Merko

Hi folks, my GC8 is suffering from an issue that nobody seems to be able to solve, and have joined this forum in the hopes that someone here could throw some more ideas to me!

Firstly, the car has the following relevant mods:
- VF34 turbo
- 3" turbo back exhaust
- Walbro 255lph fuel pump
- Turbotech manual boost controller
- Overboost fuel cut is disabled
- Also running a standard Z4 ECU. Ie the car has not been tuned. However it is not leaning out. Wideband AFR gauge showed the ratios to be about 10-10.5:1 with boost at 16psi. So if anything it's a bit rich.

Now, I've had this problem for about 4 months now, and am all out of ideas. The car is a Japanese import with a V2 STi EJ20G. The car cuts power at about 5000rpm, as seen in this vid I made here:

http://www.youtube.com/watch?v=CwhgC...ature=youtu.be

The power cut is directly proportional to boost level. Ie. at 15psi it will cut at a little over 5000rpm, but at 10psi it will cut at a little over 6000rpm etc. So less boost = later power cut. Now I know what you're thinking; coil packs! right? well...

The following has now been replaced to try and eliminate the problem:
- Coil packs with known-working coil packs
- Spark plugs
- Walbro fuel pump was swapped with another new Walbro pump
- Cam sensor
- Crank angle sensor
- Made sure there's no rusty grounds for fuel pump wiring (apparently common issue).
-Plugged in my old (known working) W6 ECU

Also the ECU throws up no codes.

So I challenge you, Scoobynet, to solve what no one else has been able to! Even my local highly respected WRX mechanic is stumped Tomorrow we're plugging in an Apexi Power FC to rule out whether it's a mechanical fault as opposed to the ECU cutting power for whatever reason.

So, please throw me some ideas people before I push this ******* off a cliff

Thanks

SOLVED: Problem was high vacuum from higher boost sucking the soft turbo inlet rubber hose shut and starving the engine of air.

MartynJ

If you have access to one, try another ignition amplifier

Merko

Ignition amplifier? I've never heard of this before Is that the igniter for the coil packs?

Ok a quick google search suggests that this is for recent model WRXes, not GC8s, but I might be mistaken!

blackvenom

Are you saying its not been mapped?

Merko

Yes but this is not the issue. As stated, the ratios are more than safe.

Infected by sti

iTrader: (6)

It may show its running correct afr's but what about every thing else that goes with it, if you have a manual boost controller then the ecu is not regulating the boost, so if its not regulating boost could it be its picking up on knock/det and retarding timing as the ecu does not have full control so its not sure on what it's doing so to speak

Have you tried taking the manual boost controller off and connecting it back up to the ecu to see if the fault still persists?

Andy Stevens

Putting another turbo on and not mapping it is a bit mad, you have no control of fuel or ignition.

It does sound ignition related, the Ignition Amp as mentioned before lives behind the plate on the turret with the MAP sensor and Boost solenoid.

Merko

Ah so it is the igniter. Will try that next too

As for swapping the turbo with no tune, this is no big deal on early WRXes with 4 plug ECUs as they are much more adaptable than later WRX ECUs. If you look on the NASIOC forums you'll find it's pretty common practice. And the car runs and boosts perfectly otherwise and did so for quite some time. I guarantee lack of tune is not the issue.

Have not tried reconnecting the stock BCS. It is not recommened to do so after swapping turbos. When the turbo was first swapped though I still had the BCS hooked up and it worked fine except it only ran at about 9psi boost (it wasn't in limp mode, this was just the effect of the VF34) instead of the 12.78psi of the TD05.

dj219957

how have you removed the overboost cut?

Merko

One-way air valve on hose to MAP sensor. MAP sensor can therefore sense vacuum but not pressure. Works like a charm and has been done by many people. It's not oveboost fuel cut however as the Z4 ECU cuts at 15.65psi, and my car will cut even at 10psi.

Merko

K update: Car was still cutting with the Power FC. Think this rules out the ECU cutting power and means it's a mechanical issue.

I wasn't there when it was being tested, but the mechanic said the numbers spat out by the Power FC were all good, so it's a bloody mystery! Though he said the power kept cutting every time the injector duty cycle got to 90%.

Baz82

Maybe time to upgrade the injectors??Thos afr's where exactly is it doing 10.5-10

scubbay

iTrader: (61)

Have you ran a voltage check at the ecu before and during the missfire? Could well be corroded earths at the ecu. There are 3 earths I believe and a bad connection at one /two or all three will give you random hard to solve missfires. Do a voltage check first.

Claaarkio

iTrader: (1)

Maybe one dodgy injector?

Merko

Shouldn't have to upgrade injectors for less than stock boost. It was cutting at 10psi too. Those 10-10.5 AFRs from memory were as soon as it came onto boost at full throttle.

