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Jakob... didn't you have the issue where you plugged in the fuel pump fuse and the engine died?
I don't get how it behaves different with the jumper (no start) and DME relay (start but quick stall). Something is really wrong and seems independent of the sensors
Okay guys! Back with results of the 3 wire bypass test.
With the fuel pump jumpered using the bypass the car cranks but does not start. The pump does turn on and the pressure does build.
With the relay reinstalled afterwards the car once again starts right up.
great ! you have found a significant problem possibly THE problem.
If you connect terminals 30 , 87 & 87b together and the car doesn't start then you have something incorrectly wired up ....possibly on the DME relay base
connecting 30 87 and 87b must start the car because that is exactly the same connections that the DME relay makes ....
If your DME relay is starting the car and the bypass doesn't then I suspect there is something wrong with the DME relay you are using .
Can you show us an image of the connections on the side of the DME can ?
Jakob... didn't you have the issue where you plugged in the fuel pump fuse and the engine died?
I don't get how it behaves different with the jumper (no start) and DME relay (start but quick stall). Something is really wrong and seems independent of the sensors
Yes that was before installing the new reference sensor, wiring harness, and the DME. What would happen is the car would crank and crank and flood. Only when I pulled the fuel pump fuse, for whatever reason the car would start and run. It would run anywhere from 5 seconds to a few minutes.
I finally got the new wiring harness and installed it along with a new reference sensor. I got everything put back together and when I went to start the car up to see if all was well I was greeted with this new issue.
So now rather than cranking/ flooding the car starts everytime I turn the key. But doesn’t stay running.
When i bypassed the relay the car cranked and cranked but didnt start, with the pump running. So that pretty much narrows it down to a spark issue currently. For whatever reason after the car starts it appears that I’m losing spark. Most likely due to now the speed sensor having gone bad or simply the gap being too big between the sensor and the flywheel.
Jacob last night I read through the entire thread and other posts that you have made about this issue and I think the answer has been staring us in the face the whole time.
As I understand it the car once started and ran fine up until the day it stopped ................then when investigating the problem you found that the speed and reference sensors connectors and their associated wiring were all burnt yes ?
I believe that was and still is the issue .
I suggest that you get your manual out and check that you have reassembled both the speed and reference sensor connectors correctly. its very easy to misread workshop manuals where connectors are concerned. Sometimes they show the connections from the front of the connector block and sometimes from the rear of the block. if you get it the wrong way round your wires will be transposed and the connections will be wrong.
Both the speed and reference sensors have a +signal wire and a - sheaf /screen wire they are polarised and must be connected the right way round to work properly.
Lastly make sure that the speed sensor is plugged into the correct connector block and double check the wiring through the connectors .
i think we are very close to solving this .
Last thing to try .
If you start the car with no throttle and hold the ignition key on to cranking for a few seconds AFTER the engine is running and see what happens ..............
if as I suspect there is an issue with the speed sensor then the engine should continue to run until you release the ignition key .
just to explain again how the failsafe system works .
When the ignition key is turned to the engine cranking position the ECU briefly activates the fuel pump to pressurize the fuel system ready for starting . The moment the engine starts and the key is returned to normal running position then if the ECU doesn't see at least 200rpm signal from the speed sensor then the ECU shuts down the fuel pump.
(Whilst the ignition key is in the cranking position the ECU is over ridden and cannot shut down the fuel pump )
if there is no signal from the speed sensor the ecu will shut off the fuel pump and the engine will die immediately which is what is happening
Jacob last night I read through the entire thread and other posts that you have made about this issue and I think the answer has been staring us in the face the whole time.
As I understand it the car once started and ran fine up until the day it stopped ................then when investigating the problem you found that the speed and reference sensors connectors and their associated wiring were all burnt yes ?
I believe that was and still is the issue .
I suggest that you get your manual out and check that you have reassembled both the speed and reference sensor connectors correctly. its very easy to misread workshop manuals where connectors are concerned. Sometimes they show the connections from the front of the connector block and sometimes from the rear of the block. if you get it the wrong way round your wires will be transposed and the connections will be wrong.
Both the speed and reference sensors have a +signal wire and a - sheaf /screen wire they are polarised and must be connected the right way round to work properly.
Lastly make sure that the speed sensor is plugged into the correct connector block and double check the wiring through the connectors .
i think we are very close to solving this .
Last thing to try .
If you start the car with no throttle and hold the ignition key on to cranking for a few seconds AFTER the engine is running and see what happens ..............
if as I suspect there is an issue with the speed sensor then the engine should continue to run until you release the ignition key .
the wiring harness was helpful it was labeled which sensor is which DG and BG speed and reference sensor respectively. I could try swapping the connections to see if that changes anything. I’ll give keeping the key turned s shot. It’s not gonna make the god aweful grinding noise from running the starter while the engine runs is it? Lol
I could try swapping the connections to see if that changes anything.
The sensors are quite a bit different in signal. (Ones a whole lot faster than the other.)
It'll either work (because you mixed them up in the first place) or not work (because they're now connected backwards.)
Originally Posted by Jacob AbuKhader
I’ll give keeping the key turned s shot. It’s not gonna make the god aweful grinding noise from running the starter while the engine runs is it? Lol
Originally Posted by Jacob AbuKhader
The noise is when the starter engages an already running flywheel. If you engage the starter from a stopped flywheel, the teeth mesh and there should be no noise squeal.
(Edit: There's always a noise...)
the wiring harness was helpful it was labeled which sensor is which DG and BG speed and reference sensor respectively. I could try swapping the connections to see if that changes anything. I’ll give keeping the key turned s shot. It’s not gonna make the god aweful grinding noise from running the starter while the engine runs is it? Lol
it will make a little noise but it will be ok for 3-4 seconds which is all you'll need to do it for to prove the point.
Just don't rev the engine whilst you do it obviously lol
I changed one. The one that I replaced was dirty with melted and exposed wiring. The other one was replaced a few years back for the issues I was having. Smoking/running rich. They left the other one in place because it was “frozen” in the bracket but the car was fixed so they left it alone. That’s whats on that work order that I posted a few weeks ago.
it will make a little noise but it will be ok for 3-4 seconds which is all you'll need to do it for to prove the point.
Just don't rev the engine whilst you do it obviously lol
Peanut, I gave your trick a shot and the car stayed on running a little bit longer. Definitely long enough to prove your point.
great ! so that proves my point completely.
the issue you currently have is related to the speed sensor signal not reaching the ECU when the ignition switch is in normal running mode .
In an ideal world you should stick an oscilloscope on the speed sensor output at both the under bonnet connector and terminal 8 & 27 on the ECU connector and confirm that the sine wave is there but I doubt you have access to one.
I'll check my notes and see what the Porsche test protocol is
This could all come down to a missing ground ... if the ECU doesn't have the correct grounds connected it won't be able to ground some of its components
heres the Porsche speed sensor testing procedure . Looks like you need to see a minimum of 2.5v sine on the scope
This could all come down to a missing ground ... if the ECU doesn't have the correct grounds connected it won't be able to ground some of its components
I believe the proper grounds for those sensors are right there on the bell housing and on the rear block.
the sensors don't have a ground ....
They are simply coils of wire that create a magnet when energised with a voltage.
One wire of each sensor is positive the other is the negative sheaf or screen which has to go back to the ECU not to a chassis ground . its the ECU that makes the necessary grounds internally
02-22-2019, 03:52 PM
