The more I learn, M5 post: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Oct. 5, 2010 9:44 p.m. gunner New Reader

The more I find out about this M5 the more I'm glad they were overbuilt.

Start with rear diff that I don't think has ever been changed. I should preface this with the fact that the records book only has the first two services stamped in it.

It took my electric impact gun over a minutes worth of trigger time before the drain AND fill plugs came out. thats each. granted it's the harbor freight 50 buck special, but that aint right. They weren't coming out without it.

I'm pretty sure the tranny was changed once. at 30k.

did I mention that the car has 90k miles on it? with both done, at least the engine has had regular oil changes.

the spark plugs look original. I changed them today. http://img413.imageshack.us/i/photo044t.jpg

any idea what the burned insulator means?

The K&N filter looked like it had never been cleaned, so that probably explains the deposits on the plug. nasty though.
Oct. 5, 2010 9:52 p.m. cxhb HalfDork

Daaang... Isnt that the generation that has the M1 engine in it? Awesome car despite all that previous owners neglect.
Oct. 5, 2010 10:05 p.m. gunner New Reader

Yes it is, despite all the neglect, it runs like a scalded cat, and sounds like a nascar. It's got an aftermarket exhaust and the plugs wires have been replaced. Thankfully they tested perfectly. funny thing, before the new plugs it ran at 3100 rpms at 70 mph, now at the same speed, it runs at 2700. maybe number 6 plug was burnt out. it was much darker than the one in the photo, and I'm talking about on the white insulator above the nut. it was weird, I've never seen a plug that was burnt like that on the top side.
Oct. 5, 2010 10:44 p.m. porksboy Dork

I think the burnt look on your plugs is from silicone release on the plug boots. I have seen it before and that is my best guess.
Oct. 5, 2010 11:23 p.m. Shaun Reader

I have seen plugs look like that when the plug well gets oil water or both down in it and it bakes off leaving residue on the plug.
Oct. 6, 2010 6:59 a.m. 93celicaGT2 SuperDork

gunner wrote:

Yes it is, despite all the neglect, it runs like a scalded cat, and sounds like a nascar. It's got an aftermarket exhaust and the plugs wires have been replaced. Thankfully they tested perfectly. funny thing, before the new plugs it ran at 3100 rpms at 70 mph, now at the same speed, it runs at 2700. maybe number 6 plug was burnt out. it was much darker than the one in the photo, and I'm talking about on the white insulator above the nut. it was weird, I've never seen a plug that was burnt like that on the top side.

Neat. I like it when simple maintainence changes gearing.
Oct. 6, 2010 9:03 a.m. Duke SuperDork

gunner wrote:

funny thing, before the new plugs it ran at 3100 rpms at 70 mph, now at the same speed, it runs at 2700.

So installing fresh sparkplugs changed you gear ratios?

[edit] D'oh! Treed.
Oct. 8, 2010 8:54 p.m. gunner New Reader

I dunno. weird. Is it possible that it was running on 5 cylinders and now on 6? Seriously, it runs at 80 mph now at the same rpm it was running at 70 mph before the spark plug change. Or maybe I should have taken the blue pill and not the red one, but YES this is what I am observing. You are the Jedi here, I am the apprentice.

I did at least figure out the stuff you can see, like plug wires, belts and engine oil were changed regularly, so it wasn't abused purposely. It even has adjustable anti-roll bars, which I assume weren't stock. So the PO tried to do some things right.
Oct. 8, 2010 10:07 p.m. motomoron HalfDork

Pipe threads are hard to break loose w/ impact, but really easy with a giant allen wrench and a cheater bar. You may have room for a 1/2" drive/14mm hex bit but on my M3 the spare tire well is too close so I have to use a 14mm allen wrench....

Also - does the tach now indicate a different idle speed and rpm at your shift points? rpm + speed are connected through tire diameter and gear ratios - spark plugs just aren't in the equation and tach send by plug wire inductance hasn't been a thing for a long, long time...
Oct. 10, 2010 2:09 a.m. gunner New Reader

I tried the cheater bar first and no joy, why I went to the impact. So I hear ya brother.

Idle did drop to about 700 rpm after the plug change too. I never did the correlation between speed and rpm at my shift points, I always shift either at around either 2500 or 3500 if I'm not trying to get around someone so I have no idea what the speeds were before the plug change.

honestly, I know you are right, but I can't get over that the speed has changed at rpms. it's not worth discussing except to say the car runs better. lets leave it at that. I do appreciate the input.