking. These two tests are super simple and quick. You can pick up a 12V LED for peanuts at an electronics supply)
On Turbo cars, the DME pin that feeds the tach also feeds the KLR in parallel. On NA cars I presume that signal is just for the tach since there's no KLR. If the car runs then the sensors are definitely ok.
To be clear, on a car with a known working tach, if it won't start and there's no tach movement, then there's no ignition signal from the DME, and therefore no point in looking at the coil or anything downstream of the DME. The problem would most likely be the crank sensors in that case.
To be clear, on a car with a known working tach, if it won't start and there's no tach movement, then there's no ignition signal from the DME, and therefore no point in looking at the coil or anything downstream of the DME. The problem would most likely be the crank sensors in that case.
In retrospect, yes, the "tach bounce" is certainly a quick diagnosis. My problem was installing two brand new sensors and being blind to the possibility that new could be bad in some way (though in this case, the defect was very well hidden)
In retrospect, yes, the "tach bounce" is certainly a quick diagnosis. My problem was installing two brand new sensors and being blind to the possibility that new could be bad in some way (though in this case, the defect was very well hidden)
This is one of the main reasons why I want to fix the tach. It started no problem. I'm going to have to do some troubleshooting when I take delivery of the car, I was just looking for a good place to start. I figured it has to be either a crank or cam position sensor. And someone correct me if I'm wrong but the distributor serves as the cam sensor correct? I'm sure this is not what Porsche call these sensors but, I'm coming from Japanese car background so forgive me hahah
This is one of the main reasons why I want to fix the tach. It started no problem. I'm going to have to do some troubleshooting when I take delivery of the car, I was just looking for a good place to start. I figured it has to be either a crank or cam position sensor. And someone correct me if I'm wrong but the distributor serves as the cam sensor correct? I'm sure this is not what Porsche call these sensors but, I'm coming from Japanese car background so forgive me hahah
I'd start by checking the wire from the DME harness that goes to the tach (the wiring diagrams are out there for download, you may have to do a search). Next I would suggest pulling the instrument cluster and checking the connections on the back. It's pretty common for the ground connections there to need cleaning up.
There isn't really a cam sensor, at least on the 8v engine (not sure about the 16v). There are 2 crank sensors - reference (position) and speed. The DME just assumes that the distributor connections are closed for a certain window based on the crank position, and it fires the coil some time within that window.
I'd start by checking the wire from the DME harness that goes to the tach (the wiring diagrams are out there for download, you may have to do a search). Next I would suggest pulling the instrument cluster and checking the connections on the back. It's pretty common for the ground connections there to need cleaning up.
There isn't really a cam sensor, at least on the 8v engine (not sure about the 16v). There are 2 crank sensors - reference (position) and speed. The DME just assumes that the distributor connections are closed for a certain window based on the crank position, and it fires the coil some time within that window.
Is it a 3 pin connector? I noticed there was a male 3 pin connector unplugged very close to where the 2 reference sensors plug into. i'll post a picture when I take delivery this weekend.
I also need to pull the cluster to see which gear I have to replace in the odometer, as it is not working. Sounds like a good time to clean up the grounds while I have the cluster out.
04-18-2018, 09:31 PM
I want it on a t-shirt.
