Multiple cylinder misfire diagnosis help request

[mark-ak]

I have a 2000 Discovery II with 86,000 miles on it. Use only 91 octane. I replaced the MAF a year ago with a new one. The engine was decarboned about a year ago too. Plugs are Bosch Platinum 4s and are year old. Plug wires are original -- except for cylinder 5 wire which I replaced when trying to diagnose a P0305, which the new MAF fixed. I get 14-15 mpg consistently, mostly non-highway miles.

The left catalytic converter is bad. It rattles at idle and needs to be replaced. Will a bad cat cause misfires?

On 1-12-2008 the SEL came on and started flashing -- I was going about 55mph. I Immediately slowed (and swore a few times) and started to pull over as the engine was stuttering. The light quit flashing and the engine started running smoothly after about 10 seconds. I checked the error code when I got back home -- I use a CarChip. These are the codes:

P1300 Unknown Powertrain DTC (Ignition system or misfire)
P0308 (cyl 8 misfire)
P0303 (cly 3 misfire)
P0305 (cly 5 misfire)

I reset the SEL and the light hasn't come back on since.

Anybody know what may have caused this or where I should start? Cylinders 8, 3, and 5 are all on the same coil. Should I replace the plugs and plug wires? Suck it up and replace the coils too? Valve cover or plenum gasket?

Any feedback on where to look, or where to start, is really, really welcome and appreciated. I've been going a little nuts trying to figure this out as something is obviously failing, or has already failed.

Thanks -- Mark

[Disco Mike]

I would suggest you start with the basics and at least replace your wires, go with a set of 8 mm Magnecor wires, they seem to work well on Rover engines.
As for the cat, it needs to be replaced to help the 02 sensors on that bank balance out the fuel to that bank.
Mike

[Elemental]

Originally Posted by mark-ak

Plugs are Bosch Platinum 4s and are year old. Plug wires are original --

Take those plugs out and put in the correct ones, and swap out your wires. Magnacore is a excelelnt choice....

F*CK! Why do people keep using those plugs? Rover already figured out what plug to use...used it!

Cat failure is unlikely your misfire. Maybe if the back pressure is too much, but I really doubt it. Swap those plugs and wires and see what happens.

Be advised.....The check engine light is blinking BECAUSE the cats are getting overfueled and self destructing.

[Disco Mike]

I know you hate the Bosch, but engines can run on plugs other then those you like, afterall, the engine was built and used A/C Delco, longer then Champions, so does that make Champions wrong also, maybe we should all switch back to A/C's to be correct.
We all know that some of what Rover does hasn't been to our benefit/correct, take our head gasket issues, GM never had these issues with the 215, Rover blessed us with them.
Mike

[Elemental]

Just because it fits in the hole doesnt mean it will work. A peice of threaded dog shit will screw into the hole.

Bosch plugs foul faster then a steak on the sidewalk.

Let me save him the trouble of typing it out.

"I just installed some $.99 champions and new wires. This thing runs great! Its like a whole new truck. The check engine light is gone, and it runs sweet.

It really surprising to me that chep plugs work better then the expensive ones..But, its a Rover.
"

There! I saved him the time of replying to us.

[mark-ak]

Thanks for the feedback. I'll start with replacing the plug wires -- knuckle them in at the coils -- and go back to Champion plugs. I put the Bosch plat 4 plugs in after reading a couple positive reviews...reviews I should have ignored.

And with 86k I'll probably drop the coin for the full Y-pipe with cats, or maybe the IMCO Universals I've seen endorsed on this forum :: IMCO Universal

If the intermittent misfire problem isn't originating with the wires or plugs but with the coil or something else is the risk of burning out a new cat worth replacing the cats now?

Here's a pic I've found helpful for reference from the Land Rover manual for Discovery II coil firing:

6,1,7,4 on left coil; 8,5,3,2 on right coil

[Elemental]

First things first...

A cats only function is to change the gases coming in into something else coming out. If you have a clinder that it's firing at all.... All that fuel is going to go out the exhaust and into the cat. The cat, is about 1000 degrees f. I needs to be hot to perform its function. When you get too much HC(Raw fuel) it actually causes it to melt together internally. THe rear o2 sensors see this happening, and tells the computer to blink the check engine light to let the driver know something bad is happening.

Ok. So, bascially, the cat is a VICTIM and not the CAUSE of a misfire.

