Can broken exhaust pipe cause higher idling?

[Zoltan]

Hello Folks,

just rebult the tranmission (replaced all bearings), and in the process the exhaust pipe broke in the middle (just under the cabin) such that there is a 2 inch gap between the broken ends. When we took out the truck for a test drive, the idle didn't settle down to normal as usual. When i turned off the ignition, the engine ran at least 10 seconds before it died. The second time, the engine shut off normally, but the idle is still high. Could this be due to the broken exhaust pipe or there's something else going on? The truck was running OK before we started working on the transmission cca 3 weeks ago.

[Zoltan]

We (my brother and I) had to extend the arms of a 6" puller to get the central bearings off, but that was it.

Now I know the anwer to my question is NO. I just had the exhaust pipe fixed and the idle didn't change at all. The engine gets hot too. No white smoke though. Shut-off is still iffy, takes 5-8 seconds for the engine to die. My next bet would be that the thermostat is stuck. I am just trying to make educated guesses here: what can go wrong during 3-weeks no driving? The weather got really wet, humidity is 100%, temp is 83-89 daily.

[Zoltan]

By HOT I mean the needle goes beyond the middle, which is unnatural for my engine. I just drove the truck to town 3-4 miles away, so never drove faster than 45mph, but it was running HOT. The stuck fan clutch would not explain the high idle. Me think the two (hot running and high idle) are connected.

[Zoltan]

Checked the thermostat, it only opens 1/8" at 200F. I am putting a new one in.

[asavage]

A failing IPC (Injection Pump Controller) will not move the IP control arm correctly, and can leave it partially in "Start" mode (providing a little more fuel than necessary), and would also explain the slowness to shut down.



See the DPC Controller thread.

[Zoltan]

I appreciate that Al, I thought that a bad thermostat would not explain higher idle and the shut down problems.

[asavage]

The SDs in 720s have no temperature compensation for idle speed -- which is why there is a manual throttle knob for warm up or whatever.

The LD28s in Maximas do have a cold idle prop.

[Zoltan]

I took out the thermostat and the engine started up fine at normal rpm. However after 1 minute the idle jumped higher. So I am moving this thread over to the DCP/ IP controller thread (please post answers there). I did the quick and dirty test on the IP controller and that checked out fine. Should I take apart the DPC next?

[philip]

SNIP When we took out the truck for a test drive, the idle didn't settle down to normal as usual. When i turned off the ignition, the engine ran at least 10 seconds before it died. The second time, the engine shut off normally, but the idle is still high. SNIP

Engine rpm will rise with the addition of more fuel ... even if ... the air throttle remains unchanged.

Fuel delivery is affected by the pneumatic governor diaphragm position RELATIVE TO venturi vacuum in the air throttle. This very sensitive signal can be affected by the EGR moving off seat at idle when it should not be so, the slightest vacuum leak in the line between the pneumatic gov and the venturi in the air throttle, and of course a leakage in or around the diaphragm itself.

That the engine took several seconds to shut down after the key was moved to OFF suggests malpositioning of the Fuel Control Lever.