944 no spark
#1
08-01-2006, 07:02 PM
944 no spark
Hi folks new to this forum, my uncle has just got himself a 944 (84my) about a month ago and it's a non starter as from a couple of days ago.
I'm on the tools myself but havent really ever touched a porsche until now.
I found that there is a supply coming to the coil but there doesnt seem to be any switching happening on the negative wire.
I disconnected the neg wire from the coil and bridged a piece of wire from the neg to earth and moved the wire accordingly to act as a switch for test purposes for the coil and it sparks just fine when doing this so I assume the coil is fine.
Bit confused as to why there is TWO sensors sitting next to each other on top of the bellhousing, I'm assuming one of them is a tdc reference sensor for the ecu but the other one ??? is it something to do with sequential timing for the injectors or something rather than a cam sensor ?.
I've not managed to get any wiring diagrams on this car so I'm kinda struggling a bit
I'm not getting any live at the plugs of either of the sensors, would have thought there should have been a reference voltage going to both sensors.
There does seem to be plenty fuel pressure in the rail when the connection is slackened off but I dont think the injectors are being signalled to open as the plugs are bone dry, I'm assuming this is due to the spark fault and the ecu isnt allowing fuel until it picks up a pulse from the ignition side.
Any pointers on this one would be apprecieated.
I'm on the tools myself but havent really ever touched a porsche until now.
I found that there is a supply coming to the coil but there doesnt seem to be any switching happening on the negative wire.
I disconnected the neg wire from the coil and bridged a piece of wire from the neg to earth and moved the wire accordingly to act as a switch for test purposes for the coil and it sparks just fine when doing this so I assume the coil is fine.
Bit confused as to why there is TWO sensors sitting next to each other on top of the bellhousing, I'm assuming one of them is a tdc reference sensor for the ecu but the other one ??? is it something to do with sequential timing for the injectors or something rather than a cam sensor ?.
I've not managed to get any wiring diagrams on this car so I'm kinda struggling a bit
I'm not getting any live at the plugs of either of the sensors, would have thought there should have been a reference voltage going to both sensors.
There does seem to be plenty fuel pressure in the rail when the connection is slackened off but I dont think the injectors are being signalled to open as the plugs are bone dry, I'm assuming this is due to the spark fault and the ecu isnt allowing fuel until it picks up a pulse from the ignition side.
Any pointers on this one would be apprecieated.
#2
08-02-2006, 12:19 AM
RE: 944 no spark
Reference and speed sensors are on the bellhousing. If your tach is not moving whatsoever during cranking (there should be a hint of bounce), then you more than likely have a problem with those sensors, the connections to those sensors, a bad DME relay, or a bad DME.
#3
08-02-2006, 07:58 PM
RE: 944 no spark
Thanks for the reply PorscheDoc I've been away since the weekend so havent had a chance to have another look.
Speed sensor ??? is that for the tacho ?
Reference/tdc sensor for ecu.. yeah ?
Sorry to seem a wally but I've never seen that exact config, the two sensors seem identical e.g shielded cables etc.
There's 2 grey 4 pin relays on there own clipped onto the side of the heater assembly away from the rest of them, not sure what they are meant to power.
I think I've managed to find the fuel pump relay at no2 on the fuse/relay board which seems to be energising.
Wiring diagram required I think !
P.S. whats DME short for ? is that the ECU ?
Speed sensor ??? is that for the tacho ?
Reference/tdc sensor for ecu.. yeah ?
Sorry to seem a wally but I've never seen that exact config, the two sensors seem identical e.g shielded cables etc.
There's 2 grey 4 pin relays on there own clipped onto the side of the heater assembly away from the rest of them, not sure what they are meant to power.
I think I've managed to find the fuel pump relay at no2 on the fuse/relay board which seems to be energising.
Wiring diagram required I think !
P.S. whats DME short for ? is that the ECU ?
#4
08-02-2006, 10:15 PM
RE: 944 no spark
Since I can't say it any better, I will quote FR Wilk:
"The reference-mark sensor detects a single set screw on the outer edge of the flywheel. All engine angular measurements are made with respect to the crankshaft's top-dead-center (TDC). The reference-mark sensor produces a single pulse corresponding to engine TDC.
The engine-speed sensor works much like the reference-mark sensor except that it senses the teeth on the starter gear attached to the flywheel. For the 944, there are 130 teeth on the starter gear and the engine-speed sensor produces 130 pulses for each crankshaft rotation. Counting these teeth gives the angular information to the computer."
If you go to www.clarks-garage.com and go to his garage shop manual, under S for speed and reference sensors, it will tell you how to test them.
As far as the DME relay goes, you can jump it using 3 wires tied together with a wire nut, and then the other ends inserted into the larger slots on the fuse panel for the relay (30, 87, and 87b). This should immediately kick on the fuel pump, then try starting the car. Make sure to pull the wire out after awhile, otherwise the pump will continue to run, as well as your wires getting a little hot.
DME stands for Digital Motor Electronics, and is the cars ECU.
"The reference-mark sensor detects a single set screw on the outer edge of the flywheel. All engine angular measurements are made with respect to the crankshaft's top-dead-center (TDC). The reference-mark sensor produces a single pulse corresponding to engine TDC.
The engine-speed sensor works much like the reference-mark sensor except that it senses the teeth on the starter gear attached to the flywheel. For the 944, there are 130 teeth on the starter gear and the engine-speed sensor produces 130 pulses for each crankshaft rotation. Counting these teeth gives the angular information to the computer."
If you go to www.clarks-garage.com and go to his garage shop manual, under S for speed and reference sensors, it will tell you how to test them.
As far as the DME relay goes, you can jump it using 3 wires tied together with a wire nut, and then the other ends inserted into the larger slots on the fuse panel for the relay (30, 87, and 87b). This should immediately kick on the fuel pump, then try starting the car. Make sure to pull the wire out after awhile, otherwise the pump will continue to run, as well as your wires getting a little hot.
DME stands for Digital Motor Electronics, and is the cars ECU.
#5
08-03-2006, 06:35 PM
RE: 944 no spark
Ahhh ! THINK I see the light now... it needs the 2 sensors instead of 1 due to the design of the pickup on the flywheel !
Used a scope on both sensors and the speed sensor gave a nice even waveform of just over 2 volts and the ref sensor gave a pulse of around 1.8v... so looking allright.
I've also since found out that the battery was flat and a jump start had been attempted without success.
This sounds like the big bad spike has got the dme.
Anyway many thanks for your help and will get the dme tested and see what happens.
P.S. thanks for the clarificaton on dme--ecu thought it was just a terminology thing LOL !
Used a scope on both sensors and the speed sensor gave a nice even waveform of just over 2 volts and the ref sensor gave a pulse of around 1.8v... so looking allright.
I've also since found out that the battery was flat and a jump start had been attempted without success.
This sounds like the big bad spike has got the dme.
Anyway many thanks for your help and will get the dme tested and see what happens.
P.S. thanks for the clarificaton on dme--ecu thought it was just a terminology thing LOL !
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