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E & F Series Fuel Pressures

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This is odd, not only for what it is but also because it just hit me after all these years. "We" consider fuel pressure below 45 to generally be bad, the lower the more likely internal injector damage is to occur. So why is the minimum fuel spec for F Series 45 PSI and for the E Series it is only 38 PSI?

 

What is the real threshold for injector damage and what is it about the E Series that makes 38 PSI acceptable?

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What is the real threshold for injector damage and what is it about the E Series that makes 38 PSI acceptable?

I guess it's part of the difference in strategies between the two applications. With the E-Series being rated at only 240 BHP/440 ft-lbs. and the F-Series rated at 325 BHP/570 ft-lbs. I would think the F-Series application requires more fueling, hence the higher pressure specs. Just my Posted Image.
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The reason the fuel pressure spec is lower on the e series is because it is tested at the back of the cylinder head after the injectors. The injectors firing will lower the fuel pressure in the cylinder head. If you test fuel pressure on an e series at the secondary fuel filter housing it will be higher like the f series. That is the reason for the different specs.

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The reason the fuel pressure spec is lower on the e series is because it is tested at the back of the cylinder head after the injectors. The injectors firing will lower the fuel pressure in the cylinder head. If you test fuel pressure on an e series at the secondary fuel filter housing it will be higher like the f series. That is the reason for the different specs.

Excellent theory and one I have not heard explained. Now, did you realize this on your own or did you hear this from a reliable source of sorts? Not doubting you, just curious. Posted Image

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If you test fuel pressure on an e series at the secondary fuel filter housing it will be higher like the f series.

Good luck checking it at the fuel filter housing.

 

Originally Posted By: Keith Browning
Excellent theory and one I have not heard explained. Now, did you realize this on your own or did you hear this from a reliable source of sorts? Not doubting you, just curious. Posted Image

I think we covered this here a few years ago. It might explain something very similar in the testing procedure in the PCED.

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Keith, it is something that I thought of my self. I am pretty sure it is quite accurate as I have been able to check fuel pressure at the filter housing and yes it is a real bitch to do.

My hat's off to you. I spent about an hour once TRYING to check fuel pressure at the filter housing.

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Hang on- IIRC, the PCED says to check FP on an E-van at he secondary FF at the same plug as an F-model, which is a real pain to access. I may have been the one to come up with the rear-of-the-head check. We did cover it several years ago with pics, here is the thread:

 

http://www.forddoctorsdts.com/forums/ubbthreads.php?ubb=showflat&Number=6394&page=1

 

 

I think I'd agree with Mike, the lower HP means (probably) lower ICP pressures which means less chance of damaging the injectors if FP falls off.

 

Or, it could be FMC changing things for no reason......

 

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I vaguely recall one of my Ford school instructors showing us a spare secondary fuel filter cap with a brass fuel pressure fitting drilled and tapped into it, that could be used specifically for checking fuel pressure on E-Series a few years back.

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I've always checked fuel pressure at the fuel pump on the frame. All of the decent fuel pressure test kits have the adaptors to "T" into the quick disconnect line. It's a lot faster and eaiser to do.

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Chris:

 

Yes, it's easier to do, but you're not getting a true pressure reading there. Like I said in the last post, what if the secondary FF is restricted? What if the standpipe is broken or the check valves on the heads are defective?

 

Why do the test if you can't rely on the results?

 

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True, but on a driveability concern I always try to get a fuel sample and change the filters anyways. I agree you are not checking the standpipe and maybe a checkvalve failure at the cylinder head. I feel that checking it at the HFCM, changing the filters, getting a fuel sample takes care of 95% of the fuel problems that I have personlally seen. If I have to, I'll get the pressure at the correct location.

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Also checking at the HFCM will not show us if the fuel pressure regulator is working properly. I don't know how many times I've had to put a fuel pressure regulator on a truck to bring the fuel pressure into it's proper spec!

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Also checking at the HFCM will not show us if the fuel pressure regulator is working properly. I don't know how many times I've had to put a fuel pressure regulator on a truck to bring the fuel pressure into it's proper spec!

More times than not, I'm replacing a regulator with injectors.

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I also change the regulator along with any injectors even if it falls with specs. The new regulator springs are 2 coils longer.

With new filters on a f-series, the pressure is boosted to 70 psi max and about 55 psi min with the new fuel gauge tester. It also helps those lazy injectors...

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Working at Rex's shop now, Brad?

 

I like the new regulator kit, however -- don't bother selling it on an E-series... see if you can get the spring seperately from ITEC -- that's the only part of the regulator kit you can use.

 

Seems a little heavy... $112 or whatever it retails at this week for a spring that could be robbed out of my ballpoint pen... speaking of which...I need a new pen....

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I like the new regulator kit, however -- don't bother selling it on an E-series... see if you can get the spring seperately from ITEC -- that's the only part of the regulator kit you can use.

Yeeeeeeeeeahhhh... but... More often than not when I test for and find a bad regulator it has nothing to do with the spring. I commonly find the rubber seal on the valve has come apart. I agree that the cover is basically not needed but the spring along with with new seals, valve and air bleed orifice really should be replaced.

 

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