qwik240z Posted October 26, 2006 Share Posted October 26, 2006 I took my LS1 240Z to get it dyno tuned last night. They had to stop in the middle of the entire process. When the car was being run under a load it was leaning out quite a bit. We hooked up a fuel pressure gauge and found that the fuel pressure was at about 52PSI We adjusted the regulator up to 59PSI and did another pull. The fuel pressure was dropping down to like 30PSI under a 3500-4000 RPM load in 4th gear. I though that maybe it was a clogged fuel filter. I pulled the fuel filter and bypassed it with a barbed connector and we did another pull. Same problem. Fuel pressure is fine at idle and up to 3000 rpms. The entire system is fairly new. Tank was boiled and coated and ran fine for several years with the L28. All the lines are new. The fuel pump is a Walbro 255LPH inline pump with a inline filter going to a aeroquip adjustable FPR. I spoke to the shop that did most of my install and they think the Fuel Pump is defective. He said that they have had about 3 bad pumps in the past 2 months. Anybody else having this problem? Any other ideas on what it could be? TIA. Any help 1 Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 26, 2006 Share Posted October 26, 2006 What diameter of fuel line is being used, and did you up size the pick up line going into the tank? A little hard to believe you are exceeding the flow capacity of the lines at only 3000 RPM. You can do a flow check on the pump. You know, disconnect a line and see how long it takes to pump a gallon of fuel/liquid. And as long as I am throwing out ideas that I don't have to trouble shoot, Pete Paraska had a problem with his tank coating coming undone and clogging his system. maybe cut open the fuel filter and check for debris. Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 26, 2006 Share Posted October 26, 2006 The fuel pumping volume drops when the pressure goes up. Trying to make 59 psi and flow a decent amount of fuel is tough on a pump. However, only able to hold 30 psi during a load seems a bit low. Why are you running so much fuel pressure? If you tune it with lower pressure the pump will have a better chance to keep up. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted October 26, 2006 Share Posted October 26, 2006 Which model Walbro is it? Model GSL392 is the one you want. Not all of the Walbro 255lph are created equal. It does sound like it may be clogging though. Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 26, 2006 Share Posted October 26, 2006 I found a Walbro 255 inline pressure/flow graph and it was flowing about 65 gph (390 lbs/hr) at 30 psi and 45 ghp (270 lbs/hr) at 60 psi. Quote Link to comment Share on other sites More sharing options...
that240guy Posted October 27, 2006 Share Posted October 27, 2006 Hey I had the exact same problem with my ls1 swap with my walbro. I actually kept clogging the pump. Since the external pump design does not have a prefilter it is very susceptable to getting clogged and getting noisy and dropping pressure. I backflushed mine using a funnel and pouring gas through the pump backward while having the polarity reversed and that cleaned it out nicely. I now have a tiny 3/8" Fram fuel filter inline between my inline pump and my tank. I have not had any problems since. I am dynoing 346 at the wheels and holding 57 psi with the corvette fuel filter/regulator. Quote Link to comment Share on other sites More sharing options...
spork Posted October 27, 2006 Share Posted October 27, 2006 It could be a defective/clogged pump. you should have plenty of fuel if the lines are sized properly. I made over 450 at the wheels running 60psi static and then 25 pounds of boost making my fuel pressure 85psi under boost. That was with a Walbro 255hp. This was on an l-series engine, but hp is hp when talking about how much fuel is needed to make it. Quote Link to comment Share on other sites More sharing options...
qwik240z Posted November 12, 2006 Author Share Posted November 12, 2006 Sorry guys. I have been away from the list for a while. So we checked out the pump and it seems to have been clogged up. The previous owner had the gas tank boiled out and sealed and whatever they used to seal it has started to peel off and clog up the lines and the filter and the pump. I had a gas tank sitting here from a 75 280Z (fuel injected) that I was planning on installing so it finally got done. With this tank, and a new fuel filter, the problem is now gone. I took the car back to have to dyno tuned and it now runs great. 327rwhp and 340RWT on a Mustang dyno. The car now has excellent throttle response and feels so much more powerful. It made more torque on the other dyno but I think that different dynos give different numbers. The butt dyno says it is way better now. Thanks for all of your help. Quote Link to comment Share on other sites More sharing options...
silicone boy Posted November 12, 2006 Share Posted November 12, 2006 On another forum (torquecentral.com) there was a discussion about fake Walbro's showing up on Ebay. They are of Chinese manufacture and look just like the real thing. Hope these don't make it into the more legitimate supply chains. Quote Link to comment Share on other sites More sharing options...
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