What does lean fuel / pre igninition knock sound like?

[JD159]

Does it sound like the rattle of a spray can? Increases slightly with rpm? Present under partial throttle around 1.5 to 2.5k rpm? Present under load and going up hill?

[v2rocket_aka944]

Yes.
More prevalent/noticeable at low RPM 1500-3000rpm or so.
North American 944s are so conservatively tuned you have to be using very poor octane gas or indeed be running quite lean and hot going up a hill to have it happen though.

[JD159]

Originally Posted by v2rocket_aka944

Yes.
More prevalent/noticeable at low RPM 1500-3000rpm or so.
North American 944s are so conservatively tuned you have to be using very poor octane gas or indeed be running quite lean and hot going up a hill to have it happen though.

I've got a chip that never quite felt right and my previous mech dialed back the fuel on the dme slightly. Going to have to investigate this further. I thought it was a lifter but I'm questioning that assumption.

[JD159]

Originally Posted by v2rocket_aka944

Yes.
More prevalent/noticeable at low RPM 1500-3000rpm or so.
North American 944s are so conservatively tuned you have to be using very poor octane gas or indeed be running quite lean and hot going up a hill to have it happen though.

Let's say it was pre-ignition, why would I hear the spray can rattle sound when reversing up a steep incline at low RPM, but not when level and loading the engine with the emergency break??

[Noahs944]

In my 944 with chip & higher compression, detonation sounded like rust flakes rattling in the muffler when under load. To determine if it's really occuring, the easiest solution is to add octane booster of race gas/very high octane gas.
Solutions typically are:
Feed it higher quality gas
retard ignition advance
reduce cr ratio
Richen afr
Add meth and h20 kit

[v2rocket_aka944]

With that description you might be hearing your CV joints clicking.
They can make all kinds of noises as they wear...

[JD159]

Originally Posted by v2rocket_aka944

With that description you might be hearing your CV joints clicking.
They can make all kinds of noises as they wear...

Heard that noise before, not those.

Feathering throttle. Acceleration. Sounds like the ball in a rattle can. Up hill. Not at idle. Not while revving. Not when ebreak is engaged and loaded.

[djnolan]

Diagnosing running problems is one of the joys of owning a car that does not have OBD2 to set a code or two and give you some clues. If you are sure it is engine related and it is doing it consistently the same, then start by checking the plugs for a fouled, lean, rich, pre-det or other signs.

upload a picture, here is a good spark plug chart:

[JD159]

Car is currently at the shop getting the clutch done.

We will be investigating this issue.

Does this sound more like a lifter or a fuel issue?

[thomasryan]

running too cool, short trips or running fat can cause a carbon build up in the cylinders which effectively raises the static compression.

if you want to try the shade tree method, fill the washer reservoir with distilled water and run a line to a manifold vacuum port. give the switch some staggered half second burst at freeway speeds. don't flood the cylinders and bend the connecting rods.

[Noahs944]

Knock typically comes under load when driving.

Whereas lifter problems often are evident when you start your engine & you can hear on the top end of your engine when you lift you hood even at idle.

When you drive with lifter issues you'd sense it in front of you, whereas the only experiences I have had with pre-detonation is again hearing it in my muffler (sounds like sand being sprayed in the muffler). It gets worse with cheap low octane fuel & better with hi test high octane fuel. You won't get detonation problems at idle. Only when you are hill climbing or laying rubber down, trying to accelerate.

[JD159]

Originally Posted by Noahs944

Knock typically comes under load when driving.

Whereas lifter problems often are evident when you start your engine & you can hear on the top end of your engine when you lift you hood even at idle.

When you drive with lifter issues you'd sense it in front of you, whereas the only experiences I have had with pre-detonation is again hearing it in my muffler (sounds like sand being sprayed in the muffler). It gets worse with cheap low octane fuel & better with hi test high octane fuel. You won't get detonation problems at idle. Only when you are hill climbing or laying rubber down, trying to accelerate.

I was getting the noise only under load in particular when reversing up a steep incline. The noise however did sound like it was in the engine bay, not the muffler.

[Noahs944]

That's not regular knock from a semi-healthy stock engine.

[JD159]

Originally Posted by Noahs944

That's not regular knock from a semi-healthy stock engine.

It's got a chip, S2 intake (on an S) and I believe the previous mech leaned out the FQS.

Also not the rod bearings. Just had those changed. Looked great. Oil pressure is good. Hoping it's the fuel

[djnolan]

I have a Rouge MAF that has some knock at idle and under acceleration. I can easily swap in the original MAP because I have a 2nd DME (original) and when I swapped it, the knock is gone.

When you are running any type of custom setup you can bet you will suffer driveability issues.

All I can advise is to make sure everything electrical and vacuum is in top shape. Sensors, ignition, injectors, wiring, lines...

[dgcantrell]

Pull the spark plugs and if any of them look "new" or the one in the picture below, it's glazed and will not deliver a hot enough spark to ignite the fuel being dumped into the cylinder under acceleration. I chased this problem on my A8 a while back. Threw $500 worth of parts at it before I figured it out.

click image upload

[JD159]

Will be checking the plugs as soon as I get it back. I dialed up the fuel to +3% but I'm still getting the noise.

If I'm cruising in second or third and go from 2k rpm to 2700rpm, it makes the clacking. It only makes the noise if I am pressing the throttle. If I let off the gas and the revs come back down the noise immediately stops.

Anybody have any ideas?? If I can't get this sorted I'll likely part the engine...

This is also a chipped 944 S. So it apparently has knock sensors.

[jhowell371]

Your fuel is too poor to handle the amount of timing advance the chipped ECU has dialed in. The S was known for having an overly aggressive timing retarding when knock was sensed so it will run on crappy fuel. It re-advanced slowly to normal in small increments leading to some performance issues. This was addressed with the S2 but don't know if you can use an S2 ECU in an S. You probably don't want to hear this but go back to your stock chip, or boost the octane rating of your fuel with an additive. Severe knocking can damage an engine quickly.

[JD159]

Originally Posted by jhowell371

Your fuel is too poor to handle the amount of timing advance the chipped ECU has dialed in. The S was known for having an overly aggressive timing retarding when knock was sensed so it will run on crappy fuel. It re-advanced slowly to normal in small increments leading to some performance issues. This was addressed with the S2 but don't know if you can use an S2 ECU in an S. You probably don't want to hear this but go back to your stock chip, or boost the octane rating of your fuel with an additive. Severe knocking can damage an engine quickly.

But would I be hearing the noise with a knock sensor??? Isn't that the purpose of the sensor??

[JD159]

I'm also running an S2 intake, which has a larger throttle body and should be flowing more air. Would that increase airflow enough to mess up the ratios and require higher octane??