12HT rough running

Joined
Jan 26, 2008
Messages
27
Location
Cairns, Australia
hi,

I have a 12 HT in a 86 HJ61 (auto) that runs fine on the road and when cold but after driving for about 30 mins. With the car in Nuetral or Park the engine rough idles/misses in the rev range 1300rpm to 1500rpm and then runs normal/smooth above or below this range.

I have tried injector cleaner, and doing a search online here without luck.

the engine has 261K on it and looks to be un touched.

any thoughts ?????
 
Joined
Nov 23, 2006
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650
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Michigan
What kind of electronic sensors does this engine have on it? Guessing by the year it has very few, but you never know. I had a problem on my Fj62, seemed to be related to engine temp, I thought that when the engine warmed up it switched to a different fuel map or something of that nature.

Wouldent hurt to go over the basics, ensure clean unblocked fuel lines, not that it should really matter, but good electrical connections, you dont have to worry about silly spark plugs...lucky guy..!!!
Any idea on the health of the engine, good compression...

Just thinking out loud...
 
Joined
Jan 26, 2008
Messages
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Location
Cairns, Australia
yes drives perfectly when warm in gear ect. not noticable unless you try to rev it out of gear.

I am on holidays about 2000km away from home having just bought my third 60 series.

I have done over 750km since picking her up driving around northern NSW.

I have no tools or workshop manuals with me, but it runs great on the highway, this is just nigling away at me , as my other hj61 manual does not do it and it has over 450000km on her.

Time will tell, probably will be expensive when i find out what it is.
 
Joined
Jan 26, 2008
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Cairns, Australia
after further investigation it would appear to have fuel dilution in the oil.

Damm should have got a compression test done. Doh

Don't know enough about diesels but in outboards this usually = sticking rings worn cylinders, carbonized/glazed up.

This may explain why it only does it warmed up?

I guess this means i am in for a engine rebuild?
 

Greg_B

 
 
 
Joined
Mar 28, 2002
Messages
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Is the fuel in oil an olfactory observation, or did you get the oil tested?

I've not found many 12HT's in which I can not make the engine shutter under no load by manually holding the throttle to about the RPM you mention (it can take a bit of playing to find the exact rpm). There is a harmonic created, and I don't have a firm answer why. It's a little harder to do, but I can make it happen when using the throttle lever right at the injection pump to.
 
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Jan 26, 2008
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Cairns, Australia
no thefuel in the oil is just my own observation as it appears to be making oil. also the oil is very clean and not at all sooty / leaves no stains on you skin ect.
 

Greg_B

 
 
 
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Mar 28, 2002
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Well, if the oil is clean, and staying clean over thousands of kms, I would hazard you have a very happy 12HT. Limited blowby = limited soot loading into the oil = longer before it blackens up. Take a sample and have it analyzed; it's the only way to really know for sure.

If it really is untouched over those kms, then the injectors are long overdue for a service and it would be wise to time the injection pump too. Check the valve set too.
 
Joined
Jan 30, 2008
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349
Location
Perth, West Oz
i'm with greg on getting the oil analysis done. do you know how may k's its done since the last oil change? if it was done just before you bought it, it might not yet have had enough time to soot up the oil yet.
if diesel is getting in the oil you should be able to smell it and the oil should feel thinner then normal. diesel getting in the oil is usually caused by dripping injectors, but you notice a lot of smoke if it was doing this. just an idea but it could also be leaking from the injector pump into the sump, as the pump is oil lubricated.
if these motors a known to shake a bit in neutral i wouldn't worry about it. one of the motors isuzu made (9.8L motor) had a very noticeable shake at about 1000-1300rpm if you revved it in neutral.
 
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Jan 26, 2008
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Cairns, Australia
thanks for your thoughts,
i will get the injectors / pump looked at when i get home.

changed the oil yesterday will see how it goes.
 
Joined
Sep 30, 2005
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438
Location
Perth Western Australia
It's called Governor bounce. They all do it. Well, mine does it, and I've seen others do it, both before and after new injectors. Don't stress.

The governor is part of the Injection pump and consists, I think, of a diaphram type device. At certain revs/pressures it must flutter a tiny amount, causing this "miss".

Diesel specialist told me not to worry about it. I can feel a flutter in the exhaust if I hold my hand over it at 1200rpm so assumed, like you, there was a disaster happening with burnt valves etc etc etc. Call it character and enjoy the drive. :)

Clean oil is a good sign.

Tim
 
Last edited:

lostmarbles

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......... the oil is very clean and not at all sooty / leaves no stains on you skin ect.
Can anyone say if this is common for a 12HT?

If it was occuring with a B, 2B or 3B engine I'd be worried that such an engine was using the wrong grade of engine oil (even if the engine was brand-spanking new)!

I'm familiar only with OLD diesels (like the B-series) and I understand these need a "detergent oil" that is able to absorb the carbon (and hold it in suspension) to prevent it building up around piston-rings etc.

And I understand the "diesel specific" engine oils have this detergent additive to distingush them from ordinary engine oils.

But I also know that some modern diesels don't seem to dirty their engine oil like older diesels do. (such as those using common-rail injection systems that use higher pressures that atomise the fuel better.)

Does a 1986 12HT come into this "modern clean diesel" category? (Because I wouldn't have expected that.)

:cheers:
 
Joined
Dec 22, 2008
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Edmonton AB
Can anyone say if this is common for a 12HT?

But I also know that some modern diesels don't seem to dirty their engine oil like older diesels do. (such as those using common-rail injection systems that use higher pressures that atomise the fuel better.)

Does a 1986 12HT come into this "modern clean diesel" category? (Because I wouldn't have expected that.)

:cheers:
I believe it is a IDI vs DI thing. I can't remember the specifics though, I will leave that to someone more knowledgeable...
 

lostmarbles

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I believe it is a IDI vs DI thing. I can't remember the specifics though, I will leave that to someone more knowledgeable...

:hmm: Hmmmm. So on that basis a 13BT (also direct injection) should be able to achieve such clean engine oil too..........

Interesting.

My indirect injection B-engine converts clear-amber engine oil to a dirty-black colour almost the instant I restart it
following an oil change.

:cheers:
 

Greg_B

 
 
 
Joined
Mar 28, 2002
Messages
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The 12HT, 13BT and 1HD-T will not soot up the oil as instantly as the 2H, 3B, etc...

But I would not call them in the same class as modern clean diesels.

I recall the double take I did years ago with one of the 1st HJ61's we brought in. Did a service, drove the truck to Kamloops and back (Vancouver area) as a shakedown. Checked all fluids; had to turn the dipstick at the right angle to see the oil. It was "that" clean after an 8 hour road trip. Sweet. Petra's 12HT darkens the oil faster then that engine, but certianly not as fast as a 3B.
 
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Perth Western Australia
My 12h-T oil remains cleanish for at least 1000kms after a change. I generally always use an additive prior to changing the oil, and I burn vege oil not diesel, so there is inherently less soot in the combustion chamber.

Good to hear others have a similar experience.

Tim
 
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