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 Post subject: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 3:00 pm 
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I Say: Fast, cheap or reliable. Pick any 2.
Vehicle: NotQik MY02 GT

Posts: 637
Location: Gold Coast
Hi All,

I have a minor surge when under light acceleration when off boost so idle up to ~3k rpm. It is quite minor & wouldn't be noticeable for a passenger but I can definitely feel it. Above 3K on partial accelerator is fine & WOT is fine the whole way through the rev range. Seems to be worse when more electrical load is on the system (air-con, wipers, lights).

This was also happening on my stock engine but I am using the same intake manifold & all electrics. Related parts I have replaced would be plugs, air flow meter, alternator. Alternator output is 13.5v on idle & 13.8-14.1 when driving @ 2krpm. I have upgraded alternator wiring (4 guage) with no improvements to the issue. Have done a UEC treatment which didn't give me clouds of white smoke so not sure if it really did anything.

Also I have a random hesitation when initially accelerating & seems to be when manifold pressure is going from vac to boost. This happens maybe once every 100kms of urban driving.

This has been occurring for years but as the issue is quite minor, I've never really done too much about it.

MY02 (2001) GT 5MT
Relevant? - Stock donk, TD-04L (12psi), catless uppipe with resistor mod (issue occurred on stock up-pie too), CAI (did it on stock intake too). New engine had coil pack seals replaced. A/F sensor in turbo manifold had been replaced also.
Body/majority of electrics have ~277000 km's on them.
No CEL's or errors from scan tool. Can sensors give incorrect readings without throwing errors?

Am fine to wrench on it myself & not too bad with electrics. Any ideas or recommendations?

Sorry for the long post but best to put all the relevant info together!

Simon


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 Post subject: Re: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 5:59 pm 
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I Say: Keep the hammer down
Vehicle: 02GT/6MT/Modtown

Posts: 31610
Location: SE MEL
When were the plugs last replaced?

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 Post subject: Re: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 6:05 pm 
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I Say: I like to breathe underwater ;)
Vehicle: '97 Forester

Posts: 1438
Location: SE Melbourne
QikGT wrote:
No CEL's or errors from scan tool. Can sensors give incorrect readings without throwing errors?

Yep they can. There's been heaps of examples of a sensor testing faulty but not throwing a code. IIRC, O2 & MAF sensors are prone to this

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 Post subject: Re: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 6:24 pm 
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I Say: Fast, cheap or reliable. Pick any 2.
Vehicle: NotQik MY02 GT

Posts: 637
Location: Gold Coast
Plugs were replaced when the engine was out approx 2000km's ago.
MAF was last replaced about 3000km's ago. Have gone through a few.

Nachaluva wrote:
Yep they can. There's been heaps of examples of a sensor testing faulty but not throwing a code. IIRC, O2 & MAF sensors are prone to this

A/F sensor has been replaced but haven't done o2 in exhaust. What range should it be in so I can test it?

Issue was happening prior to both.


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 Post subject: Re: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 6:54 pm 
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I Say: I am a Subarist!
Vehicle: 06 JDM STi Foz

Posts: 1952
Location: Sydney
MInor hesitation can be caused by a split intake inlet hose.
The stock intakes are prone to splitting before the clamp on the turbo intake.

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 Post subject: Re: Minor surging/random hesitation
PostPosted: Wed Apr 02, 2014 9:53 pm 
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I Say: Fast, cheap or reliable. Pick any 2.
Vehicle: NotQik MY02 GT

Posts: 637
Location: Gold Coast
It looked ok when taking it off to replace the engine recently but looks can be deceptive. I bought a new intake but on delivery, it was terrible quality & would have needed clamps on all the fittings as they were very loose so I chose not to install it.

I need to replace the turbo gaskets as I had to re-use the up-pipe to turbo gasket (Subaru said was in stock, engine was out, got there & they only had 1 - needed the engine back in that day) so I will look at getting another intake & do it one hit.

Any other ideas?


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 Post subject: Re: Minor surging/random hesitation
PostPosted: Sat Apr 19, 2014 12:07 am 
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Vehicle: My00 gt

Posts: 103
Location: Sydney
I had the same problem but surging worse even at wot, went through 3 mafs and then discovered I had a split in the inlet pipe just before the clamp on the turbo. replaced with an aftermarket silicone one and re calirbrate of the ecu 3000ks later it's running perfect. might be different to your situation but they sound similar. Hope you get it sorted.


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 Post subject: Re: Minor surging/random hesitation
PostPosted: Mon Apr 21, 2014 2:30 pm 
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I Say: I like to breathe underwater ;)
Vehicle: '97 Forester

Posts: 1438
Location: SE Melbourne
QikGT wrote:
Nachaluva wrote:
Yep they can. There's been heaps of examples of a sensor testing faulty but not throwing a code. IIRC, O2 & MAF sensors are prone to this

A/F sensor has been replaced but haven't done o2 in exhaust. What range should it be in so I can test it?

Sorry dont know that.

Sounds like the inlet pipe is a better place to start. Have a look at build threads on here. Most people seem to upgrade their inlet pipes to silicon as one of their first upgrades. Maybe do a search for silicone turbo inlet pipe

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 Post subject: Re: Minor surging/random hesitation
PostPosted: Fri Apr 25, 2014 7:47 pm 
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Vehicle: My00 s/turbo

Posts: 181
Location: Nairobi, Kenya
2 questions
1. would this affect fuel consumption (i.e. using lots of fuel if there is a split)
2. I looked on ebay, they are all for the Impreza, i remember reading that the engines are similar
will this fit MY00 SF5 Turbo ?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0475326851

if not which Impreza engine is the same?

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 Post subject: Re: Minor surging/random hesitation
PostPosted: Tue Apr 29, 2014 4:59 pm 
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I Say: Fast, cheap or reliable. Pick any 2.
Vehicle: NotQik MY02 GT

Posts: 637
Location: Gold Coast
I found one of the T pieces for the vacuum lines going into the intake to be cracked. I have repaired that which seems to have definitely improved the issue.

Looks like I'll need to check/replace all the vacuum hoses.

Can anyone tell me if/what this vac line should be connected to?
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