The first thing to do is cure the misfire.

Internal Gasoline engines need 5 things to fire... air,fuel,compression,timing, and spark.

Being the other clyinders are not misfireing, you can assume for now the timing and air is ok. That leaves fuel, Spark and compression. ALL of which are testable.

Oh those, we know we have Shit spark plugs and worn out wires.

I instructed all my student that if the get a misfire code, the first thign to check is what brand of spark plug is in it and how worn is it. Taking on plug out is good enough.

If the gap is too big, its probably worn out.

If its black or fuel soaked, that also is a good clue.

And, the big reason I though that is because there are so many spark plugs out there that the weekend warrior can choose from. Their is no other part that gets changed nearly as often by backyard Bob. If the plugs are the correct brand and part number, then I start hunting for fuel concerns or compression..


Dont replace the cats just yet. Get it to run first, then see what happens.

[Disco Mike]

I agree with you in that the catis not the primary cause, but let me ask you this. If a cat is bad, won't the 02 of that side try to correct the exhaust by leaning out the whole bank thus having an imbalance between the 2 banks with possible power or roughness issues?
Mike

[Elemental]

Originally Posted by Disco Mike

I agree with you in that the catis not the primary cause, but let me ask you this. If a cat is bad, won't the 02 of that side try to correct the exhaust by leaning out the whole bank thus having an imbalance between the 2 banks with possible power or roughness issues?
Mike

Which O2? Pre or post cat? Either way, no. Lean condition produce poor emissions too. And, too lean can cause a misfire. The computer isnt aiming for this.


Pre cat is a feedback fro the computer to let it know if its in Stoich(14.7 Af). The front o2 couldnt care less.

The Post cat watches what coming out to confirm the cat operation, AND up to 10% of fuel trim.

But, the computer, expect on cold start and fuel trottle, is aiming for 14.7 Air Fuel on each bank.

[buick215]

Just to add a complication here,if the "brick" of one of the cats has broken up and is rattling around, it is very possible for it to block off the outlet and prevent the exhaust gases from exiting.This rapidly builds pressure in the downpipe and stops a fresh intake charge entering the cyls on that bank.No fresh air,no bangs.Very common in the UK on Freelanders fitted with cheap cats.
Just a thought - he did say the cat was rattling.

[RudemanRB]

Time for a Tune up. it's plug wires

[mark-ak]

Originally Posted by Elemental

Just because it fits in the hole doesnt mean it will work. A peice of threaded dog shit will screw into the hole.

Something like this?



Didn't get much spark.



Seriously though, I ordered some Champion double platinum plugs (part no. 7318) yesterday and plug wires (STI/Spark Transfer International wires). Wasn't surprised to find that plugs or wires were not in stock anywhere in Juneau. I'll try to get a picture up of the Bosch plat 4s that I'll pull out, especially if they're really fouled, which is a pretty good bet.

Thanks again everybody for feedback and advice regarding misfire and cat issue. I'm wondering if the left cat didn't break up and cause some blockage as buick215 suggests as a possibility. In any case, a bad cat definitely isn't helping anything.

[Rovin4life]

if you were in my shop, without a 0420,0430 you cant really condemn the cats unless like buick said its causing a no start issue.

but with 5 and 8 on the same coil and thus each one grounds thru one another the diagnosis would be one coil plus a wire for number three. its not bad to do number five and eight.

just pull up the upper intake and pull it out.

[scotth]

had the exact samething happening to me. Same cylinders misfiring. I tried everything. This when on for several months and I took it to a local LR mech. He told me if it was the coils it would happen all the time. The coil either works or it doesn't. He said I had carbon build up on the valves and they were not closing like they should. He had some type of machine that cleaned the intake and valves. It took about an hour or so. It has been 2 weeks and it hasn't misfired yet. Seems he was right. My truck has more power and I can tell a difference in the way it runs. Don't fool with the seafoam or do it yourself cleaners. I tried that twice and it didn't do any good. Maybe something you might want to try.

[Rovin4life]

actually that would be a bg fuel injector flush.

actually that doesnt take care of the problems.

the exhaust valves get sticky and the injector service only takes care of the intake valves.

its the 44k that comes in the system that takes care of the exhaust valves. Bg guy told me himself.

But to tell if you got a sticky valve the misfires occur above 2200 rpms.