HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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high fuel pressure woes

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high fuel pressure woes

Post  matt5r951 on Sun Oct 30, 2016 11:37 am

So while setting car up for dyno tune, car experienced high fuel pressure the entire time. It was as high as 82 psi and I think the lowest we could get it was 68psi, and he tuned at that even though it was still 10 psi higher or so than normal. Car has the Walbro 255 pump with the stock LS fuel filter/regulator assembly. However, on a GM, the filter/regulator apparently is close to the tank, so the return line is pretty short. On my car, the assembly is in the right front of the engine compartment, so the return line is almost the length of the car. That alone would probably increase fuel pressure, but we disconnected the return line at the filter/regulator and dumped it into a bucket and it dropped to 65 psi or so, still a little high, but at least showed the regulator was working. Then we dropped the tank a bit because it looked like the return line might have been pinched also increasing the pressure, and that seemed to help.

The tuner tuned car running around 68psi, but also warned me that that high pressure will be hard on the pump and it will probably prematurely fail, but how long, who knows. He recommended relocating the GM filter/regulator closer to the tank with a short return line if there's room. Well, it was a new pump (2nd Walbro) and it had about 500 miles on it, so I left it as is. On the way to Grattan Raceway a few weeks ago, pump failed and left me stranded.

Do you guys think it's likely the Walbro pump failed from running 15-20 psi higher than normal just after 500 miles? Or do you think something else is going on? Do you agree I should relocate the stock GM filter/regulator closer to the tank and put a shorter return line on? This is the 2nd Walbroo 255 pump that has failed after not many miles (but too high FP). I'm thinking of putting the Bosch HV pump on and hopefully between that and relocating regulator I'll be good to go. Thanks for your help.

Matt
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Re: high fuel pressure woes

Post  sharkey on Sun Oct 30, 2016 1:35 pm

this is one of the reasons i dont like the gm filter/regulator assembly, i dont find they work well with high output pumps. ive run them fine with a 190lph pump on a stock ls, however i find once you put a bigger pump in the pressure isnt as predictable. i had terrible issues with my cobalt ss supercharged when i put an aem 320lph pump in it (same sort of setup, however the regulator isnt in the filter its in the fuel basket with the pump), the pressure would slowly creep up to 90psi, the regulator just wouldnt allow enough fuel to return.

the only tips i can give if you want to keep running that filter/regulator setup is to make sure you have an actual ac delco, not an off brand filter. however since you already have a return line at the front of the car id put on a proper vacuum referenced regulator (like an aeromotive). this will give you rock steady, predictable fuel pressure. vacuum referencing also gives more tuning resolution.

sharkey

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Re: high fuel pressure woes

Post  matt5r951 on Mon Oct 31, 2016 9:07 am

Thanks Sharkey. The tuner said they've had some issues with the stock GM filter/regulator, so they run the aeromotive regulator on all their high HP cars. I was trying to keep things simple and cost effective, but looks like I should go with the adjustable regulator and hopefully be done with it.
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Re: high fuel pressure woes

Post  turbobob924 on Tue Nov 01, 2016 12:39 pm

I had to run an adjustable FPR in my turbo buick and planned on using another one for the new 5.3 setup.

This gets me thinking... what is the correct FP that the LS likes? I thought is was 58?


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Re: high fuel pressure woes

Post  sharkey on Tue Nov 01, 2016 2:08 pm

58 psi is what is stock, and what most people run with a factory computer. changing the fuel pressure would require a complete re-map of the injector tables.

sharkey

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Fuel System Pressure & Volume Checks

Post  mildracer on Thu Dec 01, 2016 5:15 am

If I may just add, for maximum efficiency, modern import fuel injection systems require that fuel be delivered at a specified volume and pressure. Because the fuel injector’s job is to mix fuel with the intake air charge, it must produce a finely misted, conical spray pattern through the fuel injector nozzle. Lower-than-specified fuel pressures not only fail to provide enough fuel for combustion at larger throttle openings, but may also introduce an uneven air/fuel charge distribution into the combustion chamber itself, which usually results in hard starting, hesitation and reduced power output.

Of course, fuel volume is required to maintain fuel injection pressure at the fuel injector nozzle. While a marginally performing fuel pump might maintain pressure at idle, its effective operating pressure will decrease as engine load increases. Outside factors such as higher ambient air temperatures, ethanol gasoline and inlet filter or screen restrictions may further reduce fuel volume by aggravating the tendency of any fuel pump to cavitate or form bubbles in the pump inlet assembly.

I wish you good luck.

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