Spark plug crud? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Stocker** · 07-21-2003, 06:53 PM

Changed plugs today and six looked okay, but #5 and #8 had a buildup of hard light gray material rising upward from the base of the side electrode. Any ideas what might cause it? Sorry, no digital camera

. I searched Google but couldn't find any pics that resembled it. Know of any sites with good plug charts/pics? As always, Thanks.

jef5150 · 07-21-2003, 07:40 PM

http://www.denso.com.au/dw/spark/spark_gen.htm............its at the very bottom of the page,,,w/pics.....jeff

**Stocker** · 07-21-2003, 09:51 PM

Excellent examples - unfortunately, none matched my plugs......

krue · 07-21-2003, 11:44 PM

Try looking in a Hayne's manual. They always have a spark plug guide in the back of the manual.

jhow66 · 07-22-2003, 12:01 AM

#5 & 8 intake ports are open to each other. Most of the time the PCV hose comes off the back of carb right above this port. If you are using valve covers without a baffle under your PCV valve it could be pulling oil into carb which the biggest part would go to 5 & 8. Just a thought.

jimfulco · 07-22-2003, 02:35 AM

Does the crud resemble what a dirt dobber's nest is made of? Crumbles when you attack it with a pocket knife?

**Stocker** · 07-22-2003, 09:26 AM

Quote:

Originally posted by jimfulco
Does the crud resemble what a dirt dobber's nest is made of? Crumbles when you attack it with a pocket knife?

Somewhat, yes, except for the light gray color, and it's quite hard - it comes off as powder when scraped with a knife.

As to jhow66s post above, that may be it. Stock valve covers (dunno about the baffle), and I have had choke problems for a long time - can't seem to get it properly adjusted. OK in warm weather, but in cold weather the engine loads up badly at idle until fully warmed up. Of course this means it's running way too rich, and all that extra fuel washes the cylinder walls, so it then burns oil.

Although the plugs are dry and the deposits are hard, I'm beginning to think I am looking at baked-on oil deposits caused by my choke problems.

jhow66 · 07-22-2003, 11:39 AM

Have you checked your choke pulloff?

**Stocker** · 07-22-2003, 02:32 PM

Quote:

Originally posted by jhow66 Have you checked your choke pulloff?

Yup! And the choke linkage has been fiddled with by a local machanic, which helped a little. But not much.

jhow66 · 07-22-2003, 02:36 PM

Keep agjusting the choke pull off rod (to open choke more) until engine will run clean at fast idle.

jimfulco · 07-25-2003, 04:43 AM

I was told years ago by an old mechanic that the crusty stuff was fuel deposits, stuff left behind when the fuel burns. I changed brands of gas & it quit happening.

**Stocker** · 07-25-2003, 09:46 AM

Interesting - I mostly use 76 fuel. Still odd it's only on #5 & #8...

JimKshortstep4x4 · 07-25-2003, 09:59 AM

Stocker,

Just a thought on your problem. Do you have power brakes and is the vacuum line they hooked up on the manifold runner behind the carb?

It is possible for the booster to leak vacuum which could change the color of the plugs. Also, any possibility of a small collant leak?

Jim

**Stocker** · 07-25-2003, 11:28 AM

Quote:

Originally posted by JimKshortstep4x4
Do you have power brakes and is the vacuum line they hooked up on the manifold runner behind the carb?

any possibility of a small collant leak?

Yes, yes, and hmmm..... not that I'm aware of - it would have to be a very small leak.

To all - I am amazed at the response from this board. I only wish I had found this place sooner than I did.

07-21-2003, 06:53 PM	#1
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Spark plug crud? Changed plugs today and six looked okay, but #5 and #8 had a buildup of hard light gray material rising upward from the base of the side electrode. Any ideas what might cause it? Sorry, no digital camera . I searched Google but couldn't find any pics that resembled it. Know of any sites with good plug charts/pics? As always, Thanks. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

07-21-2003, 09:51 PM	#3
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Thanks, Jeff Excellent examples - unfortunately, none matched my plugs...... __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

07-21-2003, 11:44 PM	#4
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	Try looking in a Hayne's manual. They always have a spark plug guide in the back of the manual. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

07-22-2003, 02:36 PM	#10
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Keep agjusting the choke pull off rod (to open choke more) until engine will run clean at fast idle. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-25-2003, 09:46 AM	#12
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Interesting - I mostly use 76 fuel. Still odd it's only on #5 & #8... __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

07-21-2003, 07:40 PM	#2
jef5150 Inline 69 Join Date: Apr 2003 Location: valleysprings,california Posts: 1,018	http://www.denso.com.au/dw/spark/spark_gen.htm............its at the very bottom of the page,,,w/pics.....jeff

07-22-2003, 12:01 AM	#5
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	#5 & 8 intake ports are open to each other. Most of the time the PCV hose comes off the back of carb right above this port. If you are using valve covers without a baffle under your PCV valve it could be pulling oil into carb which the biggest part would go to 5 & 8. Just a thought. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-22-2003, 02:35 AM	#6
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Does the crud resemble what a dirt dobber's nest is made of? Crumbles when you attack it with a pocket knife?

07-22-2003, 11:39 AM	#8
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Have you checked your choke pulloff? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-25-2003, 04:43 AM	#11
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	I was told years ago by an old mechanic that the crusty stuff was fuel deposits, stuff left behind when the fuel burns. I changed brands of gas & it quit happening.

07-25-2003, 09:59 AM	#13
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Stocker, Just a thought on your problem. Do you have power brakes and is the vacuum line they hooked up on the manifold runner behind the carb? It is possible for the booster to leak vacuum which could change the color of the plugs. Also, any possibility of a small collant leak? Jim



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.