HPDI 150 Help, RPMs Low (Fixed, Maybe!)

[Andrew93]

Any HPDI experts here?

I am loosing some top end RPM's on one on my 2003 HPDI 150's, changed props and same issue. Compression was good last fall, I plan on checking again, fingers crossed. All filters have been replaced including the metal can filter after VST and mystery filters. Injectors serviced also. Cannot get past 4400 RPMs without overtiming motor. Linkage is ok and TPS shows proper voltage range on YDS. O2 sensor cleaned. I plan on looking around for a fuel leak on the high pressure steel braided lines where they were off to service mystery filters, YDS shows strong fuel pressure with no dips while running. If supply to the HP pump was an issue would the high pressure in YDS dip or be low also?

Over on THT I was recommended a leak down test. If compression is good I don't understand how this will help, on a 2 stroke it would only test head gasket and rings right? Reeds are isolated at top dead center and no valves like in a 4 stroke. I was going to buy a harbor freight leak down tester unless its not needed with a good compression test.

I was hoping for the neutral switch to be the issue but that seems to test ok on YDS in and out of gear. I was so confident I ordered one, might put it in anyways. Motor starts and idles great, slow to catch up on RPMs to the other motor but will catch up to 4400RPMs. If reeds were an issue wouldn't it idle bad?

Also in YDS I was able to kill the spark on each cylinder. On the effected motor engine pitch changed but nothing crazy, unaffected motor RPMs increased but that motor wasn't fully to temp either. How would I go about testing coils? Maybe 1 is bad under load? Anyway to test for that?

Attached are screenshots of YDS with each motor WOT. I know port motor is low RPMs also but figure that will balance out once the other in figured out.

 

[DogBone]

I'm having a similar issue on both of my 2006 175 HPDI motors. I was sure it was a fuel issue on the VST filters, but I changed those and problem persisted. You've gotten further than me on the filter changes, I've yet to change the mystery filters. My motors both stall around 4000 RPM, and my YDS software shows no fault history. It feels like a fuel flow issue, with my flow rate topping out at about 15 Gal/hr for the combined motors. However, when getting on plane the fuel rate is much higher than 15 Gal/hr. Could it be a fuel restriction pre-VST or low pressure diaphragm pumps not supplying the VST bowl fast enough? That might explain why we can get on plane (VST tank is full at start), but not maintain fuel flow to maintain speed. I'm perplexed my issue is on both motors at the same time. I've switched tanks and the problem persists. One motor did exhibit the problem first, but the second soon followed. I need to check my fuel pressure at the VST pump when running, to see if it is starving for fuel. Sorry if I'm rambling, just trying to brain storm what the issue could be for both of us.

 

[Andrew93]

I replaced all the LP pumps also. These motors are new to me this year and I went though all those usual suspects when I mounted them on the boat. My motor does not stall, stays running strong and just nothing happens top 3/4 of the throttle, I can see intake valves opening on YDS and TPS voltage change.

your issue sounds more like that metal can filter after the VST, easy to change. I am trying to figure out if there was a fuel restriction issue wouldn’t I expect to see to drop in YDS final pressure? Tomorrow I’m going to take boat out of water and run in a barrel and inspect for leaks in the fuel rails where all that was apart, maybe a nicked o ring. I’m eager to run a compression test also but terrified at the same time…

 

[DennisG01]

Since you used the term "losing some top end RPM's"... can we take that to mean that it used to be better? Changing props would only be a band-aid in that situation, not a solution.

I'm not sure where the sensor for fuel pressure is on your motor... where is it located? I'd put a fuel pressure gauge on the rail and see what you have there.

Did you inspect and/or replace the VST filter? Drain the VST tank to check fuel quality? Do the engines run off a shared tank or separate tanks?

 

[DogBone]

I haven't replaced the metal can filter, but will do that soon. If the VST is not getting proper fuel supply, I would think the VST pump pressure (around 40 psi) would drop. It has to be monitored with a fuel pressure guage on the Schrader valve. But one would also think, the high pressure pump would also drop if it were starved for fuel. I haven't used my YDS while running, but need to do so. Do you have normal power coming out of the hole getting on plane? If it is coil or spark related, I would think power would be diminished and noticeable during that high power demand situation.

When you reach max RPM and you give it more throttle, does the engine try to stall?

 

[Andrew93]

Since you used the term "losing some top end RPM's"... can we take that to mean that it used to be better? Changing props would only be a band-aid in that situation, not a solution.

I'm not sure where the sensor for fuel pressure is on your motor... where is it located? I'd put a fuel pressure gauge on the rail and see what you have there.

