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Discussion Starter #1 (Edited)
During a dyno tuning session yesterday the tuner was unable to simultaneously optimize the AFR at idle, light load and full boost conditions. He could program the G-Force so idle and full load was fairly close, but then it was pig rich (9.x:1) at light load and would therefore yield terrible gas mileage. Adjusting the AFM by adding spring stiffness made little difference, but did allow it to more accurately measure airflow at higher boost. He generally seemed to have the biggest problem getting enough fuel at idle, with the engine frequently stalling from being lean (18-19:1 at idle). He began to suspect that the stock FPR wasn't accurately adjusting pressure.

Without a way to measure fuel pressure he tried the following which allowed him to correct fuel under all conditions. He disconnected the vacuum/boost line from the intake to the FPR and with some extra hose inserted a check valve in the line. It effectively eliminated vacuum at idle from acting on the FPR diaphram to reduce fuel pressure. At zero or any boost level it would operate as always and increase boost accordingly. This change obviously netted higher pressure and fuel flow at idle and now allowed him to adjust it with the G-Force.

I know I've always heard of fuel tuning issues with the G-Force with 550s and complaints of high fuel consumption. Does this sound like a reasonable work around measure because of the G-Force/550/stock FPR combination or is it more likely a faulty FPR/fuel pressure issue? I'd prefer not to replace the FPR as I will need to remove that nice new WolfKatz rail to do it and then re-tune it again. Is there any issues with not applying vacuum to the FPR considering AFR has been successfully accomplished? Is there a special type of check valve that should be used as this one was just what he happened to have on his bench.

Driving home on the highway afterwards felt normal, but a couple of times seemed a bit jerky under varying very light throttle conditions at lower speeds on city streets. Also I noticed boost no longer reached the preset 17 psi on the SBC-id towards the end of our tuning session and while driving home and wonder if the check valve might be the cause. The tuner didn't think it could leak enough to do that but I'm not sure.

Bruce

(composing new thread below)

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Whether your thing is burning up the race track, autox course, drift course, or the street, there are four key points that you need to understand and master to do it well, and safely., and it.
 

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No firsthand experience myself, but I guess I would start by testing the fuel rail pressure under various load conditions.

That check valve has to have some kind of controlled leak or bleed. Otherwise the diaphram on the FPR would pressurize up to 17 psi and stay there. Wouldn't expect it to affect the boost controller though since the vacuum/boost signals are via different hoses.
 

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twoina2 is right. I, however, will take it a step further and say that this is a very hodge-podge way of fixing an AFR issue. You either need a better ECU or a better tuner. My guess is both.

By the way, I hope you aren't running 550s with the stock pump and fuel rail.
 

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Discussion Starter #5
flyboy said:
twoina2 is right. I, however, will take it a step further and say that this is a very hodge-podge way of fixing an AFR issue. You either need a better ECU or a better tuner. My guess is both.

By the way, I hope you aren't running 550s with the stock pump and fuel rail.
I have to get a pressure guage on it first to see what is happening with the regulator. I had recently changed the fpr and may have installed another bad one. While it did solve one major fuel problem it may have created another one. I do have a Wolfkatz rail and Supra pump. I'm really paying a high price in money and performance for the desire to keep things closest to stock on the car by keeping the ECU, fpr, and AFM. And it's time for a wideband O2 sensor too.

It was interesting troubleshooting but a make-shift solution to his tuning problem. At least I know how to proceed. If it's not the fpr, I'll have to assume it's some limitation of the G-Force/ECU combo. This is different tuner than I had before, and the only other one north of the 49th parallel that has the equipment to tune a G-Force! He seemed to know his way around the G-Force pretty well from what I could tell.

He had led me to believe that after tuning the AFR that he would then adjust timing, using the dyno to hold the engine in each rpm cell for a moment while advancing timing to find peak torque before moving on to the next. However, when the time came he was reluctant to do that, apparently because it puts the engine under too much strain. I figured he would have to check timing in order to ensure it wasn't too advanced for safety, never mind trying to maximize power. Once I get the fuel problem fixed I will be going back to finish the tuning. Any ideas on how to handle the timing issue?

