Tricky-Ricky Posted December 29, 2007 Share Posted December 29, 2007 Just looking for the possible causes of a slight misfire i have, mainly noticeable when holding the RPM at anything from idle to 2.000 RPM when stationary, haven't noticed it under load, but thats not to say its not happening. It could either be fuel, coil pack/plug related, or plug, but could also be EMU related but i doubt it as i haven't changed anything just lately, So how many people who have had a misfire, have effected a cure and how? Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted December 29, 2007 Share Posted December 29, 2007 Mine does it, and I've seen lots that do it. Only really noticable at idle, or if held at a fast idle. Doesn't cause any problems under boost, not even at 1.8 bar! (With racefuel) I've tried changing the plugs, coils, cleaned up all the connectors, tried different ignitor packs, different ECU... I've been told that its down to running colder plugs, but to be honest, I'm not sure thats true. I've given up looking now, but now I'm subscribed to this thread, I'll keep an eye open just in case. Quote Link to comment Share on other sites More sharing options...
jevansio Posted December 29, 2007 Share Posted December 29, 2007 You're prolly looking for "out there" examples now after trying the basics. I had one, would always miss at 1500 rpm, tried everything, turned out to be crank position sensor!!! This was my thread. Quote Link to comment Share on other sites More sharing options...
bondango Posted December 29, 2007 Share Posted December 29, 2007 Have also seen many Engines do this at Idle and fast revs with no ill effects at WOT or under boost. seemed to be prominent with hot engines causing it, so dunno if it something as simple as fuel evap? or component breakdown under heat Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 29, 2007 Author Share Posted December 29, 2007 Interesting replies, I'm kind of glad I'm not alone, jevansio your quest turned up a CPS problem, but surly with a std ECU it would trow up a code? I am actually starting to wonder if it may be down to running bigger injectors, and the duty cycle being so low in that area, that it is causing lousy atomisation, coupled with colder plugs, mine is nowhere near as pronounced when cold rich mix, and manifests more as it warms up. Quote Link to comment Share on other sites More sharing options...
Robert Posted December 29, 2007 Share Posted December 29, 2007 I have this problem aswell, mine might be the coil packs but once they have been changed we will see. Quote Link to comment Share on other sites More sharing options...
gaz1 Posted December 29, 2007 Share Posted December 29, 2007 i have always had this problem from when i went hybrids and then single, i changed all the coil packs but to no avail, new engine and turbo system, new mapper, will see if that sorts it Quote Link to comment Share on other sites More sharing options...
jevansio Posted December 29, 2007 Share Posted December 29, 2007 Interesting replies, I'm kind of glad I'm not alone, jevansio your quest turned up a CPS problem, but surly with a std ECU it would trow up a code? I am actually starting to wonder if it may be down to running bigger injectors, and the duty cycle being so low in that area, that it is causing lousy atomisation, coupled with colder plugs, mine is nowhere near as pronounced when cold rich mix, and manifests more as it warms up. I was running an AEM at the time Rick, It was a very funny problem, was fine when the car was cold, when it warmed up it showed up. We reckoned the CPS was breaking down as it heated up (like bondango mentioned). I'm also running 880cc injectors & plugs 2 grades colder, the miss is totally gone now. HTH Quote Link to comment Share on other sites More sharing options...
Mike B Posted December 29, 2007 Share Posted December 29, 2007 I always thought that the larger injectors were hard to control at idle, due to the imprecision that you get opening and closing. Smaller injectors give a much more accurate smaller dose of fuel; large injectors, when run on very small duty cycles, are inaccurate, hence the odd misfire...? Quote Link to comment Share on other sites More sharing options...
absz Posted December 29, 2007 Share Posted December 29, 2007 If its happening only at certain rpms, then also check your throttle postion sensor. i have come across this on a few different model cars. but the sensor works in the same way as most cars. has a carbon tracking that tends to wear out, but will not put a fault light up as its still within the spec. easy to check using volt meter. PS just my 2p worth:) Quote Link to comment Share on other sites More sharing options...
