Xantia V6 broken exhaust (update: and rough low rpm running)

[Mandrake]

Well, ECU etc swap if you don't want to try the battery terminals first. But I would 100% change them myself.

A temporary ECU/CPH swap is definitely on the agenda, David Hallworth has kindly offered to let me try the ones out of his Activa V6 conversion donor car which is SORN'ed pending engine gutting, its just a matter of finding a common time when we can look at it, so it could be a while away.

Meanwhile I've been thinking more about it and was watching another one of ScannerDanners new videos (as you do ) and realised there's another possibility I've overlooked for intermittent misfiring that gets worse when it gets hot - intermittent shorted turns on an injector as demonstrated in this video:



The only basis I have for believing the injectors are not at fault is that I did an injector balance test once last year using an exciter and measured the fuel pressure drop - which they all passed.

However that was done on a cold engine and the failure mode demonstrated in the video above is that as the engine heats up a shorted turn develops in the winding in the injector. This causes the inductance to drop dramatically and upsets the current ramp drawing a lot more current and too quickly.

This would affect the mechanical on time of the injector and because the injectors are wired in parallel if the ECU has over current protection then one shorted injector would steal current from the other one in the pair possibly causing the one that's not faulty to fail to fire at all.

Being very intermittent and tending towards being worse when hot does fit the symptoms I'm seeing. The only way to diagnose or rule out this problem is to look at the current waveforms for the injectors, so I'm seriously thinking about stumping up for a current clamp probe that I can use with my scope and multimeter.

It would also allow me to identify (or rule out) any problem with the injector and coil pack primary side drive from the ECU, which is the thing most likely to be wrong with the ECU, if anything is. Whether I get the current clamp before or after the ECU swap remains to be seen (obviously I wouldn't if the ECU swap did fix it) but that's my line of thinking at the moment.

Any problems with power feeds etc will show up as problems in the coil and injector current waveforms as well, in short those two sets of waveforms tell you pretty much everything you need to know about the ECU outputs that could potentially be causing a misfire.

Another thing to try is pulling the fan relays (without a battery disconnection event) as this will reveal current supply inadequacies. Don't boil it though.

I would try this except symptoms usually set in well before the fans kick in, and I haven't been using air conditioning lately either, yet the symptoms are still there. There is a noticeable drop in engine revs when the fans do kick in but I think this is more a symptom of the engine lacking power and/or mis-misfiring under sudden load increases as it does a similar thing when I try to accelerate off the mark.

[addo]

It's worth trying. The problem fans I have seen, draw excessive current especially at low speed due to internal friction (rear bushing). It's more than enough to cause a stumble or poor running. I suppose a shortcut would be to pull the maxi fuse immediately when the car started misbehaving, without even stopping the motor.

[Mandrake]

Perhaps. Another thing I was thinking about was the possibility of a faulty diode in the alternator causing "spikes" in the electrical supply that could upset the ECU, I'll put my scope on the alternator output when I get a chance to rule that out.

It's unlikely but it needs checking and is easy to check. (I suppose disconnecting the exciter wire for a quick test drive would prove it one way or the other as well)

Cold morning this morning - 6 degrees which is 4 degrees colder than the previous morning low this autumn, despite also being a bit wet and damp the car was running quite well. Still a little bit of hesitation but it had a lot more power than recently that lasted for the whole 15 minute trip without fading away.

Co-incidence ? Or a small confirmation that maybe under bonnet heat build up does provoke whatever the fault is ?

[lexi]

I have the flame thrower felt blow torch here. Bring it round and I will heat it and do a Glasgow insurance job on it

6deg eh? in 6 weeks we may be praying for that temp. You lookin forward to another Scottish Winter mate?

[Stempy]

I have the flame thrower felt blow torch here. Bring it round and I will heat it and do a Glasgow insurance job on it

6deg eh? in 6 weeks we may be praying for that temp. You lookin forward to another Scottish Winter mate?

Well at the least it would finally close this thread...

[addo]

Team WFA would buy it, I'm sure - if only for the challenge of sorting it within 24 hours.

[Northern_Mike]

Team WFA would buy it, I'm sure - if only for the challenge of sorting it within 24 hours.

Surely you mean 2.4 hours?

[Mandrake]

I have the flame thrower felt blow torch here. Bring it round and I will heat it and do a Glasgow insurance job on it

Alas, only 3rd party

6deg eh? in 6 weeks we may be praying for that temp. You lookin forward to another Scottish Winter mate?

I know. Depends if its going to be a clear crisp snowy winter or a grey rainy wet mushy winter...

I actually don't mind snow if its clear and crisp, its when things turn to mush and it rains all the time...

[addo]

Surely you mean 2.4 hours?

Nah, there'd be a 2000 mile test drive included.

[xantia_v6]

I have the flame thrower felt blow torch here. Bring it round and I will heat it and do a Glasgow insurance job on it

6deg eh? in 6 weeks we may be praying for that temp. You lookin forward to another Scottish Winter mate?

