All Things V6...

[CitroJim]

Got more bushes than a garden centre has it David?

Actually, taking a break from the C5 is possibly not a bad idea. Return to it later with a fresh mind...

[DHallworth]

Jim,

There's 6 bushes on each side at the back plus another 3 bushes that hold the differential in place.

There's then another 4 or 6 (can't remember which) at both sides on the front as well!

David.

[DHallworth]

Right, as the Freelander was finished I decided I'd have another look at the C5. As a genuine crankshaft sensor was only £19 I thought I'd order one and see how we got on.

I changed the sensor and the car ran on 5 cylinders for a few minutes. I stopped it whilst I went to get my laptop and when I went back to the car it won't run again. I'm now getting a permananent fault on the engine speed sensor on the Lexia. I am going to try and trace the wires from that sensor back to the ECU and check for resistance, failing that I might try and measure the resistance of the sensor at the pins on the sensor and again at the ECU to make sure there's nothing sinister going on.

That's all for now.

David.

[xantia_v6]

Is that "not" or "now"?

[DHallworth]

My bad... it's meant to be "now".

Have edited the original post.

David.

[CitroJim]

She's really putting up a fight David. Are you sure you don't have an XM cunningly disguised as a C5 there?

[Mandrake]

I think you're on the right track now David. Right from the start I was suspicious of the crank sensor signal based on the fault codes and the intermitent lack of RPM reading from the gearbox.

Since you replaced the sensor and it then started and ran but later failed I think we've established that there is definitely a problem with the crank signal to the ECU, but also that the original sensor probably wasn't faulty since it went for a while but stopped again despite the new sensor, which most likely points to a wiring fault.

By fitting the new sensor you've probably disturbed the wiring enough that it was able to run, but the vibration of the running engine especially with a misfire probably disturbed it enough to lose the signal again.

As long as the wiring isn't too hard to get to it should be possible to narrow it down... my guess would be corrosion on the terminals of the connector at the sensor end, (is it somewhere where coolant can spill ?) an internally broken wire, or a wire that has rubbed through and is intermittently shorting to earth.

Continuity checks between the ECU plug (unplugged from the ECU of course) and the sensor connector and also checking for shorts to ground should reveal the problem.

Don't worry about the single cylinder misfire for the moment, its probably just a fouled plug due to all the attempts at starting it when spark wasn't working, or another possibility is that the misfire is in fact caused by the crank sensor wire intermittently shorting to earth as the engine vibrates slightly, causing a random missed spark.

[Chris570]

I would be inclined to look at which cylinder isn't firing and make sure that the non starting problem and one cylinder down problems aren't linked, would seem a co-incidence to have 2 seperate problems manifest themselves at the same time, considering it ran fine and on all 6 before.

Just my 2p's worth

[KP]

Have you been put off the other project you were thinking of taking on then David

[DHallworth]

Well I'm pleased to announce that the C5 is starting first time and firing on all 6 cylinders instantly now.

I got a paperclip and bridged the connections in the plug then took the plug off the edu and stuck two pins in it to get the multimeter probe onto it. There was no resistance showing on the cable. I rerouted the cable, and put the plug back in the ECU, grabbed the key, tried it and it started first time and fired on all 6 perfectly. It's been started and stopped several times and is still alive.

Guess the proper test will be wait 24 hours and try again as that's been it's usual trick so far!

Will, I'm not going to touch that Supercharged RR. After being out in dad's new 4.4 TDV8 I quite fancy one of them or a 5.0 rather then the 4.2. Be interesting to see what the new RRS is like too.

David.

[Citroenmad]

Progress! Maybe the C5 will be all the car you ever need and you can let someone else have the liability of a RR instead Though, I doubt that!

I'd keep your P38

[Mandrake]

Hi David,

Excellent that you've got it working again, at least we know its the crank sensor signal

The only thing is I doubt what you have done has fixed it permanently, you must still have a broken wire or a short somewhere that will come back to bite you at a later date...

It's not 100% clear to me how you tested with the multimeter from your description, are you saying that you unplugged the crank sensor, used a paper clip to short the two pins at the connector, then measured between the crank sensor signal pins at the engine ECU connector ? (with it unplugged from the ECU of course)

If so when you say "There was no resistance showing on the cable", do you mean it was short circuit or open circuit ? You might have your terminology mixed up as a short is what you should be reading, which is "no resistance". I'm guessing that you actually measured no change, eg open circuit.

If so there must still be a bad connection or a break in the wiring somewhere that rerouting the cable has temporarily bodged... can you try wiggling the loom about while its running or while your meter is connected as before ? If the meter has a continuity beep test mode you can hear a brief break in the tone as you wiggle the wires and they go open circuit.

I'd hate for it to stop working on you again 50 miles from home...

[DHallworth]

Simon,

It was a short I measured in the cable, as in 0.0 ohms resistance on the cable. That was with wiggling as well. There appeared to be no change in the reading with the cable being pulled, pushed, twisted and wiggled about.

The only thing I did do was use a pin to close the gap on the pins connecting to the ECU after I'd had a pin in them to attach the metre to. I guess it's possible that it was a bad connection at the ECU as Luke did say that the ECU was loose etc when he got the car.

If it breaks when away from home at least it then becomes the AA's problem and not mine! Failing that I'll wiggle the cable going to the crankshaft sensor

I've given it a wash today and gone round all the trim with a soft brush to get the green off the car, it's washed up quite well

David.

[Hell Razor5543]

If you are GOOD with a soldering iron, it could be worth having a look at the ECU connector. If it was loose, then the vibration could have damaged a solder join enough to cause the ECU to drop out of the loop.

[DHallworth]

The pins on the ecu itself looked ok, they connectors in the plug are a smaller version of a spade connector and I just wondered if one had been spread slightly to stop it making a reliable enough contact.

Anyway, I gave it a very quick wash tonight to get rid of the green stuff (managed to miss several bits!) and then ran it to the farm next door as I needed a word with him and took a couple of snaps of it on his yard.







The bumper and headlight washer need new clips and then realigning so I'll order them tomorrow then it's just tyres and a back box on the exhaust and she's ready for MOT!

David.