Flat Spot?

[kevvyp]

Not quite sure if that's the correct term but over the last couple of days after she has been idling for a while (like in heavy traffic) and then go to move off I get a "Flat Spot" doesn't do it all the time just now and then, I noticed a bit of a dark smoke cloud after she picks up again, any ideas on the cause?

2007 D40 2.5D manual

 

[Old.Tony]

Sounds like the turbo isn't spooling up like you'd expect. I wonder if your turbo has a problem, the actuator has a problem, or if one of the charge air hoses (any hose between the turbocharger and the intake manifold) has started ballooning under boost.

 

[kevvyp]

Thanks for the advice old Tony, it seems to be running fine under normal driving conditions and even after short idling periods, only seems to happen after prolonged idle, it almost feels like the ignition has been turned off then off she goes again.

 

[Old.Tony]

If you start the car and let it idle for about 2-3 minutes and then take off (engine should still be fairly cold), how bad is the lag?

Just wondering if it's a heat soak into the charge air hoses.

 

[kevvyp]

it doesn't happen until the engine is warmed up and i have been stuck in traffic, i'm not sure the term Flat spot is correct, after sitting in traffic and i move off it is ok in first (manual) and after changing to second it will then lose power for a split second (as if engine turned off then on) i don't push the nav to hard i usually go to about 2500 between gear changes, it started to happen every day since Wednesday but didn't do it this morning, probably some electrical gremlin.

 

[4BYFOR]

it doesn't happen until the engine is warmed up and i have been stuck in traffic, i'm not sure the term Flat spot is correct, after sitting in traffic and i move off it is ok in first (manual) and after changing to second it will then lose power for a split second (as if engine turned off then on) i don't push the nav to hard i usually go to about 2500 between gear changes, it started to happen every day since Wednesday but didn't do it this morning, probably some electrical gremlin.

Sounds like your fuel rail relief valve.. have you checked for any codes?

 

[Old.Tony]

At 2500 rpm you'd be lucky to push 15,000psi on the rail - about half its capacity. Very worthwhile checking for codes.

Does it ONLY happen when changing into second, or does it also happen when it's changing into other gears? I am wondering if the gearbox is thinking it might still be in neutral.

I hope it's not a stupidly curly one like Siringo's 4th gear 4LO flutter where the fuel rail pressure starts a roller-coaster just for selecting 4th. That one might be a software fault in the ECU, but yours could just be a neutral sensor issue.

I'd love to see a graph of the fuel rail pressure during an episode.

 

[david m]

Hi flat spot, had that issue in my 2009 STX d40 2.5 auto. I would put my foot on the pedal to move off and it would flat spot and then take off. Nissan could not come up with a solution. I now have a 2012 STX with the V6 diesal and guess what, it has developed the same issue. Started doing it at about 5000k mark.
Mentioned this at the 10,000k service, but Nissan could not make it happen when driving the car. Seems like it does it when i take my foot off the brake pedal and push the accelerator down to move off.
It's annoying, and yes you really notice it in stop start traffic.

Cheers

 

[kevvyp]

Sounds like your fuel rail relief valve.. have you checked for any codes?

no not yet, if it keeps doing it i will clear the ecu.

 

[kevvyp]

At 2500 rpm you'd be lucky to push 15,000psi on the rail - about half its capacity. Very worthwhile checking for codes.

Does it ONLY happen when changing into second, or does it also happen when it's changing into other gears? I am wondering if the gearbox is thinking it might still be in neutral.

I hope it's not a stupidly curly one like Siringo's 4th gear 4LO flutter where the fuel rail pressure starts a roller-coaster just for selecting 4th. That one might be a software fault in the ECU, but yours could just be a neutral sensor issue.

I'd love to see a graph of the fuel rail pressure during an episode.

Only into second and only after prolonged idle, might wipe the ECU and see what happens.

 

[Neilsk]

This wouldnt be related to the recall nissan is doing on the d40s? with the EGT sensor?

 

[Old.Tony]

This wouldnt be related to the recall nissan is doing on the d40s? with the EGT sensor?

Doubt it, he's got the 2007 D40 and my 2009 D40 doesn't have EGT sensors. Could be the turbo actuator/vacuum hoses/etc, the car is a few years old now and those hoses could have suffered a fair bit of heat damage by now.