How to tell misfire VS detonation under boost?

[bpu699]

Alright, I am lost here... Have another thread on my car running to rich under boost. But thought I would bring this question out on its own...

Under boost, car running rich, how do you tell detonation vs misfire?

Temp out side 40 degrees (cold!)
Oversized intercooler
new NGKbp8es plugs gapped at 0.3
0.8 boost spring
AFR dip to <10 under a heavy foot
Premium gas

If I step on the gas all the way to the floor, car burbles/rapid pops/ as boost gets to >0.7 and AFR 10.5 or less... Usually <10

If I press on the accelerator 1/2 way, still gets to 0.8 boost (takes longer) but AFR comes down more slowly, doesnt dip below 10.5 and usually no burbles or funny sounds...

I feel like an idiot, but not sure what detonation sounds like. I here about rattling coins in a can, and it doesnt sound like that... I hear that it could sound like a machine gun...not sure if it sounds like that... Its not LOUD, if thats what that means... It sounds like the sound you make when you purse your lips and blow...

Its almost like the REV limiter is kicking in, but it cant be as it happens at 5000 rpm or so. The car doesnt slow down, or stagger, or anything like that. It pulls great...

Any definitive way to tell the difference?

The fact that its cold outside, its running rich, seems to argue against detonation (which is usually LEAN and HOT)...

Does the fact that depressing the accelerator 1/2 way does cause it, also suggest a misfire?

I was thinking about retarding the timing 10 degrees...If that makes it WORSE, then its a misfire as this would make the car run even richer. Certainly this shouldnt make DETONATION worse, right? If it makes it BETTER, it could be detonation... Does that make sense? Am I wrong here?

I can slowly figure this out, I just want to make sure I am not repeatedly running my motor to reproduce this sound if it is in fact detonation...

Listened to a bunch of youtube videos, not sure I hear what they are trying to show...

Again, any help appreciated, how can I exclude detonation as a concern here?

[Tippy]

If you're less than 10:1 AFR's, misfires are very probable.

What's your timing at for 0.8 bar?

[GJF]

To me........ If you take a 20 x 20 porcelain floor tile, lay it flat, and hold a hand full of 1/16th E70 TIG welding rods vertical. And dropping them on top of the tile. That is literally the exact sound of detonation under boost in an air cooled engine. Misfire can be a loud pop to a uneven exhaust note under power. Also if your popping under load make sure your spark plugs are good and tight.

[Tippy]

^ tinkalinkalink

[JFairman]

I wonder if there's some leaks around intercooler o-rings. Air flow metered air leaking under boost pressure would make it run rich when flooring it.

[pkabush]

Originally Posted by GJF

To me........ If you take a 20 x 20 porcelain floor tile, lay it flat, and hold a hand full of 1/16th E70 TIG welding rods vertical. And dropping them on top of the tile. That is literally the exact sound of detonation under boost in an air cooled engine. Misfire can be a loud pop to a uneven exhaust note under power. Also if your popping under load make sure your spark plugs are good and tight.

That's a really good explanation of what detonation sounds like.
I agree with the others, sounds like you're already running rich. I've had similar conditions with leaking O-rings I'd take Jim's advice and start there. You could also pull a plug and see what it looks like.

[356911930]

I too would agree with Jim. When you say parse your lips and blow (que in Ronnie here) do you mean like an old fashion "raspberry"? If so that would possibly be a seal or o-ring as Jim has stated.

Best of luck,

Rahl

[bpu699]

Originally Posted by 356911930

I too would agree with Jim. When you say parse your lips and blow (que in Ronnie here) do you mean like an old fashion "raspberry"? If so that would possibly be a seal or o-ring as Jim has stated.

Best of luck,

Rahl

Thanks guys... will keep looking...

Just added to my other thread, as I Was checking my timing and it looks like my boost retard isnt working so well... Suggest detonation, though it doesnt sound anything like mechanical pinging... it does sound like a "raspberry..."

Help with ignition timing please... my 930 is now farting...

I love this car... and thats a good thing... because it always seems to "need" something...

[Alan L]

Here is a link - this topic has occupied many thread pages.
Need a photo of Dist. Vac line.
If you do a search for dual pot dizzy you will come up with a few.
I do suspect you have a 3.6 pulley. One reason for that would be to increase fan speed (by about 10%). What you can do is cut a strip of paper to the right length for you timing (dge x 1.09), and lay it on the pulley and mark the end of the strip for your timing mark. I think the 3.6 engines do run more timing - which explains a lot with your dilema.
Alan

[bpu699]

Alan, I posted this in the other thread...

I bought a high end digital strobe light... The second mark to the right of z1 isn't anywhere near 28 degrees btdc... It's at about 36 degrees btdc...

What I started with was about 6 degrees at idle, and 24 at full advance...

The vacuum port of the distributor doesn't seem to do anything... Doesn't hold vacuum...

The boost port retards, but very little. If you are supposed to have 10 degrees of retard at 5psi... I gave 3 degrees....

Not sure if I am chasing my tail, or the boost retard failed. I checked it at idle, setting idle to 10btdc and adding 15 psi to the boost retard nipple. It retarded 3-5 degrees... Tops... Yet as a fluke, if I did vacuum to the boost port, it advanced the timing 8 degrees?! Seems like the diaghphram moves, no?

Confused...

I didn't have any of these problems when I had the bosch platinum plugs...all correlated to switching to ngk... Though I just can't see how that would make a difference if the distributor is malfunctioning? Scratching my head... Confused...tired.