Unsure of voltage check, the car is currently being looked at. I have heard of the bad grounds not being a rare problem though. The car looks as if it sat idle for a few years in Japan, and has a fair bit of surface corrosion in the engine bay. Also looks like it's been exposed to lots of sea salt. So it would be possible. I have already cleaned up a few ground in the past. Do you know where the 3 ECU ones you speak of are located?

scubbay

iTrader: (61)

B43 pin 22 and pin 11, main earth B44 pin 14

retarded

I am thinking your experiencing boost spikes, just enough to **** off any ECU your using and fooling it into thinking its overboosted. A manual boost gauge might pick that up but more than likely it wont. However the ECU only has to read one erronous measure and it will cut boost to protect the motor.

What Im thinking is with the manual boost controller, its letting the turbo nail the pressure in a quicker way and as a consequence the ECU is having to overcompensate?
I guess one way to disprove the theory is to remove the manual boost controller, or dial it down a bit and see if it improves.

By the sound of it you have explored pretty much every other option. Only other thing that comes to mind is MAF and to be honest I dont know how sensitive the GC8 is to MAF inputs, but I do know that newage ones suffer badly from ****ty MAF inputs. Given the machine has sat idle for a while perhaps the MAF is ****ed?

Best of luck with it mate and I do hope someone can help you.

retarded

another quick thought - just saw your in Adelaide.. its bloody hot down in oz right now and you said you were getting 10.5:1 AFR... perhaps the hotter air is actually resulting in a real AFR of 9 or 8 or something? Has this problem only occured now its warmer down there? Hell i dont even know if massive overfueling is going to cause what your experiencing but it kind of fits in my mind... too much fuel - ECU cuts it a bit, you lose power. But then extra boost would reduce AFR - more air... yet you say it cuts out less if your running less boost... bugger.

Andy Stevens

That is not true, the algorithms for the JECS ECUs are very good on the 4 plug, but actually increase in capability with the 3 plug ECU and onwards, you would get way more out of your setup with a mappable option (ESL is twin map, mafless, knock control, full diag, 3d boost control, full logging, etc etc for 295GBP).

That aside, it does seem like you have a separate issue that needs fixing first, and it feels ignition related. Swap out the ignition amp. What is your plug gap set at? If it isnt at 0.6mm, bring it in.

Electrically, check cam and crank sensors for noise if you have access to a scope, and check the earths are good, especially the one to the back of the inlet manifold.

You could check your fuel return as well to make sure there isnt an issue there, but if it is still running 10s when the problem occurs, that seems less likely.

overboostUK

I had a similar problem... turned out to be the restrictor pill was too small and partially blocked! So small and so simple, yet so often overlooked!

Merko

Got the car back today. The guy who was looking at it can't find the issue. He's also tried changing the coil pack igniter, checked a few grounds, hooked up a fuel pressure gauge to see how it behaves on boost and that all seemed good. He's convinced the problem is electrical but can't find what it is. Sending the car to an auto electrician next week.

Also the problem 100% is not the injectors or lack of tune. Spark plugs are about 6 months old. They're NGK PFR6B with 0.8mm gap. Gap isn't the problem though, and as far as I know, platinum plugs shouldn't be re-gapped. There's no way in hell the spark is blowing out at 14-15psi and 4,800rpm like it's cutting now.

Also there is no restrictor pill as I'm running an MBC.

Could you be more specific as to the location of this ground so I can check it?

Claaarkio

iTrader: (1)

Have you tried different plugs? I changed mine 6 months ago then developed a misfire recentlym when i changed my leads, turns out one of the plugs was cracked! Easy fix in the end but I had dismissed them as they were so new!!

Dave

Andy Stevens

You can't really know the plugs aren't a problem unless you try reducing the gap to see if it has an effect, as well as inspecting them as mentioned above. That would be my next thing to try.

Shaks-STI

iTrader: (7)

Whats headers do you have?

JdcTypeR

iTrader: (19)

I had a similar problem and it was a loose earth on the inlet manifold

Stefen1

iTrader: (1)

I also had a similar problem - see thread https://www.scoobynet.com/general-te...over-5-5k.html

Bob Rawle

Running those mods you could simply be running the maf out of range, you quote that lower boost increases the point of it happening. there is setting in the oem rom file.

Andy this is probably what i discussed with you some while back.

As a thought.

cheers

bob

Merko

Bit of an update. To eliminate the coil packs being the problem once and for all, I've done the newage coil pack conversion. Although the car seems to fire up quicker with less cranking and is possibly slightly smoother at low revs, the power cut remains

The inlet manifold ground is fine. I'm not sure where to check the ECU grounds though? I understand where the pins are on the ECU, but where do the wires actually ground?

Regardless, I'm going to change the spark plugs over in the next few days to 100% eliminate them as the issue.

As to the AFM, I've had this issue for so long now that I can't even remember how I know it's good lol. I think at the beginning the guy that had a look at the car put a spare in and it solved nothing. Pretty sure the Power FC figures also showed it was good from what I recall the guy telling me. And if the AFM is maxing out, how do I solve this?

The car is booked in to see an auto electrician on the 8th of January so fingers crossed he can solve it, otherwise I don't know what else to try.

Also to the person who asked what headers I have, they are stock.

jason_2013

Check the silencer pipe in the rear exhaust box hasn't collapsed. Check all of the exhaust for restrictions.

bugblue1

iTrader: (3)

chap who was having his car mapped after me had same sort of problem turned out to be speed sensor...