Low voltage at in tank fuel pump connector

[mpap89]

So my fuel pump was making the humming of a dying fuel pump. I replaced it with a high flow ebay one and it worked for a few seconds but there was a kink in the outlet hose from the top of the fuel pump carrier so the engine died since it wasn't getting any fuel.  I repositioned the pump and the outlet hose correctly so that the flow wasn't blocked but it wouldn't fire up again.  I assumed that i'd burned up the motor by running it while the flow was blocked so i check the pump on a fused temporary 12v line from the battery.  It purred like it should.
I checked the voltage at the pump power supply and it was about 9.5v.  I'd been cranking the motor while trying to figure out this problem so i hooked the battery up to another running car with jumper cables to provide enough juice for the fuel pump. Now i'm getting 11.5v at the pump power supply but still no humming from the pump. 
I decided to replace the 5 pin fuel pump relay but that didn't work either. 
I'm running out of ideas at this point.  i've confirmed that the fuel pump still works so it seems like a low voltage problem to the fuel pump power supply.
Any thoughts?

Thanks
Michael

edit: this is a 1991 e30 318is

[monty23psk]

If you jumped the battery with another and got the ~12v, then your battery is going bad or your alternator is not giving enough juice. I would start by testing both of them as it looks to be an electrical issue. These items are the the mother and father of the car's electrical system. My .02

[DesktopDave]

The fuel pump relay is a 4-pin unit, likely an orange case Bosch "456." The main relay is the 5-pin, typically a white plastic case.

Have you checked the resistance on your crank position sensor? You should be seeing about 680 ohms between pins 1&2. Also be sure the CPS head is clean, and it's not too far away from the crank trigger wheel. Spec is about the width of a credit card.

[bmwman91]

If you see 9.5V at the pump, check to see what you get on the terminal blocks up on the firewall. Check both the BIG one with the giant black wire going to it, and the smaller one above it that has a ~4mm black wire going to it. If you get 12V at the big one and less at the small one, then you most likely have a break in the smaller wire by the fusible link, which is on the smaller black wire about 18" from the battery. Anyway, we can go over dealing with that if that is indeed the case.

[mpap89]

Ok, i checked the voltage at the battery and the terminals near the firewall and i got the same 12.5 volts. 
The cps resistance gave me 1.175 (?!) unless i was measuring it incorrectly.  i was checking pins 1 and 2.
I'm getting 11 volts at the pump power supply then it spikes to 12.5 when i stop cranking. 
The power coming into the fuel pump relay (the correct 4 pin one) is 12.5
i swapped this relay with the other 4 pin next to it to no avail.

Could it be the CPS that's giving me all these problems.  Is it just a coincidence that my CPS happened to crap out on me right in the middle of kinking the fuel line and having to reinstall it?

thanks
Michael

[DesktopDave]

Are you sure you're measuring ohms off the crank sensor pigtail? It sounds like you're measuring the cam position sensor instead - that should be 1200 ohms or so. Both these sensors are the same except for different wire lengths.

If your ohms scale is on the wrong range (K Ohms), 1.175 is a good reading. Try the other one, that'll be the crank sensor. You might see something like 0.68 if you're still in K Ohms. It can vary +/- 10%...so anything from about 600 to 800 ohms should be OK. BTW, resistance on the other wire pairs (2&3, 1&3) should be very high, like 100 KOhms or so.

Also be sure the sensor head is clean too - it's magnetic, tends to collect rust and oil.

You're not going to believe this, but if the computer (DME) doesn't see a good signal from the crank sensor, it'll shut off the fuel pump relay. Worse, it won't set a code.

Speaking of codes, have you retrieved them from the DME? Look up "stomp test" if you haven't pulled them yet.

[mpap89]

i couldn't get an resistance readings from 1 - 3 or 2 - 3 on the sensor.  I think i'm following the cable correctly from the sensor on the front of the head as it's the top one of the two coming into the same place.  I could also have my multimeter set incorrectly. 

Is removing the head cover as simple as unbolting all the 10mm heads and pulling it up?  i can't seems to get anywhere with doing that and can't get a look at the CMS.
I did the stomp test and got 1444 which is no errors.
 

[bmwman91]

You'll want to set the meter to 2K or 20K.

[mpap89]

i get 1.26 when set to 20k

[DesktopDave]

Test the other connector too. IIRC the crank plugs into the lower harness connector.

Looks like you have your meter set to continuity/diode test. No biggie, it'll still work. Try the 2K range, see if that makes a difference. The reading won't change, just multiply any of those 'K' settings by 1000 to get the ohms. 1280-ish for the cam, 680-ish for the crank.

You should be able to see the cam sensor bolted to the front of the head. The cam cover does come off once all those little bolts are removed. Be careful putting them back in - they're very prone to stripping their holes.

[mpap89]

so i ended up taking my car to a patient mechanic that used to help me with my 1969 1602.  I quickly got a call back that i had blown the fuel pump fuse and that was all that was wrong with it.  I blew another fuse later that evening which leads me to think that the new fuel pump due to it's higher flow rate draws more power and requires something more than the 7.5 amp fuse that the e30 usually requires.  I guess i wrongly assumed that if i'd blown a fuse there wouldn't be ANY power coming through. 

so this week of frustratingly crawling around in the back of my car is all due to a 30 cent part.
regardless, thanks for all the help

Michael

[monty23psk]

if you got a TRE pump, you need to put a 15 amp fuse. I just went through this.

[DesktopDave]

Thanks for the update - glad it's resolved. I'm also glad that it was something reasonable. No shame in throwing in the towel & going to a pro. BTDT many times.