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> Need 3.2 conversion electrical help
mepstein
post Aug 13 2017, 12:20 PM
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I can't get my fuel pump to run unless I jumper the plug for the DME relay. The car starts and runs with the connection jumped but the fuel pump then runs all the time. Just want to know where to look and what to do.
I'm very electrically challenged so you might need to really dumb it down for me. Thanks
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Steve
post Aug 13 2017, 01:06 PM
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You did try another dme relay? Otherwise the Bentley 911 Carrera manual is what I used to wire and trouble shoot my conversion.
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Spoke
post Aug 13 2017, 01:21 PM
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I had a similar problem on my 930. Engine would run, then lose power. Sometimes it wouldn't start. The pump wasn't running. I traced it to the relay (not sure if 930 calls it DME) not making contact. I took it apart to find a smaller relay inside with some circuitry. Pulled the smaller relay off and found the contacts were barely making contact and sometimes wouldn't. Bent the relay contacts and haven't had any issues for 2 years.
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mepstein
post Aug 13 2017, 01:30 PM
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Tried 4 new relays. One was solid state.
Flummoxed.
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porschetub
post Aug 13 2017, 01:36 PM
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The solder joints can also fail on them too,pop the cover off and have a look,could just be the contacts as Spoke mentioned,normally they are pretty reliable.
If you have to buy a new one don't buy it on price...URO part one is about half what a decent one is worth (IMG:style_emoticons/default/lol-2.gif) .
Nice to have it running eh (IMG:style_emoticons/default/beer.gif)
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mepstein
post Aug 13 2017, 01:45 PM
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QUOTE(porschetub @ Aug 13 2017, 03:36 PM) *

The solder joints can also fail on them too,pop the cover off and have a look,could just be the contacts as Spoke mentioned,normally they are pretty reliable.
If you have to buy a new one don't buy it on price...URO part one is about half what a decent one is worth (IMG:style_emoticons/default/lol-2.gif) .
Nice to have it running eh (IMG:style_emoticons/default/beer.gif)

They are all new and none are uro.
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Spoke
post Aug 13 2017, 02:04 PM
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QUOTE(mepstein @ Aug 13 2017, 03:30 PM) *

Tried 4 new relays. One was solid state.
Flummoxed.


Doesn't sound like it's the relay. Are the schematics online somewhere? I'd like to help but would need the schematics to follow the electrons. (IMG:style_emoticons/default/beerchug.gif)
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Spoke
post Aug 13 2017, 02:11 PM
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QUOTE(mepstein @ Aug 13 2017, 02:20 PM) *

I jumper the plug for the DME relay.


Which pins are you jumpering? I see this DME relay schematic online:

Is this the correct schematic?


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Spoke
post Aug 13 2017, 02:14 PM
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Some tests with your voltmeter:

put a small wire in the socket at 85b then install the relay.

Turn the car on or crank and measure 85b to ground. I think it should be 0V.

Put a small wire in the socket at 87 then install the relay.

Turn the car on or crank and measure 87 to ground. Should be 12V.
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Steve
post Aug 13 2017, 03:34 PM
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This manual is awesome!!
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Steve
post Aug 13 2017, 03:36 PM
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Steve
post Aug 13 2017, 03:42 PM
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jim912928
post Aug 13 2017, 06:38 PM
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I hate wiring...do you have the red wire (fuel pump) coming out of the dme harness going straight to the fuel pump? It should and just put an inline fuse to protect it (25A).

Here is the link for my 3.2 wiring:

http://www.914world.com/bbs2/index.php?sho...7&hl=wiring
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mepstein
post Aug 13 2017, 06:42 PM
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QUOTE(jim912928 @ Aug 13 2017, 08:38 PM) *

I hate wiring...do you have the red wire (fuel pump) coming out of the dme harness going straight to the fuel pump? It should and just put an inline fuse to protect it (25A).

