modified 89 GT question

[y_do_i_try]

I have an 89 GT with the following done:

rebuilt motor about 5,000 miles ago after spinning a main bearing
- new Super Duty T-5 just installed with Centerforce Clutch and aluminum flywheel, adjustable clutch cable, new quadrant, and firewall adjuster
- aluminum Ford Racing driveshaft, aluminum 3 row radiator
- BBk Cold Air Intake and SSI Intake manifold kit with 75 mm Throttle Body
- Ford Racing 30 lb injectors and Granatelli MAF Sensor tuned for cold air and 30lb injectors, BBK adjustable fuel pressure regulator with a fuel pressure gauge attached to the fuel rail
- 2.5"flowmaster with no cats and Mac shorty headers
- nothing done with the iginition except 9mm spark plug wires and a ford racing distributor cap and rotor
- i just checked the timing and it is set to the stock setting, fuel pressure gauge reads from 40-45 psi when running
- nothing done with ecu

Right now I can usually get the car to start, but once it fires up, it starts to idle EXTREMELY rough until it kills itself... i'm new to tuning this car and have no idea where to go from here....do i need some kind of chip for it, a new ecu, do i need to adjust the timing or fuel pressure....I just really want to get this car running and with all the transmission stuff I had to do I don't have the money to take it to someone to get it figured out....I was wondering if anyone knows anything about tuning these cars with just little aftermarket things done or what I have to do so I can drive my mustang before the snow flies.....THANKS FOR ANY HELP!!!!!!

 

[loder]

it sounds like you may have the ground wire loose or not connected that is in your injector wiring harness i beleve thet it is tan or some light color like that . also to adjust your fuel regulator remove the vacume hose and adjust it while its running i usually set mine around 35-38psi for 30lb injectors.

 

[jrichker]

See the "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

Your injectors are about 2 sizes too big for the mods you have. Put the stock MAF and 19 lb injectors back on the engine. The stock injectors are good for 270 HP with some room to grow.

Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See Automotive Performance Software / Interactive JavaScripts Calculators to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

Larger injectors require a larger fuel pump.
Copied from the FORD RACING PERFORMANCE PARTS catalog:
PROPERLY SIZING FUEL SYSTEM COMPONENTS
Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”
Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.