Missfire help.

[John Dixon]

OK, I have a missfire on my engine at all revs including idle. Cyls 2 and 4 not running at all - see vid here http://uk.youtube.com/watch?v=xwE1LD4XrO0 You can hear the difference in the exhaust bypass too.

Diagnostics so far:

Compression test - all cyls 16bar

Removed sparkplugs from engine and grounded them. Turned engine over and all plugs sparking.

Manually shorted ECU outputs to check each coil on correct output - OK

Manually shorted ECU outputs to check each injector on correct output - OK Increased coil dwell time - no change.

Ran new heavy gauge +ve/-ve lines directly from battery to coils. No change.

Swapped coilpacks from 1/3 to 2/4 - missfire still on 2/4

Swapped injectors from 6/8 to 2/4 - missfire still on 2/4

Swapped ignition modules from bank to bank - missfire still on 2/4

Swapped coil sub-harnesses from bank to bank - missfire still on 2/4

Changed sparkplugs - no change

Any ideas greatly appreciated, it's really annoying me now!!!!

I'm beggining to wonder if it's something physical, maybe the injector angle is off on these 2 cyls and the fuel is running down the manifold wall instead of entering the cyl as a mist or something. Will need to investigate more when I get time.If I enrich the mixture on all cyls then re-connect the injectors on these 2 I can get some spitting back like you normally get through the intakes with a too-lean mixture.

[darinz]

I had a problem with a miss with the POS Link ecu I fitted originally. The EBC was interferring with the relevant inj. ie is EBC was aux 7 then inj 7 would miss. What it specifically did was increase the injector open time so at idle it was really bad but as load increased it ran OK.So we did like you have done and checked everything before we said no it is an ECU problem.

Worth thinking about?

[Carl H]

john,the symptoms you've described are very strange indeed...but even if the injector angle was off and fuel was just running into the bores it still would fire (altho crappy) but would still hit.is it possible the ecu is doing something funky...doesnt make sense that if you manualy test for spark and it is there that it wouldnt kick...perhaps order is off?

[Stinky]

What about fuel? Are you absolutely certain the injectors are firing? Do the plugs have any fuel/carbon on them when you pull them out? Tried starting fluid/brake cleaner/propane directly into the tb to see if it makes a difference?

Is it possible the firing order is mixed up?

[John Dixon]

I'm pretty sure they're firing. I know the injectors are good as I swapped them around so no prob there. They have 12v supply and are wired to the ECU correctly. Also, you can hear them click if you put a screwdriver on them and put your ear against it.I'm going to try spraying some easy start in but I ran out of petrol / light when I was messing around last time and now I'm working away for a fortnight Firing order I've assumed is 1-8-7-3-6-5-4-2Suppose it's possible it's an ECU problem but unlikely I think, can substitute it for another one and try it too.

There is deff fuel going in there, the plugs are black. Also on one, the insulator is 1/2 black 1/2 white as if it's being cleaned down one side - maybe by fuel dribbling onto it?

My money is on most likely a machining problem on the runners or something at the minute I think.So frustrating only getting a few hours to look at it every few weeks

[elwesso]

hmmm.. Could you consider adding a hotter plug to those cylinders just to see if it would start hitting..

Could the injector be leaking a little, but arent you using top feeds?

i would think the injector angle would have to be WAY off to cause that kind of issue, like almost spraying sideways?

[SuperHatch]

Could this be an issue with your custom CAS trigger wheel?

Meaning, it's firing, but the timing is off enough that it's not firing at the right time/injecting at the right time.

[maxnix]

Firing order is correct, but I wonder how you achieved increased compression and if that might require a modified plug reach?

How do the plugs look? And which plugs are they now?

[John Dixon]

Yes, I'm using top feeds. Thinking maybe more like the transition from the injector boss to the runner has not been bored out correctly or something.For the custom CAS wheel, don't think so as the other cyls are firing OK and it only uses one ref (90deg BTDC No 1) not 8 seperate ones like the nissan ECU.Increased compression was incorporated into the piston design, no changes to the heads. The plug reach on nearly all the projected NGK's I've lookd at is almost the same. The BKR7EIX were protruding perfectly into the combustion chamber (tried them with the head off).Currently it'd got PFR6B in it but both these and the BKR7EIX work in all the other cyls fine.