Bruce
 

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Discussion Starter #6
oldster said:
I didn't know that you could tune a GForce........:(
Absolutely. He sits in the car with his laptop and makes adjustments to fuel while watching his wideband O2 monitor! When he's done he downloads and burns a new chip and plugs it into the G-Farce board that's been added to the stock ECU. It's 1990's technology a it's best :smile:
 

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"...inserted a check valve in the line. It effectively eliminated vacuum at idle from acting on the FPR diaphram to reduce fuel pressure."


It also makes the FPR a sealed chamber, unable to vent any pressure applied to it. Once you boost to, say, 15 psi, fuel pressure will be increased 15 psi, and cannot return to normal.

bill
 

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Discussion Starter #8
billwot said:
"...inserted a check valve in the line. It effectively eliminated vacuum at idle from acting on the FPR diaphram to reduce fuel pressure."


It also makes the FPR a sealed chamber, unable to vent any pressure applied to it. Once you boost to, say, 15 psi, fuel pressure will be increased 15 psi, and cannot return to normal.

bill
The check valve is actually just teed into the line to defeat only manifold vacuum from acting on the fpr diaphram for idle conditions. You're referring to pressure applied to it under boost, and when boost is released the pressure would be released back into the manifold. Does that sound right? I have detected some occasional jerkiness so you've got me wondering now.
 

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I can't envision your system, I think Bill is right. I will let him answer your question, however.

As for your initial answer to me, if he has access to the whole fuel map, then your car should run flawless! You should have any issues in the least with a tuned car!

As for the load-holding. I have held my engine all the way up to 28" of absolute pressure (2" vacuum) above 2500 RPM on the dyno numerous times. Certainly the cruise portion (8 and more inches of vacuum) can be tuned with a load-holder to perfection.

If you are getting really high coolant temps, then unplug the sensor on the radiator. That will turn on the fans full-time. Then, just wait at idle for the coolant temp to come back down and do another 2-minute load-hold. You should be able to flush all cells out that way in the cruise range up to 8". I would think 2" is attainable, but that could just be my car.

I have no idea what your tuner is doing, but you shouldn't have these fueling issues! I therefore think there is a part of this story we all are missing here. I wish your tuner could take part in this thread.
 

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Bruce H. said:
Absolutely. He sits in the car with his laptop and makes adjustments to fuel while watching his wideband O2 monitor! When he's done he downloads and burns a new chip and plugs it into the G-Farce board that's been added to the stock ECU. It's 1990's technology a it's best :smile:
Aha, not too many people are equipped with prom burners though...........:)
 

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Discussion Starter #11
Just picture the hose and tube that runs from the intake manifold across the top of the fuel rail and fits onto the stock fpr. Take off that hose, insert a tee into it and connect the tee to the fpr again with another short hose. On the third part of the tee attach a small check valve. Under boost conditions the pressure is unimpeded to the fpr as before and fuel pressure increases with boost. Under vacuum (at idle and really low load) the check valve opens to eliminate manifold vacuum in the hose so the vacuum can't work against the fpr diaphrahm and lower fuel pressure. In effect the check valve is keep the fuel pressure up slightly until there is a boost condition at which time the check valve has no effect.

Hopefully it will all get figured out! Checking the fuel pressure and fpr is where it has to start, then go from there. I have heard the Techtom is somewhat limited and I'll check with ATS as they are doing their first ROM tune with 550's according to another thread. If it's an ECU issue, they may also have a problem...I'm hoping they will also use the stock fpr.
 

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Okay, I see what you are saying now.

If that check valve is left open in the engine compartment, you are ingesting unmetered, unfiltered air. Not only is it a hazard to the health of your engine, it will cause it to run very poorly as the air is unmetered and the AFR is inevitably affected.
 

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Discussion Starter #13
flyboy said:
Okay, I see what you are saying now.

If that check valve is left open in the engine compartment, you are ingesting unmetered, unfiltered air. Not only is it a hazard to the health of your engine, it will cause it to run very poorly as the air is unmetered and the AFR is inevitably affected.
Agreed. I'll also be installing a good wideband so I can detect a problem, no matter what causes it. Thanks for the input.
 
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