Yes. Did all that. Thanks
Got tied up today but will work on this tomorrow.
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Spoke
post Aug 13 2017, 07:20 PM
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Looks like a pretty simple circuit:

1) Ignition key provides power to 86; 85 is ground thus top relay should turn on.
2) With top relay on, battery voltage from 30 connects to 87; 87 should be 12V.
3) 87 is also top of bottom relay coil; 85b from DME must be grounded to power bottom relay; bottom relay provides path from battery (pin 30) to 87b.

Tests:
Jam a small wire in plug for 87, install relay, turn ignition on, test 87 to ground; measure 12V

Once 87 verified at 12V:
Jam a small wire in plug for 85b, install relay, turn ignition on and/or crank the engine, test 85b to ground; measure 0V. DME should provide ground at 85b. If not, the issue is with the DME.
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mepstein
post Aug 13 2017, 08:30 PM
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I know the dme is good. Runs fine in other cars.
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Steve
post Aug 13 2017, 09:24 PM
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Do what Spoke suggested and put an ohm Meter on pin 20 of the dme. It should be grounded while cranking the starter. If it's not then something else connected to the DME is causing the problem. Have to troubleshoot each sensor / inputs on the DME to figure it out. I have had lots of interesting problems with my injection that I used the Bentley manual to trouble shoot.
Motor won't start after installing for the first time
- turns out it was a pinched fuel line under tank which doubled the fuel pressure
Car sat for 3 years and wouldn't start (rustoration)
-Pelican guy's on there 911 forum recommended unplugging the injectors one at a time. After unplugging the last one it started and ran on 5 cylinders. Shut motor off and plugged it back in and now it runs fine on all six cylinders for over two years now.
The flywheel sensors are also known causing no start issues. Some people replace them and get rebuilt injectors when they overhaul the engine.
Otherwise mine runs great and I have not had any problems besides the above.
Not bad for 33 year old original motor with a bazillion miles on it!!
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mepstein
post Aug 13 2017, 09:46 PM
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QUOTE(Steve @ Aug 13 2017, 11:24 PM) *

Do what Spoke suggested and put an ohm Meter on pin 20 of the dme. It should be grounded while cranking the starter. If it's not then something else connected to the DME is causing the problem. Have to troubleshoot each sensor / inputs on the DME to figure it out. I have had lots of interesting problems with my injection that I used the Bentley manual to trouble shoot.
Motor won't start after installing for the first time
- turns out it was a pinched fuel line under tank which doubled the fuel pressure
Car sat for 3 years and wouldn't start (rustoration)
-Pelican guy's on there 911 forum recommended unplugging the injectors one at a time. After unplugging the last one it started and ran on 5 cylinders. Shut motor off and plugged it back in and now it runs fine on all six cylinders for over two years now.
The flywheel sensors are also known causing no start issues. Some people replace them and get rebuilt injectors when they overhaul the engine.
Otherwise mine runs great and I have not had any problems besides the above.
Not bad for 33 year old original motor with a bazillion miles on it!!

Remember, i did say my car starts, I need to figure out why the fuel pump wont run unless I remove the dme relay and jump it with a wire. But I will follow all the advise you guys have given me and report back. As always, I appreciate the help.
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shoguneagle
post Aug 13 2017, 10:02 PM
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Do not over look the DME Relay socket itself; shorted, bad spade connectors, etc. particularly the pins you are jumping and the fuel pump runs.
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McMark
post Aug 14 2017, 07:02 AM
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If you've tried the DME in other cars and they run....
And you've tried multiple DME Relays and none work....

That only leaves the wiring itself and the AFM.

Disconnect the DME wiring.
Pull the DME Relay.
Multimeter on Ohms, test between DME pin 20 and Relay pin 85b.


If that works tests good (0 ohms)...
The fuel pump only runs when the AFM flapper is open. So get access to the air filter side of the AFM, turn the key on (everything reconnected), and push the door open. That SHOULD turn on the pump. If it doesn't, the wiring between the AFM and the DME may be suspect, or the AFM contacts inside may be suspect.
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