Time2Kill Posted April 29, 2009 Report Share Posted April 29, 2009 I have a 2003 Silverado with a 414 I just swapped in and I'm having problems getting it tuned. The AFR keeps fluctuating at WOT. Although I think I just narrowed the problem down. I'm running the stock fuel pump, with a Walbro Inline pump. It then goes up to an adjustable fuel pressure regulator which feeds the rails and sends the excess fuel back to the tank. When I turn the key on, the fuel pressure goes up to 58 psi (where its set at) and then quickly drops pressure as soon as the pump turns off. It will drop down to 10psi fairly quickly, then after another 10 seconds or so drops down to 0psi. Is this normal for an '03 Return style fuel system? As far as I understood it should hold pressure when the key if off, so I'm assuming either a bad check valve in the pump or a split in the fuel line in the tank. I cannot find fuel leaking from anywhere else. Quote Link to comment Share on other sites More sharing options...
Krambo Posted April 30, 2009 Report Share Posted April 30, 2009 I'd say normal because I have a similar set-up and my pressure drops off as well. With the Aeromotive FPR, it drops off much slower than the stock FPR though. I logged my FP at WOT and it is rock solid at 62psi for a 1-2-3 gear blast. Idle FP fluctuates alot though due to the choppy cam and choppy vac the FPR sees. Quote Link to comment Share on other sites More sharing options...
Time2Kill Posted April 30, 2009 Author Report Share Posted April 30, 2009 (edited) I'd say normal because I have a similar set-up and my pressure drops off as well. With the Aeromotive FPR, it drops off much slower than the stock FPR though. I logged my FP at WOT and it is rock solid at 62psi for a 1-2-3 gear blast. Idle FP fluctuates alot though due to the choppy cam and choppy vac the FPR sees. What are you running for a fuel pump? I called the manufacturer of my fuel pressure regulator and they said that there should not be a pressure drop as soon as the pump turns off. Under WOT, I'm seeing a 5 to 10 psi pressure drop. I capped the vacuum port on my regulator so it's not seeing the vacuum of the motor. Also, did you mount your regulator before the inlet of your fuel rails? Edited April 30, 2009 by Time2Kill (see edit history) Quote Link to comment Share on other sites More sharing options...
Krambo Posted April 30, 2009 Report Share Posted April 30, 2009 (edited) I have a stock in tank and a Walbro in-line (same set-up from my Radix days). When my pumps shut off, it takes a good 20 seconds to drop to about 20PSI and then another minute or so to go to 5-10. This is similar to what I saw with the stock 03 set-up AND the radix set-up. I feel you should have the regulator see the vacuum of the motor as well. I have fuel come in on the rear driver's side rail, X-over to the passenger rail at the front of the intake, and the FPR is on the firewall side of the passenger rail (return). It is vac referenced and my FP increased as vacuum increases. Your Regulator should be the last piece on your fuel system's fuel path...at least with the areomotive EFI boost/vac referenced one. Here is the best pic of the fuel rails and FPR: Edited April 30, 2009 by Krambo (see edit history) Quote Link to comment Share on other sites More sharing options...
Time2Kill Posted April 30, 2009 Author Report Share Posted April 30, 2009 I have a stock in tank and a Walbro in-line (same set-up from my Radix days). When my pumps shut off, it takes a good 20 seconds to drop to about 20PSI and then another minute or so to go to 5-10. This is similar to what I saw with the stock 03 set-up AND the radix set-up. Everything that I can find online says that this SHOULD not happen. I'm just wondering if its the cause of my problems. On the dyno, I can have one pull at 12.8 AFR, then the very next pull will be at 15 or 16 AFR. I've been chasing this problem down for two weeks now, and this is one of the last possible things that I can find. Quote Link to comment Share on other sites More sharing options...
misterp Posted April 30, 2009 Report Share Posted April 30, 2009 ...Your Regulator should be the last piece on your fuel system's fuel path... The in-tank walbros feature a built-in one-way check valve, it is not possible for fuel to bleed-down 'backwards' through the pump. I bet that if you check the pressure BEFORE the FPR you'll discover that it's still got a good 58-psi head to it even as you observe the rail pressure trickle down to nothing. Replumb your FPR so that it is used as a 'back-feed' regulator, like Krambo's example. Another example setup: Fuel comes in from the back, Y-block distributes to the fuel rails - rails see full [regulated] pump pressure - Unused fuel plumbed from front of rails into regulator; FPR dumps excess back to tank to maintain rail pressure (return line not shown/attached, use your imagination!) - Or some plumbing variation thereof... Mr. P. Quote Link to comment Share on other sites More sharing options...
