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Author Topic: mv6 misfiring  (Read 2484 times)

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Mole

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mv6 misfiring
« on: 13 March 2007, 06:57:37 »
Yesterday my car started doing a funny thing. The engine would not rev past 4500. It was like the rev limiter was cutting in. It had been quite wet when it happened in the morning. Last night on the way home it got worse to the point of not getting much past 2500 revs. It wasn't wet then. The only thing I can see is a small amount of coolant dripping from the rear of the exhaust manifold on the left(n/s) cyl head. I think the coolant loss is head gasket related but is this what is causing the engine to run this badly? If I'm really gentle with the throttle I can get the revs up further  but if I press the pedal then it coughs and splutters and the EM light comes on briefly. Could this be fuel pump/pressure related?
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Admin

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Re: mv6 misfiring
« Reply #1 on: 13 March 2007, 07:46:19 »
Well you know we are going to say check the fault codes... ;)

It is going to be a sensor issue, question is, which one...

Oh and are you sure it is coolant and not condesation from the air con?
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TheBoy

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Re: mv6 misfiring
« Reply #2 on: 13 March 2007, 18:04:07 »
Read the codes, though it may only be a sympton of another problem.

DIS isn't wet is it? Oil in plug wells?
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Mole

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Re: mv6 misfiring
« Reply #3 on: 14 March 2007, 20:28:59 »
Read the codes today and they are 74 and 19.
Definitely coolant dripping from rear of n/s head. Much lower than the DIS.
When I bought the car I was told the aircon had been disconnected(with a hacksaw)and the HBV was leaking which I replaced it with a new one.
No oil in plug wells.
I didn't use the car at all today or yesterday and it has been dry here but the car is still unwell.
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TheBoy

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Re: mv6 misfiring
« Reply #4 on: 14 March 2007, 20:36:36 »
Quote
Read the codes today and they are 74 and 19.
Definitely coolant dripping from rear of n/s head. Much lower than the DIS.
When I bought the car I was told the aircon had been disconnected(with a hacksaw)and the HBV was leaking which I replaced it with a new one.
No oil in plug wells.
I didn't use the car at all today or yesterday and it has been dry here but the car is still unwell.

I'd have to double check 2.0l codes, but for v6, 19 = dead cert knackered crank sensor, 74 = MAF
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Re: mv6 misfiring
« Reply #5 on: 14 March 2007, 20:43:21 »
Yes dead right on both.  ;)

73/74 is a common weird additional code when crank sensor is on its way out.

Get one VERY swiftly!
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Marks DTM Calib

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Re: mv6 misfiring
« Reply #6 on: 15 March 2007, 07:53:18 »
And the water leak will be coming from the valley....either the coolant plate for the heat exchanger or the stat to block seal....
« Last Edit: 15 March 2007, 07:54:08 by Mark »
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Mole

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Re: mv6 misfiring
« Reply #7 on: 19 March 2007, 23:19:40 »
I did some further investigation tonight and I got mixed results.
First I disconnected the battery for 15 mins or so then read the codes again. Oddly with nothing having been done to the car including being driven there were 2 new codes. Along with 74 and 19 I also now have 38 and 98
It was indeed the stat to block seal that had let go(cheers Mark). Luckily I have a large bag of rubber seals as the stat and adjoining pipe seals don't come with the head gasket set I bought.
When I had reassembled the engine and started it the rev counter and speedo started working again but the misfire was still there. When I say misfire what actually happens is the rev limiter cuts in at 3500. Is this limp home mode? It absolutely will not go past 3500 revs now. Below that it revs and idles fine.
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Mole

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Re: mv6 misfiring
« Reply #8 on: 19 March 2007, 23:25:30 »
Oh and the "superchip" I ordered from Germany arrived today and I can't try it.
Bugger!!
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sounds2k

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Re: mv6 misfiring
« Reply #9 on: 19 March 2007, 23:35:06 »
well the fault codes you describe can be looked up here, the first two I had when my crank sensor wiring was dodgy - code 19 is crank sensor incorrect signal - but for some reason it also seems to generate the code 74 too (air flow sensor high voltage) ... go figure. Sensor changed, the garage cleared the codes and neither have returned ...

the last two codes seem to relate to the oxygen (lambda) sensor .... hmmm ... haven't been down south and filled up at tesco's or morisson's lately have ya?  ;)

I wouldn't have thought they would cause the RPM to be limited though ... over to the experts  ;)
« Last Edit: 19 March 2007, 23:37:09 by sounds2k »
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Mole

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Re: mv6 misfiring
« Reply #10 on: 19 March 2007, 23:38:21 »
Filled up at tesco last week but I thought the dodgy petrol was only way down south.
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Re: mv6 misfiring
« Reply #11 on: 20 March 2007, 08:27:58 »
Change crank sensor... I suspect all will be good when that is done.

Bought an Omega a while back, drove ok, until you hit 3,500rpm then it would not go any further, almost as if you hit the rev limiter.

Seller had been told gearbox was shot and would cost £800-£1,000 to fix.

1 crank sensor later and all was beautiful once more (especially the profit myself and Mark made on it!). :)
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Mole

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Re: mv6 misfiring
« Reply #12 on: 25 March 2007, 20:47:52 »
Crank sensor changed and all is well with the engine. Yay!
The clocks on the other hand have stopped working again. Back to the vibrating rev counter needle and no speedo. Very hard to determine how fast I'm going as I pass speed cameras.
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