Pinking... but high CO at MOT?!?

Hi guys, I'm at a loss!

Put the range rover in for its MOT last week. Pretty certain it was going to fail but it had to be done!

Well it thankfully only failed on balljoints passenger side and high CO (0.49 first run fast idle and 0.35 second run fast idle) on its Emission test.

Its a 95 4.0, no LPG just good old petrol around 75K

Only outstanding issues are it taking ages to start from cold or if left for a while when warm like its losing its fuel pressure and has to pull it back up from the tank and this past wee while it been pinking when you plant your foot.

Pinking wise, had a look in the bay and noticed the drivers side knock sensor was looking a little melted so assumed it was that. It had to go in for its MOT before I could change it but got it swapped out today and its still pinking!

Now I've always assumed pinking was being caused by a lean mixture or ignition timing but from the MOT fail it looks to be running rich???

The long cranking time I have yet to get to the bottom off. when cold or been left standing more then an hour if you depress the valve on the injector rail it just hisses a small amount of air??? Fuel pressure reg maybe?


Been trying to get hold of a pal who has an MSV faultmate to scan it but in the meantime I borrowed a mates OBD11 scanner on the off chance it would shed some light, it connected ok but no fault codes are showing but as mine is OBD and his is listed as 96 vehicles onwards I'm not sure how well this can be trusted.

I'm not bad with the spanners so where should I be looking first? Had a read through RAVE and think it could be a camshaft postion sensor as what I understand from reading is that it sorts ignition timing and knock control and the car will still run even if its failed? Am I right or am I barking up the wrong tree entirely?

Could one of the Lambda probes been playing up? If so, can I test this on the drive with a basic multimeter and how or will I need something more specialised?

Any help would be muchly appreciated!

A few years ago my P38 was pinking under load and was also down on power. The power issue made me investigate the MAF sensor which I replaced and both things were sorted straight away, never pinked again.

Should add that was on a Thor engine and not a Gems.

Pinking is cause by the fuel mixture being ignited by heat/pressure before the plug fires. Usually down to poor fuel quality. Can be caused by bad plugs or glowing deposites in the combustion chamber though.

Well it does pink less with petrol from the JET petrol station and more so with ASDA fuel.

The pinking started when the water pump seal failed. Managed to catch it before it cooked as I was sitting on the drive if that can help shed some light on anything. I do wonder if all that boiling water might have damaged the cam sensor in some way.

I was always told a leaner mixture would pink for that same reason as you describe Wammers, resistance to heat but that was along time ago in college! Any thoughts on a culprit? Or am I going to have to get it scanned to lend any clues?

As for the MAF, I'll give it a clean and see if that helps any and report back.

If anyone else has any ideas please throw me some info, I've got till monday next week and I'll be bald at this rate!

Frostycab said:

Well it does pink less with petrol from the JET petrol station and more so with ASDA fuel.

The pinking started when the water pump seal failed. Managed to catch it before it cooked as I was sitting on the drive if that can help shed some light on anything. I do wonder if all that boiling water might have damaged the cam sensor in some way.

I was always told a leaner mixture would pink for that same reason as you describe Wammers, resistance to heat but that was along time ago in college! Any thoughts on a culprit? Or am I going to have to get it scanned to lend any clues?

As for the MAF, I'll give it a clean and see if that helps any and report back.

If anyone else has any ideas please throw me some info, I've got till monday next week and I'll be bald at this rate!

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You may have a plug with a sharp edge on it that is glowing that can cause it. Or glowing carbon build up. If yours has a HC engine it will require higher octane fuel. The higher the octane rating the less likely the fuel is to pre ignite. Eg LPG is very high octane and connot be compression ignited.

Frostycab said:

Well it does pink less with petrol from the JET petrol station and more so with ASDA fuel.

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Supermarket fuel is lower quality than oil company stations'.

HC? I never knew landrover fitted any of the range rovers with HC versions of the V8... guess everydays a school day!

theres allways been a choice of both

Need to retard the ignition timing somehow, maybe the crank sensor has been disturbed.
Not well up on these modern petrol engines but LPG needs more advance as it burns slower, Petrol less advance than LPG but if pinking then too much advance.

landowner said:

Need to retard the ignition timing somehow, maybe the crank sensor has been disturbed.
Not well up on these modern petrol engines but LPG needs more advance as it burns slower, Petrol less advance than LPG but if pinking then too much advance.

