Fuel pressure issue - Lightning Forum | LightningRodder.com
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post #1 of 57 (permalink) Old 08-05-2017, 07:55 PM Thread Starter
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Fuel pressure issue

Alright so my truck isn't actually a lightning, it's a lightning swapped 4x4. Jj is trying to get the tune right on it but for some reason it leans out under load. I believe Jj has added close to 50% more fuel to the tune (correct me If I'm wrong), and it still won't go richer than a low 14 Afr. This is in 3rd gear pulls making 6 psi at the max. The truck is also going into open loop so it should be going rich. I have tested my regulator at idle to see if it is raising fuel pressure with boost by pressurizing it with a bike pump and the fuel pressure does rise. So I don't think it's the regulator but I could be wrong. Is there any test I should do before I tear Into my fuel system? The truck has 40 psi for for pressure at idle. I did notice that the second I turn the truck off the pressure drops to 20 psi immediately, then will be at 0 within 15 minutes. I also don't smell any fuel or see any leaks. I'm running duel 255 pumps with a stainless Y in the tank with stock fuel lines, 97 rails with an adjustable regulator, and siemies deka 60s. How much current draw should I see front these pumps? Is it possible that only one is turning on. Maybe a line popped off the Y?

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post #2 of 57 (permalink) Old 08-05-2017, 08:24 PM Thread Starter
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I also don't know what the fuel pressure is when I did these pulls. I only have an underhood fuel pressure Guage. I'll be able to rig up a system tommorow that will let me see the gauge while I'm driving tho.

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post #3 of 57 (permalink) Old 08-05-2017, 08:48 PM
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What size return do you have? Regulator could be functioning normally, but the dual 255's could be over running it, preventing its normal operation. You need a fuel pressure gauge to make sure, but that's where I'd start. I bet it doesn't rise with boost because the return line is too small.

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post #4 of 57 (permalink) Old 08-05-2017, 08:50 PM Thread Starter
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It's just the stock size return line. Wouldn't that cause for an increase in pressure on not a decrease tho since it's on the return side?

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post #5 of 57 (permalink) Old 08-05-2017, 09:01 PM Thread Starter
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I don't know what would cause a sudden 20 psi drop when the pumps turn off, then the slower bleeding off to zero. The only thing I can think of is one of the rubber lines on the hat is bad. That would cause a rapid leak at higher pressure then slowly leak down at lower pressures

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post #6 of 57 (permalink) Old 08-05-2017, 09:02 PM
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Like Logan said, you need a fuel pressure gauge..
You might consider re-wiring the pumps with some 10 gauge wire.
Use the the 12v running the pumps for a relay trigger wire.

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post #7 of 57 (permalink) Old 08-05-2017, 09:05 PM Thread Starter
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I have a gauge but it doesn't really do much good since it's on the rail. I'm gonna rig up an extention for it tommorow so I can drive it with the gauge on the wiper cowl. I was originally gonna rewire the truck for the pumps but was told by multiple guys on here it wasn't necessary. I new I should have just done it anyway.

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post #8 of 57 (permalink) Old 08-05-2017, 09:09 PM
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Quote:
Originally Posted by 2thousand5four View Post
I don't know what would cause a sudden 20 psi drop when the pumps turn off
Bad pump...

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post #9 of 57 (permalink) Old 08-05-2017, 09:10 PM Thread Starter
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Quote:
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Bad pump...
I hope not. I guess I'll be dropping the tank tommorow to test everything

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post #10 of 57 (permalink) Old 08-05-2017, 09:32 PM
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Return line too small. Over running the regulator.
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post #11 of 57 (permalink) Old 08-05-2017, 09:36 PM Thread Starter
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I don't mean to sound stupid here but can someone explain how a return line that is to small would cause a drop in pressure? I figured if would increase pressure if anything

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post #12 of 57 (permalink) Old 08-05-2017, 09:39 PM
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Fuel pressure issue

Doesn't let the regulator act as it should. Pressurizes the diaphragm and it won't build pressure 1:1 like it should.

You need to get a gauge and take it for a drive. Get into boost and see if pressure rises. You can rent a gauge from any box store auto parts place.

I didn't listen either and threw parts at my truck for a month.


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post #13 of 57 (permalink) Old 08-05-2017, 09:47 PM Thread Starter
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I have some braided pressure line that will work as an extention for my fuel pressure gauge. I'll just run that up to the wiper cowl tommorow so I can zip tire the gauge there and drive it around. Assuming is not building fuel pressure like and should and Before I start replacing the return line is there anything else I should look at? Is it worth dropping the tank to check the pumps out and make sure the lines did come loose or anything? The truck has a body lift and is on 35 inch tires so it's not hard to drop the tank.

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post #14 of 57 (permalink) Old 08-05-2017, 09:53 PM
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I've seen this before...One of the pumps is over powered by the other and it's letting the fuel pressure to bleed off.
Is the return line the same size on NA trucks as a SVT?

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post #15 of 57 (permalink) Old 08-05-2017, 09:55 PM Thread Starter
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Quote:
Originally Posted by Certified Drunk View Post
I've seen this before...One of the pumps is over powered by the other and it's letting the fuel pressure to bleed off.
Is the return line the same size on NA trucks as a SVT?
I believe so. I'm not 100% sure tho. I have heard about the one pump thing being stronger than the other before. A lot of the swap guys I talk to just went to a single 340 pump. Probably would have been easier for me to do that.

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