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Old 11-06-2011, 02:48 PM   #1
goyal99
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Default How the FUEL pump relay gets signal from DME??

My 96 ti recently developed a weird fuel pump related problem. - I've tested the fuel pump and it's working fine...it spins freely and the fuel filter has been changed with a new one.

The problem is that I can JUMP (energize) the fuel pump by connecting the 30 and 87 pins after removing the FP relay and the pump runs fine...When I plug in the FP relay, I get NO POWER at the fuel pump and no power at the fuse (#18).

I have switched the relay with the DME relay and other relays and I still get no power at the pump....The DME relay an FP relay are next to each other and have the same pins and numbers in my '96 ti.....the minute I remove the relay and JUMP the 30 and 87 terminals I get power at the relay and fuse!!! - I get constant +12V power at terminal 30 (red wire) and power at terminal 86 (red/white) when key is in ignition or start position. I know the green/violet wire (terminal 87) goes to fuel pump itself.

My question is: WHAT kind of signal terminal 85 get from the DME?? It might be from the crankshaft or from some other sensor but I don't know for sure....Can anyone know for sure so I can solve my fuel delivery issue??

Thanks in advance - Bill

Last edited by goyal99; 11-08-2011 at 01:16 PM.
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Old 11-06-2011, 08:07 PM   #2
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The crankshaft sensor is involved in the circuit to the fuel pump. I don't know which terminals are involved, but if the DME doesn't see what it wants from that sensor, it won't power the pump. Hope that helps.
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Old 11-06-2011, 08:26 PM   #3
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Per the ETM, the DME grounds pin X6301 pin 4 (relay signal 85) to pick the relay.
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Old 11-06-2011, 10:06 PM   #4
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Quote:
Originally Posted by John Firestone View Post
Per the ETM, the DME grounds pin X6301 pin 4 (relay signal 85) to pick the relay.
In addition, the DME has to see the flywheel turn a certain RPM thru the crank sensor for the DME to provide ground path (terminal 85 or 86 don't remember) for the DME relay to pick up and close the contacts 30 and 87.
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Old 11-07-2011, 01:58 AM   #5
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thanks for your replies.....As I was expecting the crankshaft gives a signal to DME and in turn the DME gives a signal (or no signal) to the fuel pump.
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it's actually pin 85 at the fuel pump relay which gets the signal from the DME...
.
I found out that my crank sensor AND my camshaft sensor were unplugged by mistake when I had the upper intake manifold off attempting to fix a vacum leak under there....I forgot to plug those two sensors in when I was putting everything back together and tried to start the vehicle a few times......Of course the engine was cranking and cranking but no start!!! Dumb mistake.
.
Was any harm done by having those two sensors unplugged and cranking the engine??? could it be any damage to DME or engine timing or anything else??
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Now that the sensors are plugged in I still can't get the proper "signal" to the fuel pump relay to run the damn fuel pump....Again if I unplug the relay and jump the fuel relay terminals 30 and 87 the pump runs but the car runs terrible and does not stay running!

I also noticed that now eveytime I attempt to start the car (ignition switch to START) the fuel gauge goes all the way to FULL (right) and then back down to EMPTY (left side). The two wires are pugged in correctly at the fuel pump end.
.
At this point it's the least of my problems but it's worth mentioning since it's related to the fuel delivery issue.

Thanks
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Old 11-07-2011, 02:56 AM   #6
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It shouldn't have hurt anything if they didn't short.

Just moving the sensor wires an cause problems on an old car. The insulation just falls apart, unplugging them could have made them short. I had to replace the crank, cam and knock sensors on my car for that reason.
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Old 11-07-2011, 10:13 AM   #7
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Not sure if the camshaft and crankshaft sensors have the same plugs. It's been a while since I replaced the whole engine.
It may be worthwhile to check to make sure you did not switch the plugs by mistake.
The camshaft sensor, from what i remember goes to the front most socket in the black plastic termination point under the intake.
Also, starting the engine with the sensors unplugged will not hurt the DME or electronics. They were just input signals.

edit: I checked my old harness, no way to switch sensor plugs. the camshaft sensor plug has two locating tabs while the crankshaft sensor only has one.

