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5.3l fuel pressure issues

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mudbog42

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Well, I just got my 86 K-5 up and running last weekend. I put in a 2003 5.3l (flex fuel engine). I have been getting check engine codes for the MAF and bank 1 & 2 running lean.

Also when I hook my pressure gauge up turn the key the pressure will rise and quickly fall. So I have to turn the key on and off about 4 times to build enough pressure to start the truck. Once started, it seems to run great. The pressure reads a steady 40 PSI at idle. Not sure if this is too low or not. I read somewhere that the flex fuel motors run at a lower PSI but not sure how much lower. Also if I pinch the return line the fuel pressure will stay, so I thought for sure it would be the regulator. I also took a reading before the regulator and the pump held a strong 75 PSI with the key on engine off.

I have replaced the regulator twice already and it still does the same thing, cleaned the MAF, no difference. Also the o2 sensors are brand new on it. I am not sure what the problem could be.

Any help would be greatly appreciated

Thanks
 
The pressure should be 55-62 psi and after initial prime shouldnt drop more than 5psi in ten minuts.Seing you replaced the regulator already the only other possable leaks other than an external leak are a bad injector leaking down or the valve in the fuel pump.You will need a special tool with a shut off valve that the fuel pressure guage goes to to check the pump for leak down.The only way to check the injectors is to lift the rail off the plenum with all the lines and injectors atached and watch if any injectors drip fuel under pressure.Any exaust leaks before or near the o2's can cause a lean code.A cracked or worped plenum with a vacume leak can cause both your codes.There is also updated plenum gaskets from GM to cure plenum leaks and the plenum needs to be checked with a straight edge.Also any leaks whatsoever (after) the maf will cause a code.Good luck.
 
Ok well I pulled up the injectors to check for any leaks and all of them were dry as can be. All the fuel is leaving out through the return line. If I pinch the return line the pressure goes where it should be.
 
mudbog42 said:
Ok well I pulled up the injectors to check for any leaks and all of them were dry as can be. All the fuel is leaving out through the return line. If I pinch the return line the pressure goes where it should be.
Click to expand...
Is that pressure(75psi) with the pump running or after the pressure builds up and the pump is shut off and the drop is checked with the return line clamped off?Not exactly sure how your checking it but the pressure should not drop even over night and clamping off the return line is a good way to check if the fuel pressure is being lost back through the pump but the pump needs to be off to check it.If its being checked with the pump running all thats telling you is the pump has the ability to put the pressure out.Also running the pump with the return line clamped off is a good way to damage the pump and its internal valve which by the way is a one way valve that is not susposed to let (any) fuel leak back into the tank resulting in key off pressure loss.You replaced the regulator a few times you said and (if) you have the corect one installed I would bet your pump is bad.
 
Its 75 psi with the key on engine off (after it builds pressure and turns off). This is checking the pressure before it gets to the regulator with no return. The pump does hold its pressure without bleeding down. It seems as if all the fuel is just going back out the return line. As soon as the truck shuts off the pressure drops to 0 psi

Also I was reading the chiltons in the parts store and flex fuel should be 48-54 psi, all others 55-62.
 
Having the vin# of the doner truck would be the best way to get the right parts for what your doing and to get the proper fuel pressure specs.Whatever you should have 0 is not good.I find it hard to belive you have had 3 including your original bad regulators.Even the wrong one will hold pressure even if its too low for your aplicaion it should hold.Very od.I would want to be 100% positive the regulator is the corect one but still cant belive all three are bad.Something with the fuel system is not right but even so is a small problem compared to the codes you have.Is the fuel pressure in spec when running and driving under a load?
 
Ok, probably wrong, since I don't think I have ever seen a GM fuel pressure regulator, but doesn't it have a vacuum line hooked to it to regulate the fuel pressure according to manifold vacuum?

If so, could that line be hooked up wrong?
Should be a small line on top.
 
Fordum said:
Ok, probably wrong, since I don't think I have ever seen a GM fuel pressure regulator, but doesn't it have a vacuum line hooked to it to regulate the fuel pressure according to manifold vacuum?

