04 Cobra possible fuel issue | Data log attchaed

[11sec335i]

Hi everyone,

I just had a ported eaton 2.76 upper, Accufab TB, 2600 SCT, 60s, dual SVT focus pumps installed. A/F was good at 11.2-11.5 the thing that is concerning me is the fuel pressure and voltage. Fuel pressure is at 40psi and then WOT it drops all the way to redline, ending at about 29PSI. My tuner is saying it's okay because the A/F is good, and I have asked a few other tuners and they are saying don't worry about it. I just have never heard of fuel pressure dropping being OKAY. Voltage drops to 12V, I did order a 200 amp alternator and am waiting on that. I was thinking there wasn't enough voltage going to the pumps possibly.

I've attached this data log if anyone wants to check it out.

 

[Blown38]

Pump doesn't quite max out. Whats weird is your MAF and FP duty cycle drop off before you let out of the throttle. Have you changed the fuel filter?

 

[11sec335i]

Pump doesn't quite max out. Whats weird is your MAF and FP duty cycle drop off before you let out of the throttle. Have you changed the fuel filter?

I changed it about 3000 miles ago. I was thinking of trying that. I don't want to throw parts at it you know? The car made 509/515, it runs good. It's just the FP concern, I'm assuming it should be in the 55-60psi range.

 

[01yellercobra]

It depends on what PID you're watching. If you're watching pressure drop across injectors it should stay at 40psi the whole time. Generally anything above 12vdc at WOT is considered good. But personally I prefer if it doesn't drop that much.

 

[11sec335i]

It depends on what PID you're watching. If you're watching pressure drop across injectors it should stay at 40psi the whole time. Generally anything above 12vdc at WOT is considered good. But personally I prefer if it doesn't drop that much.

I am watching pressure drop across injectors, correct. It drops like I said as low as 28PSI at the top of the tach, but A/F maintains. I have had a few tuners say, if A/F is good don't worry about it.

 

[01yellercobra]

It's using the injector pulse to make up for the lower fuel pressure. I'm at work so I can't view the log, but if you're not monitoring injector duty cycle it might be worth checking it out. Hopefully the new alternator fixes everything.

 

[11sec335i]

Gotcha, I didn't check that. The tuners I've spoke with all say it's not a concern. I feel like ummm low fuel pressure is ya know? Maybe they are saying that because, they are saying what you said.

 

[Blown38]

What AFR are you seeing?

Here's a Pic of the log.

 

[11sec335i]

11-.2 - 11.5

 

[HPLouis]

Your datalog looks exactly like mine and we have similar mods (I have a BAP instead of Focus pumps though). I spoke to Greg at RET and the original owner and they both said the same thing you're hearing. I'm at 11.0-11.2 A/F, 12.5V, 85% Injector duty cycle, 27 for pressure drop across injectors (I start at 39.6 like you), 802 for MAF, 1.66 for load and 23 degrees of timing at 6000rpms. The car made 508/481 with the mods in my sig. I'm planning on upgrading the alternator to see if that'll help. I'm like you, even though I'm told it's OK, it does worry me.

 

[HPLouis]

It's using the injector pulse to make up for the lower fuel pressure. I'm at work so I can't view the log, but if you're not monitoring injector duty cycle it might be worth checking it out. Hopefully the new alternator fixes everything.

I was told the same thing. When the BAP kicks in around 4500rpms, my FP duty cycle hits 100% and stays there from 4500rpms and up and I was told that the injectors increase the pulse width to compensate for all that and that's why my A/F stays strong throughout the whole run, even though the fuel pressure gets low.

it's still something scary to see though. I'm kind of glad to see this thread and seeing that others are saying the same thing. I was getting anxious about the FP

 

[11sec335i]

I was told the same thing. When the BAP kicks in around 4500rpms, my FP duty cycle hits 100% and stays there from 4500rpms and up and I was told that the injectors increase the pulse width to compensate for all that and that's why my A/F stays strong throughout the whole run, even though the fuel pressure gets low.

it's still something scary to see though. I'm kind of glad to see this thread and seeing that others are saying the same thing. I was getting anxious about the FP

Yea I hear you. I don’t get what the injector pulse does to make up fuel pressure. Changed the fuel filter and it’s still the same. JDM tuned the car and swears it’s fine how it is.

