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  #1  
Old September 25th, 2006, 20:45
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spark plug help

After reading some stuff on running lean after installing headers I decided to pull a spark plug and check.

I honestly can't tell whether or not I'm running lean. The white insulator would suggest I am but there is an awful lot of carbon deposits on the top threads suggesting a rich condition.

Please advise.


Last edited by j99xj; September 25th, 2006 at 20:50.
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  #2  
Old September 25th, 2006, 21:56
lilredwagn lilredwagn is offline
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Re: spark plug help

This is a bit more helpful than the page in the back of the haynes manual:

http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html
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Old September 25th, 2006, 22:55
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Re: spark plug help

Thanks for the link. My spark plug looks about a 23, "hot or lean, but ok."

I'm not running hot because my coolant temperature hardly ever exceeds 210, if ever.

So I must be running lean.

Here are my mods:
flat K&n filter
removal of the intake restrictor
60 mm bored throttle body
62 mm spacer
pacesetter header/downpipe
2.5 cat
2.25 high flow cat back

All these mods put me at about 215 to 220 horsepower at SEA LEVEL. Thats 187 hp at 5000 feet. 220*0.85=187

If my stock 22.5 lb/hr injectors are designed to support 190 hp stock, at sea level, then why can't they support 187 hp at 5000 feet??

Is this a fuel pump/pressure issue?
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Old September 26th, 2006, 00:30
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Re: spark plug help

You are close to the point where injectors become a concern, but not there yet. But there are a few things you can do to richen the mixture without springing for new injectors. An adjustable MAP can help alot and is needed if you move up injectors anyway. Moving the IAT to the intake tube will probably get you where you need to be and hardly cost anything. You can always get an adjustable FPR too.
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Old September 26th, 2006, 14:52
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Re: spark plug help

Will a Map adjuster work for a 1999 4.0 with OBDII?
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  #6  
Old September 26th, 2006, 15:29
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Re: spark plug help

Quote:
Originally Posted by j99xj
Will a Map adjuster work for a 1999 4.0 with OBDII?

Yeah what he said, the only difference is on a 98. So does a 98 have 22.5lb or 24lb injectors?
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Old September 26th, 2006, 16:16
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Re: spark plug help

Quote:
Originally Posted by CartsXJ
Yeah what he said, the only difference is on a 98. So does a 98 have 22.5lb or 24lb injectors?
I think 96-99s are 23.2 lb/hr. This is what Dr. Dyno says.

Mines a 99 but I have the 22.5 kind.

But anyway it would be super nice to know if map adjusters work for us. It would be the next thing I do to my Jeep when I get time to do so.

Last edited by j99xj; September 26th, 2006 at 16:20.
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Old September 27th, 2006, 13:57
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Re: spark plug help

Quote:
Originally Posted by j99xj
Will a Map adjuster work for a 1999 4.0 with OBDII?
I don't think it will. I've heard from a few people the computer just corrects to the correct voltage. You might have to go with an adjustable FPR.
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Old September 27th, 2006, 14:08
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Re: spark plug help

I just found a guy that said he got his to work on his 98 from this post:
http://www.naxja.org/forum/showthread.php?t=98312
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