Rock steady idle (tach) for the first time since new...

[zman]

While idling, the tach on my truck has been jumpy since it was new. After talking to others, I thought this was normal. After my idle started getting noticibly worse (30k miles), I took the truck to the dealer to have it checked out. The tech monitored various sensors for about 5 minutes each while the truck was idling. He noticed that the crank sensor signal was a little erratic. After ordering and finally replacing the crank sensor, my truck idles with absolutely no movement on the tach - rock solid for the first time ever.



Since the tach is jumpy on so many of the trucks out there, I'm wondering if there are a bunch of flakey crank sensors straight from the factory.



While the truck was in the shop for its original testing, the tech also determined that I had a leaky DD2 injector (#2 cylinder) which was causing my noticibly bad idle. He was cool about it and asked me to swap in the originals (before I brought the truck back in to have the crank sensor installed) so he could retest everything again to make sure there wasn't something else wrong. The tech owns a CTD and is always asking me about the mods on my truck - that's how he knew about the 2's. (BTW, DD sent me another set of injectors with no hassle!) I also had the EZ off. Can't wait to get the power goodies back on the truck. What a dog my truck is without that stuff!!!



Steve

 

[Alan Reagan]

Good info. My tach has been rock steady since she came off the lot but I've seen a couple with the fluctuation. Thanks for this posting. Fluctuation may be an indication that the sensor is going bad.

 

[1tuffram]

How much fluctuation where you having?? My truck only has 80 miles on it and I notice at idle the tack jumps maybe a needle or two widths. I also noticed the same on other truck I test drove, so figured it was normal.

 

[zman]

I was seeing a fluctuation of about +/- 25 to 50 RPM at idle. The fluctuation was fairly erratic and without pattern.



I was also having an occassional fluctuation at cruising speed as well. I haven't looked to see if that particular fluctuation is is also gone. I'll check that next time I'm on the road and report back.



Steve

 

[NVR FNSH]

How much is a crank sensor? Might be easier than going thru the dealer... . My truck does the same thing and I've gotten various answers that range from 'it's normal' to 'it fluctuates with the alternator cycling in/out'



Brian

 

[GTop]

My tach also was jumpy at idle. Since I put the DDII's in the tach stays steady at idle. For the last few days my tach has been really erratic and jumpy when accelerating lightly. Maybe the crank sensor on mine is on its last leg??

 

[zman]

Ok, it appears that the fluctuation while cruising down the highway is essentially gone. There is still a very very slight fluctuation, but much less than before.



I have a couple of other observations regarding the idle characteristics (in park or neutral) of my truck. The idle is erratic while the truck is cold. Once it warms up, it is rock solid. If you step on the brake while idling, the idle gets erratic again and smooths out just as soon as you let off the brake.



After a warm restart, the idle is erratic for a short period of time, then smooths out.



Idle is still erratic when the truck is in gear (auto). Just about any load placed on the idling engine causes erratic idle.



The EZ is back on, DD2's go back in on Saturday.



BTW, the sensor listed at about $48, but was covered under warranty.



Steve

 

[dmurdock]

I can top that...

try this...



at idle, my tack jumps a little... .



turn the lights on. . it's rock steady.

 

[cade]

I'll top your topping...

Mine is eratic at idle, never makes it over 1900 no mater how fast the engine reves... . then quites all togeather when I turn the lights on!!



Then again thats on my '87 Ferd



My 98. 5 seems retelatively solid.

 

[Jff24Gordn]

Re: I'll top your topping...

Originally posted by cade

Mine is eratic at idle, never makes it over 1900 no mater how fast the engine reves... . then quites all togeather when I turn the lights on!!



Then again thats on my '87 Ferd



My 98. 5 seems retelatively solid.

yea. .

Well my diesel has a 300 rpm lope below 1200 rpms. Sounds like the cam has 4" lobes. That Case 2290 sounds mean, just injector pump is ready to go out.