12ht Rough Idle / White Smoke / Stalling at Low RPMs - Drives Fine at High RPMs (1 Viewer)

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Sep 10, 2019
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New Mexico
I've got a 12ht swapped 2h HJ75 Troopy and it's been running like a champ for the past year with no hiccups. Yesterday when driving, it began to idle low and rough at stoplights. When I'd take off, it'd sputter until about 1800 RPM, blowing a haze of white smoke. Then once I'd hit 2000 rpm, it'd clean up, stop smoking and be fine. As soon as I'd slow down at a stoplight though, the idle would dip and it'd be rough again. All of 1st and the first half of 2nd would be rough but 3-5th was like normal.

I drove home, replaced the fuel and air filter, checked the Bosch replacement primer, didn't see any noticeable leaks. I also checked the idle speed per the FSM and did the typical troubleshooting it recommended.

Some notes/questions:
-Turbo boost is fine and turbo is operating as it should.
-Last year I installed a Webasto pre-heater to heat up the coolant to make cold starts easier (we live at 7,000').
-The PO ran the return diesel line from the injection pump back to the main supply line right below the injection pump just outside of the hard fuel line above the chassis rail, so I installed the diesel drip line for the heater into the return. All these clamps are super secure and there are no leaks. It's never given me an issue and I've been running it all winter long.
-Should I run the return back to the tank or at least the filler neck overflow?
-I filled up the tank yesterday at the gas station two blocks from the house. It was really cold out so I didn't want to cut the engine off after starting it up immediately so I left it running while I filled up. I doubt this has anything to do with it but it's worth noting.

I'm stumped here and hoping it's not the injection pump or injectors. It's been running fine up until this point and the injectors nor the pump show any leaking fuel.

Thoughts?
 
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Joined
Feb 7, 2011
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PORTLAND, OR
John, I would rule out bad diesel first with some known good fuel in a container. An air leak would generally be opposite of what you are experiencing as far as idle rpm to higher.

I had a tank of bad diesel (standing water in the tank) a few years back in my Hilux and it took me a while to rule out everything out. If it just randomly happened after a fill up thats a smoking gun for me. Once I confirmed I never went to that service station again and now I always ask an attendant when they were last filled from the truck.
 
Joined
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New Mexico
John, I would rule out bad diesel first with some known good fuel in a container. An air leak would generally be opposite of what you are experiencing as far as idle rpm to higher.

I had a tank of bad diesel (standing water in the tank) a few years back in my Hilux and it took me a while to rule out everything out. If it just randomly happened after a fill up thats a smoking gun for me. Once I confirmed I never went to that service station again and now I always ask an attendant when they were last filled from the truck.

yeah that’s my thinking too. I filled up in a small town in Northern New Mexico. The station was pretty run down but didn’t have other options. Ok. I’ll try some good diesel in a jerry can. Thanks!
 
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Called the station and the manager assured me their tanks are clean (he filled his truck up on the exact pump I did - he remembered the Troopy from yesterday.) New Mexico is such a diesel state I can't imagine a station getting away with bad fuel.

I'm super stumped on this one. I plumbed it up to a jar of clean diesel from a Chevron, primed the filter and it didn't change the rough idle (the RPMs at cold crank are normal). When I crack the bleeder at the filter when it's running, it's a solid stream of fuel. I let it idle for a few minutes and it just sat there holding RPMs. If I pushed on the gas, it would chug until it hit 1800 RPM.

I'm reading all the various threads here on Mud and a few Aussie forums but can't find anything... The lift pump, IP, and everything seems to be operating just fine.
 
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One item I need to add to my stuff on board is a bottle of red 911 in case I ever get bad diesel.
As to what’s going on I can’t think of anything else, just seems odd that it happened all at once. Must be something just let loose, now have to find what 😐
 
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I experienced some of this in my BJ73. Symptoms: truck runs down the highway fine at high engine load, but when slowing down exiting the highway it dies. Slowing down at a stoplight it dies unless I keep revving it. Solution: New rubber fuel lines under the hood and a new fuel filter. Electric pump pushing fuel through filter for good measure.

AFter removing and reinstalling original rubber lines and spring clamps(hardened older and weak) it did not seal as before and allowed air leaks and not enough suction at low RPM to pull the fuel. I had an electric pump on hand so I put it in the line prior to the filter to help push fuel to the IP and not rely totally on the IP to suck it from the tank.............It would probably run fine now without the electric pump, but I haven't bothered to remove it to check.
 
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So I plumbed up a cycling bottle (12oz), primed the pump and it drove better (more power, less chugging) but then it would go through the 12oz bottle of diesel in a block. I guess the 12ht pulls a lot of fuel but also sends a lot back to the return line. Going to buy a longer fuel line hose and run it to a jerry can. If it runs great, it's the fuel. If it's the same, it's gotta be the pump/injectors. Bah.
 
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I went down to NAPA and got some 5/16" fuel line. I ran the return fuel line from the IP into a new supply line, and took this new line back to the cab with a jerry can filled with Chevron diesel and some injector / IP cleaner additive. it's driving mostly like normal, although it is still slightly hesitating at take off and pulsing a bit at idle. To be honest, it could have been doing this before.

The white smoke is still there at takeoff but after 10 laps around the block it got less and less severe. I turned the off-boost fuel down to see if it remedied this. Seemed to help a little bit.

