[LMCorley]

Having throttle and running issues with a 2023 Uforce 600, with 130 miles. Ive had it over a year so I’m assuming the warranty is out. While cruising around in the mid-range the throttle will surge and you can hear it cutting in and out through the exhaust. It’s almost like you are bouncing the throttle while driving. If you’re sitting still in neutral and give it a little gas holding the pedal in one spot it will do the same, surge up and down and pop through the exhaust.  Idle seems fine and it accelerates strong with plenty of power. Just the mid-range steady throttle given issues.  Any ideas on what to look for or known issues would be appreciated.

I have checked plugs, fuses, spark plug, and looked for damaged wires.
No check engine light, been having trouble getting my OBD2 scanner to connect.

[NMKawierider]

Those are some of the symptoms of a fuel supply issue..which could be a pump problem or a filter problem or...water in the tank or a stuck tank vent check valve. Check those and take a fuel pressure & volume test. You will need a gauge for that.

It is also symptoms of an air intake problem or restriction or incorrect data from the engine speed sensor so check that as well. You will need a service manual for the testing of sensors. Yeah..welcome to off-road machine ownership.

Just an afterthought-one would think if it had anything like low fuel pressure or a problem with a sensor there would be an error code and flashing light on the dash.

[LMCorley]

Thanks, that’s definitely some stuff I hadn’t thought about yet. I still cant believe the engine light hasn’t come on. I just ordered a new OBD2 scanner today so hopefully I can at least see if anything is pending. I had been using a cheap bluetooth one with my phone and it won’t connect anymore. I’ve tried to check the basics but haven’t seen anything obvious yet.

[LMCorley]

I was able to check for codes, it shows nothing pending. I’ve inspected every fuse and rely, wire harness. I pulled the fuel pump, visually looks ok, pump pressure holds at about 35-37 psi after prime and before starting. While running it’s 41-44psi.  I checked the o2 sensor with my obd2 reader, it looks ok to me, quickly switching from .1 -.7. Spark plug looks good. Checked for vacuum leaks by spraying starting fluid around throttle and intake, got nothing. Cleaned map sensor, no change. Pulled fuel injector, nice fine spray.

Again, it idles fine, and accelerates strong. Only while cruising or trying hold a steady throttle it will very in rpms, surge up and down and pop through the exhaust.

Any other ideas and things to look at would be appreciated. Really don’t want to pay the dealership to look it over only to say they all do that.

[NMKawierider]

I don't like the variances in fuel pressures. Others I know of pressure up into the 40s (42-47psi) and hold there no matter what. And being 2psi low makes a lot of difference so if it's fluctuating between the 30s and 40s while running it would make for massive surging. Can you rig a tester on the line and watch it while it's doing this?

[LMCorley]

The fuel pressure gauge I have mounts in line so can be used while running. The 37 psi was after the pump primed and before starting. When started the pressure jumped to about 44psi. I varied the throttle while watching the gauge and it stayed between 41 and 44 psi. The 35-37 psi was only with the key on and no start.

It was acting up while I varied the throttle.

[NMKawierider]

The fuel pressure gauge I have mounts in line so can be used while running. The 37 psi was after the pump primed and before starting. When started the pressure jumped to about 44psi. I varied the throttle while watching the gauge and it stayed between 41 and 44 psi. The 35-37 psi was only with the key on and no start.

It was acting up while I varied the throttle.

Exactly..others prime to operating pressure and hold it and no matter how much throttle you give it...it stays. Yours should pressure-up to around 47.86psi and only have a variance +- of 2.9psi (.33Mpa +- .02Mpa from another model CFM) and not while changing the throttle. All inductions are that it has a fuel supply problem. Could be pump...could be pickup screen ..could be filter. Test the flow rate. Should be around 35 Lph.

[LMCorley]

Ok, did some more testing. On a flow test I got 138 lph, got 2.3l in 1 minute and did the math. 

On psi again, at idle 40-45 psi, 2200 rpm 38-45psi. 4000 rpm 35-45 with dips as low as 32 and highs to 47. Very erratic and fluctuates more when it’s acting up and popping.

Bad pump?

[NMKawierider]

Ok, did some more testing. On a flow test I got 138 lph, got 2.3l in 1 minute and did the math. 

On psi again, at idle 40-45 psi, 2200 rpm 38-45psi. 4000 rpm 35-45 with dips as low as 32 and highs to 47. Very erratic and fluctuates more when it’s acting up and popping.

Bad pump?

Bad something...My guess is pump but it can be water in the filter too. Check all that when you take the pump out. The Liters Per Hour and pressure I posted was from a 23 1000 so your putting out 138 liters per hour when a 1000's only needs 35 seems a bit strange.

[LMCorley]

On the flow test I ran the fuel line in a jug, and powered the pump for 1 minute. Measured out 2.3 liters multiplied that by 60 to get the 138 lph. That’s a first for me so hopefully that was a correct method.

As far as I can tell there is no fuel filter other than the sock on the pick up. Fuel in the tank is clean and fresh.

[NMKawierider]

On the flow test I ran the fuel line in a jug, and powered the pump for 1 minute. Measured out 2.3 liters multiplied that by 60 to get the 138 lph. That’s a first for me so hopefully that was a correct method.

As far as I can tell there is no fuel filter other than the sock on the pick up. Fuel in the tank is clean and fresh.

Ok..well the pump I believe does have the regulator built in and it controls volume and pressure so...If it were me I would first consult a CFM tech, then replace the pump. Who am I kidding.. I would replace the pump anyway...lol. Hay do check the tank's vent check valve. It can stick shut as easy as open and if shut, it won't let air in as the pump takes fuel out making vacuum...that the pump will have a hard time fighting against.

[LMCorley]

Thanks for the help, I'm going to get a pump and go from there. I did run it with the gas cap off to rule out a vent issue. I'll report back in a few weeks, fixing to go out of town.

[NMKawierider]

Thanks for the help, I'm going to get a pump and go from there. I did run it with the gas cap off to rule out a vent issue. I'll report back in a few weeks, fixing to go out of town.

One more test: Check for water in the tank by jacking the front up then the left side. This will pool any water in the right rear corner of the tank and at least on the Zs accessible to a siphon hose to draw it out.

[LMCorley]

Just an update. I installed a new fuel pump, fuel pressure is rock steady at about 48psi and never moves. Fuel pressure no longer bounces around everywhere. However, it still surges and pops through the exhaust. I’ve double checked everything and continue to find nothing. To me it acts like a vacuum leak, sucking air from somewhere but haven’t found anything.

Again, starts and runs good with plenty of power but won’t hold a steady throttle and pops through the exhaust.

Clean fuel always, stored inside, good fuel pressure and volume, good spark plug, o2 sensor and any other sensor I can monitor via obd2 checks out ok. No corrosion or frayed wires that I can find, and all fuses have been swapped and are good. It is very drivable just aggravating that a new unit doesn’t run right. What am I missing, lol

[NMKawierider]

Test the engine speed sensor..aka crank position sensor. Physically take it out after ohm testing to inspect the pickup for debris. Common on many other models.