How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Daniel Wilson Your Own Question
Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 5132
Experience:  Owner at DJ Wilson
65405794
Type Your Medium and Heavy Trucks Question Here...
Daniel Wilson is online now
A new question is answered every 9 seconds

I have a 1992 Peterbilt 379 with a N14. When you start the

Customer Question

I have a 1992 Peterbilt 379 with a N14. When you start the truck cold, the idle is at 650-700 rpm,
but 15-16 minutes later it will increase to 1000 rpm and stay there the rest of the day. I have timed
this several times. No codes, idle bump switch doe's not work,( has voltage ) changed throttle position
switch, checked oil pressure switch below air compressor. I have had it in several shops, and nobody
can figure out the problem.
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Daniel Wilson replied 2 years ago.

Hi John, my name is***** will be glad to try to help. If there are no codes and the fuel system checks are good, Overhead is good then try recalibrating the throttle position sensor. IGN switch on push slowly to the floor and back up to the top 3 times then IGN switch off. Next check your engine position sensor for problems as this gives the ECM engine speed signal. Check your ECM switchable and battery power and grounds to verify you do not have low voltage to the ECM and finally try a test ECM or have yours reflashed with the most current updates. Be sure all your battery to starter connections and grounds are clean and tight, batteries test good and the charging system tests good. Let me know

Expert:  Daniel Wilson replied 2 years ago.

Hi John, Did you get this resolved? I wanted to follow up to see what you found and if my information was helpful to you or if you still needed more help? Let me know and I will get this question closed out for you if you don't need further help with this. Please feel free to rate or accept if you found my information helpful as that is how the experts receive credit for their time helping on the site.

Customer: replied 2 years ago.

We pretty much had already tried everything you suggested. Still haven't

resolved the problem. The fact that you can time it each time to 15 to

16 Minutes is what is baffling me. Its got to be some temp sender sending a signal to the ECM. If it where wiring or settings, it would do

it when it was first started in the morning as well. But it has to run for

a consistent amount of time when started cold. Then stays at 1000 RPM the rest of the day. It starts to come off of 650 RPM around 13 Minutes.

It is set at 650 RPM in the ECM. ( Strange )

Thank You !!

John

Expert:  Daniel Wilson replied 2 years ago.
Thanks for the update JohnCheck and verify the EPS ( Engine position sensor signal) is not giving false or erratic readings for engine speed signal to the ECM and also verify the Settings and parameters in the ECM for the idle shutdown timer are set correctly. I would try a test ECM if available or have yours reflashed/reprogrammed with the most current updates. Let me know.

Related Medium and Heavy Trucks Questions