Fuel pump relay problems

[AudioNToxication]

So, great news.
My car died on me the other night.
I thought it was the TRM walbro i stuck in the car. That would have been great if that was the case.
Turns out its not. If i hot wire the pump from the battery it runs and the car starts.
Checked the wiring from the fuel pump relay to the rear connector,
its good checked that i was getting voltage to close the relay, i am.
Problem is the switched ground on pin 85 of the fuel pump relay that is closed by the motronic, its not grounding.
I tested the grounds as indicated in the wiring diagram on the motronic end connector.
Naturally this would mean i am not getting the signal from the CPS telling the Motronic to ground that.
Its a new sensor, and its all intact.
If i ground the relay, the car runs. I figure that sort of eliminates the crank sensor as a problem.
the only thing i haven't checked is the wiring from the crank sensor up, but if the car runs when i get the pump running.. its probably not that. (will check tomorrow)
The part that really has me confused, it will have this problem on one 173 ecu, and a spare i have both.

If anyone has any insight on this, id super appreciate it. i have done a ton of searching, read some posts by Ranger on the spec E30 board and followed this trouble shooting guide i found on here for bad DME stuff.

http://www.r3vlimited.com/board/showthread.php?t=144233

I really dont want to ghetto rig it and just ground the pin 85 to the chassis, but i know that will net me a working car.
I feel like it was wired this way for a reason.
It just seems like i cant seem to find the obvious problem.

[spdracrm3]

wiring?

year and model?
CPS is good if engine runs at all as it provides the signal for spark timing

have you checked the integrity of the wire from pin 85 of FP relay to the DME? the DME might be working switching ground at the main connector but if the wire is broken between them circuit wont work. a way to confirm is to check for the power thru the relay at the DME connector, should be 12v with key on at correct pin in DME connector (this is the voltage that the the DME grounds to activate the relay)

[AudioNToxication]

its a 1988 325ix
I checked from 85 to pin 3 for continuity.
I also bought a new fuel pump relay just to be safe.
when you say check for the power though the relay at the dme connector is this what you mean?

[spdracrm3]

its a 1988 325ix
I checked from 85 to pin 3 for continuity.
I also bought a new fuel pump relay just to be safe.
when you say check for the power though the relay at the dme connector is this what you mean?

well if your grounding the FP relay manually and it works its not the relay

a continuity test is one way ,but doesnt check the circuit when loaded which can induce resistance in some larger circuits . usually not a problem on a low current control circuit such as this (checking the voltage coming thru the relay all the way back to the DME is just another way to check circuit integrity,you can even load it with a test light rather than a meter) if you are sure pin 3 is the correct control circuit to pin 85 of FP relay than that eliminates that possibility .

dont know why DME will control spark and injectors but not activate FP relay, strange for sure ,just for kicks if you have a meter check voltage at DME pin 3 key on and key in crank position just to see what readings are.

[AudioNToxication]

Nah thats a really good point you make, i was just reading that in another thread that luke had.

"First, make damn sure you have a testlight. I mean a $5 cheapie is fine, they sell one at WalMart for $5.37 or whatever, that is just fine. I hear of you NOT having an actual LIGHT BULB I will quit offering any help...seriously, have a test light in your hand."

i have tested the pins at the pump, that was the first thing i did, weirdly enough i got voltage when i turned the key, thats why i went out and got another pump. Though, that did me no good, when that was the case i hot wired the pump. found out the pumps both worked and led me on this adventure.
Load might be the key factor here. i am pretty sure it is but not totally.
like i said i was using that DME testing thread i had linked in on my OP.
Ill check that tomorrow and see what i get. Im getting real tired of this cars shit. but
its unique and i hate to kick it to the curb because i don't get what its issue is. Id rather see it on the road running than wasting away..
Guess im weird like that.

[spdracrm3]

well like you said you can always hot wire it with a switch and know it works (its a built in security feature ) but im like you want to know why ? not hack it....so no your no weird

you've load tested the entire FP circuit by grounding pin 85 at FP relay and having the pumps run enough for car to run ,now its just figuring out the relay control issue

[AudioNToxication]

right,
I am just convinced that its a ecu problem.
I have two and it occurs on both.
Its nice that some of these parts are so cheap.
I tested the grounds though the ecu harness to the body and they were good.
As far as testing 85 to the connector i never got to it, I had my aunt here. who i hate.
but tomorrow is a new day!

