Odd situation on Dyno

[Brsmustng93]

Need a little help to figure out whats going on with my fox. Little background on the car. 88 5.0 converted to mass air, 5 spd, ud pullies, 70mm tb, cold air intake, electric fan, shorty headers, h pipe. 2.5" exhaust. Car has 3.55 gears, and possibly a cam, stock intake manifold, and what look like stock heads. Car has aeromotive fp regulator and 19lb injectors. Base timing set at 12 degrees.

Had the car on the dyno yesterday, & first pull was 179rwhp & 258rwtq. Afr was super lean in the entire rpm range between 15-17. So we adjusted fuel pressure from 39lbs up to 46. Made second run, car picked up power. Now at 190rwhp & 264rwtq. Car was still lean, but better. So we added more fuel pressure, now at over 50psi. Once again car made more power, but still lean with AFR in the 14 range. So last pull we maxed out fuel pressure to 62psi with vacuum line off, added 2 more degrees of initial timing and the car put down 235 rwhp and 309rwtq. However the car still only had AFR in the mid 13 range.

To me something seems wrong here. This car should not be maxing out the 19lb injectors with the limited mods, & the car should not be making this kind of power... All pulls were in 4th gear which I believe is the 1 to 1 ratio and done on a dynojet. Below is a snap shot of the sheet.

 

[stanglx2002]

With the background you mentioned that its a converted Mass Air, but didn't mention which computer you went with A9L, A9P, or A3M? Also, what MAF are you currently using?

Both of the above items could greatly effect the tune and what the computer is "thinking" it is getting compared to actual.

 

[Brsmustng93]

Running an a9l with stock maf

 

[FastDriver]

Could be a lot of things.

First and foremost, a bad or improperly calibrated MAF. Try swapping it. By my math, at 62 psi, your 19 lbs injectors are acting almost identically to 24 lbs injectors. If you weren't so adamant that the MAF was stock, I would suspect that it was actually tuned to 24 lbs injectors. I know you said it's stock, but perhaps it either isn't or perhaps the stock MAFs varied from one model of EEC to the next. It's not a stock Cobra EEC or MAF is it?

Also, check your codes.

Another approach might just be to swap in 24s, reset to stock pressure to lighten the load on both the injectors and more critically, the fuel pump. While upping pressure adds flow for injectors, it inhibits flow on the pump. I don't know if it hurts pump life. I think that would be likely, though. The car is making everything it should on the dyno, if your heads are indeed stock. The rule in tuning a car is always give a motor what it wants. Yours wants 24 lbs injectors. Maybe just put some in. Run hard once and read all plugs to ensure it's equal across the board. Then, just enjoy the car.

 

[Boostedpimp]

stock intake, heads and 70mm throttlebody... I'd probably look over the heads real well and see what they actually are

 

[Dan02gt]

I agree on the MAF being suspect. Did you happen to monitor your fuel pressure through the run to ensure its not dropping off as fuel demand goes up?

 

[Brsmustng93]

No I didn't monitor fuel pressure during the pulls . I think I will try some 24lbs injectors & see what happens. According to the data, the car wants more fuel. So we will see if I can gain a few more hp with a richer AFR

 

[FastDriver]

Keep the 19s in case you resolve the issue, later.

 

[mikestang63]

a bone stock 302 makes about that same HP... I agree sounds like the MAF is not right..