Engine Mgt Unit problem? - Omega MV6

I have some symptoms which I believe is most likely to be the ECU, but
thought I'd canvess opinion before sending it away.

The car is a '98 3.0 MV6 omega, so uses the Motronic ECU (model number, if
I've picked the correct number off the unit, is 0 261 204 589).
The symptoms are as follows;

3 months ago had a couple of instances of car simply not starting - orange
light remained on during turnover. Left it a minute, and it was fine. No
reported faults from the ECU, (orange light always off during running), and
the car has NEVER stalled once running. This happened a few more times
until around 6 weeks ago when it just would not start. I was suspecting
Fuelpump relay, and took to tapping the relays etc (yes - I realise this
isn't very scientific, but I was in a car park with no tools). When it
didn't work, I left it overnight and called the AA to tow me home the next
day. Between us, Mr AA Man and I decided that there was no fueling, and
maybe it was a sticky relay, or maybe a dodgy/sticky fuel pump. He gave it
a "tap" and sure enough the car started. I now believe this to have been a
red herring.

Through a little investigation, I found that when the car would not start, I
was getting around 3V on the fuel pump fuse - so this did point to dodgy
relay (I thought).
Now the car is totally dead - In that I just cannot get it to start, It
turns over, but the MIL stays on and it doesn't fire at all.
So - I checked the relay (in fact opened it up and cleaned the contacts and
tested it) - I also swapped the Fuel Injection and Pump relays just to
eliminate each other from the problem. My logic was that possibly the fuel
pump WAS drawing a heavy load when it started up (and of course this is
likely to co-incide with turning the car over, so the terminal voltage will
be down a bit, hence the current will be greater), so sometimes the bad
contact would result in failure of the pump to start, but when it did, the
car would run, and it wouldn't then stop.
I've then found that actually the relay was NOT being energised - remember,
all I have is a Haynes diagram and I was not sure if the pump should be
energised and run all the time the ignition is on (closed loop system, like
on the Jetronic systems per Cavalier etc), or if it's modulated by the ECU.
I guessed the later - but either way it's the ECU's job to energise that
relay, and it wasn't. As a check, I bypassed the relay (piece of wire), but
the car remained determined not to start.
Next thought process was crackshaft sensor (I gather these are a weak point
on Omegas) - and decided that it was time to read out any fault codes. I'd
done this before, just before the AA incident, and it was always OK - I use
the paperclip method, and just got a continual cycle of "12", so I'd not
suspected that anything had changed.
So, having "reset" the whole lot by leaving the battery disconnected for a
few hours, and also made sure it was fully charged, I reconnected
everything.
Now I'm getting the following codes:
12 (expected)
73 (Air Flow sensor - low voltage)
57 (Idle Speed Control valve - interruption)
53 (Fuel Pump relay - low voltage)
19 (RPM signal, crank sensor - incorrect signal)....I might expect this one,
as the car is obviously not running

So - I am not convinced that suddenly all these sensors have failed, so I'm
suspecting the ECU - Which will cost in the order to £35 quid to have looked
at, and I think about £100 to rebuild.

Things I've not tried
- Replacing the relays....I'm sorry, but I resent the cost of £20 for a
relay - that is extortion. It's not a "special" relay and similar rated ones
(which unfortunately don't fit the pinout) are only around £2 in RS.
Anyway, I've independently checked mine on the bench. The coils draw the
correct current, and the on resistance is < 0.1Ohm.
- Check for spark - I need to do this - if there were no fault codes, I'd
suspect the ignition module, but with all these fault codes, I think it's
unlikely.
- Checking injectors...not sure how to do this other than with a meter on
the signal wires.

One other point - All these "low voltage" errors made me suspect the
earthing on the car, so I connected big jumper cables from -'ve to the
chassis and the block. No change.

Any other suggestions, before I submit it for diagnosis? I am an electronic
engineer, and pretty handy with these type of things normally, but I'm a bit
stumpped now, short of trailering it to a Vx dealer, and parting with many
hundreds of pounds!

Sorry for the very long post - but I wanted to avoid backwards and forwards
questions...I think all the info is here.

HELP!!!!!!

Rich

 

Follow Up:

ECU has been off the car now for two days, in the warm.

I went out to check the spark, having had the battery on charge for two days
(it was a bit drained from excessive attempts to start).

The car has started!!!!

The fault codes remained, but I restarted it 20 times (apparently this
clears fault codes if the fault is no longer detected). MIL now blinks 1 2
only - so all codes are clear.

Could this have been low battery???? I HAD charged it, but maybe the fault
codes were "low voltage" as a result of a genuine low battery.
I'm not convinced about this - I reckon it's still luck/intermittent, but I
can hope.

Time to stick the car in for trade-in!!

Any other thoughts?

Rich

 

Go with your gut instinct and replace the battery - especially if it's
an original. Would explain the effect as the cold weather set in.

 

Crank sensor would be my guess. If it isn't reading an engine speed on
cranking then the ecu won't know to turn the fuel pump relay on.

 

The fuel pump relay as stated will only energise if the engine is turning.
I'm not sure if it gets its signal from the crank or cam sensor or even the
ign side. The older carltons used to be very prone to this and they got the
signal from the ign ( coil set up though ).
Have you tried cavweb forums they are shit hot on this type of thing with
huge amounts of experience in v/halls.

 

I'd sort of agree - but it all started in August!!

Still - £30 for a battery is better than a new crank sensor (at £80).

Rich

 

I thought the same thing, but baulk somewhat at £80 for a simple hall effect
sensor. Still - maybe it's the only way.

Still - If I can trade it in while it's running, then it becomes the dealers
problem!

thanks for the advice,

Rich

 

If you find a garage with a scanner they will be able to read live data. If
when you crank the engine over the crank signal stays at 0rpm you know it is
buggered.
By the way - they are a king size bitch to change - I think Vauxhall must
fit them before they fit the coolant pipes cos it is all trapped behind
them.

 

I'd give autovaux a ring - they charged me around 40 quid for a crank
sensor for my X20XEV, whereas Vx wanted 100. Next day delivery to the
other end of the country.

Can't remember their phone number but their website is
www.autovaux.co.uk - donyt bother with the email facility on their web
site though, from personal experience they seldom bother replying :-(.

Probably worth joining the 'omega_owners' group on Yahoo!, lots of
Omega expertise over there.