01MAROONz2890

Just like the title says guys I'm trying to track down a grmelin and I want to check fuel pressure at WOT to see if its falling off up top can hptuners log fuel psi at the rail? If so can someone tell me how to set it up

KRAZY K 2000 TA

iTrader: (5)

none of the cars have a pressure sensor so no.

01MAROONz2890

Ok well here's the issue the car has a crate ls6 in it. I used the tune from a c5 z06 and jut adjusted it a bit for the bolt ons my car has.. Ie headers full exhaust and ported tb. The car runs great an pulls hard up top. The problem is I don't have a dyno nearby and the injector duty is up to 100% at 6500. The car is using the stock 02 28lb injectors. Could the fuel pump be getting weak causing the high injector duty? Or is the ls6 with full bolt ons simply maxing out the injectors. I sent the tune files over to some good tuners in the area and they all said the tune looks good.

MeentSS02

iTrader: (11)

Fuel pressure isn't something you can pull from the OBD-II port on these cars - I'm pretty sure it isn't monitored by the PCM at all. You can hook up an aftermarket electric fuel pressure gauge and tap into the signal wire from the sending unit. My autometer gauge is 0-5V, so I bring that signal in just like I do my wideband through the EIO interface. That lets me monitor it with the tuning software, although the gauge in my car is just as effective if I'm trying to trouble shoot an issue. In my case, I was also getting a very high injector duty cycle, but found out it was because my pump was dropping 6-8psi at WOT...some of that has to do with having the regulator in the back of the car instead of at the rails, and some of it has to do with the weak stock f-body pump.

01MAROONz2890

Ok good to hear it's still the stock pump in the car after 125k and 9 years I guess it could be a little tired. Can it wait for a couple months or is this something I should correct ASAP I dontget On it all that much. Is it really killing my top end Hp all that much? I'll probably do the racetronix kit but since im away at school its pretty hard for me to do it right this minute

MeentSS02

iTrader: (11)

As long as your AFR at WOT is in line and you have control over it, you are fine - if your AFR goes lean and doesn't respond to adding more fuel to your tune, then you have a problem. Otherwise, it can wait.

One piece of advice...if you go the Racetronix route (I just did), do NOT buy anything directly from them. Buy it from one of their distributors instead (like Lonnies Performance). If something goes wrong and the pump fails like mine did, their customer support absolutely sucks, and you will be stuck with the bill.

redbird555

iTrader: (14)

Thanks I appreciate it! Where did you get yours from? I had one on my old firebird and no I see they offer a "mild" upgrade pump for $109 or the regular pump for $150 what did you go with. I also just wanna clear this up. I know the injectors arent really supposed to run over 80% duty cycle while mine are right at 100% at WOT am I losing any top end because of this or is the weak fuel pump just making them work harder? The afr and such is in good shape by the way.

MeentSS02

iTrader: (11)

I got the regular Racetronix upgrade from Lonnies Performance. Just give him a call (his business hours are great), and he'll get you set up.

Injectors, as a rule of thumb, aren't supposed to be run over 80% IDC because they just aren't as consistent at that level and above. If your AFR is in line, you aren't losing any top end even with injectors running wide open (100%). New (bigger) injectors will give you a little more fine control over the AFR, but they won't net you any more power.

jimmyblue

iTrader: (11)

I have rigged a Kavlico pressure sender and SW fuel
pressure gauge onto one of my Actron cheapo fuel
pressure gauges. This combo puts out a 0-5V signal
that you could put to the EIO interface like any other.
The Actron was just an easy way to get a Schrader
compatible fitting.

Fuel pressure is one thing that is an unknown / assumed
value as far as the PCM is concerned, and the best idea
would be a return type system with the regulator at the
rails. Otherwise you embed fuel fade errors into the air
tables, and fuel fade changes over time w/ filter crust
etc.

2xLS1

iTrader: (25)

Injector duty cycle has nothing to do with fuel pressure. It is only based on what the computer is commanding for the injector pulse width and the rpm. WOT IPW is determined by the airflow calculated at that RPM and what is commanded in the PE table. Fuel pressure will have an effect on the actual A/F ratio, but not the IDC.

MeentSS02

iTrader: (11)

You'll have to explain that one to me, because I think it has everything to do with the fuel pressure. If your fuel pressure is dropping off at the upper end of WOT, the injectors will have to stay open longer to squirt the same amount of fuel (after all, we are still trying to maintain the proper AFR).

2xLS1

iTrader: (25)

Changing the tune to compensate for lower fuel pressure will change the IDC, but just the FP changing will not. The values in the tune will not change on their own if fuel pressure drops.

MeentSS02

iTrader: (11)

I see what you are getting at, and that is true - I was looking at it more from the user compensating for the effects of lower fuel pressure like I've had to do in the past.

2xLS1

iTrader: (25)

I was trying to answer the OP question "Could the fuel pump be getting weak causing the high injector duty?"

01MAROONz2890

thanks 2xls1 so just to clear it all up the injector duty cycle is NOT affected by the fuel pressure correct? meaning the high injector cycle has something to do with tune? like i said i dont think a bolt on ls6 can max of the 28lb injectors but i could be wrong. if that is in fact true it probably means that the motor is running a tad rich up top because the motor really cant be using the amount of fuel the injectors provide working at that high of a duty correct? i just want to make sure i'm understanding how all these things work thanks

MidknyteRacer

Bigger injectors,

2xLS1

iTrader: (25)

If the tune was right with normal FP and then the FP drops, the IDC remains the same, but the A/F will be leaner. If the car's A/F was tuned with low fuel pressure then it could be the cause of higher IDC. I have also seen high fuel trims that carry over into PE mode that add to the WOT IPW that makes the IDC go higher and fixing the tune so the fuel trims don't add fuel in PE mode lowers the IDC. But again, it is the tune effecting the IDC, not the fuel pressure. IDC is merely a mathematical calculation of IPW and RPM.

IDC = IPW x RPM / 1200

01MAROONz2890

well like i said the car has never been to a true dyno it was tuned using a mail order tune from a bolt on c5 z06 seeing as thats all it is just with a manual tb and an auto tranny. so it was assumed when i did the tune that the car had good fuel pressure and last time it had a wideband hooked up it did. so essentially its not the fuel pump causing the high idc? because even if it was bad the pcm wouldnt know that and still command the same idc? so could it be maxing out the injectors or could it be that the tuner added more fuel to be safe and not make it go lean up top

MeentSS02

iTrader: (11)

It could very well be that the tuner added more fuel up top to compensate, but seeing as it was a mail order tune, how did he know your car's AFR? Did you provide him a log, or is he just shooting in the blind?

Honestly, there seems to be a lot of beating around the bush that could easily be solved by just tossing in some larger injectors; granted, that costs money. When I was having this exact issue years ago with my bolt-ons only LS1, I dropped in some larger injectors, changed the injector flow rate table, and was on my way.

01MAROONz2890

Ya I hear ya lol but like you said bigger injectors cost money and being a full time college kid spare cash is pretty hard to come by atm lol. The afr was taken using a friends wideband o2 but since he and i no longer speak its pretty impossible to get it back again. From what I've learned here its not the fuel pump causing the high idc, and the car pulls hard up top and doesnt skip a beat i suppose if the fuel pump was weak I would feel it breaking up in the high rpms