new to mustangs,need tuning help


New Member
May 16, 2010
ive recently built a 347 for a fella,in a 87 fox not much on fords or mustangs,but i do machine and build engines for a living.
it has forged crank.eagle rods.srp forged pistons.block is zero decked. heads are world product windsor sr. 2.02 valves,cam is a blue racer wolverine...510/.534 lift.stamped steel roller tip rockers for now. trick flow track heat intake,1 inch plenum spacer.75 mm stack polished throttle body and spacer.30lb injectors,matching maf,changed computer and harness to a maf harness?air pump and a/c comp removed, i have an adj regulator to put on. long tube headers.h pipe into flows
got it up and running,seems to have a surge.dips low enuff to cut off.right now i have it idles up a bit to keep it running. i have to reset the tps now cause he mesed with it and left it loose and it moved. question is what do i need to do to do some fine tuning? im reading a bit on here on quarter horse and some other stuff, but have no clue what is what. just getting it to idle smooth is a plus right now. lemme know what to start with. well,ive got to start with putting another starter on..the heat just killed this new one..
also its ging back with a 150 shot of gas
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New Member
Nov 3, 2009
When it comes to late model EFI cars, modified engines generally need to be retuned by someone who understands the required changes. On the EEC-V cars (94-04), the spark timing is calculated by load. Load is calculated by Mass airflow, rpm, and cubic inches. Any changes to MAF or cubic inches requires a retune. On 05-up cars, forget it. Everything you do requires retuning. They are very sensitive.

Luckily, you've got a fox to work with, which is remarkably forgiving. Spark timing is an rpm-based calculation, so load doesn't affect it. Changing base timing settings changes all the spark tables globally. So adding 3 degrees base adds 3 degrees to every part of the timing maps, including the WOT total timing (which is 26 degrees total if your distributor is set to 10 degrees base).

Your main complaint right now is idle. The larger camshaft dilutes the intake charge due to the increased overlap. That means more idle airflow is required to compensate. What's happening to you is that the motor isn't idling fast enough, so the computer raises the idle (via the IAC) to compensate. But then it overspeeds, and the computer cuts the idle quickly, which drops it too low, so it raises it quickly... as you can see, idle hunting ensues.

The cure for that should be in reprogramming the idle airflow tables in the computer. But on Foxes, you can get away with increasing airflow thru the throttle body in other ways. You could open the throttle plate more, but that would put the TPS sensor higher in voltage, which screws you up. It needs to be between .9 and 1.0 volts at idle, regardless of where you set the throttle plate at idle. You could modify your TPS sensor to make it more adjustable, but that's a hack. You could drill a hole in the throttle plate instead, but that's trial and error and if you overshoot the hole size, you won't be able to get it to idle down.

Ford Racing used to make an IAC spacer that had a screw in the side of it, which leaked air from one side of the throttle plate to the other side of it, just like the IAC does, except you control this extra leak with the turn of a screw. That piece would be ideal for your situation, to fix the idle air problem. An induced vacuum leak might also work, but the leak would have to get it's air source from the air intake tube, otherwise the MAF meter won't be measuring it.
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