1G Problem after 550's and Walboro Install

[ChvyKc]

I have a 91 AWD Talon. I just installed a set of Precision 550cc injectors and a Walboro 255 HP fuel pump that I just bought from Extreme PSI and now the car falls on it's face when the boost comes in. It just backfires repeatedly like the ECU is taking timing out for some reaon. I haven't had a chance to install the AFC II yet, but I was just wondering if that was normal and if the AFC is going to fix that or could something else be wrong?

Mods are:
Stock Turbo
N1 Cat-back and DP
Tubular Manifold
Ported 02 Housing
Boost is set at 15 pounds

Extreme PSI forgot to give me the wiring harness for the fuel pump and I had to use female speaker terminals in order to get it in. I am certain that the connections are good and solid, but I was wondering if this could cause a problem as well. I am going to call them tomorrow and get the harness shipped out, but I will like to get this problem fixed before this weekend (big race event this weekend)

The O2 voltage is right at .96 when the boost starts to come and it stays right there throughout the backfiring. I have no other kind of data logging and that is the only thing that I can go by. I know that is running rich, but would that make the car run like that under boost?

Any help will be appreciated, I am sure you guys can help me out.

Thanks,

David

 

[oldman]

I just installed a set of Precision 550cc injectors and a Walboro 255 HP fuel pump that I just bought from Extreme PSI and now the car falls on it's face when the boost comes in. It just backfires repeatedly like the ECU is taking timing out for some reaon. I haven't had a chance to install the AFC II yet,

You're running rich because of several reasons.

1. 255 without an afpr, your stock fpr is being overrun.

2. You can just install bigger injectors without any fuel tuning device, put back the 450s until you install the afc and logger to tune with.

3. Are you venting?

 

[Sk8er07999]

Your simply running too rich. I ran my 255 with stock fpr for a long time and a friend of mine still does. Yes you need a tuning device so you can "turn the fuel down". For now put the 450's back in if you want to be able to drive in boost. Get that afc in and take another shot at the 550's.

 

[oldman]

Your simply running too rich. I ran my 255 with stock fpr for a long time and a friend of mine still does.

Is that why you have one now? Were you logging while running without one? Do you realize the thread starter is already having difficulty understanding the relations between ecu/fuel/air/tuning?

My point is we should first provide him with factual information before you give him your personal oppions as how you were able to get around those facts. I'm well aware of people running the 255 without afpr but same holds true for bov venting and running larger injectors without afc, would you recommend them as well?

 

[Sk8er07999]

I am not trying to start a fight or state what is right or wrong. I am speaking from my personal experiences and the experiences of my friends. Story time: I personally installed the pump first on 450's. Car ran fine slightly rich but didn't fall on it's face under boost. I recently installed a 255 on a friends car running stock 450's and stock fpr. Car runs fine with bov vented running stock 1g mas. We all now venting is a no no when running 1g or 2g mass air flow sensors blah blah blah. Anyway, second on my list was to install the larger injectors. Put them in and under boost car sputtered, fell on it's face, and blackened the sky's with unburnt fuel. Turned the MAFT negative until car would boost. Had to go pretty far negative but got the car to pull really hard. The only reason I got a AFPR was because I heard that it's easier to tune when you have more control over the fuel system and that yes the stock fpr gets over run. So I did. Well I raised base fuel pressure and the only thing it did was improve idle and drivabilitly at low RPM. Another reason I did this was because my injectors are rated at a higher fuel pressure then stock. So after install I did not notice much of a difference. Yes I was using a logger before and after the AFPR install. Although I didn't really try to tune it and still haven't, WOT did not seem to be affected after the AFPR install.

Oldman:

By saying the stock fpr is over run, what does that mean? Fuel pressure raises? Stays the same? Or is lower then stock? Loses the ability to control fuel pressure? I have never understood what is meant by saying the stock fpr is over run.

ChvyKc:

I would say install the AFC and subtract airflow(fuel) until you get the car to run under boost. Then continue to fine tune it regerncing the logger often. This is how lots of dsmers sneak past fuel cut. Pay close attention to the logger to make sure you don't go too lean. With MMCD you can set it up to make a beeping noise when knock occurs or o2 voltage drops below a certain pre determined value.