Next step is to drop the tank, clean it out and blow out the fuel lines. It seems like either I got into bad fuel or had accumulated enough sediment/water over time in the tank to finally cause a problem.

Here's a video of the idle: https://radavist-static-production.s3.amazonaws.com/uploads/2021/03/IMG_6926.mov

Does that sound normal?
 
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What in line pump did you install?
One like this: Amazon product
It will run off of 12 or 24V. I tend to have one of these laying around the garage to transfer fuel and "polish fuel" (cycling through a good filter) that sits over the winter in my boat. My fuel filter is mounted close to my IP. I did this because it was quick and easy just to test it. A better place would be tucked up above a frame member back by the fuel tank so it is pushing the fuel all the way to the IP and will over come any air leaks or old bad hose in your supply line. There are often multiple clamps and pieces of metal and rubber lines between the tank and under the hood. I have the pump in line just before the filter with only the hose clamps holding it in place so it doesn't make noise through the body. Wired directly to the fuel cutoff solonoid for power. I keep a barb fitting and hose clamps in my toolbox to bypass if the filter fails or the pump fails so I can still get home.

The pumps are good to have around, but before you order one you might try some new rubber lines and clamps+ new filter. At a minimum cut the used/stretched part of the old hose off and reclamp with a good new hose clamp. Whichever clamp it is that you have been disturbing recently is the likely culprit.

There are some purist out there who may say if you have a problem in your IP lift pump then to fix that is the right thing to do. Yes they are probably right if that is the problem. However if a $14 inline pump gets you back on the road and driving for some time (mines been in 4 months with no issue) you might as well postpone/avoid the expense.
 
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I went down to NAPA and got some 5/16" fuel line. I ran the return fuel line from the IP into a new supply line, and took this new line back to the cab with a jerry can filled with Chevron diesel and some injector / IP cleaner additive. it's driving mostly like normal, although it is still slightly hesitating at take off and pulsing a bit at idle. To be honest, it could have been doing this before.

The white smoke is still there at takeoff but after 10 laps around the block it got less and less severe. I turned the off-boost fuel down to see if it remedied this. Seemed to help a little bit.

Next step is to drop the tank, clean it out and blow out the fuel lines. It seems like either I got into bad fuel or had accumulated enough sediment/water over time in the tank to finally cause a problem.

Here's a video of the idle: https://radavist-static-production.s3.amazonaws.com/uploads/2021/03/IMG_6926.mov

Does that sound normal?
It sounds like it's missing a bit on occassion. Mine did this a bit. My learning experience: Had fuel starvation problems-couldn't find proper filter local-installed cheap small inline filter-This clogged after 6 months and fuel starvation again-bypassed filter and drove for maybe 1/2 tank while looking for proper filter-found proper filter(carquest/advance) and installed-fuel starvation with new filter due to air leaks and reusing old hose and spring clamps too many times-Installed e-pump and new lines/clamps-fuel starvation gone, but somewhat rough idle and a little white smoke likely due to trash in injectors from running without filter for 1/2 tank-ordered new injectors on amazon for $140ish and poured a bottle of diesel clean in the tank-rough idle cleared up after 1/2 tank with diesel clean-installed new injectors anyway-smoother idle/ less white smoke/more power at mid throttle/lower EGT's heat buildup/better fuel economy-dripping fuel from filter due to the fact it is pressurized by the pump-installed new O ring in fuel drain and all is well.

The worst thing I know of in a diesel tank is Algea. I saw this refueling vehicles and HMMWV's at remote locations from 55 gal. drums in the PI. Unlikely that is your problem but if it is that is one case where you really have to drop the tank and drain/clean.
 
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Makes sense. We're dropping the tank tomorrow, cleaning it, blowing out the hard fuel lines. Replacing rubber lines with 5/16" and redoing any plumbing. Should fix it. Going to get the IP / Injectors refreshed the next time I have a month or two to wait.

I have a Ryco filter I'm going to install with a built-in separator. This truck had a 2H fender-mounted filter before the main fuel filter. It had all kinds of s*** in the bottom of it when I removed it.
 
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Okkkkayyyyyyy. Emptied the tank. The first gallon or so was diesel and water (makes sense as water settles on the bottom) - really milky diesel. Flushed the tank out, lightly blew the fuel lines out, put in some fuel/tank cleaner and it's driving like normal. Still kinda smokey but I suspect there's still air in the lines. Going to run some Liqui Moly Diesel Purge this week and work on lining up an IP/injector rebuild.
 
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and work on lining up an IP/injector rebuild.
Be careful with that. When I asked about them about 10 years ago, I didn't come across too many shops that had actually done a rebuild because they last as long as the engine. An older guy who had his own injection shop told me he hadn't rebuilt one, but did 12ht injectors regularly and he was a Japanese specialist.
Anyone who tells you it needs a rebuild should have a good explanation of why its needs a rebuild. I would want to see the figures its getting on a bench test before I let them open it up.
 
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Be careful with that. When I asked about them about 10 years ago, I didn't come across too many shops that had actually done a rebuild because they last as long as the engine. An older guy who had his own injection shop told me he hadn't rebuilt one, but did 12ht injectors regularly and he was a Japanese specialist.
Anyone who tells you it needs a rebuild should have a good explanation of why its needs a rebuild. I would want to see the figures its getting on a bench test before I let them open it up.

makes sense. will probably just do injectors then.
 

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