|
Author
|
Topic: Inconsistent Spark Plug Readings
|
Reed's '65 vert
Journeyman Posts: 33
From: Houston, Tx , US
Registered: Apr 2004
|
posted 11-30-2005 11:05 AM
   
Yesterday, I checked my plugs to see how the engine was running and discovered that my plugs varied in color. It's a stock 289 four barrel with an 1.08 Autolite 4100. Following are the plugs and their conditions.1. OK
2. Bone white
3. Borderline rich
4. Rich
5. OK
6. Bone white
7. Bone white
8. OK The lean (white) plugs show no signs of detonation. At first, I thought I found a pattern with the stock intake manifold runners. On the drivers side, the lean plugs correspond to the lower runners while the normal plugs correspond with the upper. However, this does not hold true for the passenger side. I did notice that I do have a slight miss at idle, but seems to dissappear over 1000 rpm. I'm pulling 20 in Hg at idle and the engine seems happiest around 18 BTDC. When I back off to around 10 BTDC, she starts to stumble and vacuum falls to around 14-15 in Hg. Could this all be indicative of a loose intake manifold or possibly a bad gasket seal between the manifold and the heads. Any help/suggestions would be appreciated.
IP: Logged |
Pierre
Gearhead Posts: 624
From: Near Paris, France
Registered: Apr 2002
|
posted 11-30-2005 04:09 PM
To complete your analysis I would run a compression test on all cylinders & install 8 fresh plugs to eliminate all other possibilities
IP: Logged |
Reed's '65 vert
Journeyman Posts: 33
From: Houston, Tx , US
Registered: Apr 2004
|
posted 11-30-2005 05:12 PM
A compression reading I took a couple of weeks ago yielded 160-170 psi across all cylinders.
IP: Logged |
n2oMike
Gearhead Posts: 2899
From: Spencer, WV
Registered: Jan 2001
|
posted 11-30-2005 05:38 PM
They'll do that if you check it if you've been idling it around. The only way to properly check your plugs for power is to run it wide open for a full run, then IMMEDIETLY cut the engine off, pull over and check the plugs.------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
IP: Logged |
Reed's '65 vert
Journeyman Posts: 33
From: Houston, Tx , US
Registered: Apr 2004
|
posted 12-01-2005 10:04 AM
Thanks for the info. I was setting the float levels on my carb and so the engine had been idling for quite some time prior to me checking the plugs.I'll get it on the road at WOT and then give them a read and see what they say.
IP: Logged |
63Kcode
Gearhead Posts: 241
From: Anna Tx
Registered: Dec 2004
|
posted 12-01-2005 03:15 PM
quote:
Originally posted by Reed's '65 vert:
I'll get it on the road at WOT and then give them a read and see what they say.
I can just hear it now" Honest officer I was just speeding to see if my car was tuned. You know that it pollutes less when in proper tune. I never drive like this normally. It's all Mikes fault!! Please don't give me a ticket. Do you mind if I pull the plugs before you impound my car"
IP: Logged |
Jake11
Gearhead Posts: 207
From: Banning,Ca,USA
Registered: Oct 2005
|
posted 12-02-2005 04:05 AM
Get some good ign. wires and re-ck.
Use Autolite,Motorcraft or AC plugs.
Unless you got little black spots on the
insulators, don't worry too much.
What's total timing?
IP: Logged |
Reed's '65 vert
Journeyman Posts: 33
From: Houston, Tx , US
Registered: Apr 2004
|
posted 12-02-2005 12:52 PM
Wires are 3 mo. old 8mm Accel radio supression wires. Plugs are Autolite 45s gapped at .035. Total timing is around 36 BTDC.Could incorrect valve train adjustment have any affect like this? When I rebuilt engine last year, I adjusted the valves with the hydraulic lifters dry based on the shop manual specs. I checked the valve stem to rocker arm clearance with the plungers bottomed out in the lifters and all came within spec. Currently, I have no noise from my rockers at all. However, I do recall that some of the springs, once assembled, were longer than the specs. I didn't go back in and add shims to bring them back under the allowable limit. If I recall, the spec for the assembled length of the spring was 1.75 in. and some of mine were maybe 1/16 of an inch over that. I had a valve job done on the heads before I rebuilt it, so I'm wondering if that could have potentially affected the height of the valve stem protruding through the head. I may go back in and re-adjust the rockers with the engine running based on the numerous threads posted already on this topic just to be sure their not too tight. Should I go ahead and add the shims to springs in question to bring them back down to spec?
IP: Logged |
n2oMike
Gearhead Posts: 2899
From: Spencer, WV
Registered: Jan 2001
|
posted 12-02-2005 02:10 PM
You're thinking too hard.Plugs will look like that after the car has been idling around. My center plugs will look way rich and carboned up after idling around, but look fine after some spirited running. Blow the cobwebs out of it, then re-check them before allowing it to idle around any.
------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
IP: Logged |
Jake11
Gearhead Posts: 207
From: Banning,Ca,USA
Registered: Oct 2005
|
posted 12-02-2005 09:45 PM
If it's running good, don't sweat it.
To read the plugs like you want, you gotta
run it full power in high gear, and kill the
ignition and coast to a stop. That's lot's
of fun. Then put them all back in so you
can drive it. Have fun.
IP: Logged |
Jake11
Gearhead Posts: 207
From: Banning,Ca,USA
Registered: Oct 2005
|
posted 12-02-2005 09:57 PM
You could have a "weak coil". That will
cause all kinds of weird prob's.
And it will look ok on a scope, unless you
have a dyno to load it on when you scope it.
If you got another coil in your stuff, try
it.
IP: Logged |
Mustangsandmore Forums
