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Old 02-26-2021, 07:15 PM
posulli88's Avatar
posulli88 posulli88 is offline
258 I6
Join Date: Dec 18, 2016
Location: Denver, CO
Posts: 322
Help me Diagnose Spark Plugs

Well, I just pulled my spark plugs and I am concerned. I have an amc360 that Rick Jones built to have just under 10:1 compression (I run 91 octane here in Denver). Its run by a Holley Sniper (which I think is probably running a bit too rich). Its a full MSD Ignition system and I probably only have around 400 miles on it total. Between a big move and other projects Ive been working on on the J10 I just havn't been able to drive it as much as I would want. Although I have now buttoned everything up and it's ready to see some miles. You can see the detailed build of the engine here:

It did bend a push rod (very minimal bend) due to the guy who machined my heads (before it got to Rick) not doing a great job and missing some measurements. Again Rick has been amazing through this entire build and the quality in his work is evident.

Anyway, Ive just pulled the plugs and most of them seem to be fouled. I know reading plugs over images is hard but Ive done my best to capture high quality images below. A couple notes:

I am most concerned with plug/cylinder 1. That cylinder probably hasn't been running because of fouling. Im trying to convince my self its fuel fouled and not oil fouled. It does smell heavily of fuel. Cylinder/plug 2 has 5 minutes run time on it. I replaced it the other day because I noticed the exterior ceramic was cracked and arcing outside the cylinder. I am running NGK FR5 plugs. Also the silver you see on some of the edges of the plugs is anti-sieze from when I pulled them. Thoughts?

77' J10 w/ 360, T18, Dana 20 TC
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Old 02-26-2021, 08:03 PM
Tripwire's Avatar
Tripwire Tripwire is offline
hey,does anyone here know how to.......
Join Date: Jul 30, 2000
Location: WA State
Posts: 4,545
I think babywag is a FI expert...or was it someone else who helped me some time ago...anyhoo i had two similar issues plugs like yours and plugs that were so fouled in 1 minute it would not run, in both instances it was the TPS, one was mis adjusted the other was wacko and sending WOT fuel when the throttle plates were closed

Abort? Retry? Ignore? >

86 GrandWag. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/229 swap BJ's 2" Lift and 31's

88 Wrangler 4.2, Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer (-:
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Old 02-27-2021, 05:23 AM
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iapexl8r iapexl8r is offline
232 I6
Join Date: Jul 06, 2018
Location: Nort Idaho
Posts: 66
does your sniper have a afr readout? if not,I would start by making sure that all the plugs are getting spark. you can do this several ways. the easiest way is with an infrared thermometer just use it on the exhaust manifold at each exhaust port while the motor is running and if one is cold it is not firing. verify cap, wire and plug on any cold cyl.
1976 Cherokee chief
1970 AMC rebel THE MACHINE
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1972 international travelette
Yes I have a problem that’s why Iam here
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Old 02-27-2021, 08:10 AM
wiley-moeracing wiley-moeracing is offline
350 Buick
Join Date: Feb 15, 2010
Location: arizona
Posts: 1,347
Wet with fuel on almost all, looks like weak ignition, otherwise all would be wet if it was over fueling. That is where I would start, then move to fueling.
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Old 02-27-2021, 11:10 AM
posulli88's Avatar
posulli88 posulli88 is offline
258 I6
Join Date: Dec 18, 2016
Location: Denver, CO
Posts: 322
Thanks everyone. I will check spark today. The Sniper does have AFR read outs. At cold idle it starts around 13.5 and slowly moves up to around 14.5. I havn't done full adjustments to WOT at all. I will look closer at it.

I set my warm idle to target 14.7. I know sniper is a learning system but know thats not perfect. I might reset the entire system and start fresh.

Will replace all my plugs and take heat measurements at the manifolds.
77' J10 w/ 360, T18, Dana 20 TC
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Old 02-27-2021, 12:39 PM
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babywag babywag is offline
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Join Date: Jun 08, 2005
Location: Land of froot loops and cukcoo-nuts, CA
Posts: 9,873
Few things to consider...
O2 sensor placement.
needs to be as close as possible to engine. Too far away they can become inaccurate.

Must have Zero exhaust leaks!
Even a tiny leak can drastically change reading(s).
Say you have a small leak, o2 reads lean, ecm dumps more fuel to combat inaccurate reading and engine runs too rich.

Is it going closed loop and staying there?

Coolant temp sensor.
Verify it is seeing actual engine temp, and display matches.
An ecm that sees low coolant temps with drastically increase afr.
If sensor is off they will run too rich.

Verify fuel pressure is correct. Too high and injectors dump too much fuel compared to what ecm is expecting.

With efi there is the huge lie/myth of self tuning systems. They ALL need tuning.
Their stock programming is generally too rich for real world imho.
Changing stock values via handheld unit = tuning.

EFI isn't a magic bullet, everything has to be correct just like any carb'd engine.
Spark, good voltage to electronics, etc.

Plugs look rich, but when did you pull them?
Best is to do a normal-ish long drive then pull them.
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