Pleasant surprise - Walbro 255

[kidrabbit84]

I purchased a Walbro 190 (GSS250) and planed on doing a rewire to support my newly ordered 50 Trim. When I got the old pump out yesterday I discovered that the previous owner had already put a Walbro 255 in it (GSS317). However he did not rewire the pump.

I have read on here that you need an adjustable fuel pressure regulator with this pump. The car has the stock fuel pressure regulator, and the car runs well nor rich.

Is a rewire necessary for the addition of a 50 Trim and MegaSquirt? If I do a rewire will I need an AFPR or is this a case of people parroting what they have read about someone else’s setup?

Adam

 

[daren_p]

Rewire is always a good idea, fuel pump flow is directly related to voltage & the factory setup see's pretty low voltage. How do you know the car runs well, not rich? Have you installed a pressure gauge to verify you are not seeing an overrun condition? This is the proper way to check if you need an aftermarket FPR but I'm going to say you probably need one.

 

[kidrabbit84]

I'll put a guage on it today. My wideband shows the car not running rich...around 15-14:1 at cruise out on the highway and in the high 12 at WOT.

 

[daren_p]

Overrun doesn't usually have an effect on WOT tuning as the need for fuel greatly increases & the fpr no longer has to bypass as much fuel. It's the part throttle & idle conditions you have to worry about, which isn't always easy to notice. Get that pressure gauge installed & see what your base fuel pressure looks like & go from there.

 

[spyderturbo007]

Be aware that running "high 12's" for your WOT AFR is pretty dangerous. Most DSM's don't like it much leaner than 11:1

 

[daren_p]

Be aware that running "high 12's" for your WOT AFR is pretty dangerous. Most DSM's don't like it much leaner than 11:1

Good observation, I didn't really pay attention to the WOT WB value. You say your running high 12's air/fuel ratio, is this on pump gas? If so do you have any method of checking for knock & any tuning method? High 12's on straight pump gas is usually dangerously lean (for our/turbo cars).

 

[kidrabbit84]

Be aware that running "high 12's" for your WOT AFR is pretty dangerous. Most DSM's don't like it much leaner than 11:1

An A/F ratio of 12 is not lean...it is rich. A lean mixture is 14.7 and up...etc 17:1.

When tunning for power you want a A/F of 12.8-12.6:1, for gas milage you want around 14.7:1, and under crusie (no load) you can get into the 15:1 range.

I still need to get a guage on it tonight. More to come.

 

[daren_p]

An A/F ratio of 12 is not lean...it is rich. A lean mixture is 14.7 and up...etc 17:1.

When tunning for power you want a A/F of 12.8-12.6:1, for gas milage you want around 14.7:1, and under crusie (no load) you can get into the 15:1 range.

I still need to get a guage on it tonight. More to come.

That is incorrect, you are miss informed about air/fuel ratio's. When the car is at idle or part throttle conditions, the ecu uses the front narrowband O2 readings to descide if it needs to add or remove fuel to get the ideal 14.7 to 1 air/fuel ratio. This is what is called closed loop as there's feedback to the ecu, as to whats going on. 14.7 is the ideal mixture in these conditions. Now when you go over a certain throttle position the ecu goes into a mode called open loop where there is no feedback to the ecu, it relies on preprogrammed fuel maps & adds fuel according to MAF readings & some other variables. When the car is WOT or in open loop, an air/fuel ratio of 14.7 is no longer ideal & is considered extremely lean under these conditions. Under WOT a naturally aspriated car will have a leaner A/F ratio when compared to a turbocharged car. For comparison our cars come from the factory with around 9.5 to 1 at WOT. On pump gas most tune for 11 to 11.5 to 1 & sometimes richer still if your running higher boost or want more timing. High 12's is very lean for pump gas, that range of air/fuel ratio is usually what you aim for at WOT when your running race gas or pump gas with meth injection.

 

[spyderturbo007]

Well put, and absolutely correct!

