Went to the dyno--really lean, help

[Kens86gt]

Well, I'm sorry to say I got the numbers from the run today.

Best HP--216 (4400rpm)
Best Torque--278 (3800rpm)

I wanted more, but it seems I need a fuel pump. At least that is what I'm guessing as my a/f ratio started climbing from 12.2 at 3500 to 16.0 at 5300rpm's.

Now the car has the stock 88lph pump and stock 19lb injectors--think this would cause the lean condition?

Based on the Mike Wesley article in the tech section, adjustable fuel pressure regulators may be a waste of money unless the injectors are maxed out.

If I can't turn up my fuel pressure without the computer "fixing" it, how else do I get rid of this lean condition?

I am installing a new 155 pump in a few days.

Mods are
Gasket ported Cobra intake and GT40 heads
70mm TB
1.6 Roller rockers
Stock cam (speed density)
Shorty headers, mac H and Mac cat-back
5 speed

[Capri306]

Was fuel pressure monitored at all during the pull?

If not, I would get a gauge and see what it's doing on the street (WOT up to ~5800 and 2nd or 3rd gear should tell you where it's at when the fuel injectors are near saturation) for some idea. A new fuel pump, injectors (because I'm paranoid about faulty injectors due to a project a long time ago), and a stock replacement fuel pressure regulator would be on my short list, just to be sure, if it were my car.

You're already doing the fuel pump, so another 30 minutes of work will ensure you're getting proper fuel pressure and volume. 155lph seems a bit much for a stock fuel system, but that's just me.

[Kens86gt]

Well I have an adjustable fuel pressure regulator coming, too, so I have the reg part fixed, too. I bought it before I saw the article by MW. There was a pressur spike under WOT (to 44psi), but it wasn't monitored when it went lean.

[Dark_5.0]

Here is your problem.

Your car is speed density so it does not correct for fuel like mass air does.

You "need" an adjustable regulator to add fuel to the mixture cause speed density will not add fuel to compensate for more air flow.

Lucky for you this is a simple fix. Increase the fuel pressure and you are good to go.

Wesleys article is specific to mass air cars.

I ran speed density for a few years with way more mods than you with geat results.

I was running 44 psi of fuel pressure with a good H/C/I package.

[jimberg]

An 88 lph would be able to pump about 130 #/h of fuel which is good to about 260 hp at the flywheel. That's at a 100% duty cycle which you can't count on. Your dyno numbers show that you are probably hitting about 250 hp at the flywheel if you assume a 15% drivetrain loss which confirms that you don't have a good enough fuel pump. The 155 should do nicely. I'm getting over 350 rwhp with a 155 right now.

Install the adj. FPR, but set it to the stock 39psi to start. Take it to the dyno and see what happens. You basically want a flat line as far as a/f ratio goes and 12.2/1 is a good place for you to be.

[Kens86gt]

Yeah, based on the suggestion from the tech page, a 155 will be fine for what I am anticipating making--270rwhp or so--I hope. I hope my torque picks up, too. I have seen similar SD combos make anywhere from 270 to 290 rwhp and 300-330rwtq.

If mine picks up that much--my car may scare me, lol.

[jimberg]

A 16:1 a/f ratio is dangerously lean, by the way. You should take it easy with your car until you get your fuel situation fixed.

[Kens86gt]

haven't been above 2500 rpm's since the dyno run.

[Dark_5.0]

I dont see how the fuel pump could possibly be the problem when he is running stock fuel pressure with speed density. His car doesnt put out any more fuel now than it did when it was stock and that is the problem

Sure a bigger fuel pump would be nice and suggested but the fuel pump is not the reason for your low dyno.

[Kens86gt]

If the fuel pump isn't keeping up at higher rpm's, then it would be the problem. I have a new pump and should have it and a fpr installed by Saturday. Maybe Dyno on Sun or Early next week. We'll see then.

[Dark_5.0]

A failing fuel pump could be part of the problem. The more parts you throw on a speed density stang the leaner it is going to run until you bump up the fuel pressure.

[Kens86gt]

Well I have also heard that maybe the computer is part of the problem, too. Something about different fuel curves and not being compatible with parts--86 only?

I'm gonna check my computer number today.

[Dark_5.0]

86-88 speed density ecu's are the same.

[Kens86gt]

Originally Posted by Dark_5.0

86-88 speed density ecu's are the same.

Aren't 87-88's Cod DA1?

Mine is VM1

[Dark_5.0]

VM1??????

I have heard they are all DA1 from a reputable source but you may be correct.

[Kens86gt]

Well, I looked at the computer today. Unless I'm stupid (could be due to my physical therapy school demands), that is exactly what it is.

So, I guess we will see how things go. I am putting the fuel pump in tomorrow and should have the reg on sat or sun. Dyno next week.