Working on an 86 Turbo. I'm trying to start the car for the first time in a while. The car turns over but does not start. I don't hear the fuel pump running. When I break the connection apart at the fuel pump to test I'm getting continuity to ground on both the ground and the Green/Black wire. I get this with or without the DME relay connected.
I also tried the DME bypass and can't get the fuel pump to activate either.
So with both leads having continuity to ground I'm guessing somewhere between the pump and DME relay I'm grounding out.
I figured I should start at the back and trace my way to the DME relay. I can see the wire go up and over the CV Axel and then into the car. To follow it further to the panel do I need to pull out the seats and carpet? I assume at some point it's combined with other wires and taped up.
Am I headed down the right path trying to find where it's grounding out or do I need to look elsewhere?
86 Turbo fuel pump wires both show ground.
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Tom
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When you turn the key to the on/run position, does the boost gauge jump to about 1? When you say you tried a DME bypass, do you mean you jumpered the DME relay? I'll have to look at the circuit to be of more help, but bad DME relay, bad alarm, and bad key switch are the usual suspects...
I'm pretty sure the boost gage as well as some others move. Yes, by bypass I mean I made a jumper and jumped all three positions. Since I made my post I also got my multimeter out and tested the relay using this YouTube video from Pelican Parts.
I'm working on bypassing the factory alarm. I came inside to fix something for work and saw your post.
I'm working on bypassing the factory alarm. I came inside to fix something for work and saw your post.
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Tom
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You might also check for spark while cranking. That might help point you in one direction of another (i.e., no life from DME vs just the fuel pump not getting power).
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dr bob
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Not a 951 owner, but a few things to try that are common to our cars.
-- Verify that the pump will actually run. Connect 12V directly at the pump, with the car harness and wiring disconnected. OK to leave the brown ground connection. Sometimes a pump that's been sitting a long time gets 'stuck', especially if the tank was empty or not empty. Dry, the pump may freeze up from old varnish as it dried out. Wet but with old fuel in the tank, varnish and sludge get pulled into the pump, locking it up.
-- Was your DMM test of continuity at the car side of the wiring with with wiring disconnected from the pump? Without seeing the wiring diagrams, no way for me to tell what else shares the contact at the DME/fuel pump relay. By description it might supply other things like injectors or the controller. If so, the reading you saw is normal. If the pump was still connected, you'd see the path to ground through the pump motor itself, maybe a few Ohms through the windings.
The pumps in my car, similar horsepower and fuel flow, draw about 5 amps running IIRC. That would be a load resistance of 14 Volts divided by 5 Amps, or a little less than 3 Ohms resistance. That's running, so the locked-rotor resistance may be less. If you were measuring with the pump still connected, the supply side would look like a very low resistance path to ground with your meter.
-- On the 928, the heaters for the exhaust oxygen sensor share the fuel pump relay contacts with the pumps. I can 'see' those heaters measuring continuity to ground with the pumps disconnected. Does the 951 use a similar method?
-- A longtime 928 sage regularly advised "relay-relay-relay" when troubleshooting no-starts. For my 928, there's an ignition relay, a fuel pump relay, and a fuel injection relay. My sole episode of being 'stranded' with a no-start was at the bottom of my own driveway when the fuel pump relay took a nap. I carry a very minimum kit of spares in the car, but that includes a relay 'jumper' with a fuse and a switch in the middle, plus half a dozen spare Bosch relays, plus a relay puller tool. When I changed the pump relay, the other two were changed at the same time.
There's a philosophy somewhere that suggests that I should 'store' the new relays actually plugged into the central electrics panel where they will save me from that failure aggravation. Keep the old ones as emergency spares in the car, or get another set of new for the ride-along duty? Easy choice.
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Can someone point me to the current flow diagrams for the 951? It would allow me a more specific diagnostic support path. I'm a diagrams/meter/test diagnostician. Always learning!
-- Verify that the pump will actually run. Connect 12V directly at the pump, with the car harness and wiring disconnected. OK to leave the brown ground connection. Sometimes a pump that's been sitting a long time gets 'stuck', especially if the tank was empty or not empty. Dry, the pump may freeze up from old varnish as it dried out. Wet but with old fuel in the tank, varnish and sludge get pulled into the pump, locking it up.
-- Was your DMM test of continuity at the car side of the wiring with with wiring disconnected from the pump? Without seeing the wiring diagrams, no way for me to tell what else shares the contact at the DME/fuel pump relay. By description it might supply other things like injectors or the controller. If so, the reading you saw is normal. If the pump was still connected, you'd see the path to ground through the pump motor itself, maybe a few Ohms through the windings.
The pumps in my car, similar horsepower and fuel flow, draw about 5 amps running IIRC. That would be a load resistance of 14 Volts divided by 5 Amps, or a little less than 3 Ohms resistance. That's running, so the locked-rotor resistance may be less. If you were measuring with the pump still connected, the supply side would look like a very low resistance path to ground with your meter.
