Hesitation when backing OFF the throttle

[wrc]

This has been an issue my Gtir has had from the start and is now next on 'the list'.

Perfect through the revs, but of for example if i'm cruising on the motor way with very very light load - the dump valve will start going mad, can feel the engine rocking forwards and back and just stutters like crazy like it doesn't know if it wants to be on throttle or off throttle.

The only thing I can think of if the tps, but I adjusted that to spec a few months back and made no difference.

Help

 

[PobodY]

That's rather odd; what dump valve is it? - The only thing I could think of off the top of my head is that you've got a lot of vacuum and it's pulling the valve open, but I wouldn't have thought it would do that under light throttle.

What mods are there?

 

[wrc]

It's nothing to do with the dump valve, exactly the same with or without it.

At the moment it's just the usual front mount, side exit exhaust etc nothing drastic.

Ive tried swapping vac lines around, just the same.



If I come of the throttle sharp ish, it's fine - if I back off slowly I then get to that point on the low throttle where it does this.....

 

[Fusion Ed]

So its either engine going into over-run when it shouldn't or dump valve opening letting metered air out causing it.

 

[wrc]

It does this with or without a dump valve fitted and I've tried another as well so can't be that.

Engine going into over-run Ed???

 

[PobodY]

Sorry, but you did say the dump valve was going mad so it's only natural that people would assume that's part of the problem.

If it's not TPS related, then could it be something to do with the air regulator gubbins? - Hows your idle; ever had any problems with it?
I'm just wondering if there's air getting past the butterflies which is causing these symptoms.

I've never had a problem on the motorway like that, but if I'm slowing for an intersection and decide to put a bit of throttle back on, mine will give a bit about three pops from the exhaust. The only time it bunny hops is when the revs are too low.

 

[j0ff]

Ed's referring to the TPS I believe. When you take your foot off the throttle, the TPS registers the throttle as 'closed' and if revs are over around 1750 rpm (depending on car) then all fuel is cut. That's 'overrun' fuel cut off
If your TPS is registering closed when it's actually 'nearly' closed, that could cause all sorts of fun

 

[j0ff]

If the TPS is anything like the skyline, then just setting it by voltage might not be enough.
Set the TPS so it's reading the correct voltage when closed, then while the ignition is on, disconnect the TPS, leave it 10 seconds or so, then reconnect. That should let the ecu re-learn where 'closed' is

Like I say, that works beautifully on the RB engines, have never tried it in the SR. I'll hook up my computer to it at some point and give it a try...

 

[Fusion Ed]

ECU doesn't learn on these cars. Its a static value. It is important to get right too or problems like this will happen. Only way to get it right 100% is to plug a computer into it and set the value to the nissan specs, but for most using a multimeter can work.

 

[wrc]

I'll bring a spare tps up with me on the 1st Ed just incase. As I said I have adjusted it via multi meter but that's never gonna be as good as doing it through a computer.

 

[PobodY]

I've cocked it up before now. - I think I set it with the ignition on, but the engine off.

 

[pulsarboby]

ive had this prob before with the 3071 internally wastegated
a lot of it is due to the way the boost controller is setup re surge/gain and the distance the solenoid is from the wastegate actuator
it also helps if you use quality vacuum line not that cheap crappy silicone shite
hope that helps fella

 

[wrc]

This problem has been with me when I had a stock t28 and still with me now running a 3071.

I'm pretty confident on problem solving but this one has me stumped. It's not drastically annoying but would be nice to get sorted lol

 

[Fusion Ed]

No problem, I'll sort it when your up!