[LEMHEAD16]

have you thought about the lifters. I had two lifters on mine that were not bled down correctly and caused what would be a misfire condition (it was on a simtest machine)

If all else fails that is an option to look into. Its kind of a pain to check that though because you have to remove the cams

EDIT: NM compression test would have indicated that unless it was a very weird situation

[John Dixon]

have you thought about the lifters. I had two lifters on mine that were not bled down correctly and caused what would be a misfire condition (it was on a simtest machine)

If all else fails that is an option to look into. Its kind of a pain to check that though because you have to remove the cams

EDIT: NM compression test would have indicated that unless it was a very weird situation

As you say, compression check was all OK and I'm using solid lifters anyway.Cheers for all the replies, keep them coming if you have any more ideas!

[Carl H]

is your ign trigger signal 'clean' and have proper sheilding.i had a pfc on my rb20 and the ign driver for cylinder 4 would intermittenly come and go before it finally went out completely.i know you're on a full standalone harness but can you make a jumperharness to plug in the stock ecu to test and see if it will run?thats how i diagnosed my problem with the pfc was thru the stock ecu and ended up just doing a full retune on the stock ecu and havent looked back since...that was about 2 years ago now.it is starting to look like the culprit is possibly the ecu, while you might have something going with the injector angle being off i'd expect it to not even run at all; you're doing all the right things to diagnose it but i would see about getting a replacement ecu just to try it out.

[John Dixon]

I think the signal is clean as all the other cyls are firing OK. It's a 12v logic signal too rather than just an inductive and is run on shielded cable. Again, I can confirm when I get the oscilioscope on it.Can't do a harnes to to stock ECU as I don't have MAF and the rest of the sensors are non-nissan.Problem with the ECU theory is that the ignition is wasted spark and the other cyl of each 'pair' is running just fine.I am going to try another ECU just in case though!

[darinz]

Have you tested the injector opening time on these injectors compared to the rest? Like I said before that was my problem. It was really hard to pick up as there was fuel and spark at the right time just to much fuel so it missed.

[John Dixon]

They're set the same in the ECU but will check it with the scope when I get it connected up. Cheers

[John Dixon]

Darinz was right - ECU Problem:OK, got the 'scope on it today.Looks like the last firmware upgrade I did to the ECU to change a PWM output table to a digital has screwed up the firing.Compared a coil firing signal off a 'pair' of cyls where both were running with a pair where only one was. Guess what, the pair with the missfire was only firing 1/2 as often!Guess that no 2, 4 cyls are only being fired on the exhaust stroke! Will get in touch with emerald on Monday, am sure they'll fix it quick but annoying how much time I wasted finding it. Hadn't appreciated just how uesful a 'scope can be on a car.

[maxnix]

Scopes are great to see what really is occurring.

If you increased compression ration requires a different plug, try the NGK Laser Iridium.

http://www.ngksparkplugs.com/p...e=nml

[John Dixon]

I'm using BKR7EIX irridiums.

[SSDwellah]

Great news! I'm glad you figured out the ignition gremlins. I can't wait for the new Youtube posting on all 8 cylinders!

On a sidenote, yeah an oscilloscope is a great tool. They are expensive though. I am trying to find a DSO now. With all the companies cutting back here recently there have to be some equipment firesales coming.

[maxnix]

I'm using BKR7EIX irridiums.

I think if you read the specifications at the above website, you may determine they are a grade down.

[John Dixon]

Cheers, will try and get a vid this weekend (if it stops snowing!).

Hadn't realised the IX were a different range. Will maybe try the laser's next time. The IX cost a few quid though so will be sticking with them for now!

[maxnix]

Good luck. We are anxiously awaiting further good news.

What's snow?

[John Dixon]

Back on 8 Will get some video but my neighbours were starting to get annoyed! Apparently it shakes the plates in the cupboards.I say back on 8, think it's actually the first time on 8. It revs up insanely quick now and sounds amazing.

[gs14racer]

Im waiting for dyno sheets!!!!!!

[Carl H]

until i see a video i dont believe it.

[maxnix]

Time to distance will be great.

What was the fix?

[John Dixon]

Dyno sheets from initial running in mapping and a vid should be within the next month hopefully if I can find time and don't get sent away to work. Need to get the air box and filters sorted out before I do any serious running. Also at the minute, the complete guesswork map I put in there is mega rich when revved up so smokes like hell when you blip it!Fix was just the updated ECU firmware!Don't understand the time to distance comment?!

[maxnix]

Don't understand the time to distance comment?!

What will it do in a straight line at WOT through the gears?