Spark plugs

happy days

happy days

Active Member
As in a previous post my 3500s had a slight misfire at high revs. As we were going to beamish I decided to remove plugs and clean them up. Misfire was cured, now nearly 400 miles later it started to misfire again, so removed one Plug at the moment and it is black. Surely not after 400 miles. I now presume it is a fuel mixture problem or is it something else. Cheers. Mick
 
Hello Mick,

Which plugs are you using? What have you gapped them at? Which plug is black? Is it dry and sooty or wet and oily? Is the insulator black too?

Ron.
 
Hi guys. Have now removed all plugs and they are all the Same, black and sooty, all the plug is same insulator as well. They are Bosch super plus and gap is set at 0.60 mm
 
Hello Mick,

I'd start by replacing all of them with Champion L92YC. They come gapped at 25thou so you should not have to change them. The gap you have on the Bosch is a touch under 25thou, but that won't bring on what you see.

I tried NGK plugs once, they too went black and sooty, so changed back to the above Champions and no more problems.

What is the compression ratio of your engine?

Ron.
 
happy days said:
cr is 9:25:1 so just a change of plugs could sort it wow
Click to expand...

It's can often be the simple things that give the most consistent results. You might find the insulators on your current plugs are breaking down over a period and get worse with heat, thermal effects can manifest in some bizarre ways. If the plugs are not sparking at a high enough voltage that might explain the apparent inefficient combustion shown by the sooty plugs. The build up of soot over 400 miles might be enough to create the misfire, which is why cleaning the plugs cures it. Go for the easiest fix first and you might be surprised by the results :D

Dave
 
well i did get some new plugs from ian while at Beamish, unipart ones, so will put them in and see what happens failing that go to Rons champion ones
 
Mick, I am following this with interest, when I got to the M6 on the way back from Beamish, I hit a deluge of rain, flooring the throttle at 65 led me into a misfire, but I could accelerate slowly and it didn't happen. I did not have this problem on the way up, but it hasn't stopped raining here since Sunday night so I haven't put the car in the garage yet (cos it's wet, and will rust, more) but I think my fault is plug leads, but I haven't ruled out plugs yet, as the wet weather affected it. I will pull my plugs (ooh Matron!) later this week and also change the leads, see what happens.
John.
 
Put the unipart plugs in and running perfectly. Time will tell I suppose. One other thing, the Bosh plugs that were taken out the threaded section is longer that the threaded section on the unipart plugs. Any significance their ?
 
The ones with the longer threads if significantly longer could be for SD1 and later heads. P6 normally has shorter ones.

How much longer are they? Is there a number on them?

I guess this could mean either the wrong plugs were fitted, or that your car has SD1 heads!

Dont know if anybody else here has a way of telling without taking the rocker covers off and checking whether the springs for the rockers are double or single???

Rich.
 
If the threaded section on the Bosch plugs is longer than those on the Unipart, and the latter are listed as being correct for the Rover 3500 P6B, then the former would seem not to be.

The threads should not protrude into the combustion chamber as the build up of soot which will encase them will make removal rather more difficult, and increase the likelyhood of damaging the threads in the cylinder head. How much longer are we talking about?

I have never seen Unipart spark plugs Mick. Glad that they are keeping you out of trouble.. :wink:

Ron.
 
rockdemon wrote,...
Dont know if anybody else here has a way of telling without taking the rocker covers off and checking whether the springs for the rockers are double or single???
Click to expand...

Hello Rich,

Measuring the thread depth in the head would give the answer,..P6 heads have a thread depth of essentially 12.5mm. All later heads from the SD1 right through to the last of the 10 bolt heads of 2004 all have 19mm of plug depth in the heads.

Ron.
 
Ok. Bosch ones are super plus, the threaded section is 19mm in length.
The others are unipart gsp 531 the threaded section being13mm long.
Their was a bit of talk at beamish that it could have sd1 heads, so further investigation is needed
 
Guessing best way is a piece of metal rod with a kink at the end so you can undo the plug and check the thread length as Ron suggests....?

Rich
 
Removed one of the plugs at the front, measure the depth of the thread on the engine and that is 13 mm approx. Certainly not 19 mm. That is as long as I'm measuring the correct part lol
 
So given what Ron says your sooting up problem is likely to be that the wrong plugs were fitted! And now the correct ones are fitted:)
 
Let's hope so. Anyway I have kept you long enough, you have stuff to do on PAE. Want to see it in the flesh so get cracking :wink: Thanks again guys
 
If you have SD1 heads then you need to put 19mm plugs in - otherwise the spark will be in a recess not sticking out into the combustion chamber.

Take the rocker cover off - there is a cast number which I think is ERC0216 for the later heads
 
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