Low RPM medium load knock...?

[cynner]

The other day I had been driving for around an hour (the car was at operating temperature) and then topped up the tank with fuel (just 1/4 tank of new fuel). When leaving the petrol station I notice a slight hesitation in idle, and soon after then I noticed my ECU data scan was showing -6 learned ignition timing off throttle and about -3 on low throttle. I drove it gently for the next 10 minutes then stopped the car for a few minutes. Upon starting again everything seemed to have resolved itself - go figure.

I've done around 500kms since then (mostly highway, had a long trip this weekend). This morning (again after having being driving for around an hour, so car at operating temperature) I filled up with fuel. This time pretty much a full tank (3/4 tank of new fuel). A few minutes after that, while driving along at highway speed the car felt like it lost a bit of power. I looked at the ECU data scan and it was showing -11 learned ignition timing.

I quickly pulled over and tried the same trick as last time - turning off the ignition and starting it again. This didn't fix the problem - even jabbing the accelerator pedal in neutral showed it was pulling -11 as soon as the revs started to increase. I inspected all hoses, inspected the MAF - everything seemed fine. I checked the ECU for error codes - nothing. As I was around 250km from home still (and no lap top to check sensors) - I ended up resetting the ECU to clear all learned values. This fixed the problem and it's been fine since then.

Any ideas? Maybe the fact that it happened after filling up with fuel is just a coincidence...

Why would resetting the ECU fix it? Could something cause the ECU to 'learn' values so out of whack?

EDIT: have been doing logging since this original post. It's knocking under medium load, low RPM - always around -3psi
Kim

[cynner]

Oh, also around the same time as this was happening - I noticed the airbag light stayed on a couple of times... (this happens sometimes when I have the ODB cable plugged in for the ECU data scan). I just happened to notice that while I was troubleshooting this fault, the airbag light did come on.

Maybe the ECU data scan is causing problems...

[dr20t]

How old is your fuel pump? And is it an upgraded or oem one?

[cynner]

Fuel pump is a few months old, and it's a Deutchworks DW65c...

Think it could be glitching?

[alexeiwoody]

Kim, and anyone else experiencing pulled ignition timing - don't be so quick to reset the ECU.

The whole reason the ECU pulls timing is because it thinks it sensed engine knock. Resetting it and making it run normal timing just means that - if your engine did actually knock, it will now have to knock again for your ECU to pull the timing and try and make it safer again.

On the other hand, if you leave it as is - the timing will get added back in automatically if the ECU sees no knock events for a while.

The airbag light comes on when you leave your tactrix plugged in for a certain amount of time, just the way they set it up. It's not a problem.

All I can think of to help - make sure it's not actually knocking. Get some knock ears onto it. If you're losing fuel pressure - check the pressure with a gauge, run some tests on that sucker. As Mick pointed out - plenty of problems with people's fuel pump installs, hopefully you noticed it early.

[cynner]

Yeah, I tried to avoid resetting the ECU - limped the car to a quiet stretch of road and troubleshooted for a while (starting/stopping - driving slowly). Was around 200km from home so in the end had to get back somehow Shame I didn't have the tactrix/laptop with me, as I would have taken a learning view screenshot.

Have just ordered and btssm dongle and a second-hand tablet - leaving the car parked in the garage until I get that set up, so I can monitor exactly what is going on.

I suppose an in-car fuel pressure gauge would be handy - anyone know of an electronic one that would connect up with the btssm somehow?

[cynner]

It's about a week later now... haven't driven the car every day - but noticed last night it has started shuddering slightly. Logs showed a bit of knock around 2000-2500rpm always at 0psi.

Matt has sent me a tweaked tune with less timing in those areas (just as a safety/bandaid fix) - but still need to figure out what is causing it... :/

[Robbks]

can't hear it?
wastegate chatter, or physical rattle setting them off

[cynner]

Nup can't hear it pinging...

New turbo was fitted not long ago - wonder if the dump pipe bolts have rattled loose a bit...

Or would the fact it's happening around 0psi suggest something in the turbo? (when manifold pressure transitions from vacuum to positive boost, is there something in the turbo that could rattle as there are no forces applied?)

[dr20t]

You need to isolate whether its just happening after you refill fuel or if you're only noticing it at that time and infact its knocking at all other times

If its related to refueling only then its fuel system related. Pressure is being lost and when you're refueling you release some pressure to refill, and potetially takes a little to pressurize again.

If happening all the time at positive boost change then could be a whole heap of things - maybe cl to OL transition / delay is too long, wg chatter, boost leak, etc

[Manaz]

Could it be dirt & crap in the bottom of your fuel tank, when you add fuel it churns it up a bit, and it takes a while to settle back down?

[cynner]

Had the car looked at... knock ears and digital fuel pressure gauge.

It's definitely knock/pinging (not wg chatter). Fuel pump looks very healthy, so it's not that. It always does it between -2 and -1 PSI (just below atmosphere... or sometimes closer to 0). Always around 0.8 to 0.9 load and between 1800-2100 rpm. I can bring the knock on by trying to hold it close to 0psi at low revs.

Matt thought maybe blow-by with the bigger turbo. Had the PCV valve looked at - opens/shuts fine and no oil in the breather hoses or top mount.

Replaced the crank sensor to rule that out... still no difference really.

Not quite sure what else to try, other than pulling timing out of the tune (apparently this will kill my fuel economy... better than that the engine though. Not sure why it's just started happening though). Maybe it was a bad batch of fuel that has put gunk in the system. Will try a couple of litres of e85 to try and clean things out...

[peadya100]

Interesting issue you're having!
Glad it's not the fuel pump. I just did mine and was worried the same could happen to me.

[dr20t]

Can you list your entire setup?

[cynner]

Yup, full setup:

Blouch TD05-18G Turbo (8cm housing, billet wheel)
Process West Top Mount Intercooler kit
Process West cold air intake kit with K&N pod filter
TCP Auto full turbo-back exhaust system with quad tips
Kobe Motorsports silicon turbo intake pipe (AVO)
Pierburg 3-port boost solenoid with custom-made stainless steel bracket
DeatschWerks DW65C Fuel Pump
Kido (Matt McLeod) ECU tune
New OCVs