S1 V6 auto back on the road at last!! - Problem solved!!

[Dean]

putting perminabt live to the fuel pump would be esy enough but its the jittery tack that makes me think electrical.

D

[sdelasal]

Matthew - some thoughts...
1. the rev limiter is there is protect the engine, perhaps the catalyst too. From my experience on other cars, if the ECU thinks the system has a certain type of fault- goes into 'limp home mode' - and reduces the rev limiter RPM. The limitation is delivered by simply cutting the fuel pulsewidths to zero - on/off control around the rev limit. So the way to figure out if that is happening is to put a 'scope on the injector connections - not something we tend to have in the tool box unfortunately. see p.522 here: https://books.google.co.uk/books?id=_sz ... on&f=false" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

The rev limiter does not use the fuel pump - that simply pressurises the fuel rail, with excess bleeding basck to the tank. Now the rev limiter could be being activated due to ECU fault - perhaps you could swop a known good one over from another car. Are there any hints in the v6 factory workshop manual about rev limiter operation?
2. another thought, if the exhaust system were obstructed, then that would have the effect of limiting airflow thru the engine. But i'd expect the engine to be able to rev higher in neutral compared to under load were that the case.
3. are the earths good!
4. Vibration .... perhaps a poor connector. or a short circuit, making/breaking at a engine resonance @ 3800rpm... Check crank position wiring,

steve

[xmexclusive]

The V6 Fenix ECU has a self correction mode.
It effectively tunes the engine to suit measured values and changes over time including items such as compression.
Every time the ECU is disconnected from the battery the ECU reverts to standard settings and restarts self correction.
A substantial test run in varying road conditions is required to complete self correction.
The ECU also continuously checks on the credibility of the various parameters of the system.
It has correction strategies for six parameters and will intelligently substitute back up values.

John

[sdelasal]

If the ECU thinks that things are unhealthy, it will protect the engine and the catalyst (rich / excess fuelling into the catalyst will damage it). So what you could do matthew, is the following. Go to one of your working cars and then one at a time, disconnect one the following...

1. air meter (+air inlet temperature?)or manifold pressure sensor - not sure what you have.
2. exhaust gas sensor
3. camshaft sensor(s)?
4. coolant temperature

and see if any one of those has the effect of bringing down the RPM limiter. If it does, that will give you a hint on where to look.

also, any chance you have the wiring to the injectors incorrect? i.e. plug connected to wrong injector


John, on the self correcting terms. The ones i'm aware of are (a) afr correction - (used when HEGO is cold and that sensor is not proving feedabck of exhaust gas afr. The system will use the HEGO switching to re-learn any necessary corrections) and (b) engine idle air correction term.

[Dean]

Im fairly sure injection is not sequential on the V6 and there is no cam sensor, the ecu would not be able to see incorrect timing.

Air temp and map sensors used with tps
knock sensor on each bank could cause issues with no eml if plugs were swapped
Crank angle
3 seperate coolant sensors for engine management, guage and ? (fans?)

D

[Dieselman]

Im fairly sure injection is not sequential on the V6 and there is no cam sensor, the ecu would not be able to see incorrect timing.

Air temp and map sensors used with tps
knock sensor on each bank could cause issues with no eml if plugs were swapped
Crank angle
3 seperate coolant sensors for engine management, guage and ? (fans?)

D

I think you are correct about the injection not being sequential, but it should be easy to check with either a scope, volt meter or NOID lamps. Even a home made LED Lamp should suffice.

All fuel injection systems have a rev limiter to stop engine damage and the effect is similar, but not the same as here.

I suspect a wiring fault caused by engine movement or vibration.

[MTXM]

Many thanks for your further contributions chaps and I did manage to find some time over the weekend to carry out a few more checks mainly in relation to the wiring. I did find a few slightly dodgy looking connectors that I was able to replace with better examples from scrap engine harnesses including for the water temperature sensor and flywheel sensor. It is very disappointing to report there has been no improvement, in fact while the engine starts eagerly it now barely revs up to 2,000rpm and is also badly misfiring! It may be that the other fuel pump I fitted is no good and I could revert to the original, while there does seem to be a general worsening of the situation. After a few internet searches restricted revving seems to be quite a common issue and another possible cause highlighted is a blocked cat that I have not yet changed. I must admit that even I am getting short of patience!! With regards, Matthew T.

[White Exec]

Had a blocked cat on the D4D a long time ago. Symptoms very much the same.
Try dropping the exhaust before the cat (could be surprisingly quiet if there is an exhaust turbo) and see what happens.

[xantia_v6]

Had a blocked cat on the D4D a long time ago. Symptoms very much the same.
Try dropping the exhaust before the cat (could be surprisingly quiet if there is an exhaust turbo) and see what happens.

If easier, you could try removing the oxygen sensor and run the engine, you should soon know if all the pressure is escaping through the hole. Measuring the back pressure at that point is good if you have a suitable gauge and adapter.

Edit - See https://frenchcarforum.co.uk/forum/view ... 21#p363521" onclick="window.open(this.href);return false;

[MTXM]

Many thanks Mike and Chris and I can now report that I completely removed the cat yesterday and it made no difference at all! In actual fact while the car continues to start on the button and ticks over beautifully, there is now almost no power at all, just about managing to run over 2,000rpm with the occasional misfire.

I will post up a further longer video later, but basically it is just sounding rather 'strangled'! Although the plugs look very good and if anything a bit weak, the exhaust fumes smell quite strong if that is any help. I am hoping that the is the same original problem getting worse, which surely must help to pin down the cause, and not something more/else introduced by the various parts changed, including most recently the petrol pump?

Any more comments and ideas would be most welcome as the car is now virtually undriveable and I am getting a bit desperate!

With regards, Matthew T.