Electrical problem 940

[Ammorack]

Originally Posted by Laird Scooby

If you've already swapped ECUs, can you confirm the Bosch number i think it should be is correct?

Yes. Ecu ends on 946 and the other 196 I believe. Can’t remember

No.
It’s 0 227 400 196
And 0 280 000 946

[Laird Scooby]

Originally Posted by Ammorack

Yes. Ecu ends on 946 and the other 146 I believe. Can’t remember

The 946 (fuel ECU) has a reputation for doing what your car is doing. It also has a reputation for being fine in one car, you remove it and the fault happens, even before you fit it back in that car or any other.

The NOID light will confirm my idea on the ECU, hopefully i'm wrong but so far, things are pointing to it.

I assume you've done all the standard checks for leaky/broken/perished vacuum hoses on/around the inlet manifold and there aren't any leaks between the MAF and throttle body?

[Ammorack]

Originally Posted by Laird Scooby

The 946 (fuel ECU) has a reputation for doing what your car is doing. It also has a reputation for being fine in one car, you remove it and the fault happens, even before you fit it back in that car or any other.

The NOID light will confirm my idea on the ECU, hopefully i'm wrong but so far, things are pointing to it.

I assume you've done all the standard checks for leaky/broken/perished vacuum hoses on/around the inlet manifold and there aren't any leaks between the MAF and throttle body?

Have checked hoses and for vacuum. There’s absolutely no leakage whatsoever. I have checked so many times. A smoke machine would be very useful. But I have checked. From MAF to tps is fine.
Those ECU’s drove fine in another Volvo. But mine didn’t

[Laird Scooby]

Originally Posted by Ammorack

Have checked hoses and for vacuum. There’s absolutely no leakage whatsoever. I have checked so many times. A smoke machine would be very useful. But I have checked. From MAF to tps is fine.
Those ECU’s drove fine in another Volvo. But mine didn’t

Did they still drive fine after? If so, you're going to be getting very friendly with your multimeter!

*** EDIT *** Forgot to mention when i posted, try pulling the Orange wire off the TPS and see if it will rev then - i still don't think it will rev past 3000rpm but useful to confirm it. Refit afterwards if there's no change.

[TonyS9]

What about a missing phase on the alternator?

How about disabling the alternator and just running of the battery?

[Laird Scooby]

Originally Posted by TonyS9

What about a missing phase on the alternator?

How about disabling the alternator and just running of the battery?

A missing phase won't cause that Tony and we've already done the disable the alternator test, no change.

A missing phase might cause it if it happened under load but it's when the load is switched off, normal charging voltage exists as well.

[TonyS9]

And can overfuelling cause rpm limitations? The engine overfuels most of the time its not a big problem. I guess you can drown the spark, but it normally chokes and dies completely, usually only when the spark is weak.

Limitations are normalled cause by underfueling, or air leaks. But needs to be a pretty big air leak. Mine will run, just about, when the inlet pipe pops off, just enough to get back to the pits.

[TonyS9]

Originally Posted by Laird Scooby

A missing phase won't cause that Tony and we've already done the disable the alternator test, no change.

A missing phase might cause it if it happened under load but it's when the load is switched off, normal charging voltage exists as well.

I'm imagining spikes on the voltage due to some weird fault, but if its still restricted in rpm with the battery then I see why you've persued engine issues. Still current load on the alternator or battery should not help smooth running. Its a weird one.

[aardvarkash10]

Hi guys - I've been lurking so I don't get in the way.

Lights and other load on would lower the voltage across the electrical system. It seems like the ECU is responding to that lower voltage, or more importantly, misreading the no-load voltage.

I'm not well enough versed in the black majic of the ECU itself to identify where and why this is happening (if it is the case). I also don't have the schematic in front of me atm, so I can't trace what may be impacting the ECU externally.

If the fault is occuring on a known good ECU, that indicates the problem is external to the ECU. The cut spaghetti behind hte dash is a warning sign as well.

Any thoughts out there?

[Laird Scooby]

Originally Posted by TonyS9

And can overfuelling cause rpm limitations? The engine overfuels most of the time its not a big problem. I guess you can drown the spark, but it normally chokes and dies completely, usually only when the spark is weak.

Limitations are normalled cause by underfueling, or air leaks. But needs to be a pretty big air leak. Mine will run, just about, when the inlet pipe pops off, just enough to get back to the pits.

It can, yes. Back in the days of what are now antique pieces commonly known as carburettors, i knew many carbs that suddenly started to overfuel and the car would just die.
I remember in particular a Mk2 Fiesta 1100 with the FoMoCo copy of a single choke downdraught Weber. It had been in the workshops for several days and none of the guys were getting anywhere. I'd recently joined as an autoelectrician so when i asked if i could have a go at diagnosing it, i was met with laughter and derision.

However, they were all at their wits end so agreed.

Took it a couple of hundered yards up the road, went back and spoke to my boss. He told me where i could find the part to borrow to prove the piont so i borrowed said part, swapped it and gave it a test drive.
An extended test drive then returned and handed the keys to the senior (in age and company rank) mechanic and told him to go and try it.

He was incredulous. Even more so when i told him the problem.

He still wouldn't believe me so i gave him the original carb and told him to refit and try it and that what was on there came from a 1300 Escort we also had in the workshop. Then the penny dropped as to why it went so well. He hadn't realised i'd used a 1300 carb to prove the point.

Every time the engine was called on to accelerate briskly (as in anything past very gentle acceleration) the carb would just empty bucketfuls of petrol into the engine so it was excessively rich and just bogged down because the mixture was too rich to fire. Dynamic flooding if you like.
Purely caused by wear.