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My 85 944 no tach bounce diary

 
Old 10-03-2018, 01:32 AM
  #1  
Joshua Leeds
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Lightbulb My 85 944 no tach bounce diary

Current issues:
  • No fuel during engine cranking (needs reverified after fuel pump replacement)
  • No tach bounce
Since I bought the 944 in April I've replaced
  • Speed/reference sensors
  • Fuel pump
  • Clutch slave cylinder (failed hopefully under warranty from Pelican)
  • Various clamps, hardware, gaskets
I've tested
  • Resistance - Speed sensor 1010 ohms from the DME connector (pins 25,26)
  • Resistance - Reference sensor 1018 ohms from the DME connector (pins 8,27)
  • DME relay - tested with a friends Power Probe - all connections tested OK - audible click just before engine cranks when turning key
  • AC voltage - Engine cranking - Speed sensor +/- 4.5V
  • AC voltage - Engine cranking - Reference sensor .01V
  • Fuel pump - 12VDC from battery to pin 4 on 9 pin connector behind vacuum booster - fuel pump ran
  • Starter solenoid - 10.5V
  • DME Relay connection
    • bridged T30 to T87b - fuel pump ran
    • 12VDC at T30
    • 10.5VDC at T86
  • DME connector
    • 12VDC at T18
    • 12VDC at T35
  • Ignition coils
    • Primary - .65 ohms
    • Secondary - 6900 ohms
My current assumptions
  • DME relay is good based on
    • Audible click from relay during starting
    • Results from test with Power Probe
  • DME is still questionable
    • Car came with 2 DMEs
    • PO said one was bad and purchased second as a replacement. Not sure which is in the car right now.
  • Speed/Reference sensors are good
    • New Bosch (BMW PN) units
    • Resistance is in spec
  • Wires from Speed/reference sensors are good
    • Resistance is readable from DME connector to sensors
    • AC current is readable from DME connector to sensors
Next steps
  • Swap DMEs
  • Verify sensor gap using oscilloscope
  • Verify continuity from DME pins 8,25,26,27 to VR sensor connectors using Power Probe
    • If short found replace wiring
Am I missing anything? I know tach bounce is a result of the DME, speed/reference sensors, and starter solenoid working correctly as is the result of the fuel pump engaging during engine starting/cranking. I know the DME provides ground for the fuel pump when engine RPM is >200 and also for the ignition coil. All in all it doesn't seem that complicated of a system. Especially with the right tools. And a spare DME. Plus beer.
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Old 10-13-2018, 10:51 AM
  #2  
T&T Racing
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1. Remove AFM from J boot and crank engine. Spray starter fluid into inlet of J boot. Does the engine start. If starts, it stalls if you increase throttle.

2.Remove the fuel rail with injectors from the intake manifold. Place each injector into a cup to get an idea on uniformity of fuel delivery rate. Crank engine and observe results and decide next action.

If 1 is yes the engine starts, then the ECU could be OK but not proof positive.

3. Put everything back together, remove the intake filter cartridge, crank engine and spray starter fluid into intake. If engine starts, warm up, and then blipp throttle to see outcome. Another piece of the puzzle.

4. Verify coolant temperature sensor using Clark Garage procedure. More information.

5. Look at all the data collected, to determine the next step.


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Old 11-20-2018, 12:04 PM
  #3  
Joshua Leeds
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Update on
Next steps
  • Swap DMEs
  • Verify sensor gap using oscilloscope
  • Verify continuity from DME pins 8,25,26,27 to VR sensor connectors using Power Probe
    • If short found replace wiring
Swapped DMEs. Was able to get the car started but I'm not 100% sure it's actually the DME causing the issue as once or twice I wasn't able to start the car after the swap. IIRC I was able to get the car to start after attempting to unplug the DME (without unmounting it but couldn't get the hook end of the connector free) but gave up and plugged the connector back in. Tried to start it again later and it started quite happily. Does anyone have any tips or a DIY on rebuilding the connections in the DME connector?

Next steps :
  • Install clutch slave cylinder
  • Connect clutch slave/master cylinders
  • Power-bleed the clutch cylinders with Motive Power Bleeder
  • Drain/fill trans fluid with RedLine MT90
  • Double-check brake lines for leaks.
  • Get 'er moving
Can anyone think of anything else I should check?
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Old 12-23-2018, 11:33 PM
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Update
Weird intermittent electrical issue. Sometimes electrical systems would work, sometimes not. Wiggling the negative battery cable would make electrical systems turn on
  • Replaced negative battery cable. Seems to have done the trick for now.
Another weird electrical issue... with the headlamp motor relay attached to the headlamp motor no power to electrical systems.
  • Work around is pull headlamp motor relay. Have tested relay without 12v.
    • Coil resistance is 88 ohms
    • Continuity on pins 30/87a
    • More tests to come
  • Next step is replace relay with spare (condition unknown)
Replaced Clutch Master/Slave cylinder and bled with pressure bleeder. Pedal seems to be losing firmness as the car sits. Only returns about half way
  • Inspect for leaks
  • Bleed system again
  • Replace hard/soft lines between cylinders
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Old 12-24-2018, 04:45 PM
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Originally Posted by Joshua Leeds View Post
Update

Replaced Clutch Master/Slave cylinder and bled with pressure bleeder. Pedal seems to be losing firmness as the car sits. Only returns about half way
  • Inspect for leaks
  • Bleed system again
  • Replace hard/soft lines between cylinders
Same thing happened to my 944 when bleeding the Master/Slave cylinders. Just continue to pump clutch, and the air in line will bubble up to the reservoir. Make sure the fluid level is higher than the clutch hose fitting in the MC
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Old 12-27-2018, 10:39 AM
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Thank you! I was fussing with it last night and did this (with the res cap off) and the pedal firmed up!
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Old 12-27-2018, 10:40 AM
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Originally Posted by T&T Racing View Post
Same thing happened to my 944 when bleeding the Master/Slave cylinders. Just continue to pump clutch, and the air in line will bubble up to the reservoir. Make sure the fluid level is higher than the clutch hose fitting in the MC
Thank you! I was fussing with it last night and did this (with the res cap off) and the pedal firmed up!
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