Well at the least it would finally close this thread...

Did anyone else notice that we missed celebrating the (first) anniversary of this thread?

[Stempy]

Seems like longer

[Northern_Mike]

I suggest we get an army of miscreants from here and drive up to Scotland in my Berlingo and fix it once and for all.

I note, with a smirk, the "(first)" in XantiaV6s post.

I'm worried I might pass away without finding out what the problem was!

Sent from my GT-I9300 using Tapatalk 4

[Mandrake]

I suggest we get an army of miscreants from here and drive up to Scotland in my Berlingo and fix it once and for all.

As humorous and appealing as that sounds Mike, I don't think a day trip would ever get this car sorted for a couple of reasons...

One is all the simple stuff that could be done in a day has already been done or ruled out as far as I can see. Whatever the problem is isn't your run of the mill typical ES9J4 problem its a real thorny unusual one, even if in hindsight the problem may be simple. I'm sure you guys could get to the bottom of it given enough time and resources, but not in a day.

The other problem is that even if something is found/fixed and the symptoms go away on the day the nature of the problem is that its extremely intermittent so it's impossible to know the same day whether anything is really fixed or not.

I've completely lost count of how many times I've done something (most recently blanked off the vacuum line to the charcoal canister) and the symptoms are either completely or mostly gone, only to return days later. So often in fact that it is seriously not funny.

There have even been times in the past where I've had the air filter box out and put it back and done no other work to the car and it runs like a dream for a few days then goes down the tubes again... explain that one. Almost anything you touch in the engine bay seems to have some temporary effect, as does resetting the ECU.

Until it runs perfectly for 3-4 weeks without any remission it can't be considered to be fixed in my opinion...

I note, with a smirk, the "(first)" in XantiaV6s post.

I'm worried I might pass away without finding out what the problem was!

You and me both Mike.

It's not all bad though, its still driving ok and all going well I'll be trying the ECU swap this Sunday which will hopefully rule that out (or fix it!) and failing that I'm looking at getting a current clamp probe so that I can properly measure the current waveforms for the injectors and coil primaries which will tell me a lot about whether they're functioning properly or not. (Even a mechanically sticking injector can be diagnosed from the current waveform)

After ECU swap and measuring the current waveforms I'm dead out of ideas though, and it will probably be down to a mechanical problem with the engine...

In the back of my mind I'm thinking about leaking head gasket or cracked head, (leaking coolant into a combustion chamber) an intermittently sticking valve, a collapsed hydraulic lifter, something along those lines, none of which I'm in a position to do anything about...

[addo]

To ask a question I cannot answer - if there is a partially shorted injector, is there a risk of it damaging another ECU's driver transistors?

Either way, I suggest you need to do some hot/cold tests with Lexia. Before setting off, note all your main cold parameters. Then, note when hot on arrival. The ECU swap is so quick the car won't really cool down, you can go for a short drive and check the hot parameters on the new one. Leave it to cool for a couple of hours (I'm sure there's a tractor to help fix) and look at the test ECU's cold parameters...

[Mandrake]

To ask a question I cannot answer - if there is a partially shorted injector, is there a risk of it damaging another ECU's driver transistors?

There's a very small theoretical risk yes, but it's extremely unlikely for a couple of reasons.

The first is that the ECU almost certainly has current limiting or over current shutdown on the outputs.

The second is that a shorted injector isn't going to be a dead short, the winding can develop one or more shorts between adjacent turns - which causes a dramatic reduction in inductance but makes hardly any difference to the resistance, depending on how many turns are shorted.

So resistance might only drop from say 12 ohms to 11.5, but because of the huge loss of inductance the current will rise very quickly instead of a gradual rise as a sawtooth shaped ramp. This will change the apparent pulse width of the injector opening but I can't quite make up my mind whether it will lengthen it or shorten it.

The faster current rise time would tend to cause the injector to open sooner that it normally would (there's normally about 1ms of delay from when the current ramp starts until the injector mechanically opens due to the slow current buildup) but on the other hand the shorted turn will weaken the magnetic field for a given current which would tend to delay or prevent the injector opening, and I'm not sure which of these two competing factors would win out.

One thing is for sure though, it would lead that injector to opening for a different amount of time than the others causing that cylinder to run richer or leaner than the rest when its shorting or possibly misfire entirely.

Either way, I suggest you need to do some hot/cold tests with Lexia. Before setting off, note all your main cold parameters. Then, note when hot on arrival. The ECU swap is so quick the car won't really cool down, you can go for a short drive and check the hot parameters on the new one. Leave it to cool for a couple of hours (I'm sure there's a tractor to help fix) and look at the test ECU's cold parameters...

The parameters change dramatically between cold and hot, but comparing hot readings on the two ECU's might be worth checking.

Also although resistance would only change a small (probably less than 5%) amount on a shorted injector, comparing the three pairs to each other when cold versus when the engine is hot and misbehaving might give some clues. You would normally expect a small rise when they heat up but if any one pair dropped instead or rose much less it would be suspicious.