 

[tkelly27]

^ +1 All rich conditions are not created equal, and you'd be wise to listen to darren and spyder. "High 12's" on pump gas is asking for trouble.

Also, +1 when he was explaining about when the 255 will cause rich conditions.

A re-wire is a good idea no matter what. An AFPR is a good idea no matter what as well.

 

[Eclipse98_RS]

If you dont rewire and dont have the AFPR and you still run just fine do you need them? I was told by a DSM shop that you dont need them, but they are a good idea. Also with a re-wire does that get rid of the surge you hear when the blinker is on?

 

[tkelly27]

http://www.contour.org/ceg-vb/showthread.php?t=2788

The more voltage you can have going to your fuel pump, the more fuel it can move. Re-wiring gives bigger wires with less resistance, so you've got more boogie in the back end.

AFPR is good to have so you can perfectly dial in your fuel pressure, or, if need be, drop the FP down to get more flow with larger injectors at huge huge boost levels on pumps at their limit (not relevent to most people). Just good to have, and if you are over running your stocker with a bigger FP, I'd say manditory. Nobody likes to idle rich, it's stinky!

Not sure about the blinker...

 

[daren_p]

If you dont rewire and dont have the AFPR and you still run just fine do you need them? I was told by a DSM shop that you dont need them, but they are a good idea. Also with a re-wire does that get rid of the surge you hear when the blinker is on?

Thats the problem, some shops don't worry about day to day & part throttle driveability. They just worry about WOT, which as I had mentioned earlier, is an area where over run isn't usually an issue. I've heard guys post well so & so made 400 something on his setup running a 255HP pump & no fpr & air/fuel ratio was fine. Well thats great but like I said, that usually doesn't tell us anything about if overrun is happening & does not mean everything is fine. Overrun isn't a linear variable so its not something that can be tuned out.

If you hook up a pressure gauge & check base pressure, this will tell you if you can get away without an aftermarket FPR. Also verify that you see the correct pressure drop when you hook the vacuum line back up. Most who thought/said they were fine without an FPR find out that isn't the case when they actually tested it out.

The fuel pump surging issue is usually solved by a rewire.

 

[kidrabbit84]

I miss interpreted the 11:1. Thought you had the scale flipped. Sorry guys.

I don't ever remember seeing this car over 11.8:1, even when it was sort of stock...I'll have to look at the fuel system a bit more. Are you certain this car will crank out 9.5:1 stock? I've tuned my intercooled T25 Miata with MegaSquirt fuel and spark to mid 11:1s. If I got into the mid 10s she would bog really badly. Maybe its cause I am driving at 5500 – 7500 ft, and that is just too rich up here; yet the code should compensate for altitude...I don't know. Maybe I am comparing apples to oranges.

Anyways more to come...thanks for the feedback so far. Once the MS is on I will put her in the 10s for initial tune. Going to rig up a pressure gauge now.

 

[spyderturbo007]

Are you certain this car will crank out 9.5:1 stock?

Yes, the ECU's target AFR is 9.5:1.

 

[kidrabbit84]

I got my gauge on it last night and it looks like she is a bit high, epically in the vacuum range.

Anything vaccum = 43-44 fuel psi
3 psi boost = 46-47 fuel psi
5 ps boost = 48-50 fuel psi
10 psi boost = 57 fuel psi
13 psi boost and up = 60 fuel psi

The factory manual recommends 33 psi at idle, and 42-45 psi at atmospheric. Your thoughts?

I have preliminary read folks setting an afpr at 44 psi atmospheric. Is this a good spot? Also is the Aeromotive AFPR a true 1:1 ratio, or is this approximate? Is the 1:1 ratio applicable on vacuum?

Adam

 

[zippyshoe]

I got my gauge on it last night and it looks like she is a bit high, epically in the vacuum range.

Anything vaccum = 43-44 fuel psi
3 psi boost = 46-47 fuel psi
5 ps boost = 48-50 fuel psi
10 psi boost = 57 fuel psi
13 psi boost and up = 60 fuel psi

The factory manual recommends 33 psi at idle, and 42-45 psi at atmospheric. Your thoughts?

