N14 governor

[Dickjr.]

I have a N14 in a 93 White/GMC with a 9 speed overdrive. It seems to have a governor that is set to 65 mph, which is fine around here but made a trip up the interstate and it was a hassle. The argument , my brother said its an electronic engine , I say not. It has a linkage on the accelerator to the pump and the old style fuel pump that is driven off the air compressor. So how does this governor work? And it only seems to work in 9th od. When I first got it the fan was stuck on and this governor must have been stuck off cause it would run 75 plus.

 

[Truck Shop]

That is an N-14 Mechanical with step time injection. Better get a manual and read up on trouble shooting the STC.

Truck Shop

 

[DoyleX]

Make sure you are getting full travel out of your pedal and the linkage heim joints are tight. Next stop the pump shop! Probably a weak spring in the gov.

The fan clutch and the governor being related is about as close to getting a gmc to be a mack

 

[Dickjr.]

What is the STC? And why does it only do it in 9th? In 8th it will go to high idle.

 

[lantraxco]

Look for something with an air line on the fuel pump, I've never seen one but an air operated mechanical limiter might exist, and would tie in with the fan clutch as it's air operated... but that's a stretch..

 

[Dickjr.]

Look for something with an air line on the fuel pump, I've never seen one but an air operated mechanical limiter might exist, and would tie in with the fan clutch as it's air operated... but that's a stretch..

I guess I need to look for the flux capacitor next? J/K. I'm sure this is some proto type deal no one has ever seen before, the truck is an ex Old Dominion tractor converted to a dump. I have driven electronic engines before and it acts just like one of those. I haven't really looked closely at it either. Going down a hill , it hits 65 mph once you start to ascend turbo begins to spool.

 

[Truck Shop]

What is the STC? And why does it only do it in 9th? In 8th it will go to high idle.

The N-14 mechanical was the first of the N-14's and was built in later 91 thru early 93. It was for all intent and purpose a good engine.

STC means Step Timing Control it controls injector timing to minimize white smoke on start up. It has two stages of timing [advanced
during cold starts and normal timing for engine load requirements. The injector timing is controlled by engine oil pressure to the STC
valve located on the left rear midway up the block. The only hoses going to the STC valve is #1 a fuel pressure hose #2 oil outlet line.
#3 oil feed line.

Remove the fuel line from the bottom of the control valve and check to see if there is engine oil mixed with the fuel. It should be clear
diesel at that port. If not the STC valve has an internal leak and is replaced as a unit.
Do you notice the injectors change pitch? The STC valve has a low and high shift point- when you hear the injectors go from a clatter to
quite that is the shift from advanced to normal timing. This injection system can be complicated to explain, but in theory it is fairly
simple. I really suggest buying the Cummins manual it covers STC and the Celect and Celect Plus engines.

Truck Shop

 

[RZucker]

The N-14 mechanical was the first of the N-14's and was built in later 91 thru early 93. It was for all intent and purpose a good engine.

STC means Step Timing Control it controls injector timing to minimize white smoke on start up. It has two stages of timing [advanced
during cold starts and normal timing for engine load requirements. The injector timing is controlled by engine oil pressure to the STC
valve located on the left rear midway up the block. The only hoses going to the STC valve is #1 a fuel pressure hose #2 oil outlet line.
#3 oil feed line.

Remove the fuel line from the bottom of the control valve and check to see if there is engine oil mixed with the fuel. It should be clear
diesel at that port. If not the STC valve has an internal leak and is replaced as a unit.
Do you notice the injectors change pitch? The STC valve has a low and high shift point- when you hear the injectors go from a clatter to
quite that is the shift from advanced to normal timing. This injection system can be complicated to explain, but in theory it is fairly
simple. I really suggest buying the Cummins manual it covers STC and the Celect and Celect Plus engines.

Truck Shop

Funny you bring up STC, Had a customer bring an older Navistar with a series 88 BC 4 to me today, eye burning white smoke idling hot and I mean NASTY. He wanted me to run the overhead... Oh wait... it has no oil pressure idling hot. its a $7000 auction truck with absolutely no history. Any bets this will be a cam bearing job in the end?

 

[Dickjr.]

The N-14 mechanical was the first of the N-14's and was built in later 91 thru early 93. It was for all intent and purpose a good engine.

STC means Step Timing Control it controls injector timing to minimize white smoke on start up. It has two stages of timing [advanced
during cold starts and normal timing for engine load requirements. The injector timing is controlled by engine oil pressure to the STC
valve located on the left rear midway up the block. The only hoses going to the STC valve is #1 a fuel pressure hose #2 oil outlet line.
#3 oil feed line.

Remove the fuel line from the bottom of the control valve and check to see if there is engine oil mixed with the fuel. It should be clear
diesel at that port. If not the STC valve has an internal leak and is replaced as a unit.
Do you notice the injectors change pitch? The STC valve has a low and high shift point- when you hear the injectors go from a clatter to
quite that is the shift from advanced to normal timing. This injection system can be complicated to explain, but in theory it is fairly
simple. I really suggest buying the Cummins manual it covers STC and the Celect and Celect Plus engines.

Truck Shop

I believe what you have described is exactly what I have. This forum never ceases to amaze me with the information you can obtain. I will examine this closer and post back. Thanks Truck Shop.

 

[Dickjr.]

If I have to replace this STC , is that a pricey part or relatively inexpensive? I do know the engine oil is in need of change, it doesn't use or leak.

 

[Truck Shop]

Funny you bring up STC, Had a customer bring an older Navistar with a series 88 BC 4 to me today, eye burning white smoke idling hot and I mean NASTY. He wanted me to run the overhead... Oh wait... it has no oil pressure idling hot. its a $7000 auction truck with absolutely no history. Any bets this will be a cam bearing job in the end?

If that 88 has a CPL of 839 or 840 those are Bermuda Triangles,Area 51 and Edward Scissor Hands rolled into one. Those engines were bad news. I even had a Cummins
service manager admit to that..

Truck Shop

 

[RZucker]

If I have to replace this STC , is that a pricey part or relatively inexpensive? I do know the engine oil is in need of change, it doesn't use or leak.

When your fan was locked on did you see a big difference in temperature and oil pressure? This is really strange that it ran good before and not now.

 

[Truck Shop]

If I have to replace this STC , is that a pricey part or relatively inexpensive? I do know the engine oil is in need of change, it doesn't use or leak.

It's been some years but I think the STC valve ran around $500.

Truck Shop

 

[RZucker]

If that 88 has a CPL of 839 or 840 those are Bermuda Triangles,Area 51 and Edward Scissor Hands rolled into one. Those engines were bad news. I even had a Cummins
service manager admit to that..

Truck Shop

Yeah, I Know. Black block.... might even be one of the Mexican Cummins remans. I need to look at it deeper.

 

[Truck Shop]

All this cummins talk wore me out, past my bed time.

Truck Shop