Stavros

Ive got, if you didnt already know, a JZX81 Chaser with an RB26 (Ie Skyline GTR 6throttle 2.6 24v straight 6 twin turbo) in it, and its had a bit of a missfire under load in 3rd gear upwards since ive owned it.

To attempt to fix it (and to get rid of the coil on plug setup, which i hate) I fitted a remote coilpack wasted spark setup, but if anything its worse, just holds back as soon as you come on boost.

I now realise that, at idle at least, it doesnt fire on number 6cyl.

We did some checks to see if we could fix it, we...

Swapped plugs over- No change
Swapped leads over- No change
Swapped positions on coilpack over- No change
Checked spark using a spare plug- Yup, as strong spark on 6 as any of the others.
(the above tests meaning the coilpack conversion clearly is working just fine)
Swapped injectors- No change
Compression tested- About 10bar across the board.

One thing we noticed though is if you hold the car at part throttle pulling the plug DID make a small difference, but it still didnt sound right, like it was running on 5.5cyls. But that just makes things even more confusing, as I guess that shows there IS fuel getting to it?

Didnt try the remove plug and watch for fuel mist, but I guess the above thing makes that a bit pointless i guess?

Im PROPERLY confused, anyone got any other ideas on other things to check and what could be wrong?

Cheers in advance.

jameswrx

If you're saying electrically it's fine then it may be a mechanical issue.. valve?

Martin-Hadland

iTrader: (2)

One of the throttle butterfly's closed?

Stavros

james- ignition wise its fine. fuel maybe not. 10bar compression across the cyls says to me the engine isnt broke either.

that was my thought (or that the idle control setup for that cyl wasnt working maybe), hence why it seemed to run at 5.5 when i hold it at fast idle.

but im pretty sure thats not possible due to them being connected in at least pairs IIRC, im not 100% though.

its always idled high too, 1.5k, but presumed (as its a common GTR bodge mod) that it used to have a vent to atmo DV on it and they increased idle speed to stop it stalling.

Paulo P

My mate had a similar problem on his R33 gtr and it turned out to be an air leak due to the inlet manifold gasket. It was an arse of a job to change it but it sorted it.

xr4x4rs

iTrader: (5)

have you tried the ignition amplifier thats sits on the back by the leads

my mate had this on his and it turned out to be that and the connector to it due to heat

worth having a look

TWoods

Air leak be my 1st guess if engine ignition and fuel is fine

PeterLucas

You could get a colour tune, see if its leaning out on one cylinder. That would show an air leak.

Martin-Hadland

iTrader: (2)

That is a common problem and well worth checking ...

dojj

iTrader: (3)

does it fire on 6 at all?
what about when you give it some welly?
if it's had this problem since you've had it and the coil pack conversion has made it worse/more noticable then i would suggest it points to the spark blowing out
but don't ask me why because it'll take me all day to try and explain, and then someone will say it all in about 3 words

magic randy

iTrader: (2)

my mate tuney had this on his r33 gtr, same sort of problem, was inlet gasget
but was a right bastard to do as well says he never wants to do one again lol

Stavros

Im confused, how can a leaking inlet manfiold gasket make a car totally run on 5cyls

Deffo not that as its now a wasted spark setup, so if it was that 1 and 6 wouldnt work, not just 6.

XRT_si

iTrader: (2)

Would explain the higher tickover but i am interested as to why it would make it run on 5?

Spray some WD40 around the inlet and see?

magic randy

iTrader: (2)

sorry was just writing wot i heard

Stavros

far as i can see it wouldnt/couldnt

xr4x4rs

iTrader: (5)

im lost with the wasted spark
i thought they all had it anyhow due to being individual coilpacks

Martin-Hadland

iTrader: (2)

Steve... Just do the WD40 test, sound advice he has given. My prediction is that this is inlet/throttle related.

Stavros

i might do WD the fucker after TopGear, still dont understand how it could run on 5 because of that though

normally there is 1 wire from the ign amp to each coil on plug.

now there is 1 wire to 1+6, 1 wire to 2+5, and 1 wire to 3+4.

so if 6 wasnt working, nor would 1.

i think

xr4x4rs

iTrader: (5)

fair enough i can sort of see where your getting lol

go with the air leak test then

Stavros

Did WD40 test, no change.

Though I dont see how an air leak can stop 1 cyl from firing totally anyhow, but I did it

Been mentioned now on GTR board it still could be Ign amp, though not sure how when 1+6 are both connected before the coilpack now? But im rubbish with electrics, so dunno.