I have preliminary read folks setting an afpr at 44 psi atmospheric. Is this a good spot? Also is the Aeromotive AFPR a true 1:1 ratio, or is this approximate? Is the 1:1 ratio applicable on vacuum?

Adam

It appears that you are seeing some overrun based on your fuel pressure while in vacuum. The recommended method of calibrating your AFPR is to disconnect the vacuum line from the AFPR and adjust your fuel pressure to 43.5 psi (2g factory base fuel pressure.) The Aeromotive AFPR should maintain a 1:1 ratio between fuel pressure and manifold pressure. This holds true for both vacuum and boost conditions.

 

[kidrabbit84]

Thanks... Looks like I will get an Aeromotive.

 

[daren_p]

I got my gauge on it last night and it looks like she is a bit high, epically in the vacuum range.

Anything vaccum = 43-44 fuel psi
3 psi boost = 46-47 fuel psi
5 ps boost = 48-50 fuel psi
10 psi boost = 57 fuel psi
13 psi boost and up = 60 fuel psi

The factory manual recommends 33 psi at idle, and 42-45 psi at atmospheric. Your thoughts?

I have preliminary read folks setting an afpr at 44 psi atmospheric. Is this a good spot? Also is the Aeromotive AFPR a true 1:1 ratio, or is this approximate? Is the 1:1 ratio applicable on vacuum?

Adam

Glad to see you had enough common sense to follow through with the test & see where your actually at, unlike some others

The std base pressure for a 2g should be 43.5 psi with the vacuum hose disconnected & plugged. The aeromotive & stock are a 1:1 ratio & this rate does continue into vacuum, so you would expect something around 37 psi with the vacuum hose connected (though this varies slightly on the amount of vacuum you see at idle). Looking at your results, the theory of 255 pump overrun, once again appears to be true. Was this still on factory wiring or did you get it rewired?

I tested my Aeromotive FPR out to check the 1:1 ratio, via a certified pressure gauge & turning on the pump via DSMLink. I found the FPR was bang on at rising the FP rate with boost.

 

[kidrabbit84]

These pressures were measured without a rewire.

I think for giggles, and future reference of anyone searching the forums, I will do the rewire, retake the pressure readings, and post.

I am glad to hear that the Aeromotive is a dead on 1:1 ratio. I am going to order one tonight.

 

[daren_p]

These pressures were measured without a rewire.

I think for giggles, and future reference of anyone searching the forums, I will do the rewire, retake the pressure readings, and post.

I am glad to hear that the Aeromotive is a dead on 1:1 ratio. I am going to order one tonight.

Defently information worth posting

 

[kidrabbit84]

Defently information worth posting

I said I would do it, so here it is:

After a minor side track of building a new motor and strapping on a 50 Trim I have finally gotten around to the fuel pump rewire. I did the rewire WITHOUT the AFPR installed and got the following data:

Vacuum: 62-59 psi
3 psi: 56 psi
5 psi: 56 psi
10-12: 55-54 psi

Results...massive stock regulator over run. Going to finish up installing the Aeromotive tonight. Thank you all for the guidance/info.

Later,
Adam

 

[DSMopar]

Ya I'm kind of leary of the 9.5:1 figures. Has anyone actually verified this with an ACCURATE wideband? Any time i've gotten close to 9 in my TT charger it misfired it was choking on fuel so bad....

 

[Talesin]

That's the ECU's stock open-loop fuel maps' supposed calculated target AFR. Not the actual. The stock fuel maps are pretty damn rich.. why you can hack a 1G MAS (but NOT a 2G!!, due to design) with few to no ill effects (aside from minor torque loss in the idle/low-end due to running a bit over-lean in closed-loop). Just leans things out a bit in open-loop, to help compensate for the stock ridiculously rich maps at WOT.

kidrabbit, thanks much for actually testing the fuel pressure... just proves the adage. Just because it runs at all doesn't mean it's running right.