 

[HPLouis]

Yea I hear you. I don’t get what the injector pulse does to make up fuel pressure. Changed the fuel filter and it’s still the same. JDM tuned the car and swears it’s fine how it is.

I did the same. Changed fuel filter and battery when I was worrying about the fuel pressure. JDM tuned my both my old coupes and my Raptor and I trust him. I've also heard great things about Greg at RET who tuned this car. I trust him too.

Again, it's great to see this thread. It helps me a little with my anxiety about this. Also, it's good to see that JDM thinks the same way. I've spoken to both Jim Jr and Sr and they are both great tuners.

 

[11sec335i]

Well that’s reassuring to know. So I guess the car is okay? I still don’t get it.

 

[Blown38]

The injector pulse just means the injector needs to stay open longer to hit the AFR the EEC is commanding. Your tune is commanding 12.0 AFR so that could be cleaned up some.

If the injector duty cycle is getting up there then they won't be able to compensate any more. Like say it gets cold outside.

I havent messed with returnless enough to know if it is typical for the pressure drop across the inj to fall off over time, but the pump is not maxed yet so....

You could put a FP gauge on the rail to check if it is staying strong. The external gauge should read boost psi amount over 40psi. IE 16 pounds of boost the fuel pressure should read 56psi.

 

[11sec335i]

The injector pulse just means the injector needs to stay open longer to hit the AFR the EEC is commanding. Your tune is commanding 12.0 AFR so that could be cleaned up some.

If the injector duty cycle is getting up there then they won't be able to compensate any more. Like say it gets cold outside.

I havent messed with returnless enough to know if it is typical for the pressure drop across the inj to fall off over time, but the pump is not maxed yet so....

You could put a FP gauge on the rail to check if it is staying strong. The external gauge should read boost psi amount over 40psi. IE 16 pounds of boost the fuel pressure should read 56psi.

I see, okay is the car good? Because the air fuel is still good?

 

[01yellercobra]

The injector pulse just means the injector needs to stay open longer to hit the AFR the EEC is commanding. Your tune is commanding 12.0 AFR so that could be cleaned up some.

If the injector duty cycle is getting up there then they won't be able to compensate any more. Like say it gets cold outside.

I havent messed with returnless enough to know if it is typical for the pressure drop across the inj to fall off over time, but the pump is not maxed yet so....

You could put a FP gauge on the rail to check if it is staying strong. The external gauge should read boost psi amount over 40psi. IE 16 pounds of boost the fuel pressure should read 56psi.

The pressure shouldn't drop off. Yes by increasing the injector pulse width the ECU can keep up the correct A/F. But like you said there isn't much wiggle room should something else change.

When I was returnless my pressure was 39-40psi all the way up to the top.

 

[cj428mach]

I haven't looked at the logs but I agree I think fuel pressure should remind constant. When I was returnless my car ran 40 psi except when getting on and off the throttle. If the maf is stalling you probably have belt slip.

 

[11sec335i]

There is no belt slip. I put a new 200 amp alternator on the car today. Made a difference in charging. It's now 13.5 or higher to redline. FP duty is a tad lower at 81 percent. I talked with Lamotta Performance today, and was told the ECU is going to tell the car how much FP it needs, so its showing 30PSI or whatever it is, then that's what it needs. As long as the FP duty is okay and the car is good on A/F it will be fine. A boost-a-pump would just lower my duty cycle and give it more room, but I don't NEED it. Thanks for everyone's thoughts!

 

[HPLouis]

There is no belt slip. I put a new 200 amp alternator on the car today. Made a difference in charging. It's now 13.5 or higher to redline. FP duty is a tad lower at 81 percent. I talked with Lamotta Performance today, and was told the ECU is going to tell the car how much FP it needs, so its showing 30PSI or whatever it is, then that's what it needs. As long as the FP duty is okay and the car is good on A/F it will be fine. A boost-a-pump would just lower my duty cycle and give it more room, but I don't NEED it. Thanks for everyone's thoughts!

Thanks for sharing this and following up on this post. I've been freaking out over datalogs myself and seeing this post has given me a lot of relief.