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Location:
Canberra
Registered:
May 2002
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Valve float: What does it feel like when driving? NOW FIXED!!!
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Fri, 03 December 2004 07:46
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I have an issue with my 4AGTE missing over 6000rpm. I've isolated any electrical faults or ignition/fuel inadequacies. The miss causes a significant hesitation, and a popping sound that you can hear from the tailpipe, and sometimes from the engine bay also.
This only happens over 14psi of boost, and gets worse from there as the boost is increased further (normally runs 19psi).
I'm starting to think that this problem is mechanical, and may even be caused by valve float, particularly since it only happens over 6k, with a lot of boost pressure behind the valve. It is an old bigport head that has probably done a lot of km's after all.
I've never experienced valve float & its associated effects, does the above sound like this?? I don't know heaps about valvetrain issues, so please throw your ideas/advice my way! 
[Updated on: Sun, 05 December 2004 02:39]
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 07:52
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What's your ignition system consist of, what's it like, and what plug gaps you using?
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 07:57
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GZE coilpacks (have tried 2 sets), factory brand new leads (tried another set of these too), two types of plugs, Denso PK20R8 platinums (0.8mm), and NGK steel BKR7E-11, gapped down to both 0.8 & 0.7mm for no improvement 
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 11:59
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Have you checked out earthing, as well as the voltage at the coil at the critical time?
Also, what ECU you using again? I had similiar issues with my Haltech a while back, only much worse, and am also trying to think up a solution to another similiar problem with a mates car, also with a Haltech.
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Location:
Brisbane
Registered:
October 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 13:20
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are u supposed to be running resisted plugs??
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 13:31
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Checked resistance of all earths, ran additional earths direct to the battery, added extra earth straps from the block to chassis etc, no difference.
Havn't had a multimeter on the coilpack whilst driving, I'm not sure how fast the readout would react, and I don't like keeping the foot buried for long at 6500rpm with it missing like crazy  I have however temporarily hard-wired the coil power (with a fused 6mm wire) direct to the positive battery cable, to be sure that there is no voltage drop issues.
I'm using Haltech E6K. Had issues earlier with trigger noise/interference, fitted an external ignition reluctor adapter (RA8) which fixed that problem, and now this pops up
What's going on with your mate's car & haltech?
[edit] MR DOHC: Yes, I am supposed to be running resistor plugs. Without them, ignition inteference with the ECU is even more likely.
Cheers
Phil
[Updated on: Fri, 03 December 2004 13:39]
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Fri, 03 December 2004 14:23
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I haven't had a chance to have another look at it for weeks, but it's a 7MGTE, fairly standard, with an E6S-8. Apparently at first the problem was intermittent, but then became pretty much constant - constant crossfiring. It's got the 3 double ended coilpacks, just like yours. With persistance, you can get it to start (amid backfiring etc.), and sort of run, but it alternates between 2 and 6 cylinders, won't idle properly, etc. I suspect it's a triggering problem. Whoever installed it made a bit of a butchery of the wiring, and also decided to mount a single hall switch down next to the crank pulley.
When 'running' (I use the term loosely!) it appears to be fuelling alright, and the laptop shows the correct RPM.
I'm thinking a rewire won't hurt the car myself...
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 00:51
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Sounds like a hairy one! Its a horrible job to sort through someone else's wiring abortion
I have 3 spare 4ag heads, I think i'll just pick the best inlet valve springs to swap over tonight & see if it fixes the problem.
I'll be real keen to see how your new cams go now, cause if I have to upgrade springs, then I may as well fit some flash cams at the same time 
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Location:
nth ringwood, Victoria
Registered:
August 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 03:04
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sounds like a ref or sinc problem ,etc the motor doesnt know when to fire and that is causing it to sound rough at high revs check your wiring from the disy and make sure it is sheilded cable ,i had the same problem with my motec a broken wire that was fine around town but put heaps of load on it and it started jumping around ,and its not the valve springs
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 05:16
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Been there, rewired with shielded cable from the CAS to ECU, earthed at the ECU end only, checked all for continuity, etc etc, still can't fix it.
I have swapped the CAS for another one too, just incase the reluctor pickups were not perfect, but that wasn't a problem.
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Location:
parra
Registered:
June 2003
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 07:41
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a similar thing happened to me fo a while...
it turned out to be interferance from the cas cables...
so they were replaced with sheilded ones then it was a problem with the temp compensation values in the ecu... they were sorted and it ran ok for a while...
about 3 weeks later the whole ecu shat itself and stopped pulsing the ignition output and it cooked my coil...
i was then forced to buy a new ecu...
i hope yours is nothing like that...
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 11:45
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| Quote: |
hope yours is nothing like that...
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So do I!
I have changed the inlet valve springs tonight, and will take it for a test run tomorrow. I'm not confident that it will make any difference, but at least it will put my mind at ease. 
Thanks all.
