Plug reading please

Ian Z · Post by **Ian Z** » Sun Sep 21, 14 2:21 pm

Chaps,
Any views on this plug by the 'expert plug readers' amongst you? Done about 1k miles. It's from a chewby small block. Seeing some pings at mid revs on mid to hard throttle., computer telling me it keeps falling on weak side of afr.
Thnx

mopar_mark · Post by **mopar_mark** » Sun Sep 21, 14 3:46 pm

I can't see the picture you loaded ?

Here's a good guide
http://www.wallaceracing.com/plug-reading-lm.html

Ian Z · Post by **Ian Z** » Sun Sep 21, 14 7:11 pm

Great idea! Thanks Mark.
Now attached...

Adrian Worman · Post by **Adrian Worman** » Sun Sep 21, 14 7:43 pm

Yeah it is a bit clean innit? See the light tan patch on the insulator? Should be that all over ideally but in all honesty with modern detergent loaded fuel blends it's sometimes hard to read clearly.
Did you mention an AFR meter?

Ian Z · Post by **Ian Z** » Sun Sep 21, 14 7:59 pm

Ade, no afr meter, just tracking blm etc on laptop off ecu. Mostly voodoo to me, but I believe blm count should be bout 128 for proper afr. This Bananarama! 140-155 (leaner) and ican see some knock counts coming up under pretty low load. From marks link it looks on rich side but with that brown patch on very white ceramic. Plug pic taken after vigorous but legal run at operating oil and water temp - not after a wot run unfortunately.

Just really trying to chase down the knock counts.

Mick · Post by **Mick** » Sun Sep 21, 14 8:31 pm

Your plugs are too hot and you need to jet down some. What plugs are they, you run edelbrock heads dont you ? what comp, carb do you run.

Ian Z · Post by **Ian Z** » Sun Sep 21, 14 8:45 pm

Hi Mick, no it's not from plymouth. This is from a chubby efi small block.

Dave-R · Post by **Dave-R** » Mon Sep 22, 14 8:53 am

That plug shows it is too lean. The change in colour on the earth strap shows the timing is a little bit too advanced but if the mixture was richer it would probably be fine and the colour change move up slightly.

The brown area down the porcelain might be an indication of a rich spot occurring at some point but you need to sort out the idle and low part throttle mixture first.

Mick · Post by **Mick** » Mon Sep 22, 14 9:13 am

I was under the impression that the ground strap was an indication of plug heat range, change of colour half way up the ground strap being optimal.

Dave-R · Post by **Dave-R** » Mon Sep 22, 14 11:06 am

Mick wrote:I was under the impression that the ground strap was an indication of plug heat range, change of colour half way up the ground strap being optimal.

That Don fella from FBO used to say it was an indication of timing advance.

Yes it could be just that the plug is too hot for the engine combo. But it does look like it's lean to me.

Without any air/fuel ratio monitoring I would be looking at manifold pressure and seeing if vacuum increased with a richer mixture. Only if it doesn't would I then look at the heat range for the plug.

Dave-R · Post by **Dave-R** » Mon Sep 22, 14 11:09 am

It doesn't look like a particularly hot plug to me when you look at chevy plugs in general.

Ian Z · Post by **Ian Z** » Mon Sep 22, 14 8:58 pm

Thanks for feedback. I've got a few checks to go through like fuel pressure etc. let you know.