1991 e31 manual trans - crank, no start M70

[6speeder]

This is my first post... please help.

1991 850i manual trans

cranks, will not start. I can get it to start (for a few seconds) by spraying starter fluid in the air intakes after the filter, i have done 1 side at a time so both sides fire independently when spraying fluid.

brand new interstate battery. both fuel pumps run when i supply 12v directly to their pins with the wiring harness disconnected. both hidden fuses in trunk are ok (tested with voltmeter). both dk's hum and open while gas petal is pushed.

i get 12v over both fuel pump fuses (#23 and 24) while cranking, BUT NOT AT THE FUEL PUMP PINS. and the voltage is VERY strong at the fuses while cranking 10.2v - 10.5. i have disconnected battery overnight a few times.

key to run, eml light turns on, then off as it should. no codes on either side after stomp test 1444, 2444.

to test the wiring between the fuel pump fuses to the fuel pump wiring harness i have supplied 12v directly to each fuel pump fuse and i get 12v to both pins of the fuel pump connector under rear sear so the wiring from the 2 fuel pump fuses are ok. the ground pin at fuel pump connector also passes continuity (sound) test with multimeter when i touch the body.

to summarize, will start with starting fluid (so im getting spark), will not get any volts at fuel pump harness for 3 seconds with key in "run" OR while cranking. so what would cause the car from preventing 12v at fuel pumps while cranking... but would allow 12v at both fuel pump fuses while cranking and allow spark (cause it will start with starting fluid)???

since im getting 12v at both fuel pump fuses while cranking am i correct in saying all of the following work:
both fusible links, both crankshaft and both camshaft position sensors, eml, both dme, dme relay, fuel pump relay, fuel pump fuses?

please help... no guessing please thanks

[BMSman]

Your post is a bit confusing...
If it runs with starter fluid you obviously don't have fuel. So if you believe there is 12V on the fuel pumps I would check for fuel pressure at the rear of the fuel rails (~40psi expected).
The fuel pumps do not turn on until the engine cranks - this is normal. I believe it requires signal from the crank position sensors.

[6speeder]

thanks for your reply. as i wrote above there is NOT 12v at the fuel pumps, neither at run (key position 2) OR while cranking (key position 3)... there should be 3 seconds of 12v at key position 2 to prime the rails and constant 12 at position 3 while cranking. fuel pressure is irrelevent if the pumps dont see 12v. the fuel pump fuses both get 12v while cranking but the actual fuel pump harness plug does not. the fuel pumps themselves also work as i applies 12v to their pins directly

[BMSman]

You have 12V at the fuel pump fuse when you crank the motor?

When you apply 12V to the fuel pump fuse the fuel pump runs?

When you crank the motor the fuel pump does not run?

Don't rely on your continuity tester to verify a good ground. You should measure the resistance as well to verify it is solid. A few ohms will register continuity but will prevent correct pump operation.

[6speeder]

yes and it is very strong (over 10v).

no.

yes, fuel pumps do not run while cranking because they are not getting 12v while cranking

what should the correct resistance be?

[6speeder]

sorry, my response to your 2nd question should have been "yes"

[BMSman]

My best guess is you don't have a good ground connection at the fuel pumps. I can't think of anything else that would affect both pumps as you have described as each pump has its own Relay, fuse and wiring, the only common element is the ground connection. Check for corrosion.

You stated you applied 12V to each of the fuel pump fuses and each pump fired up ok? Exactly how did you do this... a wire from battery +ve to the fuse?

[6speeder]

the ground is spotless. x494 in trunk behind passenger tail light

yes thats exactly what i did. i temporaily used a short wire from the B+ jumper terminal under the hood to each fuel pump fuse

[cartoonz]

for what it is worth, the ground lug for that circuit is in the right rear of the trunk. (which you obviously found while I was typing -edit)

But there is still some things ambiguous here... you're new here, welcome... but is this car new to you?
Have you ever had it running, or did you get it this way?
Just to clear a lot of this guesswork up... which is really all any of us are really doing, since we are not in front of your car by the way...

You seem convinced that the PUMPS actually run if you apply power directly to the fuse, yes?
Not "it shows voltage at the connector" but the pumps actually run?
As in "I can jumper voltage to the 2 fuses and the car will start"

[clubE31]

fluel pump relais.....!?

[6speeder]

@cartoonz:
ive had her for 5 years. i bought her in working order... she was running fine.
yes
yes
yes


@clubE31
im getting 12v over both fuel pump fuses while cranking so from what i understand the fuel pump relays must be working.


could someone confirm the LAST paragraph in my original post

[dragon850]

If you had truly tested both pumps by putting a pressure gauge on each line at the back of the engine and applying 12v to pumps but pumps still wont run on their own then your issiue is most likely one of the crank sensors gone bad.

[6speeder]

thanks dragon for your response. i have not tested the fuel pressure at the back of the engine. wouldnt 12v at fuel pump fuses while cranking rule out the 4 camshaft and crankshaft sensors? and the eml light turning on, then off also rule them out? it also fires with starting fluid so i have spark. where would be the best place to install 2 schrader valvea to test the fuel pressure

[razman850]

The fact that both fuel pumps dont get juice while cranking leads me to suspect a sencor like dragon pointed out, highly unlikely for both pumps to go bad at same time. Lack of a cam or crank signal is causing it to cut power to the pumps.

