Going Lean Under Boost - Advice?

[VETDRMS]

I just installed the following and now I am having a problem with it going lean under boost:

1) Walbro 255 - rewired
2) Charged Air Systems AFPR
3) FIC 750cc Injectors
4) Autometer Fuel Pressure Gauge mounted on Banjo Bolt

Baseline fuel pressure was set to ~43.5psi at idle with the vacuum line disconnected from the AFPR. I verifed the AFPR was working by applying pressure to the vacuum signal line, fuel pressure rose directly with pressure.

Car idles great with DSMLink global fuel comp at -40% with deadtime set at 315. The car drives fine and idles with wideband A/F of 14.7:1.

When the car should switch to the high airflow table and enrich the fuel it stays lean, like 13-14:1 on wideband under boost.

I am not quite sure what to check at this point, any ideas would be appreciated!

Thanks,

-Travis

 

[silvah_gsx]

Have you done a log with DSMlink? You're probably just not properly tuned for whatever boost you're running, but tell us what the log tells you and we can go from there.

FYI "13-14:1" is richer than 14:1...if that's not a typo, then I don't see what the problem is.

 

[Kevin Jewer]

That is WAY too lean at WOT

I would post a log of this (hopefully you already have one and don't have to risk another pull) if this forum allows it. Too many things to check to go rambling on about...

 

[VETDRMS]

Hey, thanks. Yes I know lower=richer. I forgot to mention that it is LEANER than the target A/F.

It was lean enough to cut out, I let out of it instantly.

I found that the regulator was not increasing fuel pressure with boost during normal operation. For some reason it would work fine when tested with static pressure but under load it would lose fuel pressure.

I put a stiffer spring in the regulator at is working better, but still off of my target A/F so it is not increasing boost on a 1:1 basis.

I will be getting a different regulator.

Thanks.

 

[awddsm95]

It is important to remember the reason why forced induction setups run rising rate regulators. It would be easy to say just adjust your tune, but if your tune was "dead on" before, I would suggest making sure that the afpr is working correctly.

The reason that we run rising rate regulators is to maintain the correct pressure differential across the injector. Most OE and aftermarket injectors are rated at an industry standard of 43.5 psi (which is the 2g's stock pressure). When setting a afpr, we set it with the vacuum line off so that the pressure differential across the injector is at the pressure the injector is rated at. When vacuum is applied via the pressure line to the regulator, fuel pressure drops. The idea is that for any given manifold pressure (+ or -) the pressure differential across the injector remains constant. Most injectors opperate well with a differential pressure of 40-50 psi across them. If it is less than this, there is a possibility of the injector clamping shut, which could potentially cause damage to your engine (plus it would run like crap).

If your afpr is working correctly, then it will maintain the same differential pressure across the injector at all times, and therefor the massflow rate will remain constant given identical pulse width (open times). Having a properly calibrated and accurate afpr makes tuning much more consistant and predicatable.

Kyle Deiwert

 

[91-gsx]

This is on topic to an extent, but I have 750cc injectors installed on my car. I have them running at a pressure of 37psi for a 1g with the vacuum line off. But... when I looked at the flow ratings that came with the injectors to show that they are flowing the right amount. They test the injector at like 43psi and it flows 750cc. Doesn't that mean that unless I have the fuel pressure set to 43psi, my injectors are not flowing 750cc?
thanks for the help

 

[daren_p]

This is on topic to an extent, but I have 750cc injectors installed on my car. I have them running at a pressure of 37psi for a 1g with the vacuum line off. But... when I looked at the flow ratings that came with the injectors to show that they are flowing the right amount. They test the injector at like 43psi and it flows 750cc. Doesn't that mean that unless I have the fuel pressure set to 43psi, my injectors are not flowing 750cc?
thanks for the help

Yes you are right on the ball , Injector flow is directly related to pressure so if your running less pressure then they are tested at, then yes you will be flowing less. Not a 1g so Im not 100% sure but I think most just bump the base pressure up to 43 psi once they have an adjustable fpr (that is if they aren't using the FP for tunning which you may need to do if you are running a piggyback system)

 

[91-gsx]

Yes you are right on the ball , Injector flow is directly related to pressure so if your running less pressure then they are tested at, then yes you will be flowing less. Not a 1g so Im not 100% sure but I think most just bump the base pressure up to 43 psi once they have an adjustable fpr (that is if they aren't using the FP for tunning which you may need to do if you are running a piggyback system)

