Thanks for all the help you guys give. I worked on MRAPS in Afghanistan and learned a lot about diesels,we had Cats from FPI,Navistar from Navistar defense and Cummins from BAE, but am no expert just know enough to get in trouble. I just purchased an f350 7.3 with 190,000 miles on it . manual trans ,4 door, single axle 4x4. Was told the truck is chipped and has a fresh air system other than that is stock. truck has good power pulls strong from start, starts fine but when you are crusing at highway speed it seems to surge randomly.there are no lights on so checked history codes.I have a Snap On Verius scanner checked for old codes only ones that had ben there was the two for exhaust pressure sensor or something like that . but none were current codes.Was just wondering where to start looking . it is really just a nuisance

Thanks Jackie

 

Welcome to FTE Jackie!

First of all, thanks a million for your service!

Secondly, I wanted to let you know I'm going to move your thread to the 1999 - 2003 7.3L Powerstroke Diesel forum. Hopefully you'll get more specific information here. This is a great group of folks with tons of knowledge....they'll get you on the right track.

 

Welcome to FTE!

When exactly is it surging? Is it consistent or random? It could be a few things so a little more detail would be helpful.

 

Does your truck happen to have any gauges? If so, does your boost fluctuate while experiencing these symptoms?
Have you already changed the oil and fuel filter?

 

I would also like to welcome you to and thank you for your service.

Slight surging can also be caused by a chip or tuner when in cruise control. It is more noiceable going down hill and does not surge going uphill. With CC off I never really notice it. During live tuning I had Jody adjust the PCM CC function but it did not completely eliminate the surge.

 

Not much of a help on this one, seems like everyones said what I would have.

We cant thank you enough for your service to this country.

 

Welcome and thank you for your service. Any gauges on the truck?

 

Welcome, and thank you for your service.. I am goign to sit back and wait for your answers, and might chime in if/when I have an idea.

 

You said that it is 'Chipped'. Can you find out more about this because at some point you may have to adjust it (different tow/performance points) or you may have to remove it in order to find out if it is causing your surging.

 

the truck has no guages. Have no idea about chip or where to find out ,i bought it from a marina going out of business . it seems to surge when holding accelerator at a constant speed . has new oil and new fuel filter.cleaned and reoiled k&n filter. Tried to do do a cylinder contribution test and tool could not do because ac was not functioning.it could be a miss but it is not consistant just randoly feels as if ac compressor came on and went off. Thanks for the compliments on serving but i was just a certified MRAP instructor for Force Protection Inc.I have ben shot at and mortared but will take nothing from the real heros, they live in some of the worst living conditions i have ben in and just love what they do. My hat is off to all MILITARY. I just had a chance to help get our troops in armored trucks so i jumped on it . Have a son in Army and son in law that just got out of Marines so knew what the needed to make their job safer.

thanks for all Jackie

 

If the previous owner said the truck was 'chipped', it could mean a few things. Could be a program that was uploaded to your PCM to improve performance. If so, there would be no visible signs that anything was altered.

Another method is to add on a custom chip and/or controller. This is normally visible by looking at the back of your PCM to see if anything is added on. Here is a link to a popular version so you can have an idea of what it looks like.
https://www.dp-tuner.com/index.php/a.../aitfile_id/6/
Some other brands interface with the PCM by adding an extension to the ODBII port, which can be found under your dash towards the right side (about where your knee is while driving...)

If you find a chip attached to the back of your PCM then you will want to ensure it's not coming loose. Make sure you remove the keys from the ignition before you mess with it or you risk damaging your PCM and then you'll have bigger problems. Report back if you find something and we'll go from there.

Regarding the K&N filter...
Is it the drop in kind that utilizes the stock airbox? If so, then you will want to make sure the lid is sealing properly. Some elements have been known to seal poorly and allow unfiltered air to your engine. This is usually due to improper installation of the lid (not getting the fender tabs inserted all the way before closing he lid...) So, check your lid and make sure it is clean and not dusty. See the photos below. Your lid and turbo should look like this.

 

One note when running all of your tests. You need to turn the heater controls to OFF. The A/C works all the time, unless in OFF, so that will trip you up on running tests.

 

thanks foir ideas . i have fresh air system no air box.I have over 30 years in the body shop industry. and have never heard of ac on all the time . as i said earlier it acts like compressor comes on and cuts out ,so maybe that is what is happening . it is low of freon so will recharge and see if that makes a difference.

thanks Jackie

 

Ac does cycle on and off all of the tie but u shouldn't be able to tell going down the highway. Is it a surge or cut out/skip?

 

If the fan controls are off, you should be able to run all the tests like KOEO and KOER as well as contribution.