Engine/Transmission (1998.5 - 2002) Audible Engine Pitch change at specific RPM/Speed

[ihegdal]

I have a 2001, AT, 25,000 miles. A few weeks ago I noticing that the engine ocasionally started making a surging noise. Over time I found out that I could consistently reproduce the surging sound within specific RPM/speed ranges. Typically at fairly light power settings on level roads at 2150 rpm/ 55 MPH. I had an Edge EZ installed (the only other engine mod was a "J" hook). I decided that I wanted to figure out if the problem was related to the Edge EZ, or something else. I disconnected the EZ, left the "J" hook inplace. Did some test driving and confirmed that the problem was still present and repeatable. With the EZ on I think the surging(engine pitch change) was at a somewhat higher rpm/speed, with EZ off it is at the rpm/speed mentioned above. Made an appointment with the dealer and took the truck in today. Took a drive with the service manager ( he drove) , demonstrated the problem, left truck for the day. The service manager mentioned during the drive that it sounded like the pump timing was changing (hunting). It was late when I picked the truck up so no technical types were available to talk with. But the report I got back read "24772 checked codes, engine has had a computer hooked to it, which is causing problems, and will void warranty, would recomend not to use it, did reset codes at this time. " There was no charge for this service.



I was surprised to find out that the ECM could code the presence of the EZ, is this typical? The impression I got from the service counter people was that clearing the code(s) fixed the problem, but the problem is still present.



Have others experienced anything that sounds similar?



I suspect that I am faced with warranty discussion issues if I want the dealer to follow up and diagnose the source of the present problem, and even more discussions if there is any question about the EZ causing the problem.



Any references to old post on this topic will be appreciated.



Ian

 

[Steve St.Laurent]

Most likely the reason they thought a computer was hooked to it was because you ran it with the J hook on and the box off. With the J hook on the wastegate your engine was allowed to build boost beyond 20 psi. Once your ECM saw over 20 psi (without the box hooked up) it defueled to maintain 20 psi and set an over boost code. The EZ box has a boost fooler built into it that doesn't let the ECM see over 20 psi. There are ways for them to tell if a box was hooked up but I doubt they went to that extent. Since you left the J hook in place and ran without a box you set an overboost code which is an extremely easy thing to find. That would also cause the surging that you are talking about btw if you were on the throttle when it was happening - the engine would increase fueling until boost went past 20 psi then it would defuel which could sound like a surging. I would remove the J hook as well and see if your surging goes away.

 

[ihegdal]

Steve,



I am new to this posting and mistakenly replied via personal message. I'll reply again here for the benifit of others who may follow this thread.



The engine pitch change variations are only noticable at fairly low power levels, ~ 6-7 psi boost.



Ian