New 351 with strange problems
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Junior User
Joined: Dec 2003
Posts: 75
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From: Port Coquitlam
New 351 with strange problems
I recently built a new 351 for my truck here are the specs.
1990 351W
.040 over
new pistons, rings, bearings and rods.
Edelbrock Performer RPM aluminum heads
arp head bolts
Ford racing M-6250-M50 cam
crane lifters and push rods
melling oil pump
ford racing roller rocker arms 1.6
BBK short tube headers ( truck )
MSD coil
Accell module
new ford pick coil in the distributor
MSD wires cap and rotor
NGK iridium plugs
351 lower intake modified to work with a 5 liter upper
I started the truck up and it runs great seems it may be lacking power this I would think is due to the fact the efi may not be up to the task. I have an air/fuel gauge on the truck and it seems it may not be getting enough fuel under moderate throttle. I have checked fuel pressure and it is perfect so this is not the problem. The number one thing that bothers me is the popping and backfiring on deceleration it drives me nuts. I assume this is because it's running rich at idle. But would like some other opinions Im about to convert this truck to carb if I can't solve these problems. It also has a perfect amount of vacuum at idle so this is also not part of the problem
Thanks in advance
1990 351W
.040 over
new pistons, rings, bearings and rods.
Edelbrock Performer RPM aluminum heads
arp head bolts
Ford racing M-6250-M50 cam
crane lifters and push rods
melling oil pump
ford racing roller rocker arms 1.6
BBK short tube headers ( truck )
MSD coil
Accell module
new ford pick coil in the distributor
MSD wires cap and rotor
NGK iridium plugs
351 lower intake modified to work with a 5 liter upper
I started the truck up and it runs great seems it may be lacking power this I would think is due to the fact the efi may not be up to the task. I have an air/fuel gauge on the truck and it seems it may not be getting enough fuel under moderate throttle. I have checked fuel pressure and it is perfect so this is not the problem. The number one thing that bothers me is the popping and backfiring on deceleration it drives me nuts. I assume this is because it's running rich at idle. But would like some other opinions Im about to convert this truck to carb if I can't solve these problems. It also has a perfect amount of vacuum at idle so this is also not part of the problem
Thanks in advance
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
That motor should move a lot more air than the stock one but the speed density EFI system in that truck has no way of knowing this so it's not going to run at it's potential. I suspect the motor is running lean most of the time so you could try increasing fuel pressure beyond spec(42psi with vacuum removed), this will increase the amount of fuel delivered in open loop which is everytime you accelerate at half throttle or better. Play with the fuel pressure and target a 13:1 A/F ratio in open loop, the computer will then attempt to lean out the mixture when it's in closed loop if you give it some time to learn.
Thread Starter
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Junior User
Joined: Dec 2003
Posts: 75
Likes: 0
From: Port Coquitlam
Thanks I will give that a try I also would like to know why everyone says you can not run a cam with anymore then 114 degrees of lobe separation this cam has 116 degrees and seems to work well. Also why would you think it is backfiring and popping under deceleration this would normally mean rich but for some reason my gauge and sense of smell seem to think everything is normal at idle.
I appreciate all the help thanks.
I appreciate all the help thanks.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
actually its less then 114* lobe seperation. so your cam is speed density friendly. question i have is whats the power range of that cam and did you follow proper break in procedures prior to driving it.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Yeah the problem is with less than 114deg LSA.. too much overlap reduces vacuum strength and since manifold vacuum is the key input used to determine engine load on the SD system the computer fuel calculations get all messed up.
Backfiring out the exhaust could be a lot of things, does your A/F gauge show it to be rich or lean when it's doing this?
Backfiring out the exhaust could be a lot of things, does your A/F gauge show it to be rich or lean when it's doing this?
Thread Starter
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Junior User
Joined: Dec 2003
Posts: 75
Likes: 0
From: Port Coquitlam
I did break the cam in properly so that is more than likely not part of the problem. The cam is a stock cam from the 1995 cobra R with a 351 it makes peak torque at 3000 rpm and peak horsepower at 4000 rpm. Under deceleration the air fuel gauge indicates rich and I cannot figure out why it's doing this. I always thought the O2 sensor was ignored under deceleration.
New User
Joined: Jan 2010
Posts: 21
Likes: 0
ditch the efi system all together. eledbrock performer, 600cfm carb, and a HEI distributer. i had the same problem after my 351 was together, only i used a trickflow intake on a SD system. my computer didnt know what it was suppose to do or what was going on. i carbed it and it'll howl 33's like thats its job.
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Elder User
Joined: Oct 2005
Posts: 677
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I agree with farmerfrank.... but try what conanski says.... I used to have an 87 mustang with a cam and head and intake and that sucker always backfired decellerating after hard acceleration.... and that think ran 12s on that motor.... so its kinda how things go with speed density.... you could also try disconnecting the O2 sensors.... that should richen up the mixture too..... its my opinion from my mustang days once you mess with the cam its better to step up to mass air EFI, and then you are still fooling the factory system with bigger injectors and bigger mass air meters to make the thing run right.... I have given up on performance EFI from factory parts.... I say if you want EFI and you want it reliable and you want to use aftermarket parts.... then pony up for the fast style systems....
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Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
mass air swap for his setup would be very very easy and can be done cheap. you can get a plug n play harness from fordfuelinjection.com (rjm) and then pick up an A9L/A9P ecu and get a dyno tune done.
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Junior User
Joined: Dec 2003
Posts: 75
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From: Port Coquitlam
Yes I wanted to do the mass air swap but I cannot buy the conversion kit from ford racing anymore I tried. I really do not feel like hacking up my harness.I have a 1995 thunderbird sc that has mass air and a ton of mods and runs awesome. I was hoping this would run well but it seems it won't, I love being able to start it in the morning and go unfortunately with a carb this will not ba able to happen. The truck runs but is very loud so being able to leave first thing in the morning is great. This is all worth sacrificing in order to get the potential out of this motor thi is not my daily driver.
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