Fuel pressure issues... - Pirate4x4.Com : 4x4 and Off-Road Forum

rcmf5525 · 05-24-2011, 09:48 AM

Having some issues with my fuel pressure...

I have an OBS Chevy that I dropped a 383 in with a 750cfm 4150 carb... I was using the stock fuel pump and tank and the only issue I had, other than it was super redneck to have the stock tank in the bed of the truck, was the ability to regulate the fuel pressure because the stock pump put out WAY too much pressure and seemed to overload the Holley FPR that I had. So I went to a fuel cell and 140ghp Summit fuel pump kit (pump, filter, reg, braided line). A bit of over kill on the pump, but that is the only one they offer in the kit... The cell is in the bed (much better looking than the stock tank!), the pump is mounted below on the inside of the frame rail, and the filter and regulator are mounted on the driver's side fender in the engine bay.

Once the engine warmed up, the pressure would start to drop from 6psi to below 3psi... I checked the pump and it was very hot... Probably didn't help that it was about 6" from my driver's side muffler so I wrapped the muffler in some fiberglass fire blanket to see if that would help out with the temp issue and I made sure the frame to engine and engine to battery grounds were good... It cut down on the heat tremendously, but it didn't fix the pressure issue... I let the truck heat up and had one of my boys watch the pressure gauge (it is on the carb inlet line) while I raised the RPMs to see what effect that had on the pressure... Low and behold, as the RPMs increased so did the pressure...

So, I have been thinking about it (dangerous, I know) and have decided there could be two reasons for the drop in pressure... Either the fuel is heating up to the point of vaporization in the lines while at idle and when I increase the rpms, it causes more fuel to move through the lines cooling it down thus increasing the pressure, or my fuel pump is being starved for amperage and the increase in rpm turns the alternator faster thus increasing the amperage output and allowing the pump to function properly... I just had my alternator rebuilt buy a local guy who does great work and it seems to be functioning properly (my volt meter took a shit on me but the in cab gauge doesn't fluxuate) and my battery is brand new so I am leaning towards the fuel temperature being the issue...

What do yall think??

GMCTruxrule · 05-24-2011, 10:27 AM

Any chance you might need to install a return line from the pump to the tank?

Im not the authority on electric pumps, I always run mechanical.

I do know that if you have fuel lines run too close to exhaust components, you do run the risk of vapor locking.

rcmf5525 · 05-24-2011, 01:09 PM

Thought about the return, but it is a non return pump and regulator... Or so Summit says...

chevy_man · 05-24-2011, 10:23 PM

Did it start out as vortec or TBI?

I would try re-routing the exhaust or fuel lines to cut even more heat out. Is the pressure so low it's not running correctly, or just not what you want it to be?

rcmf5525 · 05-25-2011, 06:53 AM

It was TBI...

Actually, it idols fine, and haven't noticed any adverse effects while driving... Just don't want to run it too lean and melt some rings... The engine is 10.5:1 at least...

I'm thinking about insulating the fuel lines and see if that helps out... Probably going to install some heat shields in between the header and the fuel filter and regulator that are on the inner finder as well...

chevy_man · 05-25-2011, 08:14 PM

The heat off the headers would make sense.

I'm surprised you had issues with the TBI fuel pump, they're only 10-12 psi although they do need a return.

Probably wouldn't hurt to put a AFR gauge in and see if you are having lean issues if you're worried about melting the pistons.

