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Help understanding fuel pressure readings

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sincityharley

Member
I just bought a fuel pressure gauge and modified it to fit my bike. It hooks in at the line that feeds the fuel from the quick disconnect to the fuel injectors. When I hit the run button before I fire it up, I am getting a reading of 40 which bleeds down to 35. It take a couple of attempted starts before my fuel pressure gets past 40 and rests at 50. Once my bike does start my fuel pressure will remain at 55. If I go riding my bike will start to sputter but never die. Ultimately I am trying to find out what that is. My first question is what PSI should I be reading when hitting the run button? Should the pressure bleed off like it does? Also I noticed a small bubble in my fuel pressure tester. When modifying it, I used clear tubing so I can see the fuel passing through. What is the proper way to expel air from the fuel line on an EFI bike. Can anyone think of a good reason why my bike would sputter while moving but not at idle.
 
When the ign. is turned on the pressure jump high then goes back down between 55 & 62 psi if I rember right. The pressure valve allows the excess pressure to blead off in the tank and should keep it a min of 55psi. The factory guage has a bleed off valve to get the air out before testing, you could put a Y with a shut off valve between the guage & the induction manafold and bleed a little gas along with traped air into a bottle then shut the bleed off valve. With the engine is running the fuel pressure should stay steady somewhere between 55 & 62psi at any rpm, I mean rock steady probably at 58psi. Does the pressure stay steady when your riding the bike and it sputters? Good chance you could has a pin hole in one of the lines in side the fuel tank or a restricted fuel filter, try draining most of the gas out of the tank and try to see inside while turning on the ign. You might see a stream of fuel being squritted from one of the lines. Bad fuel pressue can make the bike act like it has a electrical problem.
 
This fuel pressure tester does have a bleeder on it and I can expel air from it. I was wondering though how I expel the air when I put everything back to together. Also I have already replaced the spark plugs, both of those bendy straw like fuel lines inside the tank, spark plug wires, the line from the tank to the injectors. I am starting to think I have a leak at the intake manifold based on other forums. Could a leak at the intake manifold cause low fuel pressure or cause the bike to sputter? I don't know if the pressure would stay constant while riding as I haven't ridden it with the fuel pressure tester on. Is that safe to do? After it starts it will stay at 55 at any RPM. The sputter only occurs while in first or second gear mostly and at low speeds. I have had the entire tank off and drained, and put back together.
 
You don't have to worry about any air when it goes back together, it will pass it The maniflod can not cause low fuel pressure. The 02 softail has the new injection system and it's very smart, most of the time if you had a manafold lead you wouldn't even know it, but it's possable and could be a cause of the sputtering. Can't say it safe to ride the bike while watching a pressure guage, just woundering if the pressure is steady when you get the sputtering? Did you also replace the fuel filter? I take it the bike is not throwing any codes to help you out ether. If it's staying 55psi at all rpm's the pressure valve & pump must be all right, do you have a fueler or tuner on the bike?
 
I have same problem, but it seems to need to warm up before it starts stuttering. Where can I get a fuel pressure gauge and adapters? It seems HD won't sell them to me.

Rich P
 
RibEye said:
I have same problem, but it seems to need to warm up before it starts stuttering. Where can I get a fuel pressure gauge and adapters? It seems HD won't sell them to me.

Rich P
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Check with a Matco Toolman, here in Jacksonville Florida my tool man services a H D dealer, Kent Moore and SPX a division of OTC also makes H D dealer tools
 
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