Help with new motor install

Discussion in 'Fox 5.0 Mustang Tech' started by axelnut1, Jul 24, 2007.


  1. axelnut1

    axelnut1 New Member

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    Where to start? I put a new ford 302/345 horse b-cam motor in my '88 stang. I did the mass air flow conversion with all new Ford parts. 70mm maf calibrated for 30lb. injectors. Trick flow street heat upper and lower intake, 65mm egr plate and Throttle body, 30lb. injectors, ac eliminator, adjustable fuel pressure regulator set at 40lbs with vacuum hose off and plugged. Idle manually set at 900rpm and set the TPS to .98v. The motor runs great but when I start it after sitting all night it idles rough, between 600 and 1200 rpm. for about 3-4 minutes then idles fine at 900rpm. No vacuum leaks, egr checked good, new ECT and ACT. IAC cleaned and checked. Reading the plugs it seems to be running a little lean. One more question, if the computer takes over and adjust fuel itself, what good is the adjustable regulator? Anyway, your help and ideas are very welcome. Thanks
  2. axelnut1

    axelnut1 New Member

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    Forgot to add some stuff

    Mustang also has a MSD Digital6 box, MSD distributor, 1 5/8" shorty headers with a 2 1/2" X-pipe into a Flow Master American Thunder cat back system.


    Sponsored Ad

  3. vristang

    vristang Advanced Member

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    lol
    That's a BIG question right there.

    If you have the ability to adjust your fuel pressure, then go ahead and bump it up 1-2psi and see what happens.

    The computer does make adjustments to the fuel based on AFR input from the O2's.
    The ecu can only adjust so far though...


    How long have you had the current combo together?
    It can take several days for the ecu to adjust the fuel to where it needs to be...


    jason
  4. ShortThrow50

    ShortThrow50 Member

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    My mods are in my sig. I have my fuel pressure set at about 41 psi. My car idles rough at about 6-700 rpm for about the same time you mentioned and then smooths out at a lopey 900 and runs great. That is something I wouldnt worry about, infact i like how it does that, because it makes it sound like it means bussiness. Im sure if you ever get the car tuned it would fix it. In the mean time just enjoy your ride.
  5. axelnut1

    axelnut1 New Member

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    Thanks

    The car has only been running since last week. Maybe 150 miles already. It runs great and except for that one minute in the morning nothing else is wrong. I need to put some 4-11's in the rear so I can enjoy the motor a little more. Thanks for the info. This is actually my son's first car. He started driving in May of 2007 so he is very excited. It is my first time ever doing anything with fuel injection and all the electronics. I dreaded it for the start but it actually is not to bad, just have to be patient with the changes. Anyway, thanks again. Later,Brian
  6. ninety15.0

    ninety15.0 New Member

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    Im betting that you are actually running rich during the time when the idle is rough and surges up and down. There is almost nothing you can do about it without getting a tuner. You have done all the proper adjustments to try to fix it but the problem stems from the increased injector size and "calibrated" MAM. The computer is still running on the factory MAF voltage curve which is different from the aftermarket piece which flows significantly more air. Those 30# injectors are too big for that engine combo. Im guessing by the way you said it was a 345hp 302 its actually the ford racing gt-40 crate motor!? this combo could actually run on the stock 19's but 24's are actually the right size injector. The combination of injectors that are too large and an aftermarket MAM are causing the majority of your and most HCI guys on this forum! A tune will fix your problem no question.
  7. 90bluegt

    90bluegt Founding Member

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    I'm going to agree with ninty15.0 on the injector size and issues with startup, your reasoning for upping the idle to 900 rpms is why? If it's for the car to idle then theres an issue as well. The car is surging when started up because of a rich issue with the injectors and MAF.

    What you need is a good tune for the car and you should be able to idle that thing around 750 or so. Take it to a shop or get a Tweecer or another tuning device and tune it yourself (you learn alot about engines with a tuning device).

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