17 replies to this topic

[Shaz]

Gents,

I have this stupid issue with my car that's starting to really annoy me.

When my car is on boost, its fine.
When you're not accelerating, and coasting, its fine.

When you touch your small toe on the accelerator and try and hold it at a certain RPM, it stutters, coughs, shits itself, and will just keep doing that, until you actually put your foot down. When you put your foot down, it will suddenly, and BRUTALLY come good, and smash 20psi no problems.


Now, I've replaced the AFM as I thought it was that issue. It was fine for a few days, then went back to what it was doing before. Maybe even worse off now.

Now this problem is very intermittent. It will do it sometimes, other times, it will be perfect. Its very strange.

Other symptoms include the car CHEWING through petrol (Which to me indicated that the car is running extremely rich (Petrol on rear bar above exhaust confirms this)). Also, if you're going up a hill in 3rd or 4th, and mash the accelerator pedal to the ground, you can kinda hear what sounds like a backfire, but from inside the motor, and then it goes fine.

Is it possible that because of the old bung AFM, my car has been running overly rich for too long, and perhaps fouled the plugs or something like that, which would cause the intermittent hesitations? Perhaps too much boost?

Also, skids didn't fix it. Just putting it out there before someone suggests doing skids. Will try and get a video this afternoon so you can see what I'm rambling on about.

Any ideas on where to look?

Cheers,
Shazza

[SAV84C]

Tried subaru upper engine cleaner yet? I had the same sorta problem in the Lib and the cleaner fixed

Im going to see big fish on Saturday, i think i have a few cans lying around

[Adam]

May be an obvious suggestion, but have you tried UEC and injector cleaner?



NINJAD!

[Shaz]

Injectors were completely acid bathed and flow tested before I put the motor in, so I would be very surprised if they were blocked after around 15,000kms.

Haven't done the UEC yet. Might give that a whirl this weekend.

Thanks fellas.

Cheers,
Shazza

[Adam]

Extra fuel could have fouled then? I have no friggin idea how they work, just guessing here!

Throwin some noob ideas around!

[RX25SE]

Before you start with the UEC, pull the plugs (all of them) and take a look at the way the engine is burning fuel.

If they are all the same (even if rich) at least you know its across all cylinders and you can start looking more towards AFM's and the like.


Do you have any codes? Does it happen more/less when the engine is warm/cold?

Is the CTS (coolant temp sensor) working correctly? This should also be checked at the ECU end.

[Shaz]

Before you start with the UEC, pull the plugs (all of them) and take a look at the way the engine is burning fuel.

If they are all the same (even if rich) at least you know its across all cylinders and you can start looking more towards AFM's and the like.


Do you have any codes? Does it happen more/less when the engine is warm/cold?

Is the CTS (coolant temp sensor) working correctly? This should also be checked at the ECU end.

Yeah, plan was to replace the plugs first, and maybe even replace the leads.
No codes. Happens equally when warm/cold.

No idea about the coolant temp sensor. Just out of curiosity, how would this affect the running of the car?
The temp gauge is working, and never goes over half.

[Grant]

A similar thing was happening to my car recently, but only after heavy rain and before the car was properly heated up. Running super rich, stuttering when trying to stay at a constant speed etc, but put your foot down a little bit and it was fine. Also after the car had heated up to operating temp it was alot crappier off boost than usual.

When we pulled my turbo off at the Mech and Tech day we discovered a big crack in the 90 degree rubber bend which is pre-turbo, but post-AFM. The crack was around the bov return and would've been causing all sorts of problems with my fuel mixtures, so I've since repaired it with some silicon tape (a new one to replace it arrived in the mail yesty) and it's come good, drives alot better and no more problemos

So what I would recommend is that you first pull out the spark plugs and check them, then check for intake leaks around your under-manifold intake. Or vice versa, whatever tickles your fanny.

Oh, and reset the ecu

[RX25SE]

No idea about the coolant temp sensor. Just out of curiosity, how would this affect the running of the car?
The temp gauge is working, and never goes over half.

The CTS signals the ECU on engine temp, yours may have a seperate sender for the gague only. Cold engines require more fuel, just like a choke in the good ole days of the carburettor.

A false signal of cold will cause the engine to run rich.

we discovered a big crack in the 90 degree rubber bend which is pre-turbo, but post-AFM.

This would mean the engine is receiving false air which the ECU has not measured. The ECU will only deliver the fuel for the air it can read, so normally this causes a lean mixture ( and may throw a O2 sensor code as a result).
A lean mixture is more likely to be noticed when driving.



Having said that, I would be checking all the intake ducting as Grant suggested.

[Marv]

When a coolant temp sensor goes the car will take ages to crank from cold, sometimes requiring you to start it with WOT to get it to cough into life. Two CTS have died in RS I've owned (similar wiring loom to V3) and both have done this. I don't think its anything to do with CTS.

I think you should put a fuel pressure gauge in your car and go for a drive. I'd bet it's fuel pressure regulator related as I recently had EXACTLY the same issue and it turned out the adjustment screw on my Sard FPR had come loose and it was running way too much pressure.

[RX25SE]

While you are poking around the fuel system, check the vac line to the reg for fuel.

If the diaphram in the reg leaks, fuel goes up the vac line.

[Murf B4]

stick a wideband in and have alook , sounds like rich/lean

[Shaz]

stick a wideband in and have alook , sounds like rich/lean

Yeah, I think Ben said something about the Walbro being too boss for the standard fuel setup or something, and thats whats causing the richness.

[Ben_20EJT]

Yeah, I think Ben said something about the Walbro being too boss for the standard fuel setup or something, and thats whats causing the richness.

yerp, think thats what it is, will have a b4 set up this week or next and hope to fix it. its kinda shit unless you on boost 24/7.

[aekOne]

its kinda shit unless you on boost 24/7.

so it's pretty useful then?

i had a walbro in my Legacy (V3 STI) and it was fine? it was ALWAYS smooth and not running rich

[Adam]

Yeah, I think I have one too.

With a stock looking FPR

[Ben_20EJT]

so it's pretty useful then?

i had a walbro in my Legacy (V3 STI) and it was fine? it was ALWAYS smooth and not running rich

not when this rig is my daily driver haha. i got this b4 pump for dirt dirt cheap so its worth a try, if its not the pump, the warlbro will be back in and its time to go hunting.

[aekOne]

the legacy was may daily driver, 21psi all day every day and loved every minute if it!