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Author
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Topic: Constant misfire at 5000rpms is killing me
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twisted54
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Member # 1981
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posted
 
 
HELP PLEASE...I've got a constant misfire at 5000 rpms and I can't figure it out. It's been on the dyno and one other shop has yet to figure it out.
Here's what I've done so far:
Ignition:
new 3924s gapped at 50
cap and rotor
stator
msd coil
wires
ignition module
fuel:
30lb injectors
255lph fuel pump
fuel pressure reg
recalibrated meter for injectors
I've also cleaned the IAC, IAT and ACT sensors.
The tuner said the injectors are now at 70% duty cycle and the air/fuel ratio is pretty much right on just like the one attached above.
He had a spare processor at his shop and we swapped that out as well as a different chip and nothing helped.
What should I check next??? PLEASE HELP
The h/c/i combo is as follows:
331
twisted wedge
xe274hr
track heat intake
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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TRIXSNK
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Member # 2844
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posted
Did you try closing the gap a bit on the plugs?
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9 Sec EVO 9 is GONE!
New project in the works.......
Posts: 3740 | From: Bay Area | Registered: May 2003
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AJBlackGT
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Member # 3936
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posted
quote:
Originally posted by TRIXSNK:
Did you try closing the gap a bit on the plugs?
yeah, try that...i posted that over on the other post at the corral.
You dont have an MSD box do you?
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90 Notch
Posts: 1896 | From: Sacramento | Registered: Dec 2003
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twisted54
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Member # 1981
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posted
I have a Crane Hi6 Ignition...what should I gap them to, 40 or lower?
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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Stangs R Us
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Member # 4495
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posted
maybe try unplugging the crane box and see if its that, if not have fun finding out what it is cuz i had the same problem and i never could figure it out so i just changed my MSD box did another tune up and changed my timing chain, oh and i went with the A9L computer.
Posts: 3100 | From: sacramento | Registered: Aug 2005
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twisted54
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Member # 1981
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posted
We bypassed the ignition and it still did it. I forgot to mention we also put a new fuel filter in there too.
I found this Ignition and Fuel specialty shop in Concord who says they can probably fix it but I need to bring information and installation instructions for every after market part I have on the car. Oh and the base price for diagnosis is 500.00 ![[Eek!]](eek.gif)
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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jaybquick
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Member # 4286
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posted
hey twstd, just realized I was on the corral forum with your same post. Maybe it is just the Dizzy screwin up.
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91 Mustang GT ET: 11.92@115
66 Mustang ET: 11.43@119
01 Audi S4 ET: 10.8@131
05 Audi S4 ET: 11.9@116
08 Audi S5 ET: 11.9@118
Posts: 416 | From: Lathrop | Registered: Mar 2004
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JohnB
Tech Moderator
Member # 969
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posted
It sounds like the pickup in the distributor is going out. A slight possiblity is the fuel pump cutting off, but I doubt it. I'd check the fuel pressure under WOT though.
Close the gap? The car isn't blown. ![[Confused]](confused.gif)
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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twisted54
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Member # 1981
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posted
Isn't the stator the pickup...If so I just changed it last week. The fuel pump is brand new as of two days ago.
Fuel pressure was dropping at WOT but after changing the injectors, reg, pump, and filter it's not anymore.
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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twisted54
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Member # 1981
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posted
I've heard on stroker you sometimes have to use a smaller gap...is that not the case? ![[dance]](graemlins/dance.gif)
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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JohnB
Tech Moderator
Member # 969
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posted
What is your CR? Unless it's over 10-1, you have no need for closing a gap. And if it is over 10-1, and you're only making a lil over 300rwhp, I'd talk to the tuner, cuz sonething's wrong. ![[Frown]](frown.gif)
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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Fostang
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Member # 3752
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posted
quote:
Originally posted by JohnB:
What is your CR? Unless it's over 10-1, you have no need for closing a gap. And if it is over 10-1, and you're only making a lil over 300rwhp, I'd talk to the tuner, cuz sonething's wrong.
autos and dyno's don't always agree you should know that John. ![[Razz]](tongue.gif)
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67' Fastback TT 408
67' Camaro Lsx
64' Corvette Fuelie
57' Chevy Bel Air Lsx
68’ Pony Convertible
66’ Pony Coupe
Posts: 3012 | From: Stockton/Danville | Registered: Nov 2003
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JohnB
Tech Moderator
Member # 969
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posted
LOL!! Well, I was trying to be nice. I guess I coulda went with something like this...