[Alan L]

Yes, I saw a bit of your other post somewhere - which is why I replied partially to both in the one reply. I do suspect your timing mark is off another later model car - which generally run some quite advanced timing. They have all sorts of electronic sensors/gizzmos that correct things when required and run quite advanced under low load. (around 30+ deg). So you could re mark your pulley. As you have worked out ; 3.14 x Dia (mm) = circumference. Then your deg of 4000rpm timing/360 x circumference will be the distance you need to mark. I still think the rich mixture is probably at issue, but if you have any timing issue, now is when to sort it.
If you do re mark pulley - go around the circumference - not across with calipers (small error).
Regards
Alan

[Alan L]

from what I read on the threads on twin pot dizzys, one line is a vac advance which will be connected to the thermo vac switch or straight to the TB - below the butterfly. Sometimes the thermo vac sw is bypassed (more emission crap). You could test that line by disconnecting when warm (if on thermo sw) or adding vac/not and watch advance of 6 deg. But often this line is even just blanked off and port left open. The other line I think is your boost retard. The mech advance should take it up to max at 4000 rpm. the boost retard should pull it back - but you have no boost so the only way to test that would be to plumb in some pressure.
That is my best guess at it so far. What seems a puzzle is why some dizzys have boost retard and the single pot one does not. My 26 deg advance is what my engine sees on boost as far as I know.
Alan

[bpu699]

Thank you for you help Alan. Plan to fix the distrinutor next... need to find out why I am not getting 10 degrees of boost retard...

The vacuum nipple on the inside of the vacuum cannister on the distributor doesnt hold vacuum... Is that enough of a "leak" to make it run rich? Doesn't seem like that a big volume of air there...

I did search for the vacuum cannisters... they are $300. OUCH. For that much, I can just buy the MSD Boost Retard! Seems more sensible, and then just plug the vacuum and boost ports...

Will see if I can inspect the distributor first...

Thank you!

[Alan L]

I think the nipple on the end of the can is your vac advance and the inner one the boost retard. Have a look at the link I posted. But I would expect the cans to hold pressure/boost. Does the outer nipple hold vac?
Alan

[bpu699]

Outer nipple seems to be boost retard... Holds pressures...

Took the distributor out... More to come

[bpu699]

Ok... Looks like it was probably detonation....

The distributor was frozen... I suspect many folks may have this issue and not know it...

Plugged lines to distributor. Installed msd btm. 26 degrees peak, 8 degrees idle. Btm takes out 2 degrees of advance for every psi from 4 or more, to a max of 15.

So, at full boost I am running 11-12 degrees advance... Which is super conservative. Plant to putz with it more this week...

Also tried dropping 1 degree per psi of boost... That dropped about 8 degrees... But had the occasional pop... Doesn't sound anything like it did though... That's gives 20 degrees at peak boost... Too much...

Will play with it more.... .

Anyone run the boost signal off the intercooler rather than the manifold? In my case, it's a straight shot to the btm, and simplifies the hose routing... Would that speed up the response time from the boost signal?

I wish to thank everyone for their help.

Thank you.

Bo

[Alan L]

I still doubt detonation - you are running pig rich on boost. I am running 26 deg (up to 1 bar periodically) with AFrs above 12. No sign of detonation.
But at least you are making progress with the frozen dizzy. I presume it was the retard arm in the can that was frozen? The collar inside the dizzy can freeze too.
I don't think it matters where you take the boost signal - it equalises throughout the system . You can't have boost in the IC without it being same in manifold. My EBC runs off IC.
Regards
Alan

[T77911S]

you have a boost leak.

I was down in the 10's or even 9's when I had a leak.

[bpu699]

Thanks guys... next weekend will search more for a boost leak... also bought 2 cans of starting fluid to shoot near connectors to rule out a vacumn leak...

Alan, I saw your picture where you added a rubber stopper to the intake elbow and pressurised looking for boost leaks... Will try that next... How did you block the air from going down the manifold?

I honestly don't know what the cause was, all I know is that its gone...

Here was the timeline of events:

1) Car running perfectly fine... but decided to change spark plugs from bosch platinum to NGK per MSD (MSD says NOT to use platinum, will overheat and glowplug...)---- note to self: If it ain't broke... don't fix it!!!---
2) Installed the NGK's, gapped at 0.4... car ran like crap under boost. At peak boost made the machine gun/farting/rasberry sounds...
3) Took plugs out, regapped at 0.3... ran better...still made same sounds but perhaps a wee-bit less noticeable
4) Checked timing...boost retarded only shave off 5-6 degrees, not 10... Vacuum port wont hold air...
5) Also saw that the green wire was chaffed near the fan enclosure... this probably happened AFTER I removed it... So, fixed the wire (shortened, reinserted into the clip, and reinserted into the distributor. Added waterproof connector to splice it in...
6) Installed BTM...had a heck of a time getting it to work... sometimes worked, sometimes, not...
7) Took it out on the road. Retarding "0" by accident... car made a couple "farts" but very few...
8) Set retard to the max (15 degrees)... so 10-13 degrees under boost... no farting/rasberries
9) Dialed it back... very little difference between retarding 1.5 degree or 3 degrees per pound of boost... either way, it hits the max retard of 15 degrees...

Trying to figure out what I could have done changing the plugs that led to this scenario... That was what precipitated this whole mess (unless its completely unrelated)... I was thinking last night, could the boost signla line have gotten compressed somehow?! Perhaps that did it... When I blow into the line by mouth, it flows, but there is a slight amount of resistance... Will check for kinks...



Still very rich under boost...

Thanks!

Bo

[bpu699]

Oh...silly question... until I figure out the optimal BTM setting...

Does running slightly retarded under boost pose any issues? Stock is 16-18 degrees... With the BTM if it takes out the full 15 degrees, I am occasionally at 12 degrees under boost for a second...

I can set it more advanced, but doing a track day Friday and want to run "safe" until I figure this out fully...