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My thoughts exactly. Unfortunately I'm more used to a good old distributor and a timing light!

Can anyone explain how the gems engine retards and advances the ignition? Crank or cam sensor? From my understanding its the cam sensor

As for LPG, I don't have it fitted and don't intend to. As I see it I bought a v8 expecting v8 economy!

Not an expert on these but most engines if your cam position sensor (phase sensor) fails they will continue to run, but they won't restart. If its got one it means it's sequential injection so it needs to know the phasing of the cam to the crank to know when to inject. If it doesn't know it it won't inject! I've never come across an adjustable one.
Pinking (aka pre ignition, detonation or knocking) can be caused by:- crap fuel/wrong octane, incorrect timing, hot spots in the cylinder, too high a compression ratio, lean fuelling, etc.. A modern engine will run as close to detonation as it can cos that's more efficient (generally) it adjusts the timing until it senses knock then backs it off (hence the knock sensor) and it just keeps on doing that to be as efficient as it can. Problem being it can only go so far and it can't adjust out problems! It's very rare for a knock sensor to fail. If you change one you have to torque it correctly cos you will damage it! They have a piezo crystal inside that generates a voltage when you get a knock, too tight and it won't work properly or you crush the crystal if it can't adjust for the knock it's more likely to be fuelling than anything else on your type of engine, the main sensor for that is the MAF (mass air flow) sensor. Presume it's a hot wire one. Cleaning may work if you're lucky, the wire filaments degrade over time and they start to read out of spec, but the ECU assumes its correct and adjusts to suit because it hasn't failed! So no fault code!!! Some manufacturers now change them at a set service interval cos they wear out. I'm ex Mercedes, they recommend changing at 60k on some models now cos they start causing probs not long after that. It doesn't matter who makes it they all work the same! If you know anyone with one the same pinch theirs to try. This can make them lean. Knock will be worst going up a hill in a high gear at low revs, yes cheap fuel will make it worse but I doubt it's actually the cause. They're not exactly highly tuned at the best of times, plus it would've always done it and all v8s would be at the super unleaded pump! Most owners are far too tight
Too add to your stress detonation can damage your engine. Normally the spark sets fire to the fuel and you get a controlled flame that travels across the cylinder (very quickly). When they detonate it just explodes with one big bang! Causing extra stress and heat that can burn holes in pistons and liners worst case! So be careful with it, don't thrash it and fix it ASAP or it could get really expensive. W

Search u tube for testing lambda sensors there's a very good video that walks you thru it

Thank diesel do, just the kind of reply I was hoping for.

Think it'll be eBay for a Maf then, I'll try cleaning this one as I've nothing to lose if it doesn't work and best case I'll have a spare.

I'll report back what happens.

Ok, Maf cleaned out with good old brake cleaner and dried. checked the rest of the inlet while I was in there and its spotlessly clean.

Possibly the placebo effect but it feels a little smoother to be honest, not so sluggish when cold but still pinking like mad when you put your foot down any more then a 1/4 throttle. Think I will order a MAF to be safe as I've said it'll alway be a handy spare.

Any other ideas I can try guys? Still can't get hold of my pal with the MSV faultmate so sadly still no idea if there are any fault codes up, it like working blind!

Just make sure it's not some dick selling a million mile knackered one! And avoid cheap no name brands cos they tend to be ****! I won't fit cheapies any more cos they Change the fault, so you think that ones fixed and there must be another but after hours of head scratching its a duff sensor, and you are seriously ****ed off!
Cars who'd have em

Other thing I forgot to mention is an air leak between the MAF and the engine gives the same symptoms as a worn out MAF.

Thanks, bought one from a breaker on ebay with a warranty/proven good etc etc as the price for genuine Sagem/Lucas new ones is frankly shocking! LR direct price is over a grand from landrover!

so we'll see whats what when it turns up. Also bought a fuel pressure reg along with a service kit as its due soon and I may as well do that as well while i'm at it.

F*****g how much!

Air Flow Meter - Land Rover Part ERR5595

hold on to your lunch!

Well, the secondhand MAF arrived and its already fitted but not a squat of difference to the pinking

Would I be right in guessing I'll need to get the adaptive values reset with a change of MAF or should I see the results straight away?