Engine "surging"

[djbock]

Has anyone experienced engine "surging", for lack of a better term. Symptoms are when at highway/interstate speeds it feels as though the accelerator is being pressed and released over and over again. The RPM's and speed remain constant but you can definitely feel a surge. I can also watch the MPG gauge swing from 20-30 MPG. Only seems noticeable when utilizing the cruise control. It is almost unbearable to the point that I don't want to drive on the highway.

Took into dealer for a sunroof that wouldn't close (I know unbelievable) and mentioned it to them. They state that the fuel is being constantly adjusted to maintain speed and emissions and reset the fuel adaptations. Needless to say this did not solve the problem. So any other ideas for when I go back to get the sunroof repaired when the parts arrive?

[TerminatorX5]

check the coils and spark plugs - i had that surging in RPMs that i actually monitored on the digital tach in the cluster, and then in INPA... after cleaning the MAF, the throttle body flap, it came to cyl 5 misfiring... the misfire was not obvious before, only after INPA said it was misfiring... ordered a $35 Bosch coil - and voila!!! everything went normal... so, the brand new fuel filter will sit in garage until i actually will need it...

do you also experience undercut in power? as if you are merging onto freeway, and there is no power to merge you into traffic...

[djbock]

No loss in power and like initial post, the RPM's stay constant. I am wondering at this point if it is a bad fuel regulator?

[ard]

^^^ if it only does it when using the cruise control, wouldnt that be a huge hint?

So if you act like cruise control and maintain a constant speed, there is no surging and no 'mpg changes'...but when you engage cruise control is surges??????????

[djbock]

Originally Posted by ard

^^^ if it only does it when using the cruise control, wouldnt that be a huge hint?

So if you act like cruise control and maintain a constant speed, there is no surging and no 'mpg changes'...but when you engage cruise control is surges??????????

True, mainly going by what the CEO tells me. I get to drive it maybe once every couple of months. But did notice it on a 450 mile round trip get-away this past weekend. Will verify that it only happens with cruise and if so point them in that direction.

[ard]

^^ That 3.5 may need to move the accelerator to keep the speed constant- the RPM will not change if the speed doesnt change, but as the load on the drivetrain (wind, hills, etc) changes, the cruise control WILL adjust throttle. And the mpg will move of course, since you are adding more throttle but no appreciable increase in speed

For me the torque of the diesel means nothing moves- just rock stable on the speed and throttle...but a smaller motor will need more 'adjusting'.

A

[djbock]

I can understand hills, wind, etc. But it does it on a completely flat smooth road. Constantly 'surging" the 3.5 hours to our destination and 3.5 hours back. Was annoying as all get out, glad I don't drive it everyday.

[Texjr]

I have been experiencing this too in my 2001 4.4l. It happens on cruse control and when driving normally. It happens mostly trying to maintain speeds. I'm not sure if its actually changing gears but its definitely noticeable. I was thinking fuel filter too.

[ard]

Originally Posted by djbock

I can understand hills, wind, etc. But it does it on a completely flat smooth road. Constantly 'surging" the 3.5 hours to our destination and 3.5 hours back. Was annoying as all get out, glad I don't drive it everyday.

AC Compressor cycling? try it with AC off.

Report back when you try it without using the cruise control, just your foot as cruise control.

Fuel filter, pump and fuel pressure regulator can impact driveability, but I'd expect some kind of code....especially a during full throttle, high power demand maneuvers- you will be drawing the most fuel and if it is having trouble you will lean out and get misfires or codes. IMO


A

[djbock]

AC on or off doesn't affect it. Foot "cruise control" no issues. So it seems to point, as ard said, towards the cruise control somehow. Will point the dealer in that direction whenever the parts for the sunroof come and i take it back in.