[spdracrm3]

DME diagram

looking at a engineering diagram of the motronic 1.3 DME shows the pin 3 output for relay control looks to be shared with a chip driving the idle control motor ,purge valve and check engine lamp (does the check engine lamp come on?), might be worth disconnecting the IAC and purge to make sure one isnt shorting and bringing down the chip such that it can't run relay control. pin 23 also in the chip but no description looks to be the O2 heater relay control per the ETM so try disconnecting that relay also

[AudioNToxication]

Alright, thats a good point you make.
Ill try that.
I did notice during cranking i had 0 voltage on pin three. so thats a problem.
i had voltage on pin 1 until i cranked then it went to nothing.
So thats also odd.
when the car was running the check engine lamp would come on occasionally.
car always ran fine, i could never get the car to stomp test though.
not sure what the story with that was. Dunno if thats related.
Doubt it. Sort of like the light on my obc clock dying about 4 days before this. likely unrelated.

[AudioNToxication]

So great news,
If i disconect the icv and the evap valve the car fires, means the fuel pump works.
Being i know the car wont idle properly without the icv i took a chance and plugged it in.
Guess what, car runs and idles
so the problem is related to my evap valve, not sure if the valve is internally shorting or if its the wiring.
Time to test that next.
Honestly, thank you so much for the help. i really appreciate it.
Sometimes its nice to have another set of eyes looking at this stuff because you can get easily frustrated with wiring.
Will test and post results, I think its important i do so because i have found plenty of unsolved threads with this exact issue.

[spdracrm3]

interesting ,good find ,wonder if it will die if you plug in purge valve ,seems ive heard/read of issue's with purge valves in past but never one that stopped engine starting

pin 1 of DME is ignition control to coil,so that voltage will drop from 12v as DME pulses ground to fire coil

Purge is a pretty simple circuit power supplied to valve from main relay pin 1 and DME grounds second pin ,if valve was shorting power it should blow fuse for main relay which is a fuse link , but if it just shorted relay output you would loose power feed to FP relay control on pin 86 which also powers injectors and IAC per 89 IX ETM,might be different for 88

E30M3's had a recall for the purge valve sticking open causing dieseling on hot engine shutoff

[AudioNToxication]

I plugged it back in while it was running, it stumbled but it continued to run, and it would re start like that.
I wonder how temp might effect it.
What ill probably do is continue to trouble shoot the wiring and check that its not the harness.
And buy a new valve since its only 74 on turner. Ill hunt around and see if i can find it for a better price.
I don't want to be left on the side of the road again. I am all done with that. I hope.

[b-rad]

Similar

Having similar issues. E30-87, S50 Engine 95
Car previously running solid.

I replaced the fuel pump in prep for surge tank, that's not in line

The FP Replay is not getting ground or 12 volt trigger to connect the larger gauge to the fuel pump. Going to check again, after finding this post.


I am worried about the ECU not giving the trigger, possible this needs to be replaced...



The trigger is Red/White, and Brown/Green stripe.
The 12Volt Feed is Red/???

The line to FP is Green/Purple stripe.

[moatilliatta]

Test for 12V with an actual multi meter on 30. Jump to pin 87. (LOOK ON SIDE OF RELAY)

If you dont hear fuel pump running and dont have fuel pressure on gauge. Fuel pump relay isn't the problem or the only problem.

Fuel pump relay gets ground from DME, 85?
Red and white should be hot with key on? 86? (Make sure has 12V with actual multi meter)

DME grounds Fuel relay when it see's crank signal.
If no ground when cranking then would start with New OEM crank sensor. Not worth guessing if your 30 year old crank sensor is worth keeping. Make sure you mount it proper so it doesn't get chewed up.

No crank signal = No spark, No injector pulsing.

The real ETK is a must or you're only guessing:

http://www.wedophones.com/BMWManualsLead.htm

[b-rad]

It's pretty difficult to read those troubleshooting manuals with it being a swap, that I did not do. Working on it... though.