6.9 Misfire - getting worse

[SELfor50]

Ok.. so the misfire mentioned when I posted about the 1kOhm vs 5kOhm leads has now got worse.

It became very apparent on the way back from Melbourne and is now throughout the rev range.
Very noticeable at Idle, and really really noticeable at high rpm's (4500-5100).

I've nailed it down to Cylinder 5 (passenger side, closest to front of car/engine bay).

Things that have been changed and not fixed it;

Ignition Lead
Spark Plug (old one wasn't fouled either)
Injector

None of the above has fixed the problem.  Tried to change the fuel line from the distributor / divider to the injector - but almost rounded the nut so didn't continue.

The old Fuel Dist / Divider had a seized piston and it won't budge so I don't have a spare one yet.  Unless I can use an M117 Fuel Divider?

Any other suggestions?  I'm farkn stumped. 

[robertd]

Hi Cam,

I am not sure what I can add at this point regarding the misfire, however my silver 6.9 had a similar
problem at the high end of the rev range (above 4000rpm) and it turned out to be a worn rev limiter spring located in the top of the distributor cap. I just replaced the small spring and it is now OK.

hope this helps

Rob

[koan]

One thing, probably not it though as you've narrowed it down to one cylinder, when my alternator died and battery volts slowly dropped as I drove along, the engine continued to run fine with small throttle opening but putting the foot down brought on a severe misfire.

Pretty sure 6.9 and 450 fuel distributors are the same, there's a Bosch number on the distributor, think the air meter housing is the same too.

Next thing  would be to swap a couple of injectors, I found the fittings on the injectors and fuel distributor to be very tight, some tapping with hammer and steel block shocked them free.

Have a look at the running engine at night and away from light, see if there's anything arcing over, maybe down the distributor cap. Also could be a conductive path inside the cap.

A compression check might tell you something - leave that till last in case of bad news.

koan

[TJ 450]

450 and 6.9 fuel distributors do carry the same part number.

My 6.9 is barely drivable at the moment, also due to a missfire with the addition of severe pinging over 2500 rpm.

I'm pretty sure that it all relates to the CIS, as I hope is the case on your car, Cam.

Tim

[koan]

I'll throw in mine's running a bit crap at the moment too. Never likes really hot weather but even on cooler humid days which it usually loves it's not running like it usually does.

koan

[TJ 450]

That's interesting, Koan.

Mine also runs very poorly on cool humid days and it pings on the hot days.

Seeing as all three of my cars are practically out of action, I'm borrowing my sister's Mitsubishi Colt.

It can only get better from here (I hope).

Tim

[koan]

Mine also runs very poorly on cool humid days and it pings on the hot days.

No, read it again, it goes really well in cool humid weather.

When we have a 40C day with a cool change where the temp drops to 20-25C in a 1/2 hour resulting in high humidity, the car runs smooth as silk, feels like it has enormous amounts of power too.

I don't get any pinging even on standard petrol with 6 degrees advance.

In fact I've been using "middle" petrol recently, 95 MON/ROM/Octane whatevers. Doubt this could be responsible for the poor running lately but it's the only thing that's changed.

koan

[motec6.9]

Just to add my 2 cents worth if you look in the owners manual it states MIN RON 98 standard Australian spec by the way CAM i am removing Bosch K-Jet from my gold 6.9 engine in transfer over to silver 6.9 let us know if it is fuel dist

[TJ 450]

I see, my mistake Koan.

Cam, it might sound ridiculous, but I would smell the nose of the spark plug for fuel, then have the injector nozzle checked for blockages

There's also chance that the fuel distributor has had flakes of rust clog up the internal screens.

Tim

[koan]

Just to add my 2 cents worth if you look in the owners manual it states MIN RON 98 standard Australian spec by the way CAM i am removing Bosch K-Jet from my gold 6.9 engine in transfer over to silver 6.9 let us know if it is fuel dist

The Owner's manual says 98 RON but also 8.8:1 compression.

Sure I've seen 95 RON on a stuck on replacement page somewhere, thought it was the AUS supplement but can't find the page, will keep looking. Maybe my memory is inventing things.

koan

[13B]

My Aus 6.9 supplement says my 8.0:1 aus motor is happy to run on 91 RON.

sounds like you need to set up a test rig like this:

Link

Sounds like I'm the only one of us here with a truly happy 6.9 K-jet which doesn't care whether its 5 degrees outside or 40...

I.

[SELfor50]

Thanks for the reply's fella's.

I've swapped the injector - so pretty confident it's not that.  The fuel line between the divider and the injector is next to swap (hopefully duck out to try that at lunch time today).  Was going to last night, but almost rounded the nut - felt itgoing and said - no we won't have that tonight. 

It is weird that it would be the actual fuel distributor - cause I don't understand how it could be on just 1 cylinder.. but yeah, maybe it's got a bit of something stuck in the hole where the line connects.

Another thing I should say is, and only confirmed this morning.. under load - it struggles.. Eg, when punching it in 1st to about 4-5000rpms, when it changes gear to 2nd, it will then really struggle....flat spot.  And then take a couple seconds to sorta kick in and get firing again.  Which then sorta says to me ignition.

Which is farkn weird..cause once again - new dizzy cap, new rotor button.  Checked the dizzy cap as a first point also last night - but being new there's no arcing inside or jumping of spark.  And no-ones drawn any led pencil lines inside. 

Compression - i'm 99% confident it's not that.  When the engine was first installed 2 months ago - we did a comp test. 150psi bang on, on all 8 cylinders.  And if it was compression - i've been told that it wouldn't come and go.. it would be constant.



On the temp front - The car (besides the misfire now) runs fine whether hot or cold days.  Though, on the colder days or humid days I agree it does feel like it doesn't need as much pedal to get it moving harder.


Great Video Ian - Me thinks I need a test-lab like that... oh, can't wait for retirement.   Have time to knock up some crazy ass ish like that. 

Will post results of fuel line swap later today.

Cam.

[SELfor50]

Good news = glad I(read- John Green) found the source of the problem now.
Bad news = not entirely sure exactly what's caused the problem - have a few theories if you read on.
Worse news = it's a farked rocker arm that's ground one cam lobe to look like the cottage roof...or knifes edge.  More like a knifes edge. 

Best news = Now I have an excuse to get both CAMS lumpified and livened up.


Theories are - When the new engine arrived it was missing 2 rocker arms.  The seller advised me before purchase that he had sold a couple off it.  So I went and used 2 from my old engine.  Turns out that the 2 used are still functioning fine.

I never really looked too closely, but it seems that every single inlet valve rocker arm is actually 2nd hand / used.  I would imagine that someone needed 8 of them or even 10 and he has put their old ones back in.  Never went to the degree of checking all these individually - but I guess it's a lesson learnt.

So... in summary - nothing to terminal.  And it will end up being an upgrade that was already planned is brought forward sooner than planned..  just means now I have to organise CAM re-grind, new valve springs, new rocker arms and probably a stall converter.   

Anyone wanna make me an offer on that race car??   

[s class]

Interesting.  You need to remove the cam oiler tube and clean it out, and inspect the ports on the cam towers where it gets its oil feed from. 

[SELfor50]

Interesting.  You need to remove the cam oiler tube and clean it out, and inspect the ports on the cam towers where it gets its oil feed from. 

The Oiler tube is supplying oil - that's for sure.. We tested it with the rocker covers off.  Just cranked it and oil was definitely being applied.

It has to be related to the actual rocker that's on that valve - as it's not happened to any othes.. before or after it on the rail / cam.
If it was blocked then the exhaust valve in front of it would also be farked.