Weird missfire problem...Please help

Coming back from the lakes meet yesterday my car developed a very nasty misfire, so much so that I ended up having to call out the RAC to have a look. It’s a bit of a difficult, and weird, one to explain but bare with me, its quite an essay.

Basically had given the car a pretty good thrashing on the final bit of the drive (as everyone did) and the driving before that was hardly sedate all the time, but the car had run very well, no probs at all. Joined the motorway to come home and after about 5 miles, I noticed a very slight misfire when holding the throttle at a steady rev (just under 3k). Basically it seemed to happen when I had been holding the accelerator steady, and then lift off ever so slightly, then press again. Hope that makes sense. The car would very slightly “judder”. Didn’t think much of it at the time.

Within about another 5 miles this had become progressively worse. First the misfire was becoming “bigger” with a bigger gap in power cut, my AFR readings and graph on my SAFC II would plummet (showing Lean) each time. Eventually it got so bad that it was happening all the time and car was bucking around all over the show. At this point if I depressed the clutch or knocked the car into Neutral, the revs would drop and the car actually cut out/stall.

Pulled off at the next services and called the RAC.

While waiting for them I took the spark plug cover off and checked all the coil pack connections and they were fine. When trying to start up it took 2 attempts each time, the 1st time it would fail, the 2nd it would start but very roughly.

RAC turned up but couldn’t find anything when they looked at it, and by the time they turned up it was starting up a bit easier and running well when idling.

Arranged to follow him for a bit to see if the probs carried on and they did, so took him out for a spin and sods law, nothing happened. Followed him all the way down the A6 to Lancaster (a good 8 miles or so) with no probs so he let me go on my way. Carried on to Preston on the A6, with no probs at all. Tried the M6 again at Preston but within about 4 miles the prob was starting to come back exactly as it did when I first noticed the problem, so pulled off and went the rest of the way on the A roads, with guess what…no problems.

Ok gauge activity: Oil pressure, temp and water temp were fine. Car was boosting ok but I was very reluctant to really open it up “just in case”. My AFR’s when poodling along at 2.5k revs were between 14 and 15, and the one time I did open it up to check these, at WOT they dropped to 10. Seemed to pull well through the revs.

This has really got me, and the RAC man confused. Im thinking it’s an injector on the way out but im a Physio not a mechanic so any help you guys can offer me would be massively helpful.

Thankyou.

had similar problem with a skyline turned out to be faulty maf sensor cleaning them works for a while but only hides the problem for a short while it will come back again however this was on a modded r32 gtr

just like to add spoke to jon r32 gtr owner he said since getting new maf sensor its never done it again.

Will mine have a MAF sensor though being a single?

I would expect a faulty MAF sensor would give spurious AFR results. But, as it's a JDM car, it doesn't have a MAF sensor anyway.

I'd check the plugs before you get too worried. Maybe the hard run knocked them out and they just carried on deterorating as you drove home.

I would expect a faulty MAF sensor would give spurious AFR results. But, as it's a JDM car, it doesn't have a MAF sensor anyway.

 

I'd check the plugs before you get too worried. Maybe the hard run knocked them out and they just carried on deterorating as you drove home.

Right then, thats job 1 for this week. Again, with not being a mechanic though, what exactly should i look out for when i take them out. What would make me think one of them is out??

Cheers.

Measure the gap between the electrode and the, er, metal army bit (sorry forgot the term). Use a feeler gauge to see if they are all the same, and of course that they are all in 1 piece....

learn something new everyday the skyline was jdm it had 2 maf sensors

do uk spec supras have maf sensors ian ~??

Gareth get your Map sensor checked out, JDM dont have MAF, but they do have MAP (absolute pressure) sensor, which if faulty could result in the symptoms you have described.

BTW do you see any black smoke?

learn something new everyday the skyline was jdm it had 2 maf sensors

do uk spec supras have maf sensors ian ~??

UK and VVTI's have MAF based sensor, (air measure before the turbo in essence).

learn something new everyday the skyline was jdm it had 2 maf sensors

do uk spec supras have maf sensors ian ~??

Yes they do, so do VVTi's

do uk spec supras have maf sensors ian ~??

One

ah cool cheers for that, so try the plugs and map sensor

Duff MAP sensor would also result in poor/incorrect AFR readings. Going by Gareths first post, the AFR's seem correct.

Just buy a new set of NGK BKR7E. Should cost you less than £20, and then you'll pretty much know they're OK.

Cheers for the replies guys. So Matt, will those plugs you have mentioned be ok for my setup, are they Iridium??

Had a MAP sensor problem with my last Supra and got to admit that the symptoms were very different on that one. It didnt missfire at all, it just didnt boost on second turbo very well. Anyone care to point out which the MAP sensor is and whats the best way of testing it.

Sorry for being a noob when it comes to mechanics but, well i am a noob really.

The plugs are nice cheap basic ones. They'll be fine in your car. I've used them in mine several times.

The plugs are nice cheap basic ones. They'll be fine in your car. I've used them in mine several times.

Thought anything over BPU you needed the IK24's at around 70 quid a set or something like that??

I'm slightly more than BPU, and they work fine for me at around 500+bhp and quite a few others use them too... Trust me

I'm not keen on iridiums at all.

I'm slightly more than BPU, and they work fine for me at around 500+bhp and quite a few others use them too... Trust me

I'm not keen on iridiums at all.

Cool, cheers for that. I know your a tad more than BPU thats why i was asking. Im running 450 Bhp myself and just wanted to make sure they would be good enough. Shoudl save me a bit of money when it comes to servicing it,.

Ok, changed the plugs and it seemed to be running ok. Managed to quite lengthy motorway trips (1 to Leeds and back from Wigan) with no probs. Then this afternoon coming back from Widnes the missfire came back. What else could this be??

Few things: Firstly, i didnt gap the plugs, i just dropped them straight in but with the missfire being the same as before i changed them i dont think its because of the gap. Secondly when changing the plugs i noticed 2 of the coil packs were loose. Ie i could take the actual connector out of the coil pack. At first the car started with hurendous missfire even at idle, blatantly it was running one spark down because of the coil pack. Now with a bit of fiddling i got the connection fine and the car was running ok.

Could it be a problem with the coil pack connection because it does seem like an intermittant problem.

Get em changed, lad.

Get em changed, lad.

What? The Coil Packs? Youve changed yorus recently havent you?? How much was the set?

What? The Coil Packs? Youve changed yorus recently havent you?? How much was the set?

I have changed mine recently. Seems to pull more strongly although as they were done at the same time that I had a CW SMIC fitted I can't say how much better they've made the car.

As for price, well I had another of Lucifers 'offers you can't refuse'. I don't know if he'll do some at the same price but I'd give him a bell.

FWIW I doubt you'll need the wiring. My mechanic had a look and said that it was sound and by cutting into the wiring and soldering I might be opening myself up to future problems. I'd go for just the coil packs and the connectors for the top.

Mate, Replace al the coil pack connectors - even if they look good! Cost me £300 to find that out! lol

I had intermittent misfiring. It did used to come up with Code 14 error though - Igniter feedback signal problem.

I have changed mine recently. Seems to pull more strongly although as they were done at the same time that I had a CW SMIC fitted I can't say how much better they've made the car.

 

As for price, well I had another of Lucifers 'offers you can't refuse'. I don't know if he'll do some at the same price but I'd give him a bell.

 

FWIW I doubt you'll need the wiring. My mechanic had a look and said that it was sound and by cutting into the wiring and soldering I might be opening myself up to future problems. I'd go for just the coil packs and the connectors for the top.

Cheers Martin, So you think it could be the loose coil pack giving the missfire.