05-24-2011, 09:48 AM	#1 (permalink)
rcmf5525 Registered User Join Date: Nov 2007 Member # 102687 Location: Hurley, MS Posts: 330	Fuel pressure issues... Having some issues with my fuel pressure... I have an OBS Chevy that I dropped a 383 in with a 750cfm 4150 carb... I was using the stock fuel pump and tank and the only issue I had, other than it was super redneck to have the stock tank in the bed of the truck, was the ability to regulate the fuel pressure because the stock pump put out WAY too much pressure and seemed to overload the Holley FPR that I had. So I went to a fuel cell and 140ghp Summit fuel pump kit (pump, filter, reg, braided line). A bit of over kill on the pump, but that is the only one they offer in the kit... The cell is in the bed (much better looking than the stock tank!), the pump is mounted below on the inside of the frame rail, and the filter and regulator are mounted on the driver's side fender in the engine bay. Once the engine warmed up, the pressure would start to drop from 6psi to below 3psi... I checked the pump and it was very hot... Probably didn't help that it was about 6" from my driver's side muffler so I wrapped the muffler in some fiberglass fire blanket to see if that would help out with the temp issue and I made sure the frame to engine and engine to battery grounds were good... It cut down on the heat tremendously, but it didn't fix the pressure issue... I let the truck heat up and had one of my boys watch the pressure gauge (it is on the carb inlet line) while I raised the RPMs to see what effect that had on the pressure... Low and behold, as the RPMs increased so did the pressure... So, I have been thinking about it (dangerous, I know) and have decided there could be two reasons for the drop in pressure... Either the fuel is heating up to the point of vaporization in the lines while at idle and when I increase the rpms, it causes more fuel to move through the lines cooling it down thus increasing the pressure, or my fuel pump is being starved for amperage and the increase in rpm turns the alternator faster thus increasing the amperage output and allowing the pump to function properly... I just had my alternator rebuilt buy a local guy who does great work and it seems to be functioning properly (my volt meter took a shit on me but the in cab gauge doesn't fluxuate) and my battery is brand new so I am leaning towards the fuel temperature being the issue... What do yall think?? __________________ People sleep peaceably in their beds because rough men stand ready to do violence on their behalf

05-24-2011, 10:27 AM	#2 (permalink)
GMCTruxrule Registered User Join Date: Aug 2005 Member # 51243 Location: Tropical Paradise Posts: 3,410	Any chance you might need to install a return line from the pump to the tank? Im not the authority on electric pumps, I always run mechanical. I do know that if you have fuel lines run too close to exhaust components, you do run the risk of vapor locking. __________________ [COLOR="Lime"][B]1999 Chevy K3500, 5.7/4L80E/14FF/stock/stock/stock[/B][/COLOR]

05-24-2011, 01:09 PM	#3 (permalink)
rcmf5525 Registered User Join Date: Nov 2007 Member # 102687 Location: Hurley, MS Posts: 330	Thought about the return, but it is a non return pump and regulator... Or so Summit says... __________________ People sleep peaceably in their beds because rough men stand ready to do violence on their behalf

05-24-2011, 10:23 PM	#4 (permalink)
chevy_man Registered User Join Date: Dec 2007 Member # 104517 Location: MT Posts: 377	Did it start out as vortec or TBI? I would try re-routing the exhaust or fuel lines to cut even more heat out. Is the pressure so low it's not running correctly, or just not what you want it to be? __________________ R.I.P. Jason Payne

05-25-2011, 06:53 AM	#5 (permalink)
rcmf5525 Registered User Join Date: Nov 2007 Member # 102687 Location: Hurley, MS Posts: 330	It was TBI... Actually, it idols fine, and haven't noticed any adverse effects while driving... Just don't want to run it too lean and melt some rings... The engine is 10.5:1 at least... I'm thinking about insulating the fuel lines and see if that helps out... Probably going to install some heat shields in between the header and the fuel filter and regulator that are on the inner finder as well... __________________ People sleep peaceably in their beds because rough men stand ready to do violence on their behalf

05-25-2011, 08:14 PM	#6 (permalink)
chevy_man Registered User Join Date: Dec 2007 Member # 104517 Location: MT Posts: 377	The heat off the headers would make sense. I'm surprised you had issues with the TBI fuel pump, they're only 10-12 psi although they do need a return. Probably wouldn't hurt to put a AFR gauge in and see if you are having lean issues if you're worried about melting the pistons. __________________ R.I.P. Jason Payne Last edited by chevy_man; 05-25-2011 at 08:14 PM.

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