Did you inspect and/or replace the VST filter? Drain the VST tank to check fuel quality? Do the engines run off a shared tank or separate tanks?

This is the first year with these motors. I wanted to rule out a bad prop, where they are twins and it the boat was not propped right I would suspect both RPMs to be about the same. I am not sure where the HPDI fuel sensor is but it reads over 700psi and never drops. I would have to rely on that where pressure is so high on these motors I would imagine. I plan on taking a reading off the VST where pressure is lower but I would imagine if that was low the HP pump would dip also, but thats a best guess.

Engines off one tank. VST filter has 10-15 hours on it from beginning of the season, I can pull and reinspect but I would imagine I would be seeing low fuel rail pressure if that was the case?

 

[Andrew93]

I haven't replaced the metal can filter, but will do that soon. If the VST is not getting proper fuel supply, I would think the VST pump pressure (around 40 psi) would drop. It has to be monitored with a fuel pressure guage on the Schrader valve. But one would also think, the high pressure pump would also drop if it were starved for fuel. I haven't used my YDS while running, but need to do so. Do you have normal power coming out of the hole getting on plane? If it is coil or spark related, I would think power would be diminished and noticeable during that high power demand situation.

When you reach max RPM and you give it more throttle, does the engine try to stall?

I bought a 20' USB cable extension to have the laptop on the helm with me. Worked good. Engine does not even hesitate when WOT. The boat is not a dog out of the hole, but that motor has to "catch up" with the other. Praying not a weak cylinder. Not having the boat in my yard to run tests makes this troubleshooting process painfully slow unfortunately.

 

[DennisG01]

So it used to be better or was it always this way since you owned? Was it different during the sea trial?

Generally, though, yes, if pressure at the rail is good that part of the system should be good. However, there's always that idea of how pressure is not the same as flow rate...

I know you checked this with the software, but physically pull one plug wire at a time - just to be sure. There should be a change in sound like you noticed, but the engine should still idle fine. You might want to advance the throttle into the mid-2,000 range if your engine has cylinder deactivation like the OX66's. Also... pull the plugs and "read them".

 

[seasick]

What does 'over timing motor' mean?

If you can turn off the spark one cylinder at a time, you should try that. Killing a cylinder at speed ( around 2000 revs) should be noticeable. If there is no change, swap the coil, plug wire and plug from the opposite cylinder to see jr the problem moves. If it does, it's one of those components.
To introduce load, do the test with the boat well tied off if at a slip and running in gear.

 

[Andrew93]

So it used to be better or was it always this way since you owned? Was it different during the sea trial?

Generally, though, yes, if pressure at the rail is good that part of the system should be good. However, there's always that idea of how pressure is not the same as flow rate...

I know you checked this with the software, but physically pull one plug wire at a time - just to be sure. There should be a change in sound like you noticed, but the engine should still idle fine. You might want to advance the throttle into the mid-2,000 range if your engine has cylinder deactivation like the OX66's. Also... pull the plugs and "read them".

The motor has lagged behind in RPMs all season. It does seem worse recently but there was always a difference between the two since the beginning of this season but that could be my imagination as far as it getting worse. I will try pulling one plug at a time manually also. From what I understand with this motor it drops 2 cylinders (#2 & #3) in neutral and all firing in gear.

I am hoping to find that "smoking gun" but I know that isn't always how these issues go.

 

[Andrew93]

What does 'over timing motor' mean?

Over Triming. Damn autocorrect

 

[DennisG01]

The motor has lagged behind in RPMs all season. It does seem worse recently but there was always a difference between the two since the beginning of this season but that could be my imagination as far as it getting worse. I will try pulling one plug at a time manually also. From what I understand with this motor it drops 2 cylinders (#2 & #3) in neutral and all firing in gear.

I am hoping to find that "smoking gun" but I know that isn't always how these issues go.

Interesting as that's a different cylinder deactivation program than my OX66. IIRC, it drops #2 at idle speeds and then it drops #2 and #5 until over about 2,100RPM... at which point all come back on line.

Just to double check... it's PHYSICALLY low on RPM's, right? Not just according to the gauge... as in a gauge error?

 

[Andrew93]

Interesting as that's a different cylinder deactivation program than my OX66. IIRC, it drops #2 at idle speeds and then it drops #2 and #5 until over about 2,100RPM... at which point all come back on line.

Just to double check... it's PHYSICALLY low on RPM's, right? Not just according to the gauge... as in a gauge error?

That is a great point but not sure how I would go about checking that. YDS and gauge read the same and when advancing past the 3/4 point of the throttle no response in the motor RPMs or performance. I would say anything is possible but I suspect the gauges are accurate.

Another thought I had was to switch the lower units to see if there was any unusual resistance in those to put more strain on engine to see if problem stays with motor or not, but they shift fine and no strange sounds or vibrations.

 

[Paul_A]

Just to verify it's not fuel line related you might try swapping hoses.

Unless I missed it you might consider checking/adjusting your crank position sensor which is what regulates timing on that motor.

The good motor is at 19 btdc which is the correct spec. I gave the new owner the factory shop manual when I sold my hpdi's but a quick search gave me that number.

Nice thing about twins is you can easily swap parts. You might also try swapping ECU's.

Also make sure every ground on the motor is clean and tight. And verify the condition of or swap the batteries. hpdi's need a strong battery.

 

[DennisG01]

That is a great point but not sure how I would go about checking that. YDS and gauge read the same and when advancing past the 3/4 point of the throttle no response in the motor RPMs or performance. I would say anything is possible but I suspect the gauges are accurate.

Another thought I had was to switch the lower units to see if there was any unusual resistance in those to put more strain on engine to see if problem stays with motor or not, but they shift fine and no strange sounds or vibrations.

I think what you mentioned there in your first paragraph nulls the idea of the gauge being bad.

If the lower unit was causing that much internal drag... the engine would likely stall at idle speeds. Although an interesting idea, I wouldn't be doing that right now. Do you have counter rotating lowers?

 

[DennisG01]

Now... I'm getting a bit out of my element here... but if I recall, there's a fuel pressure regulator on the backside of the VST that if clogged, can cause a restriction in the amount of fuel? Not sure on that, though... but may at least be worthwhile checking into.

 

[Andrew93]

Just to verify it's not fuel line related you might try swapping hoses.

Unless I missed it you might consider checking/adjusting your crank position sensor which is what regulates timing on that motor.

The good motor is at 19 btdc which is the correct spec. I gave the new owner the factory shop manual when I sold my hpdi's but a quick search gave me that number.

Nice thing about twins is you can easily swap parts. You might also try swapping ECU's.

Also make sure every ground on the motor is clean and tight. And verify the condition of or swap the batteries. hpdi's need a strong battery.

I did notice that timing off. I was trying to see how the adjustment worked but google searching did not seem like there was one other than the crank positioning sensor being off. Is there something else that would cause timing to be off, also is 14 vs 19 a lot? I will try and find the service manual online, I had a few SEALOC manuals kicking around but I don't think for this motor.

I will look at swapping fuel supply lines also but I would think I would be seeing fuel pressure issues as well.

 

[Andrew93]

Now... I'm getting a bit out of my element here... but if I recall, there's a fuel pressure regulator on the backside of the VST that if clogged, can cause a restriction in the amount of fuel? Not sure on that, though... but may at least be worthwhile checking into.

From my OX66's that fuel pressure regulator becoming clogged I think put too much pressure into the fuel rails. It's the end of the loop that puts fuel back into the VST if I understand it correct, but worth checking if the VST ends up back off.

 

[Andrew93]

This is a link to my dropbox with the YDS readouts when I was trial running in the bay. This was my first time really playing with YDS and I made the recording after running around a few min on each motor and figured I would play around with the readout when I got home. Saw the neutral switch off killing cylinder 2 & 3, had high hopes and went out again and expected to find the switch faulty. It visually looked fine and when the computer was hooked up cylinder 2 & 3 were activating and deactivating as they should. Shame on me I cannot be positive if I had the motor in gear or not when I saved the recording, with RPMs at 875 I would have thought I was in gear, but maybe not?

Dropbox - File Deleted - Simplify your life

www.dropbox.com

 

[Andrew93]

Just to verify it's not fuel line related you might try swapping hoses.

Unless I missed it you might consider checking/adjusting your crank position sensor which is what regulates timing on that motor.

The good motor is at 19 btdc which is the correct spec. I gave the new owner the factory shop manual when I sold my hpdi's but a quick search gave me that number.

Nice thing about twins is you can easily swap parts. You might also try swapping ECU's.

Also make sure every ground on the motor is clean and tight. And verify the condition of or swap the batteries. hpdi's need a strong battery.

I found the manual online and bought the electronic version. Spec for timing is 5 +/-3, 1 at 875 seems way off when the other motor is 8 @ 775. Could something other than the crank positioning sensor do this? 2 degrees out of spec a lot in the opposite direction of the other motor, I imagine anything out of the range is unacceptable but would this cause symptoms I am having or is something else causing the symptoms and timing is a secondary effect? If that makes sense.