Missfire/Spitting

[Polabear]

This question is aimed at the manual vr4 owners mainly but anyone knowlegable enough please feel free to throw in.... OK I have been experiencing what can only be described as a misfire/spit/or blowback through the exhaust, but only when I turn my boost controller on, this is definately NOT an overboost as this happens anywhere from 2.5-5000 rpm and at the higher rev range it logs well below my safe overboost limit on my boost controller ..0.79...0.93 bar my safe limit is set to 1bar with a 5% knockback.

I knew I had a plug off so all plugs have been replaced, during this fault finding process, the fuel regulater hose has been removed to ensure I am getting max fuel..(query fuel pump) air filters have been removed car tried and replaced .....and even the maf has been replaced, but it still persists. fault codes have been checked...this returned absolutely nothing (good to see in one way) this is doing a lot of combined heads in....as it ONLY happens when the boost controller is turned on, the boost controller is a Blitz dual sbc running with ratios of 44,47,50,53 and a gain of 16 for what it worth...any ideas people... :sad3:

[enigma]

It sounds to me like fuel cut, as stated about a zillion times before its not necessarily boost related. Under hard load the turbos are dragging huge amounts of air through the MAF and this is likely to initiate fuel cut which will be a violent misfire a bit like you are describing. With the colder weather upon us you will be getting more mass of air through as it is colder and therefore denser, probably why it is starting to manifest itself only now. Knock the boost back a fraction, you will stop the problem and not lose any power (colder air, more fuel, same power!)

[zentac]

easy way to test it, turn the boost controller off and see if it still happens. I should not happen under standard boost. If it cures it then its fuel cut

[Legnum Boy]

All this talk about fuel cut has got me thinking.

Im guessing that the standard fuel cut level is set reasonably safely and hitting it occasionally will not have much detrimental effect to the workings of the engine.
We know that, in standard form, the turbos are set to deliver less than 50% of what they are actually capable of , so by that example, fuel cut should be set with a good safety margin in mind.
I for one, will not be investing in an FCD, as I just know that something would give out, judging on my previous history. :rolleyes:

As for hitting fuel cut, of course it varies due to ambient air temp, but I would guess that its nearly always above 1.2 Bar and has sometimes been as high as 1.5 Bar although, I do sometimes wonder at the accuracy of the AVC-R pressure sensor.
Im off to by an expensive analogue pressure gauge..... just in case.. :$

[zentac]

Ive hit fuel cut at very low bar before, by pulling away from say 30mph in 5th gear you can hit fuel cut before the boost builds up.

[enigma]

Yep, I have hit fuel cut at 0.7bar before in 4th at about 3000rpm :lipsrseal

[Legnum Boy]

Thats never happened to me. All my incidents have involved mid to high revs and lots of indicated boost pressure. :(

A common fuel cut moment for me is - motorway speed, in 5th, in tip mode, foot off gas - foot back on gas..... BINGO!

Works 2 out of 3 times.... :-D

Still gotta fine tune that A'PEXi, I guess... :$

[Polabear]

Thank you all for the benefit of your info... ;) and yes Richard the low speed low revs then floor peddle thing does result in coughing/spitting.... :sad3: but riddle me this, Spirit is running higher boost ratios than mine on his car and has NEVER experienced this problem..... :| so here is another question, do the turbos spin up any faster, therefore producing more air faster in a manual car than in an auto....? :dozey:

[enigma]

Every car is different Sean! Just because the settings are the same doesn't mean you will get the same characteristics!

Also I guess there is a difference in the characteristics of a manual vs an auto. In a manual you are off the gas to change gears, the revs drop, the turbos spool down, you dump, then you gas it and suck huge gobs of air through! In a auto we just press the pedal!

Get Pete to try nailing his car from 2000rpm in 4th at about 30mph........I can almost hear it cutting now!!!! ;)

[Spirit]

Get Pete to try nailing his car from 2000rpm in 4th at about 30mph........I can almost hear it cutting now!!!! ;)

Must admit thats something I never do I guess, usually I potter along in normal mode and then hoof it in kickdown and she usually drops to 2nd or 3rd gear and have yet to experience the effect Sean is getting.

