I've got Spark Knock!

[BigJ]

I'm intrigued by BigJ's "octane sensor" explanation... does anyone know if there is an "octane sensor" in the fuel system? (my experience is that the computer sets the timing based on the knock sensor feedback... )

Nooo I didn't mean to imply there's an "octane sensor". You're experience is exactly mine, and its what I was referencing.

As I understand it, an ECU will advance spark to the point of auto ignition (as sensed by the knock sensors), then retard the spark until the knock sensors detect things have quieted down (usually with some added buffer away from the 'edge'). It does this dynamically and iteratively across the RPM scale and MAF inputs since, depending on your state's laws, 87 octane (for example) could actually be as low as 84 or as high as 91. It needs to handle a wide range of octanes and fuel qualities.

That's all I was trying to say.

 

[FSM06]

I heard a slight rattle type sound when i tap the gas quickly and especially when coasting.

I don't mean to step into a perfectly good conversation, but I have one quick question...........I don't believe I have ever heard spark knock under the two conditions mentioned above, especially when coasting. Are we SURE we are after spark knock?

Spark knock generally occurs at the top of a hard accelleration or under a heavy load and a minor amount IS acceptable. If it is spark knock and it is excessive, I would agree that a faulty knock sensor could be suspect.

FSM

 

[MarkT]

Nooo I didn't mean to imply there's an "octane sensor". You're experience is exactly mine, and its what I was referencing.

As I understand it, an ECU will advance spark to the point of auto ignition (as sensed by the knock sensors), then retard the spark until the knock sensors detect things have quieted down (usually with some added buffer away from the 'edge'). It does this dynamically and iteratively across the RPM scale and MAF inputs since, depending on your state's laws, 87 octane (for example) could actually be as low as 84 or as high as 91. It needs to handle a wide range of octanes and fuel qualities.

That's all I was trying to say.

I got that... and all I was doing was wondering if there was such a thing! These new Fords have all sorts of cool new technological marvels that it would not surprise me if there was an octane sensor! :mrgreen:

 

[BigJ]

I got that... and all I was doing was wondering if there was such a thing! These new Fords have all sorts of cool new technological marvels that it would not surprise me if there was an octane sensor! :mrgreen:

 

[MarkT]

I don't mean to step into a perfectly good conversation, but I have one quick question...........I don't believe I have ever heard spark knock under the two conditions mentioned above, especially when coasting. Are we SURE we are after spark knock?

Spark knock generally occurs at the top of a hard accelleration or under a heavy load and a minor amount IS acceptable. If it is spark knock and it is excessive, I would agree that a faulty knock sensor could be suspect.

FSM

I have. A quick burst of that "marbles rattling in a tin can" sound when getting back on the throttle lightly. It would quit after a brief second. Didn't do it under heavy load. Only light load acceleration. It was a Chevy 4.3 HO. I had a GM scan tool at the time which did not detect any faults. But the fuel trim was at max rich. So I started looking for vacuum leaks. Turned out to be a defective (electronic feedback) EGR valve which was allowing way too much air into the engine but was acting normally "electronically". (I found it by blocking off the EGR with a homemade plate. Instant fix. New EGR valve and all was good.)

Since RIKU said the dealer tech test drove and confirmed the noise as "spark knock", didn't question it.. but of course it could be something else... good point...

 

[Falcon]

I love all the combined knowledge represented on this forum!

Know what you mean Cowboy. I spend most of my time lurking on the forum just soaking up all the wisdom out there. But what I REALLY like, is that we are all so adult about it. You don't see anyone YELLING IN CAPS OR WORSE YET, BOLD CAPS trying to make a point. Nor do you see any personal attacks, outright or even implicit. Forums are about discussion... and discussion is about differing opinions. Wise men and women realize that the best and most correct knowledge is a conglomeration of truths... some you agree with, and some you don't. I am proud to be a part of this group of Ford Raptorites, and am continually impressed by the civility shown here.

Falcon

 

[Xjrguy]

know what you mean cowboy. I spend most of my time lurking on the forum just soaking up all the wisdom out there. But what i really like, is that we are all so adult about it. You don't see anyone yelling in caps or worse yet, bold caps

i still say it's the ******** maf sensor!

FYI, there is another nanny that prevents a reply in all caps (I just tried)

 

[Falcon]

i still say it's the ******** maf sensor!

Fyi, there is another nanny that prevents a reply in all caps (i just tried)

OH DAMN! I need an Off-Road mode for the Caps Nanny now! <G>

Falcon :taz:

 

[BigJ]

Those conditions have me confused too FSM. Coasting especially. I've not put an AF gauge yet in my Raptor to see, but my experience says that modern ECUs go stoich when coasting; they trim AF to somewhere around 14.2-14.7. Although I suppose it's possible to knock in that state, I don't think it's likely.

I'm no expert, but I don't suspect the MAF. At light throttle or coasting, the RPMs are low, and at low RPMs don't our systems rely on a VE table lookup, rather than MAF input?

Maybe I missed it, but has Chris plugged in something that can datalog? Something like a Dashhawk? A log from something like that set to record knock retard would be incredibly illuminating.

 

[MarkT]

Those conditions have me confused too FSM. Coasting especially. I've not put an AF gauge yet in my Raptor to see, but my experience says that modern ECUs go stoich when coasting; they trim AF to somewhere around 14.2-14.7. Although I suppose it's possible to knock in that state, I don't think it's likely.

I'm no expert, but I don't suspect the MAF. At light throttle or coasting, the RPMs are low, and at low RPMs don't our systems rely on a VE table lookup, rather than MAF input?

Maybe I missed it, but has Chris plugged in something that can datalog? Something like a Dashhawk? A log from something like that set to record knock retard would be incredibly illuminating.

I understood RIKU's description to say that the pinging occurred when tapping the throttle during coasting... not that he was experiencing a steady pinging during coasting. (That would be extremely unusual especially since during coasting I believe the fuel is shut off completely?)

My understanding (or perhaps misunderstanding?) of the problem is what led me to believe "something" is creating a lean condition during cruising and then under light acceleration (when the mixture needs to be quite a bit richer than stoichiometric) it pings. Extremely lean conditions usually lead to uneven combustion which creates pressure spikes in the combustion chamber which causes sudden, explosive burning (and pinging).

It could be a combination of many little things. During cruising mixture is set to the lean side of things already... "something" (air leak, CAI) could push the table settings to full rich and it still wouldn't quite be rich enough, say in the low 15's.... High ambient air temps really increase the combustion temps compounding the problem... or???

It would be great to see the complete data... I'm sure the Team Ford guys will figure it out.