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Vct Clicking On And Off/no Fuel Cut On Decel

89CAL

By 89CAL,
in Engines & Forced Induction

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89CAL Grand Master

89CAL

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As topic says, my car has started being a bit strange.

I was going through the R33 workshop manual and stumbled accross the procedure for setting idle and thought I'd check it. So unplugged one of the TPS plugs (manual says to do so, I always thought it was one of the AAC plugs you were supposed to disconnect) and anyway, ended up unplugging both and had the car idling for a bit, didnt seem to make a difference to the idle so plugged the TPS back in then all of a sudden my VCT started clicking on and off continually at idle.

Now it clicks off then about 1 second later clicks back on then stays on for 2-3 seconds then does it all over. Keeps doing it. Thought this was a bit weird but anyway took it for a drive and gentle driving around the VCT was staying on so I thought it wasnt a big deal

Then went for a drive and on downshifts it has no fuel cut on decel till it hits 2000rpm or so. and even then its unstable comes and goes

I played with the tune but set it back to how it was before I started and the only other thing I did was unplug the TPS plugs and plugged them back in (while running)

Anyone have any ideas?

So details:

1994 R33 GTST

Power FC

usually supporting mods

HKS GT2835KAI

If I unplug the TPS plug (on the wires not on the actual TPS) the VCT stops clicking on and off, but I'm guessing this is the plug that tells the ECU when VCT should be on or off

any ideas would be great :)

89CAL Grand Master

89CAL

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O.K I've done a bit more playing around and found that the idle is sitting above 900rpm and the VCT is on then every so often it drops below 900rpm and the VCT turns off then it quickly shoots back up over 900rpm.

So I think thats an idle issue, wether the VCT is causing it to hunt or wether the slight hunting is causing the VCT switching I'm not sure but I'll play with the idle anyway so hopefully that will fix that

Will this be my problem with the fuel cut or not?

Driving it just now I have worked out that the fuel cut works above 2500rpm then it starts injecting fuel again. My fuel cut on the power FC was set at 1300rpm and I dropped it to its lowest setting which I think is 900 and made no difference

rob82 Mentor

rob82

Posted
Posted

Put the decel enable back to 2500rpm with the disable at 2200rpm then disconnect the vct solenoid and the see how it idles. Sounds like you maybe dealing with multiple issues. Isolate the things that can affect the idle then work out what's wrong.

89CAL Grand Master

89CAL

Posted
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Posted

Put the decel enable back to 2500rpm with the disable at 2200rpm then disconnect the vct solenoid and the see how it idles. Sounds like you maybe dealing with multiple issues. Isolate the things that can affect the idle then work out what's wrong.

The setting is only for when the Fuel Cut is no longer active to prevent stall with the power FC. It's supposed to be on fuel cut till it hits that value.

Might unplug the VCT but and see what happens. Will try and borrow another TPS to see if thats the problem as well.

89CAL Grand Master

89CAL

Posted
  • Author
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Seem's to have fixed itself :S

I had a badly hunting idle but just wound the AAC valve out a bit and it was all good. I reloaded my last save of my tune onto it just to be safe but noticed nothing wrong with the monitering on FC-Edit

VCT stays off now unless a slight amount of throttle is applied (TPS V is about 0.48 when it switches on, so doesnt seem like the TPS was out of adjustment) So its back to normal

Seem to have decent F/C on decel again now.

Bit of a weird one, thought it was going to be a problem so happy it fixed itself

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