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Got it. Thanks. Do you have any idea where the 86/85 trigger circuit goes to? Other than fuse 43 in the engine bay? Trying to find a way to diagnose why the car isn’t sending the 12v pump signal. I also found this picture- I didn’t think anything fuel pump related was here but it says AMG on it. Maybe related? It doesn’t look burnt or anything.
I PMd you Barry but also posting this here in case anyone else has come across it or will in the future:
I got everything wired up with the new relay but the car isn’t getting power to the pumps. When I jump the fuel pump circuit pins 30/87 or manually apply 12v to pin 86 the pumps run fine, so I think I can eliminate the relay and actual fuse pump circuit as being the problem. But for good measure I replaced the 30amp fuse (this is on the fuel pump circuit and not the trigger circuit right? Or no?) and tested the spare relay I got with no change. When I hook a multimeter up to the trigger circuit pins 86/85 it reads 0 and jumps to .06mv when the pumps should be running, basically nothing. Fuse 43 is not blown and I replaced it anyway for good measure. Anyone have any ideas on what I could try next?
Revised schematic attached! Sad to say I mixed up module designations previously, now corrected.
Pins 30 and 86 should be hot (+12v). Pin 87 goes hot when the relay solenoid is triggered. Pin 85 goes to module N3/10 Motor Electronics control module pin 36 connector 4 (NOT the rear SAM as I previously indicated). Since pin 86 is hot, the only way to trigger the relay is for pin 85 to go to ground.
The relay will trigger for approximately one second when the key is turned to position 2 to pressurize the fuel lines. After that the fuel pumps turn off until the ECU receives a signal indicating the engine crankshaft is rotating; at that time the pumps re-energize.
Thanks for the info. So if I am understanding correctly, with the car off, and multimeter ground hooked to the battery, pin 30 should read 12v, pin 87 should read 0, pin 86 should read 12v and pin 87 should read 0?
im confused what it means when you say to trigger relay 85 needs to go to ground. Pin 85 is ecu connector 4, pin 36, which is fuel pump relay control, so I’m assuming the ecu determines when to send the ground down that wire which completes the circuit to activate the relay solenoid? And the hot side of that circuit- pin 86, just flows straight from ecu connector 5 pin 9 (ecu fused power) (f43). Is my understanding accurate?
when I test for voltage at each wire, I show 0V for 87 (normal) , 12v for 30 (also normal) but for both pins 86 and 87 I see the same value of 1.25V. Assuming this is not normal what could this indicate? Unless I need to be hooked into a specific ecu ground to test these? But not sure how that would make sense.
Assuming that the fuel pump relay circuit goes directly from the ecu/fuse to the trunk there is a wiring problem along the way or an ecu problem.
Ok so obviously the ecu needs to be on for pin 86 to be hot, when the car is in key position 2 (where it should prime for a second), I am reading 12v off pin 30, 0V off pin 87( this SHOULD be 12v for that second of priming, then go back to 0 until the ecu is ready to start, right?) and I’m reading 12v on both 86 and 87 pins , which doesn’t make any sense to me because if that circuit is complete it means 1. The ecu is trying to turn the pumps on, and 2. The relay should be engaged and reading 12v on pin 87 as well
Maybe I am not understanding electricity. Bear with me!!
Basically you need to check if the Motor Electronics control module pin 36 is grounding, and I guess you'd be testing for that brief moment that the ignition is switched on (otherwise would need STAR to manually engage for testing). If not then the issue is upstream of everything you've been tinkering with. If it does ground them you can work from there and start by applying a ground to the back side of pin 85 and see if the pump engages (ignition ON). If so then you have a control problem...
You could also connect the clamp end of a test light to positive and the other end to either pin 85 of the relay or pin 36 of the Motor Electronics control module and see if it flashes for a second or two after ignition on. That would tell you what the control side is doing (or not doing).
