Misfire

NJV6 · Post by **NJV6** » Wed Sep 19, 2007 7:25 pm

HI,

I have some sort of misfire (and so does the vehicle!). The motor is a Quad cam 3.5 V6. It is more than running on 5 cylinders, but it just doesn't sounds quite right, not as even as it was or should be.

It is most noticeable at idle - as mentioned it still runs on 6 but not as healthily as it should.

Has 104,000km and had new plugs at 97 000 when the cam belt was done. They are 100,000km platnium plugs and quite a mission to get at. (removal of inlet manifold)

They have 3 coils which supply 2 plugs each.

I am not a modern electronic dude. and have no idea where to start.

It is worst when hot hot, such as a long working climb off road. It is not very noticeable when cold.

:idea:

's?

Steve_t647 · Post by **Steve_t647** » Wed Sep 19, 2007 8:21 pm

I think one of the coils may be deteriorating (carbon tracking) I would check the leads first then see if I could find another coil pack, keep swapping them out with the spare till you find the funny one.

As for testing find a decent hill and go up with it failing and disconnect a plug and see if it is worse and cycle through them.

paule · Post by **paule** » Wed Sep 19, 2007 9:28 pm

When did this start, before or after u replaced the plugs?

NJV6 · Post by **NJV6** » Wed Sep 19, 2007 11:36 pm

What an episode!

I can't recall when it started I'm afraid. I think it may have been after but really I don't know. It is hard to test as it sounds ok when it has a few rev's on, possibly down on power but you do get used to what you've got and want more!

I have just got all 6 plugs out. They 'look' ok, they don't all look exactly the same thou. I will take the coils somewhere tomorrow morning and get them checked.
One plug where the coil pushes onto it at the very top looked slightly rough but wasn't burnt lokoing as if anything was jumping.

Azza · Post by **Azza** » Thu Sep 20, 2007 12:24 am

NJV6 wrote:I have just got all 6 plugs out. They 'look' ok, they don't all look exactly the same thou.

They should all be a nice even 'tan' colour, if you have 1 plug that 'looks' a little different (darker or lighter), start checking everything that is associated with that plug/cylinder.. check the gap on the sparkplugs (this should fine with default gap though), check the HT lead to the plug (though you do say there is no sparking/grounding), check the cap...

if there is 1 plug that seems way different, you might want to look at valves on that cylinder, they might be carboned up and not seating properly (requiring a valve grind) or maybe even burned out completly (though the plug colour should be pretty extremely different if this is the case) :shock:

You might be able to solve a carboned valve problem by running a bit of 'fuel additive' in your tank

paule · Post by **paule** » Thu Sep 20, 2007 7:23 am

Well said. Another way to help remove carbon is to water into intake with engine runing, just hold revs up and dont use too much. Its alot like steam clean.
Also look at the ens of coils where leads fit as these can rust/corrode/burn. Have a look inside and around lead ends, sumtimes they look a bit white loofn compared with the others.
Yesterday I replaced coils/lead assembly with waste spark set up on mitsi lancer, very similar simptom.
Mitsi can source leads and coil ends at good price but coils are pricy. I bought complete set from Kempys for good price.

NJV6 · Post by **NJV6** » Thu Sep 20, 2007 7:55 am

Thanks guys you have been most helpful

Top left looks a little different to the rest... It is more black around the electrode....?

This is looking at the tops of numbers 2 & 3. Number looks looked rough compared to the other 5.

Azza · Post by **Azza** » Thu Sep 20, 2007 1:49 pm

Are the black deposits on the 'number 1' (top left in 1st pic) sparkplug dry and sooty or wet and oily?

Mattman · Post by **Mattman** » Thu Sep 20, 2007 4:51 pm

Can you get to the leads whilst the motor is running? If so using a set of plug wire pliers pull the plug leads off one at a time.

You will know you have the right one when the idle doesn't change at all.

If you have a multimeter you can check the coil resistance across the primary and secondary windings and also the plug leads.

Matt.

paule · Post by **paule** » Thu Sep 20, 2007 5:53 pm

With waste spark if u disconnect plug lead while running u effectivly drop 2 cylinders, so can be a bit difficult to use this method.

Mattman · Post by **Mattman** » Thu Sep 20, 2007 6:04 pm

True, the lead must be earthed for the other plug to fire.

Matt.

paule · Post by **paule** » Thu Sep 20, 2007 6:10 pm

Ive been thinkn, difficult I know, but that plug has been burnt on the HT connection only on that cylinder, BAD plug? Maybe more than that, what is happening in that cylinder to cause that, maybe lean mixture needing higher voltage to fire. This can be due to a partially blocked injector.

NJV6 · Post by **NJV6** » Fri Sep 21, 2007 6:49 pm

Mattman wrote:You will know you have the right one when the idle doesn't change at all.

