Engine Code Reading Rich Mixture


New Member
Nov 16, 2013
pittsburgh pa
I have a 98 mustang gt 4.6 I just bought the car but i dont think it had any type of decent tune besides a cheap superchips micro tuner tune to it. it has 30lb injectors fuel pressure regulator a bbk 78mm throttle body 4inch intake bored .20 over je dome pistons. a full pi head intake manifold and cam swap and underdrive pulleys. My engine is throwing codes for rich mixtures. i was wondering if i was to get a dyno tune which i plan on will this solve my problem. i would imagine with this many mods you would need more than the superchips micro tuner to tune it
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so even with all of those air adding mods it would be okay to run on stock fuel pressure. it is adjustable its a aeromotive fpr

Fuel injectors are designed to operate with ~40psi drop across them. A stock set of injectors for that car are 19#s, rated across a 40PSI pressure drop. Your 30# injectors are able to flow 58% more fuel across that same pressure drop. That's tons and tons of fuel. There's no need to augment it with additional fuel pressure on top of that.

The whole idea of going to larger injectors is that you don't need to adjust the fuel pressure upward. Using the FPR to up the pressure is often done when one can't afford a proper set of appropriately sized injectors.

With those mods I would think a set of 24# injectors on the stock pressure would suffice. 30#s is fine too but the PCM definitely needs to know their size...

I'd leave things be for now but when you go to get it tuned set the FPR to the correct pressure before commencing the dyno tune.
There are parameters within the PCM itself stored in the form of tables and others called "scalars" that store this information. These can be programmed using an SCT tuner but you'll need a tune made up for the SCT to transfer to the car.

I'd suggest talking to the Bama guys through American Muscle. They can probably write you a tune. You'll need to tell them your PCM code as well as every mod the car has. That can then be loaded into you SCT and burned into the car.
well i have a liquid filled gauge on my driver side fuel rail. and aeromotive specifically says do not use that with theyre product because you will get a inaccurate reading. i believe they are right i turned it up to where it was at 40psi at idle and wanted to kill itself out. i have it idling at 19psi just fine right now i ordered another gauge do you think i should put the other gauge right on the pressure regulator
Don't set it to 40psi when at idle. Set it there with the key on, engine off (KOEO) or pull the vacuum line off the regulator.

Remember you're looking for a pressure drop across the injectors of ~40psi. At idle, the intake manifold is at ~20inHg vacuum which is about -10psi of pressure (with respect to atmospheric.) Therefore, at idle, you'll want ~30psi of indicated fuel pressure.
I mean they say specifically say on aeromotive do not use liquid gauge use dry gauge so im just gonna leave it sit until it comes in I dont want risk running it without knowing. im gonna put my wideband in it also to be safe