Hi all. I've started having the very weird problem in the past few weeks. My Z suddenly won't rev past 5000RPM either on heavy boost with my foot planted or gently creeping up there on light throttle.

 

On heavy boost (foot to the floor) sometimes i'll just get a sudden cut out at 5000RPM. Other times it just get to 5000RPM and sound's like it's hit a limiter and you get the BRRRRRRRRRRR noise!

I've done the usual and cleanned all the connectors, PTU, MAS connector ETC with electrical contact cleaner. They we're clean anyway to be honest with no Green corrosion on them.

It idles smooth, boosts strong with no hesitation up to 5000RPM.

Any idea's what it could be please? Thinking possibly the MAF could be on it's way out possibly or maybe new spark plugs?

Don't wanna go spending out on Plugs and stuff only to find it's the MAF that needed replacing!

 

Hope someone else has had this problem at High RPM and managed to fix it, Please HELP!

have you checked for boost leaks? sounds like your in some kind of saftey mode.

As above, sounds like a vac/boost leak, maf would limit to 2.5k if dead

Draxan had an issue with high rpm cut out and it turned out his oil was too thick and meant the valves couldn't move quickly enough. Just a thought.

have you checked for boost leaks? sounds like your in some kind of saftey mode.

Yeah no boost leaks, checked that and like I've said it'll do it just on gental acceleration at 5000rpm running no positive boost what so ever. Very weird!

Draxan had an issue with high rpm cut out and it turned out his oil was too thick and meant the valves couldn't move quickly enough. Just a thought.

 

Thanks for your reply but put new oil in recently, the same brand as I've been using for the past 12 years! No issues there!

Yeah no boost leaks, checked that and like I've said it'll do it just on gental acceleration at 5000rpm running no positive boost what so ever. Very weird!

 

so turbos not kicking in...

 

how did you test for boost/ vac leaks?

CAS ? My Chronic misfire that started at that rev range was a detoriating CAS

 

Does it do it in every gear ?

 

Mine did

Blocked cat ?

pipe of actuater or a turbo.

Comments Jeff ? Took long enough to find mine with it only happening at high revs didn't it !

 

And that isn't a complaint !

so turbos not kicking in...

 

how did you test for boost/ vac leaks?

 

I have a boost leak tester that plugs into where the airfilter goes and presurised the system. Also have special smoke matches. Yes HKS 2530 turbo's kicking in all right! But as i keep saying it does this off boost as well!

CAS ? My Chronic misfire that started at that rev range was a detoriating CAS

 

Does it do it in every gear ?

 

Mine did

 

Yeah guess i might be that. It only used to do it occasionally in the summer and then it would be ok again. Started to do it more often than not now!

Check the MAF as well but mine started out with an occasional misfire under load at about 4500 - 5000 rpm going up through the gears I only managed to the power by short shifting ! when it finally gave up the ghost it wouldn't have any Power at all from starting cold and I mean NO power, Hardly moving, until it the engine warmed up and then it suddenly came ok. Turns out that gave Jeff the Clue he was looking for The falty CAS was 15 degress out when cold ! All we concluded was that that had been the problem all along and it had started misbehing at High Revs in normal running

 

Some mornings it would start off ok but as soon as any dampness in the air it came back

What i have a hard job understanding is how does the cas sudenly become 15% out if youve not touched it>.

What i have a hard job understanding is how does the cas sudenly become 15% out if youve not touched it>.

 

Yeah must admit in 12 Years of Z ownership i have never touched the CAS or taken it off so can't see how it can be out. Also use my Z as a daily drive!!

What i have a hard job understanding is how does the cas sudenly become 15% out if youve not touched it>.

 

Now that is a very good question and I can't answer it... however I can confirm that it does happen.

i bought an almost bran new one and it was finer for a year or so then a month after my new engine sent it it just jumped 15% and had to be replaced... really didn't help my turbos at all. :(

Well it was making the ECU think it was 15 degrees out I meant ..... electronics playing silly buggers

Have you checked the ECU for fault codes?

Have you checked the ECU for fault codes?

No not yet so gonna get it on the ConZult at the weekend. Weird thing on the drive home from work tonight it was fine again. Full boost all the way to 7200rpm. Bet it won't do that tomorrow tho!

That's exactly what used to happen with mine !

 

It could start off fine and then after an hour so it would suddenly play up. Usually when I needed the power ! That's why, as I said above, I resorted to short shifting to get around it There is enough torque available for that strategy

Ok this problem can be difficult to track down, having said that I know from the experience we had with Tony`s zed and that of another customer both the afm and the cas unit can be the culprit.

