HELP - ECU diagnostics

[Boatbuoy]

Hi All,

I'm hoping the PH faithful can come to my aid, I'm at the end of my tether with this damn car now.

I started a thread yesterday because the engine wont run for more than about 5 seconds, the thread is here:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

I'm really worried that I've fried the ECU, but I really don't know how to diagnose what's going on. The car is in East Northants, I am on the south coast mid week and I'm trying to get it to an MOT on Saturday.

Does anyone have the diagnostics software and the required lead who might be willing to help me out?

Best Regards,
Olly

[CerbWill]

I have an ECU lead I can loan you. I can post it today if that's any use? Software is available on the internet but needs Win XP to run. If you don't have a Win XP device you'll need to use Virtual Box or similar to run XP in. I can provide the software and some instructions for that depending on how sorted you are IT wise. PM me if you want to take me up on the offer or want any more info.

[EvoOlli]

For better software take a look at this thread please:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Byker28i]

I've got laptop and lead, in Swindon, or Chippenham during workign hours if it's anyway en-route?

[Boatbuoy]

The car is in East Northants. I already put a shout out on the cerbera Facebook group, but no replies yet.

CerbWill has offered his cable which is very generous but we are struggling with finding an XP laptop.

[CerbWill]

You can give EvoOlli's software a go if you don't have Win XP, or use the instructions here to run windows XP as a virtual machine in Win Vista/7/8/10

[Juddder]

I'm in Central London, W2, and have laptop, lead and even a spare ECU you can borrow.

The ECU is currently EPROMed for a Cerbera Speed 6 but I have an APC so can copy the EPROM for that if you have an APC

BTW you don't need an XP laptop, I use my Mac with Virtual Box running and a USB -> Serial lead - there's some pictures here for you

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[gruffalo]

Hi Ollie,

I can help you out but not till next week as in the Alps right now.

We could try my ECU in your car as well to see if that helps although the mapping will be a mile out.

I have a laptop I can leave with you and a lead, where in Hants is the car?

Cheers
Martin.

[Boatbuoy]

Hi everyone,

I thought it only polite to update you all on the latest situation, given that you all jumped to my assistance so readily!

So, I borrowed another 4.2 V8 ECU to prove to myself that mine was dead. Except it isn't. The borrowed unit produces the exact same result, i.e. Press the ignition button, fuel pump runs (the immobiliser has been bypassed remember), fuel pump stops, press start button again, engine fires, runs for a few seconds and then dies (even when revved), the fuel pump then runs again.

However, my starter motor clutch/bendix has now given up and refuses to engage with the flywheel.

I now suspect that the crankshaft sensor is dead. Either the battery short killed it or the progressive failure of the starter bendix caused enough swarf to gather on the sensor to supply a duff output. Would that make sense to anyone?

The problem with this theory is that if the crankshaft sensor is dead, why does the engine fire in the first place? Does the AJP ECU have a default 'map' that the engine runs to for a few seconds until it has gathered data from the various sensors? It has been suggested to me that the RV8 does this, and if the AJP does the same then seeing as the only timing data comes from the crankshaft sensor it would make sense (in my mind at least).

Any alternative theories?

Best Regards,
Olly

[Boatbuoy]

Hi everyone,

I thought it only polite to update you all on the latest situation, given that you all jumped to my assistance so readily!

So, I borrowed another 4.2 V8 ECU to prove to myself that mine was dead. Except it isn't. The borrowed unit produces the exact same result, i.e. Press the ignition button, fuel pump runs (the immobiliser has been bypassed remember), fuel pump stops, press start button again, engine fires, runs for a few seconds and then dies (even when revved), the fuel pump then runs again.

However, my starter motor clutch/bendix has now given up and refuses to engage with the flywheel.

I now suspect that the crankshaft sensor is dead. Either the battery short killed it or the progressive failure of the starter bendix caused enough swarf to gather on the sensor to supply a duff output. Would that make sense to anyone?

The problem with this theory is that if the crankshaft sensor is dead, why does the engine fire in the first place? Does the AJP ECU have a default 'map' that the engine runs to for a few seconds until it has gathered data from the various sensors? It has been suggested to me that the RV8 does this, and if the AJP does the same then seeing as the only timing data comes from the crankshaft sensor it would make sense (in my mind at least).

Any alternative theories?

Best Regards,
Olly

[ukkid35]

Good news is that a new crank sensor is only £13 inc Shipping

http://www.ebay.co.uk/itm/291486181251

But I do realise that continually swapping stuff out can get very dispiriting.

[Juddder]

Boatbuoy said:

I now suspect that the crankshaft sensor is dead. Either the battery short killed it or the progressive failure of the starter bendix caused enough swarf to gather on the sensor to supply a duff output. Would that make sense to anyone?

The crankshaft sensor on our Mercedes had an intermittent fault where when it was hot it would stop responding and the car wouldn't start. Let it cool down and the car would start fine

Got the garage to replace it after doing the diagnostics on the car, and the car is all happy again and has been since

As the guys above say it's cheap to swap out and would make sense as to why the engine cuts out, but not sure as you say why the car would allow to try and start in the first place!

One other thing to try is connecting the diagnostics software (or the later EvoOlli's MBE Tool software) to the ECU and seeing what fault codes it is showing?

Guessing it probably would log the reason it turns the engine off - you can see how it logs in this thread here

[gruffalo]

I have a spare crankshaft senor if you want it.

[Boatbuoy]

Hello all,

Like before, I thought you'd all like to hear an update on the current status of my little conundrum. I now have A WORKING CAR!

Previously I'd got to the point of suspecting a sensor (namely the crankcase sensor) had failed. As a side issue my starter motor had failed and while replacing it at the weekend I found a loose cable, labelled as 'oil switch' (thanks to those who responded to my thread on the location of the oil pressure switch!) I plugged it in, and hey presto it all works!

So my theory about a faulty sensor output was right, just not the one I thought.

All I can think is that at the time of the electrical fire that started all of this, my tugging of looms and cable runs to prevent the battery cable shorting must have dislodged the oil switch connection.

Such a simple thing causing such massive personal pain. Anyway, case closed!

Cheers, guys!
Olly

P.S. The reason this has all taken so long is that I've been changing jobs and moving house. The car went on hold until I was settled. I wasn't being lazy, honest! Although I have to say my enthusiasm was waining at one point!

Edited by Boatbuoy on Monday 5th October 22:15

[ukkid35]

Are you saying that a disconnected oil pressure switch causes a No Start?

This is far from idle curiosity as I have a no start, and I've just replaced the oil pressure switch.

[gruffalo]

I don't think it does, my sensor is broken giving no oil light but the car runs perfectly.

4.5 though not a 4.2.

[Boatbuoy]

Well I dunno then. In my (simplistic) mind the oil switch cable joins the loom that goes to the ECU. The ECU would need to override the sensor at start giving the engine time to build pressure, then look for a signal after a few seconds. Or is that too advanced?

All I know is that my car didn't work, and now it does. That was the only thing I changed.

Martin, are you sure it's not just the oil light bulb that's blown?

Olly

[gruffalo]

No the bulb is fine, if I pull the wire off the sensor the light comes on. I have the SPA gauges in my car and the whole thing lights up red if oil pressure is too low, much easier to see than the rather dim light in the speedo.

[Boatbuoy]

Then I'm stumped! All I know, and care about is that my car works!

MOT on Saturday, hopefully!

[fatjon]

There is no oil pressure cut out on the MBE so that seems unlikely to be the fault. Regardless of that, pleased you are back on the road. Try not to light it again