Question: Will it run with the fuel pump relay terminal 30 and 87 jumped?
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Last edited by bazar01; 11-07-2011 at 11:01 AM.
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Old 11-07-2011, 02:28 PM   #8
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The two plugs, camshaft and crankshaft each has 3 wires abd they are next to each other where they plug in. Their sockets, like BARAZ01 indicated, are NOT interchangable so in other words the plugs do NOT fit in each other sockets....it makes sense, right?
.
So the plugs were NOT shorted....now they are plugged in correctly. . Like I mentioned earlier, even with the two sensors plugged in, the fuel pump is still not running with the pump relay installed and the fuse gets no power (with a test light). When I jump terminals 30 and 87 with a wire (unplug relay) the pump runs all the time as expected.....The car attempts to start but it spatters and bucks and it sounds like backfiring!

The plugs are bone DRY but pressing the schreider valve (on the fuel rail) spits out FUEL....very strange

I will take out the fuel pump next and check to see it it's operating correctly...It's a USED fuel pump which I installed because mine died not too long ago. So it could be that the pump is actually running but not putting out the correct fuel volume....just a shot in the dark at this point.

The MAIN PROBLEM is the non-operation of the fuel pump when the fuel pump relay is installed and all the other sensors seem to be installed and plugged in....I can only get the fuel pump to run when I JUMP TERMINALS 30 and 87 at the fuse box.

And the fuel gauge going crazy (going all the way to right and then back to left) everytime I try to start the car....that's all folks!!

Later
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Old 11-07-2011, 05:19 PM   #9
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If the DME does not see a signal from the cam and crank sensor it will not run the fuel pump or fire the injectors. Hence the dry plugs.

How about you toss a code reader on it and see what it says.

here is what the insulation in the cam and crank sensors look like probably look like....

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Old 11-07-2011, 06:41 PM   #10
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Quote:
Originally Posted by goyal99 View Post
.....I have switched the relay with the DME relay and other relays and I still get no power at the pump....
As soon I read that part I got flashbacks from my ordeal. I know itís a totally different system, but when I swapped in the incorrect relay in the SAP, it was 4th of July inside my engine harness.
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Old 11-07-2011, 08:13 PM   #11
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Quote:
Originally Posted by Shellback View Post
As soon I read that part I got flashbacks from my ordeal. I know itís a totally different system, but when I swapped in the incorrect relay in the SAP, it was 4th of July inside my engine harness.
Now I'm having flashbacks. Been there, done that, as they say. I'm still getting all of that sorted out and it hasn't been fun.
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Old 11-08-2011, 01:21 AM   #12
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Quote:
Originally Posted by bullmand View Post
Now I'm having flashbacks. Been there, done that, as they say. I'm still getting all of that sorted out and it hasn't been fun.
I don't know the reason your car's wiring got messed up, so I can only talk about my situation. But you're right - it's painful and frustrating chasing electrical and wiring issues.

The DME relay and the fuel pump relay in MY CAR are the same....They look the same and have the same pins and numbers. That's why I swapped them. Also it seems to me that they are a couple of other relays in the fuse/relay box with the same pins and color (light green) as the DME and FP relays.

I don't think I fried my wiring or the DME by switching the relays but now you have me thinking about it....It's possible if one of relays went bad to short the DME but like I said in my vehicle BOTH the DME relay and the FP relays are indentical...Can anyone else verify this on their vehicle??

Mine vehicle is an 1996 5-spd.....the attached photo shows the wiring of the DME and FP sockets of my car.

Also is there a site when I can find the wiring diagrams for the 318ti?? Any help will be appreciated....Thanks
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