17 replies to this topic

[Lev]

hello all

 

i have a strange issue:

z22se with turbo conversion. boost is set to 1 bar. all is looking ok, car pulls strong and nice..untill it hits 6500rpm. there it stalls like the rev limiter were kicking in..only that is not the real case as it is set to 7200rpm. so started doing some tests and found this only happens if the engine is running on boost. what i mean: if i disconnect the the blower side pipe of the turbo eg at the throttle body then basically engine runs as NA, no issues hitting 7200rpm, or even 7500rpm. similarly, if under boost, at 6500 it stops revving further but if easing up on the throttle pedal then it again  starts creeping up till 7200 rev limit.

when opening the gap up a bit on the spark plugs, same issue happens around 4000 rpm..

 

so looks like this thing only happens when engine is running boosted. i have tried replacing the coil pack and went for coil on plug solution using coils from a 1.8 tfsi seat engine..but again, same stuff. tried a full blown race coil, no joy. so after all it does not seem to be related to the voltage the coil can produce.

 

the AFR reading does not indicate running lean so looks like still there is some sort of ignition when hitting 6500 and surely there is enough fuel getting in..almost comes out of the exhaust..

 

also tried removing the full exhaust system but again same symptoms.

 

i am using a standalone ECU with map sensor (sensor checked agains analoge gauge and were ok) and all seems to be ok, cannot see any particular error code either. my plugs are some iridium laser stuff but single-electrode..

 

and yeah, there is no ride by wire here.. bowden converted.

 

any ideas very appreciated

 

cheers

Lev

[vocky]

could it be blowing the spark out ?

 

try a smaller gap or triple electrode plugs

[Bargi]

What are the spark plugs and the gap of the plugs? I had similar problems under high load over 4.5-5k rpm with a 1mm gap. Closed it to .75mm and all good. For very high boosted engines .4mm is not uncommon.

[TFD]

Like said above. Stay away from iridium doubletriplemega platinum spark stuff. Get a decent 2 grade colder oem plug and gap to 0.7/0.8 mm.

 

Good luck.

[siztenboots]

Yep gap them much smaller , I run .65

[Nev]

I agree, it is likely to be too much spark plug gap, meaning that the inlet charge pressure combined with swirl as it enters the cylinder is stopping the spark. OR Do you have a MAP sensor that is triggering a "safety" feature in your ECU ? OR If you have modified your pistons, maybe they are not "squishing" the charge as intended for the head design. On my engine (Z20LET) the pistons are meant to be cupped at the edges to promote pushing the inlet charge towards the centre of the cylinder. However the pistons I actually use don't do this (which was a worry initially), however it does ignite fine in practice. I use NGK Iridium 9 (the coldest) spark plugs with a gap of 0.6 mm for 2.5 bar of boost and don't have an issue. However, my head and valves will be quite different to your's so the swirl design will be different.

Edited by Nev, 24 January 2015 - 07:46 AM.

[Lev]

thanks for all the replies.

 

i will try to close the gap a bit, not sure about the safety ECU feature and will check with 3-pole oem plugs.

 

indeed, i run wiseco 8.9:1 pistons and standard, unmodified z22se head.

 

cheers

[Lev]

i have tried triple electrode plugs (beru) with direct coil on plug ignition...and...no joy...darn it! same stuff: 6500rpm and it won't rev over under boost...

 

any further ideas to try/check are highly appreciated.

 

cheers

[TFD]

With what gap distance?

[Lev]

about ~0.5-0.6ish gap

[Bargi]

Can you get any logging from the ECU? What ECU are you using?

[siztenboots]

sounds like it might be firing the fuel injectors at 50% on each half cycle , rather than full sequential injection. on the z20let this happens when the ecu can not determine camshaft valve timing , due to the cam sensor. as a result it does not know which cylinder out of each pair is at tdc and on a induction stroke , or a power stroke.

[CraigyT]

Have you tried a recent compression test? I had a similar problem a few years back,turned out the head was lifting off the block. Also try a set of cold single electrode plugs. I use ford 071c plugs gapped at .6 and they work well.

Edited by CraigyT, 05 February 2015 - 07:47 AM.

[2-20]

I had a similar trouble on an Lancia Delta integrale.

The problem was the cranck sensor gap being too large (but within the tolerances at the max value).

Took me a while to sort it out as the gap looked correct.

Lancia asked for the ECU replacement at that time...

[Lev]

well, currently using ignitech ecu which is possibly not widespread on cars..

 

the service dudes suspect the ECU to be a misfit after all and they now are to replace it. hopefully that will resolve it....

 

not sure if this would actually be a sensor issue as the engine happy to rev to even 7500rpm if not on boost (ie compression side pipes disconnected)

[Lev]

so looks like the bug is found...revving to 7000+ now also ok

[Bargi]

And the problem was?

[Lev]

well, wanted to do some testings myself before....and then once indeed i can rev it then confirm...

 

however some other glitches now resulted in same situation so can only believe what the tuners found:

basically the problem is that above ~6500rpm engine pushes out such amount of exhaust gas that it cannot fall through my turbine wheel which pretty much stops the show. and as not having any boost controller we added a vacuum valve that would open up the waste gate a bit at ~6000 to reduce the amount of gas passing thru the turbine wheel. It worked, tuner hit ~7100rpm, but out of pure luck found a broken pipe, so after changing it the boost immediately jumped up a good 0.3 bar all over so that pretty much left the top rpm at ~6500...

 

so possibly i would need a proper electronic boost controller..

or

simply do with ~6500rpm as limit. I might simply go that way. car measured ~330bhp/400Nm WITH the busted pipe letting boost out to the atmosphere..

or

a bigger turbo, but actually i just moved to a smaller one: garrett gt2560r as this spools up so early essentially pretty much like driving an NA car. I had ~1bar around ~2000rpm with the busted pipe..so this one has a huge usable range: ~1500rpm--6500rpm...but if feel like sacrificing some boost at the lower range then can adjust the valve and again let some extra gas out from ~6000 thus again make it possible to hit ~7000rpm.

 

cheers

L