Weird pulsing when coasting downhill with cruise control on

[AussieAnth]

Hi Guys

I've started noticing a weird issue sometimes in the last month. I've got a 2013 manual GLX dual cab. 3" exhaust, Tony's Dominator MK1 chip and EGR module. Cant think of any other mods that might possibly affect it.

On long trips, with cruise control on, when going downhill, even a gengle gradiant, the engine seems to pulse....occasionally. Its kind of like someone is rapidly tapping the accellerator, just enought to give it a little boost, but you feel it about twice a second if that makes sense, for several seconds at a time. Seems to go away once the cruise control kicks in as the road flattens out.

It doesnt seem to do it all the time. I've noticed it at least 4 or 5 times now. At first I thought the road was rippled or something, but there's definatly a pattern emerging.

This sound like anything familiar?

UPDATE: I'm on page 2 of the "Re: Surge Problem with MN Triton" thread, and Im now seeing descriptions of exactly the same issue. So I guess its "surging". I never bothered reading that thread as I thought it was an early MN issue thats since been resolved.

[Rd1]

It's the cruise control kickingon and off. My ute does the same. Touch the throttle and it stops or cancel cruise and it stops. No prob

[AussieAnth]

It's the cruise control kickingon and off. My ute does the same. Touch the throttle and it stops or cancel cruise and it stops. No prob

hmmm, yeah Im not sure if its a cruise control issue or the common surging issue. I'll have to do some test driving without CC on, drivng steady down hills, and see if I can reproduce it. That should indicate if its one or the other.

Mind you, in the Surging thread, loads of people describe the surging exactly as I do, using CC driving down hills. Having said that, plenty experience it with a cold engine at low revs.

Funny thing is, I havent noticed it until just after I got the 15,000kms service just before Xmas. I'll have to keep an eye on this one.

[Rd1]

I happens to me on one spot on the hey just south of coffs on my way home every time. It's just a slight run down hill. On steeper hills it runs past the set cruise speeds and does not happen to me. In the spot where it happens to me I just touch the pedal and keep it above the set speed by a k or 2 for 200 m's until I hit the flat then take my foot off and its gone. Try that and try coming down the hill without cruise just you holding the speed and see what happens.

[Kevin Lucey]

Mine is stock standard and I have the same issue, so I don't think it would be anything to do with your mods. I am under the impression its just cruise control shutting of repeatedly as well.

[Rd1]

I have exhsust, chip, windbooster, think it just might accelerate to quickly back to the set speed.

[Geoff3DMN]

My 2013 GLX+ does exactly this, I've always assumed it's the cruise control since it only seems to happen when I'm driving in the country on highways (and then I'm on cruise control).

The dealer has 'been unable to replicate the fault'.

[AussieAnth]

Some of you might want to read this thread about surging, to see if it applies to you. Its 11 pages long, but I only had to hit page 2 before I found matching descriptions.

The descriptions and situations that this surging applies vary wildly, but there are several members describing the exact same scenario as I do above, so it might very well be surging....or perhaps just a CC issue.

viewtopic.php?f=18&t=6366

If it is surging, I would expect I can replicate it without CC engaged. Time will tell.

[AnOldFart]

Some of you might want to read this thread about surging, to see if it applies to you. Its 11 pages long, but I only had to hit page 2 before I found matching descriptions.

The descriptions and situations that this surging applies vary wildly, but there are several members describing the exact same scenario as I do above, so it might very well be surging....or perhaps just a CC issue.

viewtopic.php?f=18&t=6366

If it is surging, I would expect I can replicate it without CC engaged. Time will tell.

Exactly right 'Aussie' leave the CC off and go for a drive on a long straight and level stretch of road and try to sit nice and steady on 80km/hr whilst you use a 'feather-light' touch on your accelerator pedal. If it's surging being caused by a sticky SCV valve then it will still make it's presence known to you under those conditions. I wouldn't rely upon just one test run if it doesn't immediately appear though ie, I would try it a few times without a -positive- result appearing before I finally eliminated the SCV as a possible cause and blamed the CC instead.

[har05l]

If it was surging it would do it on any road gradient.

[Cowboy Dave]

There seem to be several different variations of what people call surging. There's a high speed pulsing sort of thing on cruise control and a low speed, low engine temperature one. I've had the low speed one on a cold motor and it's a violent coughing, lurching sort of a feeling like an intermittent fuel blockage or something. There was a hotline fix (ecu reflash) for a high speed surging - like 110-120km - but I only know about that because my idiot dealer didn't listen properly to my explanation of my low speed surging and applied the ECU reflash fix for high speed surging. Which made no difference to anything at the time. I found mine went away when I stopped using Caltex diesel all the time. I now use shell diesel maybe 80% of the time and some occasional BP ultimate and caltex only when I'm stuck with it. Whether that is a complete fluke or the fuel was really the issue I'll never know. Not exactly scientific but it costs nothing to try it.

With the high speed surges I suspect again that there is more than one kind of surge. One seems likely to be cruise control behaviour. In the auto the ECU seems to vary the torque converter behaviour and possibly boost to maintain speed and revs. I've had mine sit on 110 in cruise control with the tacho needle never moving once while the ECU varies settings other than throttle to keep the speed and revs constant. It was a bit disconcerting for a while as you could feel increased acceleration (like up a hill) but the tacho wouldn't move at all.