Sounds good but it isn't a full misfire, just a little one. It definately runs on 6 or more like 5 1/2.....

NJV6 · Post by **NJV6** » Fri Sep 21, 2007 6:53 pm

That photo of the plugs is not actually that well repesented. I'll try and get another. It is not at all oily.

I do occasionally get pinking (usually 2000rpm ish) under load when it is hot such as a period of idling.

I am getting the coils tested. I think since I've come this far I might pull the injectors...

Petemcc · Post by **Petemcc** » Sat Sep 22, 2007 7:51 am

do you run 91 or 95? maybe try 95 if you are currently using 91 might fix the pinking

NJV6 · Post by **NJV6** » Sat Sep 22, 2007 8:58 am

The DOHC Paj's are designed for 96. I run 98 when I can but only Queenstown has it down here, otherwise 95.

scratcher · Post by **scratcher** » Sat Sep 22, 2007 6:15 pm

that pinking is odd for that motor. they should have a knock sensor to stop that.pull both topbelt covers off, align TDC and check all marks line up

NJV6 · Post by **NJV6** » Sat Sep 22, 2007 6:46 pm

Definately all line up. Checked that and checked it again.

Actually thining about it now, This miss is only since it went in to get its' cam belt done, I took it back becasue of this mis and to cut a long story short it has had 3 cam belts in 5000km, so I know the timing is correct.

I have got the coils back and they tested fine.

Then was suggested about dicky injectors. Clamped the return fuel line to increase fuel pressure and make the injectors go better - That made the mis noticeably worse almost to the point it was probably dropping the cylinder completely.

What next?
New plugs at $30 each....?
Compression test?
Still a dicky injector?

Mattman · Post by **Mattman** » Sat Sep 22, 2007 7:16 pm

It doesn't sound fuel related if increasing the fuel pressure increased the mis problem, still sounds like an ignition problem.

Using a stethoscope or similar can you isolate the misfiring cylinder?

Are there leads from the coils to the plugs, were these tested with the coils? Perhaps just replace that one affected plug.

Might be worth getting the codes read to see what the ecu is seeing, might be something completely different.

Matt.

kdub104 · Post by **kdub104** » Sat Sep 22, 2007 10:15 pm

go check the resistance of youre leads! start with the basics dude...specially if its affecting under load and diff temps

NJV6 · Post by **NJV6** » Tue Sep 25, 2007 10:10 pm

What should they be dude?

I got 1 at 14.7 & 2 at 18.3 on the 20k ohm setting......

Azza · Post by **Azza** » Tue Sep 25, 2007 11:44 pm

NJV6 wrote:That photo of the plugs is not actually that well repesented. I'll try and get another. It is not at all oily.

hard to make an accurate assessment based on the photo, but if it's not oily and is indeed sooty and black... it is most likely that that cylinder is running rich (too much fuel)... because it is only present on 1 cylinder it could be a sign that the injector on that cylinder could be sticking.

rangimotors · Post by **rangimotors** » Wed Sep 26, 2007 9:30 am

Hard to tell if thats ok for your leads or not, you'll probably find they only break down with the high output that the coil has, if they were cracked or something you probably wont get leakage with such a tiny flow (guessing you used a multimeter which will be putting out bugger all) thats why appliances etc are tested at either 500VDc or 1000VDc

NJV6 · Post by **NJV6** » Wed Sep 26, 2007 4:06 pm

Injectors came back - all good.

Lead set is $220 for 3 leads.

paule · Post by **paule** » Wed Sep 26, 2007 11:10 pm

Borrow sum1 elses coiland lead and fit to the one that had burnt plug.

Azza · Post by **Azza** » Wed Sep 26, 2007 11:28 pm

Have you done a compression test?

Az

NJV6 · Post by **NJV6** » Thu Sep 27, 2007 4:55 pm

Got Compression guage. Found it. :cry:

Front to back

----------160
180
----------185
170
----------185
100

So what the .... has caused that to happen. :cry:

1 cylinder a bit to low i'd say. :cry:

What do I do now? I am no home mechanic. :cry:

Smurf · Post by **Smurf** » Thu Sep 27, 2007 5:16 pm

I don't know if yours is a contact motor, but with your timing belt being installed incorrectly a while back there is a chance that one or more of your valves are bent from hitting the top of the pistons

NJV6 · Post by **NJV6** » Thu Sep 27, 2007 6:59 pm

It is a contact motor.

I'm positive now it has only been like it since the belt was done the 1st time. If you have ever timed a 4 cam motor taking the belt off can be a bit of an episode. In terms of letting the tension off the cams which is held in place by valve springs.

Maybe the mechanic just let it off 'Bang' creating a bent valve? And there is 24 of the barstards! That was my 1st thought 5000km ago....

Who knows. It is all back together and running now. Will take it to get a leakdown test done, find out where the leak is. Then we can go from there.

Thanks peeps.