Air/fuel ratio problems

[Ripon]

ok i posted earlier about a lack of power, like at the high rpm.

Well i took my car to the dyno. Now before i discuss my dyno, my car has just some minor things, 373 gears, msd ignition, K & N cold air, 9mm wires, mac off road h pipe with 2 chamber flowmasters and is a 95 vert 5.0 with a rebuilt tranny with performance parts/shift kit.

Well dyno came in as i expected, rather shitty. 150 hp at the rear with like 190 pounts of torque.

What was interesting was my fuel to air ratio. Instead of the normal 13 air to 1 part fuel, I was running 18 to 1 part fuel.

So basically im starving my car. With that in mind, i checked my fuel pressure it was at 35 pounds and i checked my injectors and they were fine. I dont know what to do other then to take it to a ford dealer and pay out the *** to have them diagnost it. It seems according to my dyno that when i increase in throttle my fuel to air ratio becomes even more lean and what is worse is taht im not pulling any codes (check service engine light). I do occasionally do get a light for like 2 seconds while im driving like once a week but then it goes off as fast as it comes on.

I have bought a new fuel pump (thanks holley) and a fuel pressure regulator (gwork bbk). I am hoping that what my friend says is true and that when i idle my car to check my fuel pressure, i am getting an incorrect reading that i am looking for because there is a big difference between driving and slaming on your throttle for more gas then just idling and checking pressure. On my dyno, when i was at low rpms with low throttle i was at 15 to 16 air to fuel ratio and when i jumped on it at 4k rpm i was at 18 rpm.

I dont know what to think or do and neither did the mechanic that was working with me.

Any thoughs or ideas are appreciated. Thanks in advance.

[FoxBuilder]

I beleave below 3,000rpm the computer will add or subtract fuel to try and obtain a perfect 14.7:1 air/fuel ratio. If your car is running lean and the ECU is not trying to add fuel (especially in closed loop). I would say air is entering somewhere downstream from the MAF sensor, or a sensor somewhere is bad (MAP/BP, IAT, CT, O2). How does the car Idle? Try taking the fuel pressure up to 38-40psi.

[chris91LX]

I had my car dynoed and had the opposite problem, I was running about 34psi and my idling a/f ratio was like 16 and steady at a little over 14 from 3400rpm and up. I bumped mine to about 40psi and it idles and runs much smoother, but I wont get back on the dyno for another month or so to see for sure where I'm at.

Are you checking your fuel pressure at the schrader valve or at the FPR? I heard your supposed to check it at the FPR for best accuracy, but I check mine at the schrader.

Are you checking your fuel pressure with the vaccuum line off and your finger over the vaccuum fitting? I was told this was the best way to check and adjust your fuel pressure as it gives accurate readings on what the fpr is set at because the vaccuum can fluctuate.

Good luck, hope you get it worked out.

[Ripon]

Im not sure haha. Im not all that atuned as to what the correct name is for what.

The guy tested the pressure at the valve that is right by the fuel injector/fuel regulator area. He tested it as the car was idling.

My dyno run showed me at low rpms and low throttle doing about 15ish on the air/flow ratio, then at wide open throttle, 18.

Thats way bad and a loss of mucho power.

I dunno, que lastima!.

I was at like 35ish psi but i know i should be higher i supose.

they took the pressure while the car idled, and not while it was in wide open throttle.

[exgmguy]

Look at the basics. You are going way lean at WOT. First replace your fuel filter. Next look at the possible failing stock pump. Idle fuel pressure will tell you nothing at all. You have to be able to see fuel pressure at WOT through the entire RPM range.

I would bet money that your pump is going.

[Ripon]

I bought a bbk fuel pressure regulator and i bought a holley fuel pump for my car.

Mind yuo i have a 95 vert gt, i dont plan on breaking 400 ponies so i got a 155 lph (i think =D) fuel pump. Hopefully does the trick.

Pray for me tomorrow.

[PKRWUD]

For future reference, pressure must also be checked with the vacuum hose that goes to the regulator disconnected and plugged. This simulates WOT. The pressure should rise when you do this. If it doesn't, unplug the vacuum hose, and see if the idle speed changes. If it doesn't, the hose going to the regulator is clogged, and is not allowing the regulator to make adjustments for WOT. If the idle does change, then the regulator is bad. next, with the gauge installed, shut off the engine. The gauge should not move for at least 1 minute. If it bleeds down sooner than that, either the injectors are leaking (not likely in your case) or the pickup tube in the tank, after the pump, has a crack in it, and is not allowing you to receive the fuel pressure you need under load.

Take care,
-Chris

[Rebel79]

Get rid of your off-road H-pipe. Thats probablty causing you to go lean because there is not enough backpressure to accurately sample the exhaust gases.

[Ripon]

It was like this before the h pipe.

I did change the 02 sensors though after i put the h pipe in.