I am running dsmlink and the settings are for 750cc injectors. If I am running them at 37psi and on the global fuel precentage that you take out, I have 40% taken out becuase that is how much it is supposed to be going by the dsmlink instructions. And I am going to set deadtime at 315. Doesnt this mean that I am running pretty lean because of the lack of the 6psi of fuel pressure? I think I am going to bump the fuel pressure up because I have to, hopefully this will make the car run for the better sense it is setup for these settings, which are the wrong settings in the current state. What do you guys recommend I do? By the way, I am in no way trying to take away from this thread, it is what got me thinking about it.
thanks for the help

 

[daren_p]

I am running dsmlink and the settings are for 750cc injectors. If I am running them at 37psi and on the global fuel precentage that you take out, I have 40% taken out becuase that is how much it is supposed to be going by the dsmlink instructions. And I am going to set deadtime at 315. Doesnt this mean that I am running pretty lean because of the lack of the 6psi of fuel pressure? I think I am going to bump the fuel pressure up because I have to, hopefully this will make the car run for the better sense it is setup for these settings, which are the wrong settings in the current state. What do you guys recommend I do? By the way, I am in no way trying to take away from this thread, it is what got me thinking about it.
thanks for the help

Yes you are correct, with those settings & that fuel pressure you will be running lean. There is a formula in the dsmlink manuel to figure out the global calculation for different base fuel pressures but trial & error work just as well. Have you logged your LTFT both Lo & Mid? These will tell you exactly how to adjust your global & deadtime as every car is slightly different & the values given are just to get you in the ballpark. The procedure for adjust these are right in the manuel & should be pretty straight forward. You need to get these setup correctly first before you make any WOT (rpm based slider) adjustments.

 

[Kevin Jewer]

The adjustment in DSMlink takes into account the pressure the stock ECU was expecting to see. If it was 37 psi before DSMlink and 37 psi with DSMlink, the global adjustment is still calculated the same way. I always recomend running the base pressure the ECU expects to see with DSMlink. If you need more injector at the lower base pressure, just get bigger injectors. This is also why I always recomend to run at LEAST 950s with DSMlink. There is no reason not to, unless you like to upgrade 8 times like I did...

Just for the record, 750s rated at 43 psi run at 37 psi will flow like 696s.

 

[91-gsx]

The adjustment in DSMlink takes into account the pressure the stock ECU was expecting to see. If it was 37 psi before DSMlink and 37 psi with DSMlink, the global adjustment is still calculated the same way. I always recomend running the base pressure the ECU expects to see with DSMlink. If you need more injector at the lower base pressure, just get bigger injectors. This is also why I always recomend to run at LEAST 950s with DSMlink. There is no reason not to, unless you like to upgrade 8 times like I did...

Just for the record, 750s rated at 43 psi run at 37 psi will flow like 696s.

I don't think that I will ever need more then 750cc and the only reason i bought them this small in the first place is because the guys at dsmchips told me it would be within their boundaries to compensate for 750cc injectors, I guess the 950cc injectors were not commonly used with their chips so they did not have much experience with them. Anyway, there is calculation that i can use to pull out more fuel from the global settings if i need more fuel and up the base fuel pressure. Do you recommend I turn the base fuel pressure up and compensate for the new 43psi base fuel pressure with the global settings? I ask this because I would imagine that if the injectors are supposed to run at 43psi, the atomization of the fuel is much better at that base fuel pressure or more.
thanks for the help

 

[VETDRMS]

Hey guys, thanks for the comments.

The AFPR does not seem to be functioning correctly. I installed a stiffer spring and set the base pressure to 43.5psi with the vacuum line unplugged. When I installed the vacuum line the pressure dropped to ~38psi, like it should. It is not going lean anymore under boost, but it is still off the target A/F, by ~2 full points. The A/F is also not constant across the RPM range like it was, it fluctuates.

How effective are the bolt on type AFPR? It is just acting like the boost reference part of it is not working correctly. I pulled the AFPR apart and all the components look to be in good shape.

I cannot make a log because my water pump decided it wanted to scream, so I am replacing it along with the timing belt and the balance belt. Good thing too as the person who owned the car did not replace the balance belt when the timing belt was replaced. The backside of the belt is covered with deep cracks every 3/8"!
I bolted the stock FPR up and with the vacuum line connected I am at 50psi.., not going to work.

Thanks.