351 tuning problems

Discussion in 'Fox 5.0 Mustang Tech' started by rc4mike, May 9, 2009.

  1. Having a heck of a time figuring out whats going on with my EFI system. I have a 94 roller 351 bored to 408. Engine pulled 460HP on engine dyno with a carb setup. Now its in my car and converted to EFI. On the dyno it starts loosing power at 5500 rpm and appears to be running erratically. Almost like injectors are firing out of sequence....according to the guy tuning. Power barely reaches 310 at wheels. Using an MSD 6AL ignition.

    Engine has a lunati 351 cam...so it's firing order is like 5.0 HO. Dizzy is setup in the HO/351 fire order. Computer is a reman A9L from 93 cobra...so they say.

    Engine runs rough, almost like its missing power on one cylinder. Ran codes, all ok. Ran cylinder balance test and it passed....ie all cylinders contributing equal power. Fuel pressure is 55 psi (i know too high....need to get new guage to verify and lower pressure) using 30 lb injectors.

    Tuner thinks i have 1 or 2 injectors out of phase with spark. Wonder if computer is not a 93 a9l....perhaps older NON HO computer...stickers are missing and case painted black. Switched all inkectors as well. Wonder if injectors too small? Also, tuner thinks engine should run like hell when pulling wires from one injector. In my case, we cant tell when one injector is disconected.

    any ideas?

  2. hhhmm not sure but I can tell you the 93 Cobra did not have an A9L it had a X3Z cpu which is not very desired. I'd also be concerned because you don't know for sure what it is. Can you swap in another one?
  3. First off 30lb injectors are too small....yo need prefably 42lb injectors if you want to put down 460HP...Also what intake are you running??? Hope the Throttle body isn't smaller than 80mm or it will cut down high RPM air flow. You need either a 90mm trickflow R or a Spider intake capable of feeding high volumes of air. I have a 383 from a 351 roller and my 36lb injectors are almost too small. I also have a 90mm Trickflow Box intake....Which is a necessity on a 408 if you want to make near that 500hp mark. Heres a pic of my efi setup.

  4. OK, so looks like you guys are thinking fuel related. I was going that way as well. Intake is eddlebrock with 76 mm CL MAF, 75 mm throttle body, 30 lb injectors. Using aeromotive compact combination regulator...guage is broken, but tuner used his guage and found 58 psi w/o engine running. They didnt check it running...strange. Later they thought my 351 cam was wrong firing order as i was using an a9l from a 93. Not sure they know what they are talking about. Firing order is the same for 93 cobra and 351. My computer is a reman unit w/ no factory sticker...so not really sure what it is. Paperwork says 93 cobra, but that could be bogus.

    I am thinking of getting a true a9L computer, 42 lb injectors and then crossing fingers. Uou think 76mm MAF and throttle would be ok?

    My fuel lines go from pump in tank to drivers side back of rail, then across front to other rail, then to inlet side of regulator, then back to tank. I have seen lots of ways to run these. Wonder if this is also part of my probblem. Guess i need to get with aeromotive to make sure. I see that you (95 vert) are running a Y-block before going to each rail. Wonder which is the better way to go?

    thanks for the help.

  5. Stuff around 75mm is good for a 331 or 347. You have a Small block but techically its a big block. Did they run a wide band sensor to see that it was leaning??? You def need a bigger intake. Look at the size throttle bodies on the vette z06 motor. You have a 408 thats why your car makes peak power around 5500rpm. With the right amount of injector and a 90-105mm intake your motor should easily make power all the way to 6500+ RPM. Check the bore on your intake and see how far you can go....a 408 isn't the motor you want to get modest with when it comes to air and fuel.

  6. yes on the wideband. Was running around 12.5 to 1? does that sound right? They were not real helpfull on the info...i am new to the tuning game. They seemed to think that engine would sputter if we removed one injector wire. However, No noticeable difference. They thought this was a sign that something was plugged in the fuel system.

