Some very strange happenings re:my misfire

[JimmySpeed]

Following on from my previous thread regarding my misfire and low compression (http://xdrivers.co.uk/forum/https://xdr ... ic.php?t=5), there have been some developments.

To begin, I had an intermittent misfire - here for a few days, gone for a week, then back again. I tried to fix it by changing plugs and coils but it then got worse!

Faults logged was misfire on cyl 3, even after swapping coils and with new plugs and then new coils, still misfire on cyl 3. This pointed to something more serious in the cylinder. I reset the codes using INPA and the EML will go out for a few days and then return at some point.

A compression test was done at one garage and was found to be slightly lower in cyl 3, so I suspected a valve problem. I didn't want that garage doing any more work (long story) so I took it home an waited for my preferred mechanic to get it in.

He did some diagnostics yesterday, he said that the misfire is definitely intermittent - he did a compression test at one point and there was no loss in compression. He then let it idle for a bit and waited until he heard the misfire (the exhaust on that side 'pops' when it does it) and retested and found slightly lower compression in cyl 3. He did do a leakdown test and found loss on the exhaust side.

He thinks this points to a sticky lifter, due to the intermittent nature of it. He says that if I had a bad valve then the misfire would never go away but in my car, it does go away for upto a week.

With nothing to lose, I put some Wynns lifter treatment in the oil today, really just to see if it made a difference. I also followed the TIS procedure for bleeding HVA lifters which is suggested when a customer complains of an intermittent misfire and/or ticking noise from the engine (I have a little ticking too).

The misfire is now gone again (for now), but now I am getting a new fault:

115 hot film air mass meter

and sometimes the car cuts out as soon as I start the engine. If I restart it it goes into engine failsafe mode and I have to use INPA to clear the fault code and reset adaptations. The next start will work fine but after shutting off it will sometimes repeat this cycle.

If I unplug the MAF completely it just cuts out immediately after starting every single time - nothing done on INPA will get it to start while the MAF is unplugged.

Its all a bit crazy TBF  :blink: What is going on?

[Rusty]

If it were my car, I would now do a full oil change.

Any additives to 'clean' things may do as advertised, but can lead to other problems as the change in viscosity and the addition of gunge busting chemicals may affect oil function.
Nothing will kill an engine faster than poor oil.

Jmho


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[JimmySpeed]

[quote="Rusty"]
If it were my car, I would now do a full oil change.

Any additives to 'clean' things may do as advertised, but can lead to other problems as the change in viscosity and the addition of gunge busting chemicals may affect oil function.
Nothing will kill an engine faster than poor oil.

Jmho


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[/quote]

Thats a good point, and I'm with you - it was already booked in on Monday to have 'the problem' looking at by a second garage and to also get a general going over including valve gaskets, oil and filter, coolant flush etc.

[Rusty]

Go careful with coolant flushes too, additives have been known to uncover a multitude of 'pinhole' leaks and before you know it you have a mobile watering can rose

Just a plain water flush should be ok unless you know of any build up of sludge/rust

Hope you ave cured the misfire, lifters can become easily blocked and lazy.

Let us know how things go next week


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[JimmySpeed]

Cheers for the advice. When I said flush I just meant change - I'm having a coolant change - I don't need to flush it for any particular reason.

Watch this space...

[shadrack]

i had a misfire on a car and it was the wiring to an injector, i had no loss of compression and also changed plugs coils etc

[Y13HYA]

I have previously had the same issue. I noticed this only happens when i start the engine and try to set off straight away it goes into fail safe mode. I thought this had something to dow ith the LPG ECU. Not sure though. Car runs fine most of the time. I have also since cleaned the MAF as i had the same Fault code. (i occasionally get the misfire too) but only on GAS, and i know that my mixture is very slight lean....

[JimmySpeed]

Mine happens on lpg and our petrol equally so that rules out injectors pump bad fuel etc as both systems are totally independent.

It has all but gone since using the wynns. It's only there on idle and less so when warm. Before the wynns it was a raging misfire at all speeds when it did it.

I changed the maf today, certainly feels more pokey than before. I would expect that from a new maf after a 11yr old one comes off! Occasional lumpy idle still there though.

It's at a garage now for a good looking over. Still getting engine failsafe on startup and have to reset with inpa to clear it.

[Geezer]

Have you checked you have the correct battery and the terminals are connected properly? I was speaking to a friend at the weekend who had as 3 series convertible with unusual electric problems. He spent £500 getting it checked out including a full diagnostic from a main dealer and they couldn't work out what it was.

In the end he changed the battery on a hunch and it fixed the problem. It turned out the previous owner had installed the wrong battery

[JimmySpeed]

Interesting. I'll check that

[Y13HYA]

[quote="mobilejo"]
Mine happens on lpg and our petrol equally so that rules out injectors pump bad fuel etc as both systems are totally independent.

It has all but gone since using the wynns. It's only there on idle and less so when warm. Before the wynns it was a raging misfire at all speeds when it did it.

I changed the maf today, certainly feels more pokey than before. I would expect that from a new maf after a 11yr old one comes off! Occasional lumpy idle still there though.

It's at a garage now for a good looking over. Still getting engine failsafe on startup and have to reset with inpa to clear it.
[/quote]

Let us know how you get on.....might be some tips in there for me too.
PS whats the mileage on your caR?

[JimmySpeed]

Will do.

Mine is on 106k

[Horizon]

Whilst you are having a garage look over your 4.6, they have a history with the hydraulic cam chain tensioners, I believe they can fail and write the engine off.
I think they just affect the 4.6, may be wrong

[JimmySpeed]

[quote="Horizon"]
Whilst you are having a garage look over your 4.6, they have a history with the hydraulic cam chain tensioners, I believe they can fail and write the engine off.
I think they just affect the 4.6, may be wrong
[/quote]

Yes the mechanic mentioned that these are worth checking. Whilst the rocker cover is off for the gasket replacement he said they would check this.

Thanks for the tip.

[JimmySpeed]

Well the saga continues - the car is back from the garage and so is the misfire. What I discovered is that it never went away - when I cleared the fault codes I reset the adaptations, after resetting the adaptations the car idled higher - at about 1k revs - this masked the misfire completely as its only there at idle and normal idle is 550rpm or 750ish with a/c on.

In the garage, they updated the DME software as mine was out of date and all of my messing with adaprations had the car forgetting how to idle properly, and of course the car now idles properly and the misfire is present.

So it looks like it certainly will be a head off job.

At least it should be a good runner after that - it has new plugs, some new coils, new MAF, new TPS (well from a breakers at least), up to date DME software, new cam cover gaskets (before we realised we'd be going back in there to do the head work), oil and filter change, gear box oil and filter change.

Booked in for Monday after next but at least its drive-able until then, the idle misfire is annoying but not hindering.