[nick-f1]

A common fuel cut moment for me is - motorway speed, in 5th, in tip mode, foot off gas - foot back on gas..... BINGO!



I have had this happen a couple of times myself, mine is standard (at the mo) and manual. Should this happen in a standard boost car? Sorry this is no help to you Sean :sad3:

Nick

[Polabear]

According to Zentac this should not happen while running standard boost Nick, but then I seem to recall you saying a while ago that you found you had an FDC fitted to your car that you didn't know you had...?

[Legnum Boy]

.... and before I installed the AVC-R, I was just using the pressure sensor as a boost gauge. I constantly recorded boost spikes of well over 1 bar, on the standard mitsu solenoid. Funny though, now the AVC-R solenoid is in place, with the apexi turned off, my boost levels are slightly lower than before, and the spikes are all but gone.

Maybe the mitsu solenoid gets a bit lazy in its old age... :laugh:

[nick-f1]

According to Zentac this should not happen while running standard boost Nick, but then I seem to recall you saying a while ago that you found you had an FDC fitted to your car that you didn't know you had...?

Yes i do have an FCD wired into the ecu but is not powered up. +ve feed disconnected. And having rummaged under the bonnet a lot since coming back from the 'Pod, have found conections where a boost gauge was fitted and the visible tee-piece by the maf the pipe going to the wastegates was split! I've Since repaired it and obviously a controller was fitted by the previous owner whom I foud out the other day at Poole Mitsy now runs an Evo....... takes all sorts I suppose :lipsrseal

[Polabear]

Yes i do have an FCD wired into the ecu but is not powered up. +ve feed disconnected. And having rummaged under the bonnet a lot since coming back from the 'Pod, have found conections where a boost gauge was fitted and the visible tee-piece by the maf the pipe going to the wastegates was split! I've Since repaired it and obviously a controller was fitted by the previous owner whom I foud out the other day at Poole Mitsy now runs an Evo....... takes all sorts I suppose :lipsrseal

It would appear that some of the previous owners of our cars were not as interested in doing things as correctly as we would ourselves........ :lipsrseal :rolleyes5

[enigma]

It is possible to get fuel cut on a standard car given the right conditions. For example, cold weather and high load at low revs in a high gear. Solution ...........change gear (and I don't mean your trousers :rolleyes5 )

[jerryd_33]

PolaBear m8 , have you checked out your ignition system ?
the same thing happened to me on my last turbo car . it was the Nissan Bluebird ZX turbo and was tuned up a fair ammount . in terms of technology it is ancient but as i said the symptoms were similar and closer inspection reveled it to be the diode pack in the distributor . the replacement of which solved the problem . hopefully this point mabe of help .

[valmes]

, the fuel regulater hose has been removed to ensure I am getting max fuel..(query fuel pump)

What's this? You might be getting more fuel than you wished for... That means your mixture is way to rich, hence: misfire/spit/or blowback

[Roadrunner]

I was getting a bit of spitting and popping recently and was advised to change to iridium plugs. Problem went away, but I don't know whether that's due to the iridium, or whether the old plugs were shot anyway.

Brian

[Polabear]

, the fuel regulater hose has been removed to ensure I am getting max fuel..(query fuel pump)

What's this? You might be getting more fuel that you wished for... That means your mixture is way to rich, hence: misfire/spit/or blowback


Hose was only removed for test to ensure that I was at least getting full fuel..didn't cure anything

[Polabear]

I was getting a bit of spitting and popping recently and was advised to change to iridium plugs. Problem went away, but I don't know whether that's due to the iridium, or whether the old plugs were shot anyway.

Brian

I already had a new set fitted at last service Brian.. but coming back from last pod meeting I had two go off on me so they were all changed by AP Motors under warranty, have just reduced both the boost gain down a notch and the ratio to its lowest figure, it appears to have reduced it quite a bit, but it is still there and sadly it has also quietened the rabid dog down.....
:sad3: