Troubleshooting loss of power at upper RPM

DelicaStuff

DelicaStuff

Member
Just noticed today on my way back from a camping trip with the family that the Delica wasn’t running right....
Lower RPM (bellow about 2800) the problem is not very present if at all, but just as I was getting up to speed on a highway I started noticing a stumble at about 2800 and a pretty significant loss of power.
I pulled over poped the engine bay open and looked for anything that would jump out at me...nothing alarming presented itself.
Revved the motor and checked the overboost protection valve and it wasn’t leaking, tightened the intake hoses a little...not that that would help what I’m experiencing but they did look like they needed a couple turns, still getting the spooldown woosh you can hear with the side exit exhaust.

I’m wondering if my wastegate is failing? I tried to watch it seems the movement in it was a bit erratic, but then again it could be sympathetic to whatever is causing the stumble/loss of power. I’ll be doing the test on that once i go get a hand pressure bulb/gauge

If the wastegate is working I may pull the valve cover and give that a good look and reset the valves and replace the gasket while I’m at it.

I’ll be doing the test on that once i go get a hand pressure bulb/gauge. I also pulled the intake hose on the turbo and gave it a quick visual, looked pretty darn good.
Nothing abnormal in terms of exhaust smoke, idle noise, etc

Anyone have any other thoughts?

Anyone experienced similar and could point me down the right track rather than me going in blind?
 
A high rpm stumble and loss of power cold be a valve adjustment. A wastegate issue will (should) not show up as anything in particular... a lack of power because it's open, or overboosting if you should pus it that hard...
Air or water in the fuel system is also a possible cause.
 
sk66 said:
A high rpm stumble and loss of power cold be a valve adjustment. A wastegate issue will (should) not show up as anything in particular... a lack of power because it's open, or overboosting if you should pus it that hard...
Air or water in the fuel system is also a possible cause.
Click to expand...
Just did a valve adjustment and went for a test ride...same thing...consistently at 2800-3000 making low power. Cyl 1intake and exhaust were too tight and exhaust on 4 was too tight, the rest seemingly good. Not getting an indication for water in the separator but can’t say I know with confidence the light works. I’ll double check that tomorrow and give it a purge and collect to see if H20 has made its way in the fuel. I get fuel at high volume fuel stations usually so I’d be surprised if that’s the cause.
It’s strange, I really feel like it is a fueling or boost issue as consistent as it is.
 
Also worth mentioning the stumble doesn’t seem to be present on the last test drive. Just the loss of power above 3k. RPMs will hardly climb above that, it actually speeds up if I let off the throttle and let it upshift, bringing the RPM bellow the 3k mark.
 
Is this something new, or something you're just now noticing?

The stock turbo runs out by/above 3k, and if you're running higher boost levels (much over 12psi) it really shouldn't be spun higher than 3500rpm. If it's an automatic, the gearing also seems to run out above 3k and redlines at 4500rpm.
All of that kind of sucks because the engine itself supposedly makes the most horsepower just above 4k. But mine seems quite flat above 3k...

what you're describing sounds pretty normal for a stock automatic diesel IMO
 
My best guess is a fueling limitation... with the stumble gone I would start with replacing the fuel filter. There's also an inlet screen in the banjo bolt at the IP. It could also be the air filter, but it would probably have to be quite dirty. After that, it gets more difficult/expensive... i.e. injectors, IP.

But I think if it was something else (turbo, IP, injectors, compression) it would be more prominent at lower RPMs rather than just at the top end.
More valve lash will increase low end torque/acceleration, and reduced valve lash will increase high RPM power (they tradeoff by changing the effective cam profile). But since you've just checked/set the valves that shouldn't be an issue.
 
I should have mentioned before...Fuel filter was changed less than 3-4000 miles ago so I’m not feeling hopeful there, same with air filter, but it’s worth looking at before I get too deep down the rabbit hole.
 
It could also be the pickup strainer in the tank... I've heard of blowing air backwards into the tank through the line at the filter to make sure it's clear. I think the IP inlet screen is more likely, but both are fairly easy to check.
 
When I bought it I checked the compression, and it was dead even between 445-450 on all 4.
I did a visual on the air filter just now, looked new as expected.
Actuated the IP by hand and it felt kinda crunchy in the last bit of the actuation (wide open throttle). Hard to say initially if it was internal or from the springs on the outside. I’ll give them a light penetrant oiling and see if that improves, if not maybe something internal is the cause and would possibly explain the issue.
May dive into fueling next, look all over the IP and make sure I didn’t miss any signs of leaks or loose parts...I did just drive a bunch of washboard Forrest service roads...
 
sk66 said:
It could also be the pickup strainer in the tank... I've heard of blowing air backwards into the tank through the line at the filter to make sure it's clear. I think the IP inlet screen is more likely, but both are fairly easy to check.
Click to expand...
Thank you!
I read about this on one of the Pajero forums, I’ll give that a look too. Really crossing my fingers for something clear to blame.
 
There's a filter screen in the IP outlet banjo as well, and that also causes trouble if it's clogged.

If the filters are clear, as a diagnostic step you could try running from a clean fuel source. Run hoses from the inlet and outlet of the IP into a jerry can of diesel, leave the engine lid up, and go for a drive. That'll eliminate any restriction/air in the filter/pickups. If it still has issues, it's in the IP somewhere. I'd suspect crud jamming up the governor or control lever mechanism.

A failed open wastegate (no boost) just feels like a weak engine, and it'll make smoke. It wouldn't usually suddenly show up at 3000rpm. A cheap boost gauge, temporarily installed in the line from the turbo to the IP, would tell you what's happening boost-wise.
 
First of all thank you so much @sk66 and @Growlerbearnz for pointing me in the right direction.

Here is what I discovered.
I took the “IN” and the “OUT” fuel banjo bolts off the injection pump and inspected the screens in them. Behold, the problem! Once you remove the in banjo bolt (careful not to drop the crush washers) the hole you just exposed has a spring inside the cavity. Carefully with a pick or thin needle nose remove the spring, under the spring is a screen filter. To remove the tiny filter, not much larger than an eraser head, I took a piece of safety wire and bent a short 90° On the top of it, I used that to carefully pull out the little filter.
Inspecting it, I discovered at the bottom of the filter that is in a cup shape, there was a pretty obvious blockage. I used a tiny pick to disturb the debris and a layer of fibrous material fell out in a tiny pancake shape. I then used brake cleaner to further clean out the filter.
The debris appears to likely be tiny cotton’ish looking fibers...how did that get there is my first thought...well I believe the likely culprit is from the fuel filter element itself. I’d bet that over time some of the fibers get loose from the element and that screen grabs them.
Either when you install a fresh filter some of the fibers that are loose come off or over time some just slough off...or a combination of both.
I had just a couple 1000 miles ago changed my filter with a Wix/Napa ...some of the fibers looked old but there were for sure some that seemed to be more fresh looking.
I am relieved to find this and hope that this story will help people in the future searching for a power loss issue.
It would probably be worth the 10 minutes of work for all of us to take a look at this screen if you don’t already have this in your maintenence routine.
It came on so quickly, which makes sense with how small that filter is, there’s a fine line between enough fuel, and not.
So yes, after a test ride the power is restored, back to operating normally, checked the operation from engine cold up to operating temp and all is restored.
AFB8ED91-8C51-4B7C-BF13-0DB2F8268B6A.jpeg
 
Growlerbearnz said:
I love a nice, simple solution. I don't love your Wix fuel filter.
Click to expand...
Yeah, it’s a little disturbing that I found newish looking fibers along with old really dirty ones. Wix is usually really good stuff. I’m willing to bet every filter out there though will have some fibers slough off...it’s probably a case where my new filter had just enough stray fibers to pile on top of another 150k miles worth of fibers to finally break the camels back.
All this made me wonder if it would be worth putting an inline filter between the fuel filter and IP. A screen type strainer that has a clear housing....but then again...it takes 10 minutes to pop the banjo off and give it a cleaning.
It will be in my list for inspection every 4th or 5th oil change from now on!
 
DelicaStuff said:
All this made me wonder if it would be worth putting an inline filter between the fuel filter and IP. A screen type strainer that has a clear housing.
Click to expand...
LOL I was thinking the same thing! I have one of these on my Mini,

2940

the (dirty) fuel comes in on the left, crud settles out where you can see it, and the mesh catches the rest. Mine has metal ends and a glass centre so it's well capable of handling engine bay heat.

...and now I've ordered one for my Delica too.
 
Hahah so did this little tale of misfortune guide you to click the buy it now button?!

You have a link or PN for that doodad? Keeping an eye on not only debris but the possibility of air or water in line could possibly be detectable in the sightglass.
 
FWIW, when I checked the banjo bolt on my IP it had the filter screen internal and non-removable... now I'm wondering if there isn't another one behind it like you found.
 
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