Fuel Pressure Checks
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Road Warrior
Joined: Sep 2021
Posts: 1,916
Likes: 1,361
From: Black Hills of SD
Fuel Pressure Checks
This is in my ongoing troubleshooting issue, I am having as the previous "Bad Coil" thread spelled out.
Got my gauge set up and did a fuel pressure reading. The book says steady 55-62 psi. I first did a leak-down test. Cycled pump, holds at around 55 and holds. Fire up. Bouncing, a lot of bouncing. Pressure is 50-60 psi at idle, rev it up, and hold steady throttle shows about 57 psi, but bouncing at the 57. Very erratic reading, very much like if you have ever done a carb synchronization, and there is no damper in the vacuum line.
Bled the overboard line to make sure there was no air, so that's not it.
Is this normal, or is it supposed to be rock solid? The pressure bounces by far the most at idle with the 50-60+ psi bounce/fluctuation.
I have a fuel pressure regulator on the way and should have it today, but I do not seem to have any lack of fuel pressure, just bouncing.
My guess it is gauge bounce from lack of a Damper inline - thoughts and experiences?
To date. Coil did not seem to do anything, plug wires at first seemed to fix the misfire. Plugs no change. I did make a set of new wires again, the second time, and this time I used solid core wires, stranded core actually. The manual has a specific resistance spec, and of course, braided steel plug wires have next to no resistance. Are these modern computer engines sensitive to needing a specific resistance? Any of you running solid wires?
TC 88 EFI - all stock.
Got my gauge set up and did a fuel pressure reading. The book says steady 55-62 psi. I first did a leak-down test. Cycled pump, holds at around 55 and holds. Fire up. Bouncing, a lot of bouncing. Pressure is 50-60 psi at idle, rev it up, and hold steady throttle shows about 57 psi, but bouncing at the 57. Very erratic reading, very much like if you have ever done a carb synchronization, and there is no damper in the vacuum line.
Bled the overboard line to make sure there was no air, so that's not it.
Is this normal, or is it supposed to be rock solid? The pressure bounces by far the most at idle with the 50-60+ psi bounce/fluctuation.
I have a fuel pressure regulator on the way and should have it today, but I do not seem to have any lack of fuel pressure, just bouncing.
My guess it is gauge bounce from lack of a Damper inline - thoughts and experiences?
To date. Coil did not seem to do anything, plug wires at first seemed to fix the misfire. Plugs no change. I did make a set of new wires again, the second time, and this time I used solid core wires, stranded core actually. The manual has a specific resistance spec, and of course, braided steel plug wires have next to no resistance. Are these modern computer engines sensitive to needing a specific resistance? Any of you running solid wires?
TC 88 EFI - all stock.
Last edited by MarlinSpike; Apr 26, 2025 at 01:48 PM.
Thread Starter
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Road Warrior
Joined: Sep 2021
Posts: 1,916
Likes: 1,361
From: Black Hills of SD
Update for anyone interested.
I believe I answered my own question. I went back out and put a line damper on the press hoe to the gauge. Rock solid at 58 psi at all throttle positions and holds solid at 55 psi after pump prime or after shutdown.
So it sure appears to me that I do not have a fuel pressure or delivery problem.
So I now have to assume I have some kind of sensor or actuator issue. Biek is absolutely running better.
New Yausa GYZ battery per Mr. H's recommendations and I totally agree - It's worth the few extra bucks. It's a nice battery.
New coil, plug wires, and plugs. Not stumbling like it was, back-firing, and kicking like a bucking bronco. It takes a little to start cold, few cranks and even a couple tries sometimes, once run, it fires instantly after that.
But, it once in a while does a chuff in the intake right when it starts now. The idle Air Controller is functioning fine when the ignition is cycled, it's clean, and does not appear to have any issues. Might still be the culprit ????
The air intake temperature sensor is clean and appears fine. Still might be the culprit ??? I don't know what else to check. I really hate EFI bikes when there is something wrong. So many things could be wrong and its so damn hard to find what it is...
Something is still not right, even though it is light years better than a week ago. I am leaning towards the plug wire that read high ohms, being some of the problem. But why no miss-fire code set ?
Now that they are both solids, it is getting good solid spark. Fuel system looks fine, all charging checks looked fine, no codes,,,,, I don't know what else to check.
Man I wish I had a carb model of the same bike.
I believe I answered my own question. I went back out and put a line damper on the press hoe to the gauge. Rock solid at 58 psi at all throttle positions and holds solid at 55 psi after pump prime or after shutdown.
So it sure appears to me that I do not have a fuel pressure or delivery problem.
So I now have to assume I have some kind of sensor or actuator issue. Biek is absolutely running better.
New Yausa GYZ battery per Mr. H's recommendations and I totally agree - It's worth the few extra bucks. It's a nice battery.
New coil, plug wires, and plugs. Not stumbling like it was, back-firing, and kicking like a bucking bronco. It takes a little to start cold, few cranks and even a couple tries sometimes, once run, it fires instantly after that.
But, it once in a while does a chuff in the intake right when it starts now. The idle Air Controller is functioning fine when the ignition is cycled, it's clean, and does not appear to have any issues. Might still be the culprit ????
The air intake temperature sensor is clean and appears fine. Still might be the culprit ??? I don't know what else to check. I really hate EFI bikes when there is something wrong. So many things could be wrong and its so damn hard to find what it is...
Something is still not right, even though it is light years better than a week ago. I am leaning towards the plug wire that read high ohms, being some of the problem. But why no miss-fire code set ?
Now that they are both solids, it is getting good solid spark. Fuel system looks fine, all charging checks looked fine, no codes,,,,, I don't know what else to check.
Man I wish I had a carb model of the same bike.
Thread Starter
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Road Warrior
Joined: Sep 2021
Posts: 1,916
Likes: 1,361
From: Black Hills of SD
Thanks Mr.H.
I was hoping someone might chime in on the stranded wires I am using & made. Not sure if I could be inducing another problem with the no-resistance wires with these modern ignition systems or not. Trying to just do single things one at a time to find the culprit. But it's really been a struggle.
When I go and get a CPK, I'm going to get a set of OEM wires too. They are surprisingly reasonable.
I was hoping someone might chime in on the stranded wires I am using & made. Not sure if I could be inducing another problem with the no-resistance wires with these modern ignition systems or not. Trying to just do single things one at a time to find the culprit. But it's really been a struggle.
When I go and get a CPK, I'm going to get a set of OEM wires too. They are surprisingly reasonable.
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