If so, could that line be hooked up wrong?
Should be a small line on top.
Click to expand...
He would have to try on purposs to hook the vacume line on wrong on a 5.3.
Only possability I can think is if you installed all 3 wrong.There is 2 o rings on the regulator and a disk screen.A big o ring that prevents external leaks and a small internal o ring.Or possably the original small o ring was left inside and preventing the new o ring from seating properly.The only other leak to check for would be through the vacume port but 3 leakers?
 
Yeah, three leakers would be a stretch.
My comment, which I wrote wrong, was not that the line might be put on wrong on the regulator, but that the vacuum line might be hooked to the wrong port on the engine.

Even so, the fuel has to be going somewhere.
There are only four places it can go.
Backflow through the pump.
Out through the injectors.
Externally onto the engine or pouring out onto the ground.
Back to the tank through the regulator.

He has checked the injectors, I think he would notice if gas was pouring out somewhere, unless it is going into the oil pan or transmission.
And that would let itself be known pretty quick.

It seems that it is going back through the regulator, but after 3 you would think he would get a good one....

Mudbog, just for fun, pull the transmission dipstick and the engine dipstick and see if you smell gas......
Also, pull the vacuum line off the regulator and make sure there is no gas there.
 
Definitely no fuel in the fluids, and no fuel in the vacuum line either. I've been doing an experiment by putting a clamp on the return line to put the pressure where it should be when running and erasing the engine codes. So far (fingers crossed) no codes when the pressure is correct, but as soon as I loosen the clamp to let the regulator work on its own, my check engine light comes back on right away.
 
mudbog42 said:
Definitely no fuel in the fluids, and no fuel in the vacuum line either. I've been doing an experiment by putting a clamp on the return line to put the pressure where it should be when running and erasing the engine codes. So far (fingers crossed) no codes when the pressure is correct, but as soon as I loosen the clamp to let the regulator work on its own, my check engine light comes back on right away.
Click to expand...
Well even if the pump was bleading back it would only cause a starting problem untill the proper pressure is acheved then should run fine.With everything Im reading Id have to try another regulator.Not the same part# if possable and make sure its installed corectly with both o rings and no old pieces inside to cause it not to seal properly.Could just be you keep getting the wrong regulator but it should hold some sort of pressure which makes me wonder.
 
what part # pump are you running ?

were is it mounted ?

all this might just be a incorrect pump for the aplication.
 
sweetk30 said:
what part # pump are you running ?

were is it mounted ?

all this might just be a incorrect pump for the aplication.
Click to expand...

I am running an frame mounted inline airtex e2000 pump. I know a lot of jeep people had have great success with this pump on the LSx conversions.

I am using a Borg Warner regulator part # 24011
 
[FONT=Arial, Helvetica, sans-serif]AIU[/FONT][FONT=Arial, Helvetica, sans-serif]Type:[/FONT] [FONT=Arial, Helvetica, sans-serif]Fuel Pump, Tank and Turbo System[/FONT][FONT=Arial, Helvetica, sans-serif]Sub Type:[/FONT] [FONT=Arial, Helvetica, sans-serif]Electric Fuel Pump[/FONT][FONT=Arial, Helvetica, sans-serif]Notes:[/FONT] [FONT=Arial, Helvetica, sans-serif]Type ROLLERVANE Volts 12 GPH Wide Open 30-40 PSI Shut Off 70-95 Ground NEG Location IN-LINE[/FONT]
The only place I could find specs on that pump are ebay.Doesnt seem you have selected the corect pump if the info is corect.
http://cgi.ebay.com/ebaymotors/Airtex-E2000-Electric-Fuel-Pump-/290460379836
 
I am going to try and call airtex tomorrow and see if I could get them to give me the exact specs on the e2000 pumps since all I can find is what people have posted in other forums
 
wasnt airtex the ones people say to stay away from for lots of problems at the parts stores. ?

biggest thing i would ask and look for is does that pump have a check valve or anti drain back valve in it to hold the pressure.
 
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