Ok, so I hooked up the multimeter to battery and back of pin 85. When car is off it reads 11.5. (At battery is 12.6) With ignition on, it drops to 100 mv for the entire time, but nothing from fuel pump and relay doesn’t click. No change during the second it should be priming, just constant
if I run a ground from battery to back of pin 85 with ignition on, the fuel pumps come on
what should I be seeing on the multimeter at pin 85? I’m assuming it should be nothing unless the ecu is sending ground, and then it should go up to 12v (and light the test light)? Otherwise what would the difference be between showing 12v off and showing 12v on? Does that make sense?
test light with clamp on positive lights up on pins 86 and 85 with car off and light constantly off when ignition on (even during priming)
Last edited by corvettekyle; 07-30-2020 at 03:44 PM.
This is an exact situation where a DVM can be misleading and a simple test light, well, illuminating. I just bought my first test light this week after 19 years of working on cars...so better late than never.
So on your multimeter you'd be checking continuity between pin 85 and ground. It should be an open circuit except when that pin is pulled to ground by the computer (or module). A multimeter will tell you the resistance with NO current flow. But weird things can happen where the resistance checks out but the relay isn't actually able to draw enough current to engage. A test light on pin 85 would pull a couple hundred mA (not that different from a relay incidentally) and a bright light will tell you the wiring is enough to support something like the coil side of a relay. A dim or no light would suggest either a wiring issue (corrosion, etc.) or perhaps a bad driver in a module somewhere (where it passes a resistance check but can't actually source/sink any current, thus the relay can't engage). You could also check voltage between batt+ and pin 85 but the same caveat as above applies. Try with the relay unplugged as well and if you get different results, then there is probably a wiring/corrosion/module type problem. Hope I explained that clearly.
With key in position 2, pins 30 and 86 should both be showing 12 volts. Pin 85 is "floating" (i.e. not connected to ground). Without having a schematic of the internals of the Motor Electronics, this implies it is what is called an "open collector" which keeps pin 36 of the ME floating. When the ECU commands it, the open collector is closed and internally connects pin 36 to ground. This closes the circuit, allowing current to flow through the relay solenoid which produces an magnetic field that "pulls" the relay closed.
Ensure you did not accidently swap the locations of pins 86 and 85. If swapped, the relay will not close due to reversed polarity. It can be easy to mix up the view looking at the bottom of the relay with looking at the socket. It was working before the swap so that points toward incorrect wiring.
EDIT: also ensure the connectors are fully seated in the relay. It is possible that when the relay was inserted, a connector was pushed out of the socket rather than sliding over the relay pin.
test light with clamp on positive lights up on pins 86 and 85 with car off and light constantly off when ignition on (even during priming)
Well that isn't right. 85 should only be a ground path with ignition on and fuel pump commanded. And if the clamp was on 12V, you should NEVER get a light on pin 86 since that's also batt+...
So I would agree that you need to verify that you didn't cross any wires up at the back of the relay harness.
Thanks for your input.
I'm surprized you considered 20.2A to be low.
I thought I had read where you wrote in another thread that WIS states to change the filter if the pump current exceeds 20A at idle, so wouldn't >20 be considered high?
I searched WIS for quite a while and could not find anything for the E55. I did find some pump currents for other engines but nothing referenced to fuel filter blockage. I'm still not convinced that's a thing (that current spikes from a blocked filter). I think that WOULD apply to the E63 where the pumps are PWM controlled and a blocked filter will require more pump power to maintain the required fuel pressure. But the E55 is just full power all the time. Does the fuel get filtered before or after the regulator? If the regulator is in front of the filters then the pumps see a very consistent fuel flow regardless of fuel demand, filter blockage, etc. Fuel is going back to the tank or the engine in whatever ratio is appropriate and the pumps wouldn't know the difference.
Thank you both again. I have been testing without the socket on, just the terminals straight into the relay to eliminate the possibility of a loose connection. I went back and rechecked each wire using the schematic and they are all correct, but now I’m even more confused because I had taken a photo of the back of the stock relay before I cut the wires and in the photo the brown/blue and red/blue are opposite than the schematic.