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Location:
tallahassee FL usOFa
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 20:37
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what's the compression???
don't bother with the springs.
you've got an ignition and/or fuel problem.
the rpm is nowhere close to max with even the wildest/strangest grind, and while you might have a single spring fail, it's beyond probability that all would fail or weaken up.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 22:59
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is the CAS hooked up the right way? ECU will either trigger on up or downslope of the AC wave, and i remember people having 4AG missing at higher rpm issues before when the CAS was hooked up backwards.
is worth a shot to try, even for one run 
as for valve float, i don't know about a boosted car, but in my K/3K/4K it was like hitting a brickwall. basically accelerating hard then it just stops gaining revs....
Cya, Stewart
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Location:
On your mum!
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sat, 04 December 2004 23:27
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TE72turbo,
I have been having the same issues recently and I have bought a heavier set of springs to fit (I thought similarly to you). As yet I have not fitted the new springs as I have been too busy.
I did have a similar problem a long time back (before I joined Toymods car club) and I did everything trying to track it down (this is how I wound up with the Wolf 3D, because in desperation I ditched the ECU). It ended up being the coils - I don't think that my current problem is coil related as the work is now shared amongst 4 of them - but I really don't know.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Valve float: What does it feel like when driving?
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Sun, 05 December 2004 01:33
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so what coil cahrging time are you both running? if the charging time is not enough to just saturate the coils, you may not be getting a big enough spark to bridge the spark plugs gap under boost conditions.. you did say you'd tried smaller gaps to no avail tho....
at 8000rpm, an engine cycle is 16ms? so between each firing event is 4ms, and coil discharge time shouldn't be more than about 1ms.... so coil charging time of 3ms?
Cya, Stewart
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sun, 05 December 2004 02:31
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If you want to change valve springs, just buy some aftermarket ones, they're not particularly expensive!
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Location:
Canberra
Registered:
May 2002
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Sun, 05 December 2004 14:44
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How'd you go replacing the springs with the head still on? I want to give this a go on mine (temporary thing until I take the head off and do it fully), but even though people say it's OK, I'm slightly concerned with accidently turning the valve a bit while the pressure is off and upsetting the seal. I was also going to throw in a new set of valve seals at the same time because I figure it can only be a good thing...
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Location:
Canberra
Registered:
May 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Sun, 05 December 2004 21:37
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Its no drama, its the second time I've done it, last time was to change all 16 valve stem seals.
I just use a threaded fitting in the spark plug hole, hooked up to the air compressor at 100psi to hold the valves up, and then use a section of aluminium pipe (similar diameter to the spring), and get a mate to lean on it to compress the valve spring to remove the two retainers. Its a bit fiddly, but works fine.
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Location:
On your mum!
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Sun, 05 December 2004 23:38
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oldcorollas- I am running 3.5ms; it used to have 5ms but we found more power keeping the charge time down
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Location:
On your mum!
Registered:
May 2002
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Re: Valve float: What does it feel like when driving?
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Mon, 06 December 2004 04:50
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| TE72_Turbo wrote on Sun, 05 December 2004 13:39 |
I cant stress enough to you all, that I have isolated all possibilities of an ignition or fuel issue  I have spent the last 2 months systematically working my way through all of the things you have each mentioned. 
anyways.......
ITS NOW FIXED!!!!
I replaced the inlet valve springs last night with a good condition set from a spare head, and it now revs cleanly with 20psi boost to 7500rpm. The springs that I removed from the head had sagged between 0.8 & 1.1mm from the specified free length.
Yellorolla: There's a good chance that heavier springs may fix yours also, like I said earlier, I had little confidence (but all hope) that valve springs really would be the issue, but this confirms it, and i'm a happy man
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Thanks Phil - I too have hope.
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Location:
Eskilstuna, Sweden
Registered:
May 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Mon, 06 December 2004 09:00
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| TE72_Turbo wrote on Mon, 06 December 2004 08:37 |
I just use a threaded fitting in the spark plug hole, hooked up to the air compressor at 100psi to hold the valves up, and then use a section of aluminium pipe.......
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This is a great thread. And what a cool idea above!!
Thanks gents
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Mon, 06 December 2004 09:47
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I was thinking pretty much of using the compressed air trick, thing is if I'm going to pull the head off and do it up not long after anyway, I might not even bother. Guess I'll just see how it goes!..
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Location:
Brisbane
Registered:
October 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Mon, 06 December 2004 10:06
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there is a special tool u can buy to compress the springs in the head, looks kinds like a 2 jaw pulley remover, just smaller, and once the collets are removed, the compressor and spring comes out in one piece and doesnt need to be re-compressed
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Mon, 06 December 2004 10:09
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I'm pretty sure said tool comes with a special price too 
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Location:
Canberra
Registered:
May 2002
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Location:
Adelaide
Registered:
May 2003
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Re: Valve float: What does it feel like when driving? NOW FIXED!!!
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Mon, 06 December 2004 20:25
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The two jaw things arnt expensive, but they only work on finned heads like the big inline 6 Ford heads. They tend not to work on the dohc heads because there is nothing to grip on. They certainly do not work on 4AGs.
The other thing is that replacing HKS valve springs that way is very perilous, or for that matter any heavier valve springs. I gave it a go once, and never again.
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