ECU & Fuel Pump Relay Help

[Eddie1990]

I've nearly finished my M20 swap into my E21, but I'm having a little trouble with the final wiring.

The car won't spark and the fuel pump won't come on unless I bridge both relays. I've fitted new ones and it's still not having it.

With the relays bridged, it works fine. Starts and runs okay.

I've heard that ECU sends signals to the relays and if they are not getting there, the relays won't work, is this true?

From a wiring background point of view, the C101 has been cut out and the required wires have been spliced onto the E21 fusebox plug.

[Speedtouch]

http://www.e30zone.net/e30zonewiki/index.php/DME

[Grrrmachine]

If you're not getting fuel or spark then you're not getting a Crank Position signal to the ECU.

http://www.e30zone.net/e30zonewiki/inde ... ion_Sensor

[Speedtouch]

"With the relays bridged, it works fine. Starts and runs okay."

This suggests the CPS is OK.

[Eddie1990]

Any suggestions then?

As said, the CPS must be fine as the ECU is happy with the relays are bridged.

[Speedtouch]

Ensure that the ECU to relay connections are all good - use a multimeter to verify continuity.

May be worth hoiking the relay box out and looking underneath for damaged wiring...

http://www.e30zone.net/e30zonewiki/inde ... g_Diagrams

[Eddie1990]

My main ECU relay is a brand new one from BMW, so that won't be faulty.

I'll check for continuity between #85 and #36.

If that is the case, what's the fix? Trace the wire and find the break?

[Speedtouch]

A new relay won't necessarily be working properly - test it by energising the coil and using a multimeter to verify the contacts are closing.

Yes, you can also use the multimeter on continuity or the lowest ohms range to check for breaks in the wire(s).

[Eddie1990]

Okay, so I've got the car started but it's misfiring quite badly. It's not the HT leads as we checked them.

Any suggestions?

[Speedtouch]

Did you let it idle for at least 10 minutes, to enable the base idle settings to be learnt?

If not, disconnect either battery or ECU and leave for an hour or so to reset the ECU, then try again.

Are you sure the HT leads are the correct way round?

[Eddie1990]

Ahhhh I never knew about that, longest it ran was for 60 seconds maybe, then we turned it off as it sounded so rough.

I'm pretty certain they are. Do you have a link for the correct order? Just to clarify what I have is correct.

I'm on my phone and the guide I used is bookmarked on my laptop so I can't link it in here.

Is there a specific order the injectors have to be in? The wiring diagrams show them as two banks of three, joined by one splice, so I'm unsure how they work exactly?

[Speedtouch]

http://www.autozone.com/autozone/repair ... 5280049ff5

http://www.e30zone.net/e30zonewiki/index.php/Motronic

[Eddie1990]

With regards to the injectors and the injector plugs, which one plugs on which?

I know they're arranged in two banks, but does it matter which plug goes on which? I imagine it does, but I can't seem to find an answer as to how they are arranged.

I know it's a dumb question

[Grrrmachine]

Bank 1 is injectors 1, 3 and 5, and goes to pin 16 of the ECU.
Bank 2 is injectors 2, 4 and 6, and goes to pin 17 of the ECU. A simple resistance test will tell you which ones are which.

[Eddie1990]

Right, I must have the wrong end of the stick or something but the banks are arranged in such a way that injector 2 surely can't be on the same "bank" as injector 6, as the wiring won't reach surely?!

When you talk about the injector numbers, are they the same as the cylinder numbers, so from the front of the engine:

Cyl 1 = Injector 1
Cyl 2 = Injector 2
Cyl 3 = Injector 3

Etc, etc, etc

[Grrrmachine]

I'm just quoting from this pic (which will load poorly on a mobile device):

http://www.e30zone.net/e30zonewiki/imag ... ection.pdf

Only time I took the injector loom off myself, it was all encased in its plastic case, so I never bothered looking inside to see how long the wires were.

[Eddie1990]

Yeah I've looked at that wiring diagram many times, but it's what the numbers of each bank actually mean. Does "no1" go on Cylinder 1, etc?

I'm not sure if I'm explaining myself well tbh.

[Eddie1990]

Okay, I've thought of a better way to explain what I'm asking.

Is this how the injectors should be arranged?



It might seem like a daft question, but it's properly puzzling me!

[Grrrmachine]

I'd really expect BMW to write No 1, 3 and 5 to match the cylinders, otherwise the numbers are meaningless. Why would Injector 3 go in Cylinder 2, if Spark 2 goes in Cylinder 2?

Have you physically tried to make the wires reach the injectors yet?

[Eddie1990]

I have the sensor on cylinder number six HT lead.

I'm almost certain that the firing order is correct in terms of the layout of the HT leads.

I've yet to have an in depth look at the dizzy/rotor arm. When I stripped the engine down and put it back together, I inspected the dizzy etc and all seemed fine at the time.

I'll check the injectors and see what's what.

I think it might well be my CTS sensor for the ECU as my cooling system was very rigged up and not functioning correctly, I'm told that a faulty sensor, or a sensor not reading quite right can cause poor running, including misfiring?

I'll check all the mentioned things in here though, and see what's what.

[Speedtouch]

Okay, so I've got the car started but it's misfiring quite badly. It's not the HT leads as we checked them.

Any suggestions?

How did you go about checking them?

Using a multimeter, they should all measure under 10 kilohms or so.

[Eddie1990]

No I mean CTS, coolant temperature sensor, apparently it can cause poor running as the ECU overfuels the engine if it gets an incorrect reading from the CTS. Blue plug is for the ECU, brown is for the clocks.

[Jookeone]

Sorry to jump in on your thread, but willnz you say;

"It should start and idle ok when cold though." with regards to the blue temp sensor.

I've been planning on checking this to find the cause of a rough/lumpy idle when cold. All seems well once warm and i'm getting what I consider good economy. Any ideas?

Cheers

[Jookeone]

I'll have a run through the wiki when I get the chance. The majority of ignition party's are new although I've not checked the HT leads yet. Have also checked for air leaks and seems good!

Because the car is my daily it's a bit of an issue with sending the injectors away but when I get an opportunity it's on the list of things to do.

The engine is a pre facelift 2.5 (073 ECU)