 

Some years ago I had this problem with a customers zed, his issue was quite specific though and basically regardless of speed or gear when ever the engine hit 4k rpm it was like an anchor had been thrown out the back end! no issue before then and the ConZult was great help as it showed the afm voltage dropping off at that point, the customer had spent money on plugs, fuel filter and pump etc plus other service items.

 

So the afm was the culprit and was an easy find in the end, just had what I referred to as a dead spot in the output voltage at 4k? strange but that was that.

 

With Tony`s it eventually turned out to be the cas unit, this was much harder to find as nothing stood out as a problem, all sensors were fine no output drop out strangely there were many red herrings too, when the fuel return feed was clamped off temp to maintain fuel pressure it was better, fuel pump issue? fuel pressure regulator issue? then lowering the boost made changes, it all got very confusing, the cas unit never seemed to be in the frame as it always showed perfect readings, even more so there was odd occasions when the problem would not be there or the rpm would raise.

 

Finally the only way forward was to start over and went through the normal start point checks, timing fuel , boost leaks etc. and then I saw it, whilst ticking over on an indicated 15 deg as it should but when raising the revs quickly the timing actually retarded !! if revved slowly it advanced !

 

The cas unit was swapped out and problem solved! was a weird one and there was no external issue with the cas unit, the spindle was fine no play and smooth to turn, thats the trouble with electronics!!

 

So my advice is get a timing light on it and see if you get the retardation when revving up, may be worth borrowing a good cas unit to try.

 

The question of how can cas units go out of timing is a simple one, over time the cam belt will stretch.

 

Jeff TT

The cas unit was swapped out and problem solved! was a weird one and there was no external issue with the cas unit, the spindle was fine no play and smooth to turn, thats the trouble with electronics!!

 

So my advice is get a timing light on it and see if you get the retardation when revving up, may be worth borrowing a good cas unit to try.

 

The question of how can cas units go out of timing is a simple one, over time the cam belt will stretch.

 

Jeff TT

 

Brilliant advice as always Jeff, thank you so much. I am due for a cambelt change early next year so guess mine could be stretched. Will get a timing light on it and check at the weekend. Also think I'm gonna replace my MAF as the sudden anchor been thrown out the back you described is exactly what I get sometimes. Its bloody Scarry when you get a gob load of power at 1.2 bar all the way to 4 or 5k then sudden power loss! Feels a boost pipe has suddenly popped off. Once I've sorted the problem I.e replaced the defective part(s) i'll post back here with the fix in case anyone else gets this. Thanks again

Ok this problem can be difficult to track down, having said that I know from the experience we had with Tony`s zed and that of another customer both the afm and the cas unit can be the culprit.

 

Some years ago I had this problem with a customers zed, his issue was quite specific though and basically regardless of speed or gear when ever the engine hit 4k rpm it was like an anchor had been thrown out the back end! no issue before then and the ConZult was great help as it showed the afm voltage dropping off at that point, the customer had spent money on plugs, fuel filter and pump etc plus other service items.

 

So the afm was the culprit and was an easy find in the end, just had what I referred to as a dead spot in the output voltage at 4k? strange but that was that.

 

With Tony`s it eventually turned out to be the cas unit, this was much harder to find as nothing stood out as a problem, all sensors were fine no output drop out strangely there were many red herrings too, when the fuel return feed was clamped off temp to maintain fuel pressure it was better, fuel pump issue? fuel pressure regulator issue? then lowering the boost made changes, it all got very confusing, the cas unit never seemed to be in the frame as it always showed perfect readings, even more so there was odd occasions when the problem would not be there or the rpm would raise.

 

Finally the only way forward was to start over and went through the normal start point checks, timing fuel , boost leaks etc. and then I saw it, whilst ticking over on an indicated 15 deg as it should but when raising the revs quickly the timing actually retarded !! if revved slowly it advanced !

 

The cas unit was swapped out and problem solved! was a weird one and there was no external issue with the cas unit, the spindle was fine no play and smooth to turn, thats the trouble with electronics!!

 

So my advice is get a timing light on it and see if you get the retardation when revving up, may be worth borrowing a good cas unit to try.

 

The question of how can cas units go out of timing is a simple one, over time the cam belt will stretch.

Jeff TT

 

so what would be external issues with this unit to look out for and if youve had a recent cam belt then the problem would seem to be even harder to dignose i guess. might invest in a spare new unit. might save a lot of troble in the future should i need it.

No external signs on the CAS !