Fox Bucks like a Bronco instead of running like a Mustang

just_jayy said:

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That's clean as heck... I like it.
And, what, no black zip ties?

(Rumor has it the General has some.)

just_jayy said:

TPS is set at 9.6v....

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I assume that's a typo. If not, I think I found your problem.

Just me but if the ECU is stock and not chipped that fuel pressure is a little high. Should be 39 psi with the vacuum disconnected. When you reconnect the vacuum it should be 30+ psi’s. Usually it’s a 5-8 psi drop when you connect the vacuum.

As load is added to the motor the pressure will increase to a maximum of 39 psi.

The code 95 you are getting is because the ECU is expecting confirmation that the fuel pump has 12V+ to run. See this thread:


Mass air ECU’s look for this.

Noobz is a good trouble shooter so check the pump out for sure. There is a wiring connector at the rear of the car just above the tank back by the bumper that can get corrosion / bad connections so check that as well. The connector in this picture is the one with the orange-ish and black connectors.



Another known issue is the rubber hose between the outlet of the pump and the pump hanger. It can rot and have cracks in it.

By relocating the ACT to the airtube you have changed the ACT settings harshly.....Id either get a tuning chip or put the ACT sensor back in the stock location.


Theres just too many factors that are controlled by the ACT sensor especially melded with the ECT sensor in some settings too..




My buddy built an 84 T-Bird with a 351w out of a F150 plus wiring harness also ECU out of an 89 Mustang and first used a 70mm MAF to match the twin 35mm TB that turned out to be for a 95 T-Bird instead of a Cobra and despite the mix-match still got the tune pretty good but not spectacular so he got a 75mm Pro-M MAF Bullet that was calibrated for the 351w plus decided he wanted to relocate the ACT to the intake tube and calls me saying all hells breaking loose so he brought the car over and I popped in the chip and did a quick around the block logfile..

This was the logfile after fixing the initial 70mm MAF mixmatch issues but neglected to check the fuel pressure as my buddy said he had it covered via the internet yet he actually didnt and it took quite a bit of finagelling to get the stoich to 14 then try more mods and a different MAF and muck it up badly......LOL




If you look at the logfile below at where the timing was at-at just 960rpm's driving around the block with initial timing set to 12* and the fuel pressure set to 43psi with the hose disconnected and 39psi with it connected instead of 39psi with line disconnected and 35.4psi with vacuum line connected............


Whats oddly funny is this T-Bird was bucking like a Bronco too plus he was lucky to still have the headgaskets with the timing spiking to almost 60 degrees advanced and the AFR at over 17 stoich.....LOL




Thats what basically happens when you put aftermarket goodies also do aftermarket mods and dont have a way to datalog to know what was going on...

After clearing up a whole bunch of stuff via my chip I used a Star tool to burn the updated tune direct to the ECU...



You may still also need to adjust your MAF transfer function............The ProM 75mm Bullet came calibrated and the calibration numbers that came on the sheet was 15% too much.....Its the same deal for all calibrated MAFs not being dead on because all engines arent exactly the same nor do they flow the same. so unless the guy calibrating the MAF is using your car the chances of having an exact match is a longshot.....

As you can see below that the ProM 75mm Bullet transfer is alot taller than a stock A9L and had to be manually added ..If you dont get the flow to voltage numbers smoothly entered the injectors will squirt the wrong amount of fuel also to mention will max out quickly..






If youre using bigger injectors you must match the high and low slope aswell as breakpoint numbers or youll overheat the injectors...






When most upgrade the fuelpump they rewire the fuelpump and separate it from the ECU and thats wrong if you dont have a chip to adjust the voltage to injector deal as the pink wire adjusts the fuel pump voltage to the fuelpump monitoring pin on the ECU plug....

One time I added a 255lph pump plus separated the fuel pump monitoring wire from my wiring and wired in a very good relay....

I noticed that on my fuel pressure gauge on the dash that when my voltage changed so did my fuel pressure and when my voltage fluxuated wildly from the upgraded G3 alternator my fuel pressure raised from the stock setting up to 42-45psi ..

With the ECU not being able to slow the fuelpump made my engine sound like it had a lumpy camshaft installed at redlights and smelled pretty heavily of gas due to not being able to slow the pump then it cooked my injectors by overdriving them against their will causing them to leak fuel pressure as they sat also to mention messed with my closed loop calculations forcing me to run always in Open Loop or always reset the computer daily..

What made me notice the issue with the excessive voltage to fuelpump speed increase was when I was running the two 600watt self powered subs and the 1500 watt amp pretty loudly while driving around the car ran pretty smoothly..


Once I put the stock fuelpump wiring back to the 255lph pump and changed out the injectors my fueling issues stopped....



Good Luck