80 replies to this topic

[Jimbo]

Gents,

I have a bit of an issue which has the better of me and I cannot figure out what it is.

Coasting at freeway speeds (100kph+) and staying off boost is rough as guts.  Best way I can describe it, the car splutters and chugs when you try to hold a constant speed off boost. As soon as you press in boost it disappears, so to remain comfortable, I'm constantly having to regulate the throttle above 0psi which is a pain in the arse on a highway. TT, so no cruise control, but it wouldn't make a difference anyway.

This issue never presents itself unless I'm doing freeway speeds at 100kph+.

This behavior was present before I swapped the engine out, so it rules out any sensors attached to the engine. My ECU is clear and it never triggers a code related to this. I replaced the AFM with a new unit about 3-4 months ago, but again the issue was present before that also. 

The only thing I can think of is maybe the BOV is adjusted too loose for the extra volume of air at those speeds. It might be playing on the BOV piston between putting +ive pressure in the top port and +ive pressure on the piston, TMIC side. The only other 2 things I can think of are O2 sensor or BCS, though I would think any issues related to them would be present at all loads/speeds.

Anyone have any other suggestions? This one has me stumped.

[Barbbachello]

Convert to single

nah but srs thats a tricky one. Fuel filter clogged maybe? Once it gets on boost the FPR ups the pressure and can make it do? 

[natho]

if you think it's the bov, remove it and block it off temporarily.

[duncanm]

Undo your line 10 mod, or do you have an aftermarket BOV?

That's an easy thing to try.

I have something which can only be termed boost stuttering at positive boost threshold some times - which I put down to the line 10 mod

[duncanm]

BTW - my cruise control needs some improvement. The incremental throttle steps are too large for the sensitive throttle at typical cruise speeds - so it gets into a slow on/off throttle cycle, and needs a little manual trim to settle down

[duncanm]

Oh - and I'm guessing cruise on the highway is when your torque converter is locked up - that's probably why you notice it then

[Robbks]

Jimbo,
Do you have a wideband?
Or RomRaider to log the O2 Corrections.

What is the vac gauge doing when it surges?

It sounds like a closed loop fuelling issue to me.

Plug your BOV to rule that out.
Could be Fuel Pump Controller playing up.

Wind up the ECV to make sure that's tight and not blowing open with the exhaust flow.
Block the secondary BPV to make sure that's not causing weird things.

Do you have a catch can plumbed in?
May be some weird flow going on if you've plumbed it backwards with regards to the PCV.

Force the ICV Closed to make sure you're not pushing flow out of the IC.

Convert to single or H6 with GT35
Or buy a Diesel!

[Niko]

Have you tried swapping in your lawn mower engine?

[Jimbo]

Good ideas all. What has me most baffled is the fact it only shows up at high speed? Why would it be present at 100kph+ and mot any less?


Fkn lawnmower.

[duncanm]

Higher pressure in intake (pre-turbo) - easier boost amongst other things, locked converter, higher engine loads at static revs.

[Jimbo]

Higher pressure in intake (pre-turbo) - easier boost amongst other things, locked converter, higher engine loads at static revs.

That was my line of thinking which made me think the BOV needed some adjustment. I can't recall it doing it when I had the stock unit on it (using a GFB T9000).

Rob, when the car is presenting the symptoms of the issue, the vac/boost gauge needle is dead still in relation to my throttle position. Doesn't fluctuate or show any movement in relation to the roughness off-boost. However, if it was an issue with the BOV wouldn't the gauge be bouncing around a bit? If the gauge isn't reflecting the symptom, fueling is my next guess.

No catch can, wideband or fancy ECU reading things. Everything 100% stock in the engine bay. ECV and ICV working perfectly, VOD is minimal and it all runs, in my opinion, to it's most optimum performance.


It's a bit hard to describe what it's doing exactly, but any speed higher than about 90kph it does it. As soon as you try to regulate the throttle off-boost (less than 0psi) to cruise along, it shudders roughly, as soon as you apply throttle it smooths out again instantly and runs perfectly. It's either on or off. There is absolutely no problem present at everyday loads and speeds (up to 80kph)

 

[Robbks]

Check the FPR vac line.
Steady vac gauge suggests fuel or less likely, IGN to me.

[Jimbo]

Brand new line on the fpr, first thing i did on the engine swap.

I did reuse my spark plugs on the new engine. They're just the standard ones Subaru sell, PFR6B's?. Not irridiums or whatever, ill have to check the invoice to confirm. Possibility?

[Robbks]

Throw them in the bin. Use BKR6E's

Check the fuel pressure.
Is the reg the same?
I.e the old 380cc greys used 38psi.
440's used 42.

Could be the pump controller.
The workshop manual details the operation of the controller and it's effect on pump flow.
Could be a changeover point causing fuel pressure to fluctuate.

It it's just got TT AIDS.

[Jimbo]

Throw them in the bin. Use BKR6E's

Check the fuel pressure.
Is the reg the same?
I.e the old 380cc greys used 38psi.
440's used 42.

Could be the pump controller.
The workshop manual details the operation of the controller and it's effect on pump flow.
Could be a changeover point causing fuel pressure to fluctuate.

It it's just got TT AIDS.

Different fuel reg. This problem existed before I swapped the complete motor in, so in theory, should eliminate anything physically attached to the motor.

I'll have a shot at adjusting the BOV first, then look into the pump controller. Probably not a bad idea to replace the fuel filter aswell. Though, as this issue is only present at highway speeds, which I don't do that often, it's no big deal. My fookin steering rack has decided it doesn't want to play anymore so need to address that first.

This issue is more of a nuisance than anything detrimental!  

[Jimbo]

So bringing this one up, again.

It seems the issue is starting to affect the car at lower speeds now, whereas it used to only show up cruising at 100+ clicks. Same symptoms, but now at much lower speeds. It's intermittent and doesn't occur all the time. 

I'm going to have a crack at the fuel system this time. I'm thinking the fuel pump/filter and fp controller are the way to go, along with some new spark plugs as per Robs suggestion. From a brief squizz at the workings of the controller and previous descriptions given, it acts as a resister and signals voltages to the pump based on engine loads.

If it was playing up, it would describe the feeling I'm getting while driving. Apply throttle slowly and smoothly held in gear (usually 3rd on the 4EAT), boost comes on nice and steady, then all of a sudden it hit's 2500/3000rpm and it feels like a switch turns on and the mixture "feels" punchier. It's the best way to describe it. 

I'm thinking the controller is delaying the load signal to the pump so when I'm getting up it, it's lagging behind on the pump speed, relative to the load. Wish I still had a freeking wideband.

Do I sound like I'm making shit up? If I were to replace the controller, what would be compatible?

Le Edite: Found it

[duncanm]

could be worth trying -- just hook the pump up to the 12V supply to the controller. It'll run at 100%.

[natho]

hows it idling? do you have a wideband?

[Jimbo]

Idles fine, don't have a wideband. Just going from "seat of the pants" feel.

At this point I can rule out anything attached to the engine as this existed before and after the engine swap.

The problem is pretty minor when you look at it from an everyday drive-ability perspective, it's just annoying. It just feels like the fueling or ignition is a bit off.


Just ordered a new fuel filter and I'll try out another controller or running 12v to the pump as you have suggested Dunc. Process of elimination!