 

[sweet97]

The stock FPR is preset to hold a certain pressure, let's say 36PSI. The Walbro 255 puts out so much pressure that the pressure "overruns" the setting in the stock FPR. Like trying to put16 ounces of water into a 12 ounce cup! The even better use of the AFPR is for the additional tuning it provides. mark

 

[heavyD]

The stock FPR is preset to hold a certain pressure, let's say 36PSI. The Walbro 255 puts out so much pressure that the pressure "overruns" the setting in the stock FPR. Like trying to put16 ounces of water into a 12 ounce cup! The even better use of the AFPR is for the additional tuning it provides. mark

You are sort of right but it's not about the 255 putting out higher pressure. The fuel return line on the stock regulator is small in diameter. A 255 flows 40% more fuel than the stock pump and the stock return line out of the FPR isn't large enough to pass the extra volume of fuel back as fast enough causing non-linear fuel pressures.

 

[bastarddsm]

guys trying to tune with the afpr is just a bad idea, and it is only a bandaide, you can use it if you are extremely rich or lean across the board, but don't use it for fine tuning. the true reason they are installed is that the stock regulator cant bypass enough fuel to control the fuel pressure at idle, and your car runs really rich and you have a inconsistent fuel pressure

have a good day kurt

 

[LousyDriver]

I've seen a dozen arguments about the need for a AFPR with the 255 pump, all based on "the car ran fine" or "The car idles poorly" has no one ever installed a fuel pressure gauge with the stock FPR on and checked the pressure? Seems like that would end the debate a little more conclusively.

 

[sweet97]

guys trying to tune with the afpr is just a bad idea, and it is only a bandaide, you can use it if you are extremely rich or lean across the board, but don't use it for fine tuning. the true reason they are installed is that the stock regulator cant bypass enough fuel to control the fuel pressure at idle, and your car runs really rich and you have a inconsistent fuel pressure

have a good day kurt

Thanks kurt I do hope to have a good day! If guys spend upto $300.(Buschur)just to bring their fuel pressure into line that is insane. The AFPR should not be the only tool for tuning but it can work in conjnction with whatever tuning aids the person has. I use a MAFT, EPROM/keydiver,wideband and Scanmaster. Together I get a good tune throughout the rpm range. mark

 

[oldman]

By saying the stock fpr is over run, what does that mean? Fuel pressure raises? Stays the same? Or is lower then stock? Loses the ability to control fuel pressure? I have never understood what is meant by saying the stock fpr is over run.

Very hard to explain and I will try and keep it as simple for you as I can. The fuel system is design for 1:1 relationship with the boost pressure. Another words, for every 1psi increase in boost you get 1psi increse in fuel pressure. Over run basically means the stock fpr is unable to bleed off enough pressure generated by a bigger pump like the 255 to keep up with the 1:1 change until the system is able to use up the extra fuel caused by the hider pressure. When does the system use up the extra fuel depends on many factors like load, injector size, what gear you're in, what rpm....etc therefore making it almost impossible to tune out the over run using afc because the change is non-linear, as we know the afc is based on rpm only.

So I did. Well I raised base fuel pressure and the only thing it did was improve idle and drivabilitly at low RPM.

http://www.vfaq.com/mods/FPR.html Read throught it, it shows you how to set your base pressure.

guys trying to tune with the afpr is just a bad idea, and it is only a bandaide, you can use it if you are extremely rich or lean across the board, but don't use it for fine tuning.

Not true, the other purpose of an afpr is exactly just that, fine tuning. No injectors will ever flow exactly what they are design to do so you can fine tune it by changing the fuel pressure and still keep the 1:1 relationship.

Remember, the problem with over run is not really the fuel pressure itself but to maintain the 1:1 boost pressure to fuel pressure ratio. Hope I made it clear.

 

[mavisky]

Look here's the solution. Install the s-afc II.

Right now your computer is expecting to throw in 450cc worth of fuel at 100% injector duty cycle (okay a little more since 450cc is at 32psi and 1g's are set at 36psi) and instead the motor's getting an additional 100cc of fuel and in actuality its more than that since your base fuel pressure has risen. Due to the 255 in there you're probably getting more like 125 cc more fuel than your ecu is expecting.

 

[ChvyKc]

Sorry for not posting this earlier, but I did install the AFC and it took care of the problem. The car was running really rich and I guess that the ECU just couldn't compensate for it. Everything is fine now though. Car ran a 13.7 at the track this past weekend. I was hoping for a faster time, but everyone that I talked to was running slower there than they would have anywhere else.

David