Shudder, Stumble, maybe....

[Marco]

All,



For all of you with the Shudder/Stumble problem.



Given that this problem can be caused by several things

(boxes, transmission, fuel pressure, just to mention a few), there

is one other thing you might check.



The Engine Coolant Temperature sensor.

( Near to the T-stat housing )



The ECM calculates the injection timing upon several inputs.

RPM, IAT, Throttle, calculated load, AND engine temperature.

From what I've seen here, it seems that the shudder occurs

mainly in colder climates and under light to medium loads.



I would dare to say the injection timing is set too high for

those operating parameters.



Basically you need to check the ECT sensor like you would do

with the IAT ( Their outputs are the same)



For more information look here:

https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=11726



In simple words, if the ECT sensor reads lower than it should,

then the ECM calculates the timing too high, thus you get the shudder in the cold and under light loads.



Marco

 

[Marco]

Give a look at this topic:

https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=33960



That's exactly what I'm talking about! It's not the gauge that's not accurate, it's the sensor that gives a too low reading to the gauge...



Marco

 

[pwr2tow]

hey Marco good to hear from you again.

I hope all is well on your side of the world.

Looking forward to that special day when you introduce your new product.

Thanks for all the work you do.



Ron

 

[Runaway]

May be on to something here...

Had to use the truck last night on an appointment, darn the luck. But anyway, temps were in the mid 30's (warm for Wisconsin this time of year). Noticed my water temps were higher than where it normally runs. Needle was above 190*. That's right, I had my winter front in yet. I remembered Marco's post here so I started experimenting to see if I could get truck to stumble in the 1700 - 1900 range. Tried about a dozen times using the different ways I've noticed in the past and couldn't get her to goof up. Well I pulled off the highway, pulled the winter front out and started on my merry way. Guess what happened when I hit 6th and came across the magic RPM band. Yup, MR Stumble came back. May have to try the new temp sensor.



I noticed not to many folks paid attention to this post. Might be worth investigating further.



Vince

 

[JPittman]

Runaway,



If you replace the ECT sensor, let us know the results. I pulled a load when it was 61* and no stumble, but did have it when it was 40*-50*. You may be on to something.

Also, how do you test the ECT & IAT sensors to see if they're working correctly?

Thanks.

 

[CLGreer]

I was having a significant stumble (engine acts like out of fuel, unable to rev, pull over to side of road, little bit of white smoke once:{) at least every 75 miles or so. Symptoms worse when fueling box on but still happened with fueling off. Unrelated to acceleration. Usually happened at very light throttle or coasting miles after a hard acceleration. P code of 1693. Would completely go away within 1 minute or 2. Then could not tell there was any problem at all. FMS monitors lift pressure. Went to the trouble of dielectric grease to the map sensor connection. Stumbled again 5 miles later. Noticed that the temp gauge did a little dip at the time of the last stumble. Remembered Marco’s post here about the ECT and checked it. All I did was unplug it, see that it already had some grease in it, wiped off a tiny amount of extra grease from the plug and then plugged it back in. Went 200 miles and had a little stumble along with a little temp dip. Have been watching temp gauge like a hawk and waiting for another stumble for the last 600 miles. No further stumbles. Fixed? I'll see. Truck is running great right now. Thanks to Andy at ADT for excellent service.

Marco, I am looking forward to the release of the MAD ECM. Keep up the good work.