Temporarily tune around WOT fuel preesure drop?

[samh_08]

I have been going lean under heavy load lately (up to 14.5:1 WOT). I hooked up a fuel pressure gauge and noticed my fuel pressure drops off to 52 psi WOT. I was wondering if I could fudge my tune a bit for now to compensate for this pressure loss? I assume this amount of pressure loss would create this drastic of lean condition...?

My injector values are as follows:
Injector Rated Fuel Pressure: 43.5 psi Your Fuel Rail Pressure: 58 psi Injector Rated Flow Rate 36 lb/hr

[mr.prick]

Don't tune around this.
Does battery voltage drop too?

[eficalibrator]

Agreed. Fix the mechanical problem (dropping rail pressure) first, then worry about finishing the tuning.

[mr.prick]

Also make sure your FP is actually dropping.
I had 2 VDO mechanical FP gauges that were inaccurate.
False lean under load could be a burnt out WBO2 sensor.

If it's from a voltage drop the injector offsets should compensate for that.
Does it miss or have any side effects other than the WBO2 reading lean?

[samh_08]

Agreed that the mechanical problem should be fixed first. Either way the mechanical problem will get fixed, but I would like to see if tuning around it for a couple days would work for now.

mr prick: The battery voltage stays rock solid at 13.9 all the way through the RPM range, maybe fluttering between 13.8 and 13.9 at times with .52vdc total fuel pump circuit drop. The walbro pump I have was supposed to be good to 650bhp and Im only about 420rwhp. Anything in my tune look suspicious and could have a hand in going lean?

[samh_08]

Posted at the same time .

As far as the FP dropping is concerned, its pretty clear that it as actually dropping constantly under heavy throttle to about 52 psi every time. The gauge says 58 psi at all other times so I assume the gauge is accurate.

I have a month old LC1 with a serial connection so I would hope that wouldn't be burnt out already. Besides that, the WBO2 seems to be in check with my narrowbands at 14.7.

If I didn't have a wideband, I wouldn't guess that Im running lean because it goes like a raped ape and doesn't miss a beat. If it is truly lean at 14.5:1 at WOT, should it be missing and running like garbage?

[mr.prick]

I had the fuel line in the tank come loose from my Wahlbro.
Maybe you have a dirty Fuel filter.
Make sure FP is dropping so you don't have to do anything unnecessary.
I've had to replace the sensor for my LC-1 yearly for my DD.

[joecar]

0.52V drop between the battery positive terminal and the fuel pump...?

Can you reduce the drop (apply dielectric grease to the connections, try swapping the fuel pump relay)...?

If you have access to an oscilloscope, capture waveform of pump draw current (using amp clamp)... this will allow you to see if the pump motor is spinning at the correct rpms... I know, this might be hard to do while spinning the engine at higher rpm... I know, it might be hard to access a scope.

Like mr.prick said, check filter and screen.

[samh_08]

.52 total circuit drop, positive and ground combined which is good considering the wires on the stock sending unit. This is a swap into a 86 monte carlo so my options with fitment and aftermarket parts are limited or all custom.

I had the pump out of the tank and checked all connections and all was good. The screen was dark so I replaced that (it was a brand new clean tank) so I guess I could replace the fuel filter as well even though its 2 months old..

Anything suspicious in my tune?

[redhardsupra]

you dont wanna do it, but if you must, here's how to do hack it correctly

http://redhardsupra.blogspot.com/200...gged-fuel.html