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Unread 07-19-2014, 09:06 PM   #1
JimG91YJ
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1991 YJ Wrangler 
 
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91 YJ stroker overfueling

I recently installed a 4.7L stroker (4.0L block) in my 91 wrangler. It runs very rough at low rpms with little power and backfires through the intake. I have replaced the temp censors in the intake and thermostat housing, also replaced IAC, TPS, Map censor, and fuel pressure regulator. Nothing seems to help. Any suggestions?

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Unread 07-20-2014, 04:18 AM   #2
Mike Romain
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Miss a tooth on the timing chain? Did you do the double check count of the 15 pins between the dots on the gears?

Low vacuum and low compression are usually the result of that, so a quick test of those might help narrow it down some.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 07-20-2014, 04:45 AM   #3
JimG91YJ
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Timing set was installed by the manufacturer (ATK performance Engines), but thanks I will check. A friend sugested advancing the cam timing by one tooth.
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Unread 07-20-2014, 07:13 AM   #4
JMickey
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Moving your timing chain by a whole tooth sounds like way too much to me. I wouldn't do it. When engine builders advance or retard cam timing it's only a few degrees. One tooth is more than a few degrees. Have you checked your ignition timing? Have you checked your crank sensor? What about your O2 sensor? Where is your Fuel pressure at?
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Unread 07-20-2014, 11:36 AM   #5
JimG91YJ
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ignition timing is correct, fuel pressure is correct, all sensors have been replaced. Cam timing was correct (15 pins between the marks), I moved it 1 tooth and it seemed to help. It runs much better, but still not right. I will call the engine builder Monday.
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Unread 07-20-2014, 05:13 PM   #6
JimG91YJ
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apparently moving the cam timing is not a good idea, it seems to run better at an idle but has no power when under a load. I changed it back to where it should be. I'm thinking that a larger throttle body might help?
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Unread 07-21-2014, 04:24 AM   #7
Mike Romain
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If it were mine, I would be talking to the engine builder about it. Backfiring out the intake isn't a good thing.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 07-21-2014, 01:23 PM   #8
JimG91YJ
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I tried, still waiting for them to call me back. I've called them several times. I won't recomend buying anything from them (ATK high performance engines). It was purchased through Summit Racing, the website says it will work in a '91 wrangler, but when I talked to them today they say it needs the computer re-programed, About $600 from Jet performance chips.
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Unread 07-21-2014, 05:43 PM   #9
JimG91YJ
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I finally found someone that knows what they are talking about, Zack Steele, owner of 505performance, instructed me over the phone on exactly what I needed to do to resolve the problem, no computer work needed.
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Unread 07-21-2014, 06:38 PM   #10
JMickey
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Quote:
Originally Posted by JimG91YJ View Post
I finally found someone that knows what they are talking about, Zack Steele, owner of 505performance, instructed me over the phone on exactly what I needed to do to resolve the problem, no computer work needed.
Ok. So what exactly were you told to do to resolve the issue?
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Unread 07-22-2014, 02:11 AM   #11
JimG91YJ
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remove the locating ear on the distributor and "sinc" the timing(with engine running at 2,000rpm turn distributer to the left, mark where it starts to break-up, same thing to right, center it between the marks and tighten down), loosen the rocker arms by shiming underneath (if it's quiet it's too tight), replace injectors with 24lb injectors, replace spark plugs with autolite 3924 plugs.
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Unread 07-22-2014, 06:44 AM   #12
jsawduste
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Quote:
Originally Posted by JimG91YJ View Post
I finally found someone that knows what they are talking about, Zack Steele, owner of 505performance, instructed me over the phone on exactly what I needed to do to resolve the problem, no computer work needed.
Your kidding right ? Zack and 505 are one of the biggest jokes/hacks and rip off artists in the world of vendors.
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Unread 07-22-2014, 05:36 PM   #13
JimG91YJ
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Quote:
Originally Posted by jsawduste View Post
Your kidding right ? Zack and 505 are one of the biggest jokes/hacks and rip off artists in the world of vendors.
I can't complain, what he told me to do worked.
I've called ATK several times and still havent talked to anyone that could help.
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Unread 07-22-2014, 08:02 PM   #14
jsawduste
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Sorry Jim but ATK isn't known for stellar service ether. Not whining but simply stating well established and earned facts from within the stroker world.

Indexing the distributor is better done at idle where you can more readily feel and hear the engine begin to stumble then when it is racing at 2,000 RPM.

The Autolite 3924 plug is a projected tip plug with roughly the same heat range as the typical Champion R*12`s. You might consider going to non projected tip plug if you have any signs of detonation. In some cases a slightly colder plug is also helpful in avoiding deto. Such as Champion R*11`s.

Your ATK engine should have come with 24 lb injectors. If not I would be asking ATK why. Typical fuel pressure should be around 39-43 psi with the vac line connected and engine idling

Good luck with your new stroker !!.
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