Fp And Fi Relays - What Provides +ve?

[GLPoomobile 958]

So my Mi has started to cut out and not restart. It's not injecting. Sods law, when I had the Multimeter ready the other day it was all fine.

 

Just had to move the car up to the next street, and going up the road it was dropping revs but not quite cutting out. Got all the way to the junction for the street (it's one way so decided to reverse in rather than risk breaking down going around the 1 way system), reversed in and it died. Managed to push it back along the street (speedbumps are fun ) and in to a space, and got the multimeter out.

 

Both relays were showing supply voltage on only 1 terminal with the ignition on, when it should be supply voltage at 3 of the 4 (having checked when it was working). I gave the ECU a jiggle about and did the same with the plugs under the dash, and got voltage to the relays, and she started.

 

So I reckon I've got a dodge connection or a break in a wire in this loom I've made. Now I have to trace it.

 

Looking at CAPS, and the loom schematic I made when building the loom, I'm trying to fathom what the actual process flow is when you turn the ignition. I mean, what is it that switches the relays to provide a voltage output to the fuel pump and injectors etc?

 

It looks as though the ignition wire from the 9 pin brown plug under the dash supplies voltage to pin 3 of the coil, which is connected to pin 4 of the amp, so effectively switching both components on.

Pin 4 of the coil is connected to pin 1 of the brown relay (Fuel injection relay?), so assume this must be a + signal, which I then assume to be connected to pin 2 of the relay (the earth), and this switches this relay on.

This relay then outputs voltage (from the +VE connection between pin 3 and the shunt box) through pin 5 of the relay to pin 35 of the ECU, pin 1 of the green relay (Fuel Pump relay?) the ICV and the injectors.

The ECU, now receiving a +VE/a signal from the brown relay now switches the green relay via pin 20 of the ECU to pin 2 of the relay (I'm assuming the relay is earthing through the ECU via this route, but since the wire is orange, I'm not sure). With the green realy now switched on, +VE is sent to the fuel pump via pin 5 of the relay to pin 2 of the 6 pin brown plug under the dash.

 

So, if I've got this right, the places I need to be looking for my fault, since neither relay is powering up on ignition, are:

1 - +VE from the 9 pin brown plug

2 - +VE at pin 3 of the coil

3 - +VE at pin 4 of the coil

4 - earth connection from brown relay

 

Am I on the right track or not?

Edited November 6, 2008 by GLPoomobile

[Stu 18]

Sounds about right to me, my understanding was that the injection relay got a feed from the switched live to the coil, and is earthed permanently. So once 'in circuit' so to speak the injectors, coil, amp and ICSV have a common 'rail' supply; upon cranking the CAS generates a signal telling the ECU the engine is rotating, and the ECU supplies the earth to the fuel pump relay and off she goes.

 

Dont forget if you're checking supply voltages at the injectors the plugs all have to be removed, and also keep in mind that the fuel pump relay wll only energise whilst cranking or running.

[mr_exe 1]

What you say makes sense, but when I had a no fuel problem it turned out to be a fault in the ignition side. Then what was happening was because it could'nt sense a spark the motronic would'nt supply any fuel, as the ingnition and fuelling are linked.

[Stu 18]

They are, in as much as if theres no supply to the injection relay the fuel pump relay has no switched live so to speak, and with no CAS signal no ground will be present to earth the coil of the fuel pump relay and hence close the contacts.

 

Motronic doesnt really monitor spark, the ignition side of things is relatively simple in that respect, and it all hinges on the CAS supplying a good sqaure output signal and the amp doing the same.

 

The only time the fuel pump relay gets earthed is via the ecu, you could obviously loop out the supply and ground to test, but this can more often than not mask the problem and add confusion.

 

The CAPS software is ace; every component can be tested against its reference values and all the testing procedure is in there.

 

That said, it obviously wont help you find a loom problem, but it might tie it down to a section of the loom.

[Super Josh 4]

Steve, I've seen this before where the crimp connections on the loom, where the relays plug in were corroded slightly.

 

So with the meter on there the voltages looked all good. But if you grabbed the relays and waggled their connectors the engine would cut out.

 

Might be worth giving the relays etc. a good wiggle and see if this causes the engine to cut out?

 

 

 

Josh

[GLPoomobile 958]

Josh, I've already wiggled the relays about. It was one of the first things I did when the problem started.

 

I'm wondering if my coil is on it's way out. My reasoning:

 

1 - It always starts first time from cold, and will run for a few minutes. The cutting out has been occurring after a few minutes of running. Enough time for the coil to build up some heat? Try and restart straight away and nothing. Leave it a minute, and it restarts. (I know that is often associated with the amp, but I don't think that is applicable here since I don't think the amp has any part in the relays being switched).

2 - It's been running lumpy, and missing a bit, and last night seemed worse than it has been.

3 - As I said, on the way up the road last night it was bogging down/losing revs but not cutting out completely

4 - There seems to be no consistancy between wiggling wires and it clearing and restarting, suggesting it's NOT a dodgy connection

 

I'm purely speculating here, and just making some conversation as it's lunch time. When I get back from my holiday I'll look at it again and I have a known working coil to swap if needs be.

Edited November 6, 2008 by GLPoomobile

[pug_ham 244 3 Cars]

What 16v management system?

 

On ML4.1 from a BX the fuel injection relay is connected directly to the shunt box with the igniition siwtched going to the fuel pump & then sending a closing feed to the injection relay but according to the 405 haynes for ML4.1 both relays are connected to the shunt box but still with a switched feed to close them, from a quick look its the same on M1.3 for both of them also.

 

On thing I have noticed from going through a 4.1 BX loom tonight is that the fuel pump relay switched feed also runs via the ignition module & coil plugs.

 

Graham.

[GLPoomobile 958]

Graham

 

It's 2 row on mine. My diagram seems to match what you have discribed, and what Stu said. Both relays have a direct connection (with no fuses, as was advised not required) to the shunt box. So it would have been that pin on each that I was reading +VE from the other night.