Help Support Bigcoupe.com

83 633CSI - No Power to Fuel Pump Relay

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: ron, bfons, GRNSHRK

Post Reply
jbmike
Posts: 7
Joined: Sun Apr 25, 2021 10:54 pm
Location: New York

83 633CSI - No Power to Fuel Pump Relay

Post by jbmike » Wed Apr 28, 2021 3:12 pm

I'm new to this Forum having recently acquired an 83 633CSI 5sp with 98k miles. Exterior and interior are exceptionally clean however the car was not running.
Simple diagnostics traced it down to a dead/frozen main fuel pump. That's was the easy part and immediately rectified with a new unit.

Now for the real problem.

For some reason I'm not getting power to the fuel pump relay and I have to basically hot wire the car (yes, I'm using an inline fuse) to the FP relay plug from the battery for the car to start.

I'm sure this must have been covered in the past and hopefully I don't get flamed for not doing extensive searches however any help/guidance to troubleshooting this would be greatly appreciated.

Thanks in advance.

Mike A.

User avatar
hornhospital
Platinum Member
Platinum Member
Posts: 2699
Joined: Sun Jul 11, 2010 6:46 pm
Location: Silverhill, AL
Contact:

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by hornhospital » Wed Apr 28, 2021 3:29 pm

Welcome to Bigcoupe.com and the insanity that is E24 ownership, Mike!

Are you getting injector pulses and spark? Whenever I hear of no power to the fuel pump relay I immediately think of a failed crank sensor. You'll lose all three if the crank (position) sensor dies. You have two sensors in the bellhousing, a position sensor and a speed sensor. They are identical, so testing is the same for either. If I recall correctly you should have about 560 ohms across two of the pins, and infinite resistance across the other pin (guys, correct me if the ohm reading is wrong). Be careful when unplugging the sensors from the wiring harness to test. It is VERY LIKELY that the plug will crumble. They are notorious for that. Just keep track of which wire goes to which pin in the harness.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"; '95 318is "Bebe"

jbmike
Posts: 7
Joined: Sun Apr 25, 2021 10:54 pm
Location: New York

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by jbmike » Wed Apr 28, 2021 4:38 pm

Ken,
The car starts and runs fine however I'm required jump power to the fuel pump relay plug for this to happen.
Do you know if power to the fuel pump relay plug is solely governed by the ignition switch?

Mike

GRNSHRK
Platinum Member
Platinum Member
Posts: 3110
Joined: Thu Apr 08, 2004 3:24 pm
Location: Gilroy (SF Bay Area) CA

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by GRNSHRK » Wed Apr 28, 2021 5:59 pm

Hi guys,

Sorry, no input, but I'm going to move this thread to the "Mechanical" forum :roll:
:mrgreen:
Bobbo
1980 633 CSi Cypress Green/Pearl Beige
2017 X5 M Sport Xdrive 35i Carbon Black/Ivory White
2005 330 Ci ZHP Cabrio Imola Red/Bone/Black
Image

User avatar
Ralph in Socal
Platinum Member
Platinum Member
Posts: 2478
Joined: Tue Apr 14, 2009 3:32 am
Location: High Desert of SoCal

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by Ralph in Socal » Wed Apr 28, 2021 9:54 pm

Schematic shows fuel pump relay power comes from the main relay. Main is connected directly to battery and powers up in run or start and also sends signal to ecu. Main relay also provides power to injectors so you’re getting power to the injectors either thru the main relay or when you hotwire

Check the female connector in the relay holders (main and fuel pump) to make sure they are all in the proper place and making good contact. The wire ends have been known to slip out of its location and therefore not making contact

Good luck

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)

jbmike
Posts: 7
Joined: Sun Apr 25, 2021 10:54 pm
Location: New York

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by jbmike » Thu Apr 29, 2021 4:51 pm

Thanks Ralph. Looks like I'm going to have a "fun" weekend :-?

olympia57
Platinum Member
Platinum Member
Posts: 1338
Joined: Thu Sep 13, 2012 1:47 pm
Location: Ireland

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by olympia57 » Thu Apr 29, 2021 7:59 pm

Having just endured a no start scenario I sympathize with you.
This should be accurate for your year of model .
https://www.hpsimotorsports.com/motronic-
Good luck .
Don
1981 635 series 1

daz635
Bigcoupe 100 Post club
Posts: 101
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by daz635 » Fri Apr 30, 2021 3:11 pm

Diagram from the 1983 633 ETM
Capture.JPG
Capture.JPG (130.62 KiB) Viewed 4002 times
Fuel pump relay draws it power directly from the battery and there should be power to pin 30 of the fuel pump relay at all times. The pump relay is
switched by grounding pin 87 of the main relay thru the fuel pump control of the motonic unit.

Are you not getting any volatge at socket 30 of the fuel pump relay?

Can you jumper the fuel pump relay between 30 and 87 like the image below to test
relay_jumpers_193_114 (1).jpeg
relay_jumpers_193_114 (1).jpeg (53.67 KiB) Viewed 4002 times
'86 Euro 635 #1887204 Schwartz (086) Buffalo Schwartz Interior
Image

jbmike
Posts: 7
Joined: Sun Apr 25, 2021 10:54 pm
Location: New York

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by jbmike » Sat May 01, 2021 9:42 pm

Thanks to everyone who replied. Amazing group of people to say the least.
Problem turned out to be a weak ground going to pin 85 on the fuel pump relay preventing it from closing the circuit.

Need to go through all of my ground straps now.

...Mike

jbmike
Posts: 7
Joined: Sun Apr 25, 2021 10:54 pm
Location: New York

Re: 83 633CSI - No Power to Fuel Pump Relay

Post by jbmike » Sun May 30, 2021 4:18 pm

Quick update to the group on MY progress. After resolving fuel pump and relay issues the car started like a champ however got into a surging idle mode once the engine was warmed. Replaced temp sensor and switch, O2 sensor and bench tested the ICV. Also verified there were no vacuum leaks. I've generally found that vacuum leaks result in a high/erratic idle - not a surging idle. Finally ordered a refurbished ICM from ProgRama (very affordable) and the problem has been resolved. Cold idle at ~1000-rpm and ten settles down to a smooth 750 once warm.

Post Reply

Who is online

Users browsing this forum: No registered users and 11 guests