Krambo Posted April 30, 2009 Report Share Posted April 30, 2009 Nice pictures Steve! When you getting that intake on? I thought for a long time on how I wanted my fuel path to run and what clinched me is that the injectors are tilted (about 15 degrees or so) toward the firewall on the driver's side and inverse on the passenger side. I figured that the fluid (fuel) path would be less restricted if the injectors were tilted toward the incoming fuel path rather than away from the fuel path. Don't know if it makes a difference or not. Time2kill, If you confirm that your fuel pressure is steady at WOT during your run, you may want to look into if your Pe mode is actually "kicking in". For some reason the trucks have their Pe Delay at like 5,000 - zero this out, Enrichment rate - set it to like 2.5 or higher. I have seen numerous 03 return style trucks and they all would drop pressure once the pumps kick off. I figured since this is what I saw on my old set-up (and many others), it was normal. I am going to check out my fuel system now that you have confirmation that this observation is "not normal" Regardless, my truck runs fine and my FP gauge and Wideband tell me that all is normal. Maybe Zippy can chime in as he has seen a few trucks that wouldn't go into Pe mode on the dyno's for some reason. Quote Link to comment Share on other sites More sharing options...
misterp Posted April 30, 2009 Report Share Posted April 30, 2009 (edited) Nice pictures Steve! When you getting that intake on? ... Soon! I am going to redo the LF line, tighten it up a bit behind the alternator. I was hoping to have this all on the truck in time for the Ennis Ford truck vs. Chevy truck meet on Friday, but parts did not get here in time. I've also got a set of ARH 1-7/8" long tubes coming (should be here tomorrow) and still waiting on the Speartech TAC module & harness... Thanks for the compliments, it looks much better in person - I got the -8AN aluminum tubing to smoothly bend UNDER a 1.25" radius, it's tight! Still have to make hold-downs for the rails themselves and brackets to hold the FPR and Y-block to the manifold, and plumb the -6AN return. Mr. P. Edited April 30, 2009 by Mr. P. (see edit history) Quote Link to comment Share on other sites More sharing options...
Time2Kill Posted April 30, 2009 Author Report Share Posted April 30, 2009 I was able to hook a mechanical guage straight to my fuel line today. It shoots up to 125 psi, and after about 15 minutes, it only went down to a 115 psi. The regulator is definitely bleeding off all the pressure. I'm currently using a professional products regulator (came with a set of fuel rails I bought). I think I'm going to pickup an Aeromotive regulator tomorrow and see what it does. Quote Link to comment Share on other sites More sharing options...
Time2Kill Posted May 2, 2009 Author Report Share Posted May 2, 2009 I talked to Aeromotive today, and also confirmed by taking my regulator apart, the regulator will not hold pressure after the fuel pump shuts off. All pressure is leaked through the return line. OEM regulators are designed to hold pressure though to be able meet EPA standards for cranking/starting emissions. Your truck in stock form should definitely be able to hold pressure which I have also confirmed in the above post. Quote Link to comment Share on other sites More sharing options...
Krambo Posted May 2, 2009 Report Share Posted May 2, 2009 Interesting. Now did they tell you to what extent the pressure should be held after pump off? i.e. pressure decay rate? Will it take a minute to bleed down or two minutes or 5 minutes? Quote Link to comment Share on other sites More sharing options...
Time2Kill Posted May 2, 2009 Author Report Share Posted May 2, 2009 Interesting. Now did they tell you to what extent the pressure should be held after pump off? i.e. pressure decay rate? Will it take a minute to bleed down or two minutes or 5 minutes? He did not tell me how long it should hold pressure for. But I can say, I just got my Aeromotive regulator (13309) hooked up today and I have it set to 58 psi. As soon as the pump shuts off it goes down to about 52 psi, and after 10 minutes it was still at 52 psi. Even though the tech at Aeromotive said it wasn't designed to hold pressure, mine is holding rock steady now after the pump is off. I really hope the Aeromotive regulator solves my problems. I'll know for sure on Monday. Quote Link to comment Share on other sites More sharing options...
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