"I'd speak with the tranny shop first, cuz if you're only making a lil over 300rwhp with a 10-1 331 stroker, you've got a converter as loose as a whore in Thailand"
What I was getting as was he shouldn't need to close the gap. Period. ![[Wink]](wink.gif) I'm guessing all the normal stuff has been checked. TPS, Ignition module, stator, etc...anything that has to do with ignition and/or throttle position??
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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AJBlackGT
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Member # 3936
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posted
I was assuming that he had a little compression when I said close the gap, i mean why have an all motor stroker with no compression ![[Big Grin]](biggrin.gif)
And its free, mine as well worth trying, .050 is a pretty big gap anyway.
Find a dizzy you can borrow and try it out, and check your grounds
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90 Notch
Posts: 1896 | From: Sacramento | Registered: Dec 2003
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2stangs69-91
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Member # 1951
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posted
I would go to a AR autolite racing plug 1 step colder and close the gap down to .040. I have experianced plugs that glaze and cause high RPM misses that only show up under load. I think it is that simple.
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69 Mustang on hold
1991 LX hatch getting a make over
1994 F150 4X4 351
2006 Yamaha V-max 1200 Modded
Posts: 3711 | From: Redding | Registered: Oct 2002
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TRIXSNK
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Member # 2844
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posted
quote:
Originally posted by JohnB:
It sounds like the pickup in the distributor is going out. A slight possiblity is the fuel pump cutting off, but I doubt it. I'd check the fuel pressure under WOT though.
Close the gap? The car isn't blown.
My bad for some reason i thought it was
Didn't mean to mislead.....
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9 Sec EVO 9 is GONE!
New project in the works.......
Posts: 3740 | From: Bay Area | Registered: May 2003
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98slowhoe 'FIFTYLX'
Uncle Frank
Member # 895
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posted
Sounds similar to the problem Yellow94GT(drew) is having. He can't find the damn thing either, and he has tryed a lot of different things. I wish you the best of luck cause it might be a while!
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AKA Franky Freaking 5 liter
Advanced Engine Development
SCT dealer
Dynotuning
Engine building
916*275*8212
88 4runner on 42's
Posts: 4206 | From: Folsom | Registered: Feb 2002
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Hungry Hippo
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Member # 537
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posted
i'd try a .045" gap and check as many of the grounds as possible
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05 S4 Avant(wagon)
09 C6 H/C/I
Posts: 2959 | From: east bay | Registered: Nov 2001
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twisted54
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Member # 1981
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posted
Today was the first time I've drove it since cleaning the ACT, IAC and IAT and it seems to be much, much better... Before I cleaned the ACT, it was black with crud all over it.
The Thermactor vacuum hose wasn't on all the way too. I don't know if either of these could have been the problem but the car hasn't misfired yet in about 20 attempts. It use to do it all the time. It might just be my imagination but I'm getting a second opinion on this in an hour or so.
Thanks guys
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3422 | From: ebay | Registered: Oct 2002
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talaposa
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Member # 2460
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posted
Looks like its time to go back to basics. I'm assuming from the threads that the ignition and fuel are O.K.
I'd look into the spring rate on those heads. Weak springs could start to float at about that rpm with the hydraulic roller setup. Cam profile will make a difference. I'd look there.
Posts: 91 | From: Auburn,CA | Registered: Feb 2003
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