I’ve been chasing a misfire on my Range Rover when cold for a while now. It’s only noticeable when the car is cold and sitting idle. If you have any load on it at all it’s perfectly smooth. It’s also perfectly smooth once warm.

The above symptoms have also been confirmed by the IID tool monitoring real time misfires.

Plugs have all been replaced with genuine LR plugs, coils have all been replaced with genuine LR coils, MAF has been cleaned and the readings appear to be within spec. PCV Valve and hose to throttle body have both been replaced with genuine LR parts as well. The replacement PCV valve you can blow air through in both directions with no restrictions. I don’t have the old one any more to check it so am unsure if unrestricted flow in both directions is normal or not.

When smoke testing it I found a leak from an o-ring on the throttle body. I’ve replaced this and confirmed with another smoke test that this is now sealed.

When I had the car idling on the ramp the other night I could hear what sounded like an air leak. I can however confirm that it appears to just be air travelling through the PCV valve and pipe to the throttle body. To confirm this, I removed the pipe from the PCV Valve and stuck my finger over the end of it and as it sucked on my finger the hissing noise stopped.

Seeing as it sucked on my thumb with a decent amount of pressure I can rule out any leaks I think.

What really surprised me though is when my thumb was over the end of the PCV pipe, the misfire stopped and the car idled perfectly when it was cold. I got the IID tool out to confirm and the misfire counter was sitting at a stable 0 on all cylinders whilst my thumb was over the end of that pipe.

Removing my thumb and sticking it back on the PCV valve saw the return of the misfire and the misfire counter on diagnostics starting counting misfires again. Interestingly, the worst affected cylinder appears to be cylinder 1, the nearest to the PCV Valve.

The car has LPG on it as well as the flash lube valve saver fluid. I did wonder about damaged valve seats but am not sure that the symptoms would clear so perfectly when blanking off the PCV pipe if that was the case.

Has anyone got any suggestions? I’m wondering about blanking off the pipe from the PCV to the throttle body and fitting an oil catch can to cure it but would rather do it properly if I can.

Thanks,
David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

This is an interesting post, I think you should pop over to sister forum range rover sport lots of similar posts there. Iv just bought a 4.2 supercharged as possible replacement for the wife's D3 as the 4.2 is ulez

There is a vacuum pipe at the rear right of the supercharger that is just push fit that causes this issue and is also used as the vacuum take off for the leg.

I'm sure I'm suffering the exact same issue but yet to find the cause.....its very common with this engine.

I know the pipe you mean behind the Supercharger. It's a rigid plastic pipe that pushes into a plastic collet with an o-ring underneath it and goes back to the brake booster. I rigged up a home made smoke tester and found that o-ring to be leaking.

LR don't list the o-ring in any of the catalogues. I did some Googling and found this kit referenced for a Jaguar.



I ordered it from Duckworths and it was around a tenner (can't remember if that was +VAT or not). I removed the pipe, teased the plastic collet out with a pick and found the o-ring in that kit to be a lovely snug fit. That pipe is now nicely secured and no longer leaking.

When listening to mine carefully it does sound like the revs are kinda surging so it makes perfect sense it's an air leak, it's just a case of finding it.

As per Dave's suggestion, I've posted here in the hope that we can find a solution for everyone

https://www.rrsport.co.uk/forum/topic59658.html

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

I didn't know about that pipe connection, it's not the one I meant. Just check on rrs and the pipe I meant causing lean A and B codes.

I've got to smoke test mine at some point.

I’m not really sure how to interpret them but to me these long term fuel trims look pretty good considering it spends a fair amount of time on LPG too.

Here’s my long term fuel trims:

Click image to enlarge

Click image to enlarge

David

You say you can blow in both direction through the PCV valve, surely this valve is a one way valve only allowing gasses from the crankcase to the inlet manifold.

Or have I read you wrong?

David Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

I’ve Googled it several times and it seems that on a brand new valve you should be able to blow through it without restrictions in both directions as it’s spring loaded and closes at a certain amount of vacuum. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Ah ok, didn't know that.

Tricky to test as well.
Also the manual is not much help as that indicates a one way valve without going on to explain properly.

David Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

Done some more checking tonight.

The Air Flow Meter seems to follow the target. This was just after it had started to come off choke.

https://youtube.com/shorts/c7Gx0BC9128?feature=share

The oxygen sensor readings are dancing around too.

I’ve made a better smoke tester tonight too.

Sounds like a good plan and I do like the smoke tester might adopt that idea if you dont mind

I saw something similar in an American YouTube video where they were using flange connectors etc, but decided the drain pipe fittings might work well enough.

It cost me £14 from Screwfix in parts, the rest of the bits we had in the workshop.

1 of these:

https://www.screwfix.com/p/floplast-underg...tid=177036

1 of these:

https://www.screwfix.com/p/floplast-screwe...tid=177284

1 of these:

https://www.screwfix.com/p/floplast-push-f...tid=177593

I've sealed the bottom one to the collar when fitting it.

For the inside of it I ordered bits from Amazon.

https://www.amazon.co.uk/gp/product/B082K6...&psc=1

https://www.amazon.co.uk/gp/product/B07KCB...&psc=1

For Power and to keep it neat and fused:

https://www.amazon.co.uk/gp/product/B07R32...&psc=1

Hoping they'll arrive this afternoon  2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Smoke tester finished this evening. Resistance wire wrapped around the wick and then fitted into the pot.

Good work. Hopefully you’re now on the path to resolving the issue!

Excellent thread David.
I was checking mine 4.4 ajv8 for vaccum leaks but didn't find any. Car also has a missfire from cold.
When I tried to remove pcv hose from the intake yesterday, and pluged the hole with wine cork, car instantly started to work better without missfire. I am now starting to believe that something is wrong with my pcv valve. Can I drive it with unplugged pcv for some time, until I find a leak or replace pcv valve? I will install oil catch can to see, how many dirt it will catch
I can't believe that this can make a such difference on idle. RR HSE 4.4 2006 LPG

https://www.ebay.co.uk/itm/114361730585?mk...media=COPY