Motronic ML4.1 diagnostics - non-starter

[davemar 16]

After doing a bit of a rebuild on my 205, and trying to get it going again I'm now stuck. It's an Mi16 (XU9J4) running the Motronic ML4.1 ECU, and used to work fine.

 

Currently it doesn't fire up. There seems to be a spark, and there also seems to be pulses going to the injectors. I'm sure there's also fuel getting pumped to the rail as the fuel pressure regulator o-ring was iffy, and fuel was leaking out, so I fixed that. So there seems to be spark and fuel, but no signs of life.

 

So I'm trying to work out how to use the diagnostic connection on the ECU. I've connected an LED via a resistor from pin 17 to +ve. When I turn the key to ignition on the LED lights as expected. Reading around it seems that you start the diagnostic routine by shorting pin 4 to ground for about 3 seconds and the LED should flash a sequence of flashes to indicate codes. But when I do that the LED just turns off. So does anyone know how to get the diagnostic codes out?

[petert 586]

Do you look here?

As per the attached procedure for M1.3, you should get 12 at the start and 11 at the end. If nothing in between, there are no faults recorded.

[davemar 16]

Thanks for those. I did have the CAPS software buried somewhere, but not running Windows these days. I'll try and get a VM cranked up.

 

I managed to get the ECU to run some self-tests by holding pin 4 to ground before turning the ignition on, then releasing after 3 seconds, then holding again for 3 seconds. This triggered the injector self-test which fired the injectors (clicking away) and flashed a 1-4-1-1 light sequence. So that looks fine.

However, when I tried to trigger a diagnostic code by holder pin 4 to ground for 3 seconds AFTER I turned on the ignition the LED first gave a 1-2 sequence (so only two sets of flashes instead of 4); then I held 4 to ground again for 3 seconds, and it gave a 1-1 sequence. For some reason it didn't want to give me a 4-number sequence.

 

[davemar 16]

Just came across this link: https://frenchcarforum.co.uk/forum/viewtopic.php?t=2086

Here is suggests on the BX16v they have 2-digit fault codes, so this makes more sense. So 1-2 followed by 1-1 suggests there are no faults.

Bit of a bugger as I was hoping there was a clue to what the engine isn't starting!

 

[Ryan 99]

The 4.1 ECU only has a limited ability to detect faults and can only really report a shorted throttle position switch or temperature sensor, a bad AFM, or an ECU ROM fault. It can't detect things like the timing being out, firing order being wrong, bad ignition amp, or a weak fuel pump.

[welshpug 1,657]

I'd start with a fresh set of plugs and confirm the fuel pressure, worked on one very recently that had an inch of water above 2 plugs!

[davemar 16]

They are new plugs, but I ought to check they are the right ones. I hope I haven't put my Impreza ones in there! I'll double check the HT lead order on the cap too.

 

I'm semi-tempted to take the injector rail off to see that they are squirting ok. They've been sat around for a long time so may have gummed up.

 

[davemar 16]

Yay!! Finally got it started!

 

It was an iffy connection on the fuel pump. When I wiggled the connector the pump would spring into life, so it seemed fine when I was testing it in isolation, but turn itself off when the connector wasn't being held. So it wouldn't start when I wasn't holding the connector.

 

So after 2 years the engine is running again. Not all joy though, as there was a lot of fumes coming up from the manifold so I think the manifold to downpipe join isn't sealed properly.