Spark plug gap 112 engine?

[LawrenceMB]

Hi, I've tried researching the answer to this but are getting conficting info;
The spark plugs listed for my 112 engine are the Bosch F78DC.. (or something like that off the top of my head) which come pre-gapped to 1.0mm, but the info for this enging when 1st released was the gap should be 0.8mm. As I say I'm getting conflicting info as to whether I re-gap them or fit as pre-gapped.
As these newer plugs have 3 earth electrodes now is it ok to fit them with the 1.0mm gap?
(reason I ask is I've got an annoying slightly rough idle which I want to cure and went to replace the plugs but they'd already been done by the previous owner with the same new design bosch plugs - so I left it - but i don't know what he gapped them to or if it's even a problem?)
Thanks in advance
Lawrence

 

[carat 3.6]

Dont re-gap the plugs, fit them as they come. Iirc your engine has 2 plugs per cylinder, maybe only 1 plug is firing on one of them.

When you removed them did any look darkend or wet?

 

[DRBC43AMG]

Keep the standard plug gap as adjusted my the plug manufacturer (1mm). You will have 2 plugs per cylinder on your M112 V6 and same as the M113 V8 engine. Both engines use the same plug reference.

 

[LawrenceMB]

Dont re-gap the plugs, fit them as they come. Iirc your engine has 2 plugs per cylinder, maybe only 1 plug is firing on one of them.

When you removed them did any look darkend or wet?

Hi mate, I didn't actually remove them because as soon as I got the covers off the engine I could see they'd been done already (they'd numbered the coils themselves 1-6 & painted white dots on the coils where the HT leads go into it to know how to refit them). I took one HT lead off at the plug end to check wh\t plugs they'd fitted & they were the same I had ready to fit myself. Being that it had 'only' done 90k & had already been fitted once with the right plugs I thought 'if it aint broke - don't fix it', especially as I was expecting it to take a couple of hours at least.
You're right though I need to puul them all out & see how they're burning, now that I know if they were fitted with the pregapped 1.0mm then that's fine.
Do the colis give problems on these 112 engines do you know?
Cheers,
Lawrence

 

[carat 3.6]

Hi mate, I didn't actually remove them because as soon as I got the covers off the engine I could see they'd been done already (they'd numbered the coils themselves 1-6 & painted white dots on the coils where the HT leads go into it to know how to refit them). I took one HT lead off at the plug end to check wh\t plugs they'd fitted & they were the same I had ready to fit myself. Being that it had 'only' done 90k & had already been fitted once with the right plugs I thought 'if it aint broke - don't fix it', especially as I was expecting it to take a couple of hours at least.
You're right though I need to puul them all out & see how they're burning, now that I know if they were fitted with the pregapped 1.0mm then that's fine.
Do the colis give problems on these 112 engines do you know?
Cheers,
Lawrence

The coils can play up, but no more than any other setup. What problems are you having?

 

[LawrenceMB]

The coils can play up, but no more than any other setup. What problems are you having?

Nothing Major, just an annoying uneven idle

 

[carat 3.6]

Nothing Major, just an annoying uneven idle

Remove all the plugs and see if any look bad, check for air leaks around the inlet manifold, and also have the fault codes read.

 

[LawrenceMB]

Remove all the plugs and see if any look bad, check for air leaks around the inlet manifold, and also have the fault codes read.

Ok mate, will do
When you say leaksaround inlet manifold, do you mean as the manifold gaskets or are they prone to vacuum lines leaking/coming off?
Thanks,
Lawrence

 

[carat 3.6]

Ok mate, will do
When you say leaksaround inlet manifold, do you mean as the manifold gaskets or are they prone to vacuum lines leaking/coming off?
Thanks,
Lawrence

I'm thinking you may have a leaking inlet gasket somewhere. With the engine running spray brake cleaner over each cylinder inlet in turn, if it upset's the idle you have a leak on that cylinder.

 

[Auto-mobile]

The leads are far more common to fail than the coils, if you have uneven idle/slight miss its probably a couple of leads breaking down.

 

[LawrenceMB]

Excellent, thanks for the advice gents

 

[andy27168]

Hi,
Had a slightly eneven idle on my C43 M113 engine (effectively a V8 version of your engine) I solved mine by replacing the "O" ring seals between the throttle regulater and the MAF, the O rings were very hard and brittle and the result was quite noticable idle was smooth and throttle response was improved, and being on the inlet side of the e ngine seems to fit the bill as a potential solution to your problem.

 

[LawrenceMB]

Hi,
Had a slightly eneven idle on my C43 M113 engine (effectively a V8 version of your engine) I solved mine by replacing the "O" ring seals between the throttle regulater and the MAF, the O rings were very hard and brittle and the result was quite noticable idle was smooth and throttle response was improved, and being on the inlet side of the e ngine seems to fit the bill as a potential solution to your problem.

Thanks Andy! Nice one - I'll check it out