    Not sure i have confidence in what they were telling me.
  7. Least you said it before me. Ive personally had Rockers loosen up and valves not open and didnt get a sputter. Its a 408 not a 4Cyl. If anything it might give some noticable hesitation on acceleration. But disconnecting an injector wont make the 7 liter engine stumble. You could run the motor with a Plug wire disconnected.Get some 42lb injectors and a bigger intake and the throttle response will be awesome. When i first built my 383 i had a 75mm Throttlebody...Big improvement when i went to 90mm. I'm sure it will be night and day difference on a 408. Higher revs want more air and more fuel. You at least need 42's.

    Oh yeah and these guys should have noticed your motor leaning out......unless the small intake choked the motor before it got a chance to lean out.

  8. i think they should have done more to try to figure this out. They are used to 4.6 mustangs...not sure they are that familiar with 351's. They started out trying to keep all FR around 12.5 all the way up to 5500 where it started cutting out. On the first pull he noticed that it took forever to get to 5500 rpm. seemed sluggish he said. I guess if air intake is too small, engine cant rev. up as freely. Thanks for the info. I will get with eddlebrock and confirm how much power their intake should be expected to feed. Guess i need to start looking for larger stuff. yeah!

  9. ok, more info. Just spoke with Lunati tech...i have a lunati cam. My cam is not recommended for 93 model EFI...too much duration, etc. Said the proper cam would make a HUGE difference. Sooooo, guess i am pulling it and having them re-grind it...yeah!
  10. Before ripping into the motor....

    The A9L and X3Z do not use the same MAF meter.
    Verify that your MAF is properly calibrated for your ecu and injectors.
    It sounds like this might be the issue.....??????

    Is the tuning shop installing a custom chip???
    If yes, then the MAF issue isn't an issue

  11. yes, they are using an SCT chip. I did not realize i had a cobra computer....going to find an a9L before i go back for tune.
  12. I'd find another shop to do the tune, while I was at it. Injectors pulsing out of sequence? I've never seen a batch fire engine run like you described, when the injectors pulsed out of sequence with the spark. These guys sound like they have zero idea what to do. You're near Houston from what I gathered by checking your IP? There's quite a few SCT dealers in the area. I'm sure one of them would have a grasp on diagnostic work, while tuning.
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  14. I agree on possibly getting another tuner. Just not sure i was getting what i should from them.
  15. You don't have to buy new parts!!!!

    You have to verify, 100% what parts you have!!!!

    If you tell the shop that you have a MAF meter calibrated to an X3Z, but in reality the MAF was cal'd for an A9L... then the tune won't work.

    Get the numbers off the MAF meter.
    Get the number off the injectors.
    Google them!

    Blaming the tune shop for a parts mismatch on your part isn't right..... :shrug:

    You may have the right parts, you may not.
    Until you verify that, you shouldn't spend any more money....
  16. OK, so i have taken everyone's advice. Here's what i did

    -new "EFI friendly" cam....at least according to Lunati
    -42 lb injectors
    -pro-m 90mm mass air(calibrated to injectors)
    -fuel pressure set to 45 psi
    -did some minor porting between throttle body and intake.

    as you can see from the attached dyno run, power and torque is now about what it should have been in the car with looses. Used to be 460 hp 450 torque with another more aggressive cam on engine dyno and carburator. Now in the car, with drivetrain loss, HP down some, but torque is close to what it was on engine dyno.

    Car seems to have a ton of power driving...its a shell now. Hope i can get that power to the ground.

    thanks for the help

    Attached Files:

  17. What is the engine combo including cam specs?? that engine does not want to rev at all..
  18. I was going to say the same thing. Did you ever get a bigger throttle body?? 75mm isnt even close to what you need so no amount of porting is going to help a 75mm throttlebody flow for a 400+ ci motor.
  19. cam is a lunati #61011 272/280 advertised duration

    Still running the 76mm throttle body, so obviously thats part of the problem. My intake is also not rated to flow enough for the engine combo(Eddlebrock performer II intake) . The recent upgrades and mods have obviously helped it a TON, but a bigger intake and throttle body is next. My MSD 6AL2 ignition was set to limit revs to 6k but repeatedly cut out at 5500 rpm, strange.


    Attached Files:

  20. What heads?? how much compression?? what is your goal for power?? I found the full specs. on that cam and it is very small for a 408..