Robert Posted December 29, 2007 Share Posted December 29, 2007 My misfire started after i had my AEM and DLI fitted, so im thinking the DLI is putting my already tired coil packs under abit too much pressure. I have swapped my TPS and still no change. Quote Link to comment Share on other sites More sharing options...
absz Posted December 29, 2007 Share Posted December 29, 2007 My misfire started after i had my AEM and DLI fitted, so im thinking the DLI is putting my already tired coil packs under abit too much pressure. I have swapped my TPS and still no change. coil packs tend to fail on load (boost) BUT the only way to check them correctly is with a scope as that will show up a weak coil pack as a wave form pattern, even at idle. Quote Link to comment Share on other sites More sharing options...
Robert Posted December 30, 2007 Share Posted December 30, 2007 you have the equipment to test them dont you abs? Quote Link to comment Share on other sites More sharing options...
absz Posted December 30, 2007 Share Posted December 30, 2007 you have the equipment to test them dont you abs? yep i can check them for you if you cover the postage. Quote Link to comment Share on other sites More sharing options...
Robert Posted December 30, 2007 Share Posted December 30, 2007 yeah that would be good, PM me your addy. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted December 30, 2007 Share Posted December 30, 2007 I've seen the misfire on cars with stock injectors, so that rules that out too... In fact, I first noticed mine doing it when I was still on the stock twins with stock 440's. Quote Link to comment Share on other sites More sharing options...
Mike M Posted December 30, 2007 Share Posted December 30, 2007 I've seen the misfire on cars with stock injectors, so that rules that out too... In fact, I first noticed mine doing it when I was still on the stock twins with stock 440's. Yep, my 93 TT will agree with you on that, I also have new coil packs and clips. What I can say is that the Iridiums made the idle and just above idle seem terrible compared to running NGKs or platinums. Wouldn't a slight air leak in the manifold cause this or a dodgy injector spray pattern? I know if mine has been sitting for two weeks it fires up on a few cylinders first before the rest follow leading me to think I have clogged injectors. And I now know compressions good on all six pots. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted December 30, 2007 Share Posted December 30, 2007 I'd guess a less-than-perfect injector could cause issues, but again, in my case, I changed injectors and the problem remained the same. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 30, 2007 Author Share Posted December 30, 2007 I am running NGK copper, and the injectors have been in a couple of months, and where flow checked before so it not that on mine, famous last words;) Quote Link to comment Share on other sites More sharing options...
dandan Posted December 30, 2007 Share Posted December 30, 2007 I've seen this on a decatted (but otherwise stock) vvti car so definitely not an injector size issue, DLI, AEM, etc etc etc...in that case it was only once the engine warmed up and at idle......(the vvti has different coilpacks and different TPS setup to earlier cars so there's an argument to say it's not those). Maybe crank position sensor? Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted December 30, 2007 Share Posted December 30, 2007 Maybe crank position sensor? I'd be suprised if it is, but that IS something I haven't changed. There does seem to be a theme here though. It only happens once the car has warmed up. Mine certainly doesn't do it during coldstart cycle. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 30, 2007 Author Share Posted December 30, 2007 I'd be suprised if it is, but that IS something I haven't changed. There does seem to be a theme here though. It only happens once the car has warmed up. Mine certainly doesn't do it during coldstart cycle. Yes i agree its obviously AFR related mine will not do it until the AFRs get up to around 13.5. Quote Link to comment Share on other sites More sharing options...
dandan Posted December 31, 2007 Share Posted December 31, 2007 I cannot comment on AFR's - only temperature (warmed up would highlight the problem but it certainly wouldn't have to be stinking hot or anything like that). Can anyone (TR if you're keen) wind your AFR's at idle down more towards the 12:1 kind of range and see what happens? Are we talking about a small blip in idle every 3 or 4 seconds or so? (A very slight and quick tiny misfire)... Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted December 31, 2007 Share Posted December 31, 2007 Are we talking about a small blip in idle every 3 or 4 seconds or so? (A very slight and quick tiny misfire)... Yep, that's the one. Almost as if it were only one cylinder at random intervals Can anyone (TR if you're keen) wind your AFR's at idle down more towards the 12:1 kind of range and see what happens? I'll give it a whirl, if I can wind the fuelling up enough to keep the stock ECU out of closed loop.... The disadvantage of piggybacks. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted December 31, 2007 Author Share Posted December 31, 2007 Originally Posted by dandan Are we talking about a small blip in idle every 3 or 4 seconds or so? (A very slight and quick tiny misfire)... Definitely not in my case, AFAIK that is just the ECU adjusting fuelling as the lambda voltage switches. Quote Link to comment Share on other sites More sharing options...
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