Sticking throttle question

[philip]

Hi I just joined but have been reading the old post for a couple of weeks. I have a 1982 datsun 2D22 pickup.

"Please take a minute and click on the "Profile" button at the top of any page, add your location (Portland, Ore or Portland, ME), and the year/model of your rig to the "Signature" block? It will prevent people from asking for this info over and over." Regarding tires, please post non engine questions to the "SD powered 720 Support Systems" forum next door.

The problem I am having now is that when I slow down to a stop the engine still gets fuel. It acts like the pedal is sticking. It does not happen all the time and seems to happen more when i drive for longer distances. I idles normal after I put in gear and give it a little fuel. the choke is not on and the pedal is not sticking. The throttle mechanism does not stick as far as i can tell.

Thanks

Welcome to the engine forum. The engine HAS to continue getting fuel otherwise ... it dies. Putting the transmission into any gear has no effect on engine RPM until you modulate the clutch. There is no "choke" in the way you're thinking. And finally, the throttle butterfly does not do what one traditionally credits to a butterfly throttle body.

So ... we're left with a vacuum leak feeding the pneumatic governor that gets larger with overall engine heat. From the framing of your inquiry, do yourself a great service by acquiring a Factory Service Manual (FSM). Al maintains in Peddle or Procure forum a list of recent FSM sales ... typically on eBay.

[asavage]

Hello, and Welcome, Shep:

Hi I just joined but have been reading the old post for a couple of weeks. I have a 1982 datsun 2D22 pickup.

Does your 720 have a diesel engine? If so, you probably meant "SD22". The other engines available in that year (in the US) are the Z20 and Z22, both of which are gasoline engines ("gassers").

The problem I am having now is that when I slow down to a stop the engine still gets fuel. It acts like the pedal is sticking.

I think when you said "fuel", you may have meant "accelerator". The fuel delivery is controlled by the injection pump (on the SD22) and not by anything you do with your right foot.

Making some assumptions, two things come to mind (if we're talking about the SD22 engine): the throttle on your engine has a dashpot, a little black can that slows the speed at which the throttle closes, should you suddenly remove your foot from the accelerator. That dashpot typically dies in a manner that makes it non-op in damping (ie it doesn't slow down anything!), but I've seen dashpots in non-SD implementations that became "sticky" and wouldn't let the throttle close well.

The other thought has been mentioned by Philip: an air leak in the pneumatic governor system to/in the injection pump ("IP"). This could be as simple as a hole or crack in the flexible or fixed lines leading from the throttle body to the IP, or it could be a crack in the IP's pneumatic governor diaphragm.

I'm sure Philip will point you to the Pneumatic Governor thread, as this topic has been well covered before. I think he's done up a nice colored drawing of the pneumatic system too. And I'm certain that a picture exists of the dashpot, as installed.

And, as Philip mentioned, you really must acquire a Factory Service Manual ("FSM"), as it's just not possible to understand and troubleshoot some SD subsystems without it. They can typically be had in the $10-$40 range, depending upon how fast/how patient one is. See this thread, which is where I post new eBay and CL FSM finds.

I'm off to the JY now . . . rumor has it there's a new SD 720 there!

[philip]

Please excuse my ignorance. Sad to say but I have a chilton manual already. I will try one more time to phrase my question and then I will do some more research. I do have the 720 diesel. SNIP

Chiltons book = doorstop AND useless for the SD.

See my first reply referencing small vacuum leaks and the pneumatic governor. Examine closely ALL vacuum hoses and the leather governor diaphragm. Vacuum test the governor per the FSM.

Also, is you SD equipped with an Exhaust Gas Recirculation system? If so, vacuum leaks feeding the vacuum amplifier will raise engine RPM by holding the EGR off seat at idle ... a different kind of vacuum leak.

[asavage]

Ditto what Philip said, both about Chilton manual and EGR system.

I don't know what putting the shifter into a gear would have to do with the idle speed. While the gasser trucks do tie shift selector position into some of the emission controls, I'm pretty sure that the SD version doesn't. That has me baffled.

Also, the dashpot thing is still applicable. You might take a look at it. It's black and round and is bolted to the throttle body/intake manifold, adjacent to the valve cover. I pulled one at the JY today, but my camera is at work (so is the dashpot, in the back of my now-disabled van. Grrrrr.). (scroll up )

But you really, really do need the Nissan Factory Service Manual. You can't get by with the Chiltons/Haynes/Mitchell/Clymer versions when working with the SDs.