I went to an MB dealer and picked up a stock relay just to test, tried both combinations of 86/85 terminals and still same result. The test light still lights up on battery positive to 86 and 85 with car off and light goes off on both with ignition on.
I am wondering if I was swapping pins could I have possibly fried something? I pulled the ecu connectors to check for burns but they look fine, and assuming anything else would have just popped f43 or the 30a by the battery
I have no idea why the stock wires would differ from the schematic. It didn’t look like anyone had been in there before me.
first picture is stock before cutting. (The brown and orange at bottom of photo is actually a dirty yellow/red pin 30) and see the red/blue 1.5mm is in pin 85 as opposed to 86 in the schematic) Second is how it is now (with new oem relay) Do you see anything glaringly obvious?
Last edited by corvettekyle; 07-30-2020 at 05:10 PM.
To update: I am fairly certain the issue is with the ECU. Everything other than the pin 85 readings with the test light and multimeter come back as identical compared against another fully functioning e55. There is just no continuity to ground coming out of the ECU pin with pumps engaged in STAR. I am shipping mine out to be cloned, hopefully the new one will solve the issue. How this happened still remains unknown, I do not know if I crossed some wires which damaged the module in the ECU that controls the closing of the open collector, or if the component coincidentally failed, as the original relay while a little burnt still does pass a bench test. Nothing inside the ECU looks burnt or otherwise damaged
The processor in the ECU energizes a transistor in the ECU which completes a ground path (the transistor will be in what is called an open collector configuration) that energizes the fuel pump relay. If by some freak accident, you happen to apply 12 v directly to the open collector of that transistor with no load / resistance between 12 v and the collector, you will definitely toast the transistor when the processor initiates an 'on' condition to the transistor.
Last edited by corvettekyle; 08-02-2020 at 02:47 PM.
To update: I am fairly certain the issue is with the ECU. Everything other than the pin 85 readings with the test light and multimeter come back as identical compared against another fully functioning e55. There is just no continuity to ground coming out of the ECU pin with pumps engaged in STAR. I am shipping mine out to be cloned, hopefully the new one will solve the issue. How this happened still remains unknown, I do not know if I crossed some wires which damaged the module in the ECU that controls the closing of the open collector, or if the component coincidentally failed, as the original relay while a little burnt still does pass a bench test. Nothing inside the ECU looks burnt or otherwise damaged
Sounds like you have it narrowed down then. I would think the computer would be more robust than that but who knows.
I may be suffering from dehydration after working on the car all day, but I can't quite figure out where to plug all the wires from the new harness.
Why are these split? Do they go into the neighboring relay? My early 2003 doesn't have fuel fuses on the right side of the trunk, do I need to get those?
Also colors seem to have changed, my relay has: - brown/green for the thin wire which goes to the ME. - thick red/yellow - thick red/blue - thin maroon/white
I have most of the car apart, and the front wire tunnel exposed, so its simple right now as long as I figure out where everything connects.
It should be harmless to just have the pin 36 wire on ME connected with an otherwise-disconnected relay. I may just start assembling the interior then finish this later once I have better info.
I can see two fuses 40 amp but don't see relays, I don't have time to open it up. This is the passenger side hinge trunk area. Please excuse the picture quality...
Sorry to res a dead thread but i think im going through the same right now. This hidden fuse , the first guy claimed it was on the passenger side of a left hand driven car....so is it the same for the opposite side driving ? I have located a fuse box in my 08 e63 that claims to have a fuel pump relay in it. Trying to see if i still need to pull the wall off the right side
Got it. Thanks. Do you have any idea where the 86/85 trigger circuit goes to? Other than fuse 43 in the engine bay? Trying to find a way to diagnose why the car isn’t sending the 12v pump signal. I also found this picture- I didn’t think anything fuel pump related was here but it says AMG on it. Maybe related? It doesn’t look burnt or anything.
That diagram is exactly how my amg looks and thats the only pump relay i can find. Smh im stressing my baby was just running so great a few days ago 😷🤕
07-30-2020, 08:35 AM