-- On the 928, the heaters for the exhaust oxygen sensor share the fuel pump relay contacts with the pumps. I can 'see' those heaters measuring continuity to ground with the pumps disconnected. Does the 951 use a similar method?
-- A longtime 928 sage regularly advised "relay-relay-relay" when troubleshooting no-starts. For my 928, there's an ignition relay, a fuel pump relay, and a fuel injection relay. My sole episode of being 'stranded' with a no-start was at the bottom of my own driveway when the fuel pump relay took a nap. I carry a very minimum kit of spares in the car, but that includes a relay 'jumper' with a fuse and a switch in the middle, plus half a dozen spare Bosch relays, plus a relay puller tool. When I changed the pump relay, the other two were changed at the same time.
There's a philosophy somewhere that suggests that I should 'store' the new relays actually plugged into the central electrics panel where they will save me from that failure aggravation. Keep the old ones as emergency spares in the car, or get another set of new for the ride-along duty? Easy choice.
----
Can someone point me to the current flow diagrams for the 951? It would allow me a more specific diagnostic support path. I'm a diagrams/meter/test diagnostician. Always learning!
dr bob
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
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Tom
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The schematics represent 9 or 10 fold-out pages in the factory manual. I'll see about scanning them to a pdf and uploading here.dr bob wrote: Sun Sep 14, 2025 10:13 am Not a 951 owner, but a few things to try that are common to our cars.
-- Verify that the pump will actually run. Connect 12V directly at the pump, with the car harness and wiring disconnected. OK to leave the brown ground connection. Sometimes a pump that's been sitting a long time gets 'stuck', especially if the tank was empty or not empty. Dry, the pump may freeze up from old varnish as it dried out. Wet but with old fuel in the tank, varnish and sludge get pulled into the pump, locking it up.
-- Was your DMM test of continuity at the car side of the wiring with with wiring disconnected from the pump? Without seeing the wiring diagrams, no way for me to tell what else shares the contact at the DME/fuel pump relay. By description it might supply other things like injectors or the controller. If so, the reading you saw is normal. If the pump was still connected, you'd see the path to ground through the pump motor itself, maybe a few Ohms through the windings.
The pumps in my car, similar horsepower and fuel flow, draw about 5 amps running IIRC. That would be a load resistance of 14 Volts divided by 5 Amps, or a little less than 3 Ohms resistance. That's running, so the locked-rotor resistance may be less. If you were measuring with the pump still connected, the supply side would look like a very low resistance path to ground with your meter.
-- On the 928, the heaters for the exhaust oxygen sensor share the fuel pump relay contacts with the pumps. I can 'see' those heaters measuring continuity to ground with the pumps disconnected. Does the 951 use a similar method?
-- A longtime 928 sage regularly advised "relay-relay-relay" when troubleshooting no-starts. For my 928, there's an ignition relay, a fuel pump relay, and a fuel injection relay. My sole episode of being 'stranded' with a no-start was at the bottom of my own driveway when the fuel pump relay took a nap. I carry a very minimum kit of spares in the car, but that includes a relay 'jumper' with a fuse and a switch in the middle, plus half a dozen spare Bosch relays, plus a relay puller tool. When I changed the pump relay, the other two were changed at the same time.
There's a philosophy somewhere that suggests that I should 'store' the new relays actually plugged into the central electrics panel where they will save me from that failure aggravation. Keep the old ones as emergency spares in the car, or get another set of new for the ride-along duty? Easy choice.
----
Can someone point me to the current flow diagrams for the 951? It would allow me a more specific diagnostic support path. I'm a diagrams/meter/test diagnostician. Always learning!
Bypassed the alarm and that didn't get any results.
I used a 12v battery to power the fuel pump and I still have a crank no start.
I opened up the DME to have a look in side and nothing looked out of place but it has been replaced at some point in time. I had a warranty void sticker with www.programainc.com and we know that's not factory. I have some pretty detailed service records on the cars up until about 2006 which is when the original owner stopped driving it because she got a new Boxster. After that it's hit or miss. I do know that the DME relay was replaced in 2003.
When I turn the key on the boost gauge goes to 1 bar and I get a little bit of a wiggle out of the tach as it's turning over.
I used a 12v battery to power the fuel pump and I still have a crank no start.
I opened up the DME to have a look in side and nothing looked out of place but it has been replaced at some point in time. I had a warranty void sticker with www.programainc.com and we know that's not factory. I have some pretty detailed service records on the cars up until about 2006 which is when the original owner stopped driving it because she got a new Boxster. After that it's hit or miss. I do know that the DME relay was replaced in 2003.
When I turn the key on the boost gauge goes to 1 bar and I get a little bit of a wiggle out of the tach as it's turning over.
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Tom
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Do you have spark if you test a spark plug lead against the block?
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Tom
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I'd suggest bypassing the KLR to see if you are losing the spark on its way through, but that wouldn't explain the fuel pump not powering up. Since you have no power to the fuel pump and no spark, you never know, but I doubt the issue is the coil per se. Seems like something upstream -- DME relay, alarm, key switch, etc. I'll mull it a bit. 