[razman850]

Did it just stop starting? Have you been working on the motor before this happened?

[6speeder]

thanks raz for your response. but its not cutting power to the pumps... im getting 12v over both fuses while cranking. when the dme kills the startup due to faulty sensor does it kill spark, fuel pumps or both?

- - - Updated - - -

nope wasnt working on the engine. just stopped starting. i was in the middle of rebuilding the glove box mechanism, key spins but neither top or bottom glovebox unlock

[razman850]

it kills the fuel supply but i think it allows spark to burn off any gas in the cylinders.

[BMSman]

This is obviously not making a lot of sense so I think we need more details...

When you measured 12V at the fuel pump fuse was this with the fuse installed or did you remove the fuse and probe the fuse socket?

When you applied 12V to the fuse you indicated the fuel pump ran and you were able to start the car; you connected a wire from battery +ve to fuel pump fuse. I assume you removed the fuse and connected to one of the fuse socket pins?

If you have not done so already, can you measure the voltage at the fuel pump fuse with a good fuse installed, fuel pumps connected and motor cranking (important that the fuse is installed)? Do you still see 12V??

[6speeder]

@raz. if it did kill the fuel supply how exactly would it do that? im guessing it would prevent the relays from firing and then the 2 fuel pump fuses would be denied voltage but im getting 12v at both these fuses while cranking. and it starts on fluid so im getting spark

@BMSman. i left the fuses in. put the multimeter probes on the top of the fuses where the contacts are exposed so the voltage carried OVER the fuses confirming the fuses are fine. if i pulled the fuses and probed the socket it im 95% positive the multimeter would NOT have not measured 12v as the meter itself shouldnt carry the current from 1 contact to the other

when i jumped the fuel pump fuses from the b+ terminal i did NOT try to start the car, was scared of what damage it would do. i did NOT remove the fuses when i did this, i wanted to energize the wire from the fuses to the actual fuel pump harness so i could test to see if i was getting voltage at the actual fuel pump pins, and they did get 12v.

i have always measured the fuel pump fuses that way, fuses in, pump attached, while cranking. not only do i get voltage but its STRONG voltage (over 10v... acceptable would be anything over 8.5 or 9)

[Wuffer]

Have you verified both fusible links in the trunk are intact/working as they should? I would be suspicios of the smaller hidden one. Both are on the passenger side of the trunk in line with red positive cables coming from the battery.

[6speeder]

thanks for your response wuffer. yes this is where i originally thought was the problem so i COMPLETELY tested both links, tested for continuity with voltmeter from the positive battery terminal to the terminals after the fuses. then i disaasmbled th fuses, wire brushed them gently, and reinstalled, then continuity tested again. also if it was one of the 2 fusible links i would NOT get 12v at the fuel pump fuses while cranking right <<< can someone confirm this?

its worth noting i have a 91 and BOTH fusible links had 80 amp fuses (not 50 and 80), others who own early model as i do have also reported both fuses were 80amp. realoem also calls for 2 80amp fuses when i search using my vin. i plan on replacing the hidden one thats wrapped in shrink wrap (the one on the larger gauge cable) with the exact same black fuse holder setup as the other fusible link (im a purist and thats as pure as i think it can be other than leaving this POORLY designed fuse as it is). but first i need to get this thing running and also send out my e31 specific BBS rc009 + rc010 rims to be lip polished and faces painted Schwartz II black to match my paint. im also looking for a single rc009 of anyone has one (i only have 4 but i want a 5th to use as spare to match)

[6speeder]

with a broken camshaft or crankshaft sensor/s would i get 12v at the 2 fuel pump fuses while cranking ??

[dragon850]

with a broken camshaft or crankshaft sensor/s would i get 12v at the 2 fuel pump fuses while cranking ??

No, power to the pumps would be cut. Install fuel pressure gauges at the back of the engine (2 lines going to the fuel rails) you will need to remove air box first. Tell us what is the reading psi if any while cranking.

- - - Updated - - -

Also, check is both throttles are buzzing with ignition on, if they are not send them to me for a rebuild.

[6speeder]

No, power to the pumps would be cut.

are you positive a broken camshaft or crankshaft sensor prevents starting by cutting the FUEL and not the spark and not both (cause it starts with starter fluid). If yes... then basically your confirming my crankshaft and camshaft sensors are working correct?

[6speeder]

Also, check is both throttles are buzzing with ignition on, if they are not send them to me for a rebuild.

yes they both buzz... i think theres an easier test than listening for the buzzing (since sometimes its hard to tell that the buzz is coming from BOTH of the dk's)... i touch the throttle butterfly "spring" that sticks out and they actually vibrate with the ignition on, almost feels like a tiny tiny shock.

i know your the man to send them to for rebuild and eventually i will, there on my to do list but since they hum they are lower down on the priority list, she has other "needs".