2015 Mazda BT50/Ford Ranger surging under light load.

3.2l Ford ranger P5AT direct injection turbo engine.
At around 50km/hr and 70-80km/hr the revs bounce about twice per second , only about 100 rpm like from 1500-1600-1500-1600rpm.
This only happens under light load especially from 70km/hr to 80km/hr.
I watched the graphs for EGR and revs and saw they were similar and unplugged the EGR to make sure - but it still does it with no EGR
command so not caused by the EGR. I smoke tested the intake and there were no leaks.
Fuel rail pressure shows the same bumps as revs - I'm not sure if there should be such a response in rail pressure or if it is actually causing the
problem?

Hi good morning,what is the rail pressure doing during the fault?see if yu can graph the rail pressure desired against actual plus air flow desired against actual air flow.it might be a relearn for the metering valve a relearn,pilot relearn,they fit the same engine in the transit.

Relearn sounds a good to me , although any common rail surging I have seen was fixed with egr cleaning and a couple of bottles of injector cleaner.

Thanks for the replies - this morning the transmission made a bit of a 'clunk' when I took off for a test drive so I took it in to the transmission shop and we went for a drive while he monitored live data - apparently the torque converter is slipping.
Regarding the fuel rail pressure - yesterday I monitored "desired" vs "actual" and it was spot on. What was interesting is that on my budget Nexpeak NX501 I could see the revs and fuel rail pressure pulsing in time with each other but the Snap-on Solus and Autel Maxisys both smooth them out.
Looks like this 3 year old vehicle needs another transmission (at 164000km)

Just a thought,,, maybe you have an torque speed input problem which is upsetting the ecm corrolation with the engine rpm,

Did you find out what was the cause, I also have a 2013 Ranger 3.2 which is doing the same.
dave

Hi Tony

i have same problem with customers bt 50 surging at 1500 any solution we have done injectors fuel line and checked switches on clutch and excillirator.

Monitor MAP while using a scan tool or a jumper wire to open the EGR valve. A fully open EGR valve should cause the engine to run rough or even completely stall.

hi did you find out what the problem was i have all the same things with mine.the gear box is a $5000 job but i need to fix the surging first .desparate to find out