# TN70A Idling Strangely



## Willfrost (Nov 7, 2013)

*[SOLVED!] TN70A Idling Strangely*

I've got a strange situation going on and I'm not quite sure what to do about it.

My TN70A has always idled a little strange at low speeds. Sometimes it will idle fine, but often it will act like it is going to die on me, then catch itself at the last second and come back up to a proper idle speed. After 5 or so seconds it slows down again almost to the point of dying, then idles up again. On one or two occasions it has actually gone dead on me, but always restarts with a turn of the key. In order to get it to even out, I can increase the throttle speed to a point greater than what I would consider a "resting idle", but at least then it isn't speeding up - slowing down - speeding up - slowing down. 

With that history in mind, I was out mowing the other day, and needed to get off the tractor to move something out of my way. I put it in neutral, applied the parking brake, disengaged the PTO clutch, and throttled the tractor down to idle while I got off. Before I could climb off, the engine died as if it had run out of gas (it has plenty of gas in it). It seemed a little strange to me but I wasn't alarmed so I turned the key to the off position and went about moving the stuff out of my way. When I got back on the tractor I turned the key to the start position, the tractor started up, and then immediately died. I tried to start it several more times, with it starting up each time, then dying within 1 or 2 seconds. I moved the throttle lever up and tried starting it again with the same results. Finally I pushed the throttle lever all the way up and started it again. This time it started just fine, and then immediately throttled up to where I would expect it to given that the throttle lever was in the highest position. I moved the throttle lever to about the half way position (intending to continue mowing) and then engine throttled all the way down and died. Ultimately I can only get the engine to start, and keep running if the throttle lever is between 75 and 100%. Moving the throttle lever lower than the 75% mark and the engine throttles down and dies. 

The fuel filter has maybe 8 hours on it, but I am going to change it out anyway as soon as I can get a new one. These symptoms don't seem like an obstruction in the fuel line to me, but anything is possible. 

If anyone has dealt with this kind of problem before I would very much appreciate some advice. Thank you in advance!

-Will


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## harry16 (Dec 8, 2011)

Howdy Will, Welcome to the Forum.

Your New Holland TN70A tractor was made in Italy, with an Iveco turbocharged diesel engine, 70HP. Nice tractor. A bit of overkill if you don't have heavier work than bush hogging for it. Diesels need to be worked hard to maintain them.

The first thing I would check for is water in the fuel. Water in the fuel can cause this type behavior. Could be from condensation, or possibly rainwater if you leave it outside. Drain the tank completely into a clean bucket and inspect for water on the bottom of the bucket. 

Also have a look inside the empty tank. If you can see sediment or water in the tank, you probably have to pull the tank and flush it out. You might try to vacuum it out with a shop-vac, but don't lose any vacuum pieces into the tank.

The older Fords normally have a fuel screen attached to the shutoff valve that sits up inside the tank. I don't know if your tractor has this screen. Some fuel pumps have a screen at the input connection. 

Have you bled the air out of the injection system? It may be that you have some air trapped at the injectors. 

I've attached parts diagrams of the injection pump, injection pump drive gears, fuel pump, turbochargers, and fuel filter. Basically the entire fuel supply system.

If you find nothing wrong with checks above, let me know and I will get my injection pump buddy to comment on your pump. We will need to know your pump make and model numbers. 

If it turns out that you have to pull the injection pump, you will need a shop or service manual to do the job. Shop manuals are skimpy on details. The big thing is getting the pump back in and pump timing set correctly. From the injection pump drive gears diagram attached, it appears you will have to pull the timing gear cover to pull the drive gear. Your manual will tell you what you have to do.

Let us know how you are making out, and if you conclude the injection pump is the problem. If so, I will get my buddy involved (he's an expert on injection pumps).


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## Willfrost (Nov 7, 2013)

Thanks for the great info! I'll start moving down the checklist you provided and let you know what I find out.


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## Willfrost (Nov 7, 2013)

*The situation seems to be fixed*

I did what was suggested in the earlier post, as well as replacing the fuel filter, then bled the injectors of air. This only made the tractor harder to start. Instead of the 1 to 2 seconds of cranking I was used to, I had to hold the key for around 30 seconds to get it to start up. Even after I had it running for a bit, if I stopped it and wanted to start it again it would take another 30 seconds of cranking. I did some more tinkering around to make sure that the fuel lifter was working properly, then finally came to the conclusion that it must be the injection pump. 

After reading the details of overhauling the injection pump I decided that it was probably a little above my skill level, so I put in a call to the dealership where I got the tractor to see what it would cost me to have them take it to their shop and service it. I spoke with the shop manager who told me to drain the tank, then pour a quart of automatic transmission fluid into 5 gallons of diesel and run that through the tractor for 50 minutes. He said the transmission fluid would lubricate the injector pump and that it would probably solve my problem. 

Immediately I noticed that the tractor started much easier. Maybe 5 seconds of cranking and it was running. I let it run for about 30 minutes at 2100 rpm, and then tried to throttle it down. Below about 1700 rpm the tractor died again. I was pretty discouraged, however I decided to let it run the whole 50 minuted prescribed, so I raised the throttle lever and started it back up. It was another easy start, and after it had run for a total of about 55 minutes I slowly tried to throttle it back down again. This time success! I continued to let it run for a little bit more, slowly adjusting the throttle up and down. It seems to be running perfectly now, and it even idles at slow speeds much smoother than it ever did. 

Much thanks to Harry for his troubleshooting advice and for the great diagrams. I would be very interested in knowing what your friend who works on injector pumps thinks of this remedy. If anyone has any questions I will do my best to answer them! Take it easy,

-Will


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## harry16 (Dec 8, 2011)

Howdy Will,

I am delighted to hear that you got it back running well. I contacted my buddy for his opinion. Here is what he said:

"ATF WILL LUBRICATE THE FUEL SYSTEM AND "UNSTICK" ANY CARBON BUILD UP ON INJECTOR TIPS AND PISTON RINGS.. IT ACTUALLY BURNS HOTTER AND "BURNS OFF" THE CARBON BUILD UP.

SOME SAY IS AN OLD WIVES TALE.. BUT I'VE SEEN IT HAPPEN WITH MY OWN EYES..

I DONT GO AROUND PREACHING OR EVEN TALKING ABOUT IT UNLESS ITS BROUGHT UP IN CONVERSATION.."

That's all he wrote on the subject. Congratulations Will. 

It might be that you have to work your tractor harder?? Usually if this is the case, the engine will start slobbering - black soot (incompletely burned fuel) coming out of the exhaust.


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## icandoit (Jun 13, 2015)

Willfrost said:


> *[SOLVED!] TN70A Idling Strangely*
> 
> I've got a strange situation going on and I'm not quite sure what to do about it.
> 
> ...





Willfrost said:


> *[SOLVED!] TN70A Idling Strangely*
> 
> I've got a strange situation going on and I'm not quite sure what to do about it.
> 
> ...


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