Other types or surge are likely being caused by dirty MAF sensors and/or MAF plugs and misbehaving SCVs.

What would be really cool is if someone could make up like a decision tree - is your surging occurring at low revs yes/no - if yes then is it happening at 110 under cruise conditions - and so on.

[Stoneman]

I've had the cruise control surge since new goin down hill

I noticed after the EGR mod it made a slight improvement
Than came back.

After adjusting my actuator arm on my turbo (2.5) it has gone and hasn't returned as yet

I have no idea why it would if it has made a difference but the over all way it drives is much better than before I adjusted the turbo
I didn't make the adjustment because of the surge though

Maybe it could give some idea to the experts of why and how......dunno?

[Rd1]

I have it I one spot 100% of the time. Only ever get it at other times when I find a similar slightly downward sloping hill. It happens when the cruise kicks in and makes the ute up to the speed, your going down hill so cruise kicks off, but your not rolling fast enough so cruise kicks back in and these jerks happening until the road flattens and then the cruise stays on to power you along the straight. Only even happen down a slight hill and done it from new.

[AussieAnth]

I've had the cruise control surge since new goin down hill

I noticed after the EGR mod it made a slight improvement
Than came back.

After adjusting my actuator arm on my turbo (2.5) it has gone and hasn't returned as yet

I have no idea why it would if it has made a difference but the over all way it drives is much better than before I adjusted the turbo
I didn't make the adjustment because of the surge though

Maybe it could give some idea to the experts of why and how......dunno?

stoneman, I've only read of people adjusting the turbo actuator on the ML 3.2 to gain a few extra PST in boost. Didn't know if was possible on am MN.

Can you elaborate more on what you did and why?

[Tony]

On MN is the VGT actuator arm, it works on a vacuum solenoid so you can only adjust out either end of the vain travel.

I don't recommend it on these as could offset fuel economy, stop VGT from moving fully out of attack position and could produce overboost issues with annoying CEL's then damage the engine, or on the other end of the scale, prevent VGT going into full attack and very poor performance. I have had a few come here like this where dealers have tried to overcome overboosting issue some seem to encounter.

Was a common practice with early Nissan ZD30 to adjust out of full attack so they didn't grenade them selves as they never controlled their boost well.


Stoneman was perhaps after a faster boost ramp up and no doubt will have noticed a difference. If went far enough, he will also see more overall boost as the VGT no longer comes completely out of attack position when boost target is met.
.

[Stoneman]

Aussieanth,

I adjusted it by shortening it by one turn only because I was getting annoyingly huge puff of black smoke on take off when I adjusted my tune, if I didn't do something someone would of called the EPA on me
My boost as mentioned Is now controlled by a dawes valve

[natsterrr]

My 2015 MN 2.5 manual has 73,000 km on it and has just started the pulsing/jerking/surging thing when going UPHILL at 110 km/h with cruise control on in 5th gear.
I’ve always accepted that going downhill there will be some accel on/off to maintain speed, and it works fine on flat, but this uphill thing is weird when it should be applying constant revs to maintain speed.

I’m wondering if this could be a speed sensor issue or some other electrical problem with the cruise control?

When I let it go a little bit the whole gear/transfer stick assembly was wobbling pretty violently from side to side. I could stop it by accelerating smoothly to just above CC SET speed, or by cancelling CC.

Anyone had similar issues?

[natsterrr]

My 2015 MN 2.5 manual has 73,000 km on it and has just started the pulsing/jerking/surging thing when going UPHILL at 110 km/h with cruise control on in 5th gear.
I’ve always accepted that going downhill there will be some accel on/off to maintain speed, and it works fine on flat, but this uphill thing is weird when it should be applying constant revs to maintain speed.

I’m wondering if this could be a speed sensor issue or some other electrical problem with the cruise control?

When I let it go a little bit the whole gear/transfer stick assembly was wobbling pretty violently from side to side. I could stop it by accelerating smoothly to just above CC SET speed, or by cancelling CC.

Anyone had similar issues?

Just got back from testing after warranty fix - the cold side inter cooler rubber hose was replaced. Drives like new now! I guess it had split and I was effectively driving without forced induction. Happy it was such a simple fix.

[Bitsamissing]

I haven't noticed my MQ doing it, but I have a 2006 Fiat that always "surges" when on the cruise control on a downhill slope of the right steepness.

I think it's just too coarse a control over the throttle at low throttle openings.

Everything's digital these days so there would be finite steps in the throttle opening when under the control of the cruise control. On steep enough downhill section, the throttle will be closed. Slightly less steep, and the throttle will be alternating between closed and the smallest opening the cruise control can give it. If that's a bit big, you'll feel the car alternately accelerating and decelerating as it tries to hold the speed.

[driver080]

I just purchased a 2013 MN with the exact same problem. Surging on slight downhill gradients with the CC engaged. Cannot reproduce the fault without cruise on, or in any other conditions. I learnt very quickly to not use CC in hilly terrain. If the downhill is long enough the surging gets progressively worse until it feels like the car is going to break something.

I live in flat country so I can live with it. I just know to disengage the cruise before going downhill. But it would be nice to know if there was a fix available. I'll keep my eye on this thread