Martin-Hadland

iTrader: (2)

Stav .. Book the shed in, we can sort it

Stavros

And TBH mate your about the only guys id trust to touch the POS anyhow, so itd have to be you!

Thought you was well busy tho, but fair enough, if i dont get any more bright ideas in the next few days its coming your way

You can fit the hydraulic handbrake and line lock while you at it

RWD_cossie_wil

iTrader: (9)

Air leak could cause the misfire, too much fuel going in as the air that is meant to be there isn't, so you get a rich misfire... ie plug cannot ignite the air/fuel mix, normally happens if it drops below 10:1 afr

Other than that I know fook all about skyline bits so can't be of any help

Martin-Hadland

iTrader: (2)

Cool, let me know if we are needed

Lee_R21Turbo

iTrader: (1)

Stav....just a thought which I dont think you've checked yet unless I've missed it...

You've changed the injector yes....but have you checked the signal going to the injector - i.e. is it getting power - check connectors etc with multimeter!!??

Also....something simple too - is the fuel pump providing enough fuel to the rail - similar symptoms to running out of fuel perhaps!

Just a couple more ideas to throw in!!

magic randy

iTrader: (2)

suppose the pins in the plug cound be bent apart too, get intermitent connection

Stavros

havent got a multimeter so no, not checked that, but yeah, could be an issue with electrical connection to that inj.

not a fuel pump thing though, otherwise all the cyls would be running wrong, not just 1 cyl not working at all.

im gonna try get an ign amp in the next day or two to rule that one out.

then cry.

or possibly carry on trying to find out whats up.

or just take it to martin as i want the handbrake and line lock doing anyhow.

dojj

iTrader: (3)

it depends of if it's leaning out at the far end of the rail or not though or there isn't enough pressure being supplied by the pump to get the fuel pressure up high enough for a decent pattern when it's at idle
when you raise the revs the pressure rises (doesn't it?) and then you might have just enough

get yourself a cheap Ł2.99 multimeter at least so that you can check the basics

Stavros

Update! Its still fucked

Right, Martin sent me a spare R33GTR ign amp he had lying around, and I plugged that in, no change

So i used some steve logic, and i "think" its ruled some stuff out.

The system the car is running is wasted spark, with 1+6, 2+5, and 3+4 sharing a coil each.

Basically when one fires, so does the other, but the one that doesnt need it just sparks for no reason, hence the name wasted spark.

This COULD explain why i was seeing a spark at 6 even though it was only running on 5cyls, as maybe the spark was the wasted one from cyl1s correct spark moment.

So, I cut cyl1 ign amp output wire.

As expected, the car dropped to 4cyls as cyl1 stopped running, but they BOTH still had a spark, meaning cyl6 clearly WAS getting its own spark, not just the wasted one.

Out of interest I cut cyl6 wire and connected 1, and then cut them both, both of which gave the expected results.

So surely (am i right?) that would totally rule out it being an ign problem at all?

glancy2081

have you checked wiring to the injector is ok with multimeter had this with a astra a had years ago tried replacing everything to find the wiring to injector was faulty

Stavros

Yup, thats one thing left to check, thats for sure.

JamesH

iTrader: (21)

Had this on a cossie before, and the electrical clip that sits inside the injector clip and then pushes onto the injector had pushed up slightly so wasn't making contact with the injector

JohnnyB

well if you have compression, spark and the fooking valves are opening then it must be fuel

Stavros

well i have compression, unless im missing something with my tests i deffo have spark, i can only presume the valves are opening, and can only presume the throttle on that cyl is opening, so only other thing i can easy check (i think, how DO i do that with a multimeter?) is if there power going to the injector.

Nash

iTrader: (3)

Small node light that plugs into the injector plug, will light up if its getting a signal.

Stavros

what hell is that and where you get one from?

boXXer

i had a similiar problem with my 3dr. basically, the car stopped running on cylinder 3 whenever it went above a certain amount of revs. i had voltage to the plug, and none of the wires were corroded.

Took the injector out, and hit it against the floor a few times, stuck it back in, and never had the problem again.

problem with a multimeter is you cant see if the plug is pulsing as its not quick enough to read the change.

Stavros

i already said i swapped injectors, no change, so obv not injectors, thats easy to test.

how to do you test power going to an injector tho?

boXXer

multimeter, stick it up the plug, read lcd screen. easy. BUT, you wont be able to tell whether the power is pulsing correctly, as a multimeter doesnt display the change quick enough.

boXXer

im pretty sure theres some sort of tool for testing pulses though, just dont know what it is.