Whats the cause detonation?

S

scrobbyd

Member
Joined
Jan 7, 2004
I hear my car detonating at 23 lbs of boost, if I let off just a little to about 20 lbs it goes away. No signs of knock on SM, PL or audible. New Alky pump, primed and set on 8, Walbro fp is about 6 to 8 months old and will be replacing very soon with Deatschwerks. At about 22 lbs of boost on up it sounds like valves clattering, then let boost go back down to around 20 lbs and clattering goes away. I verified knock sensor about 6 months ago when I installed audible. I've attached a PLer file if anybody is interested.

Thanks
 

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Looks lean to me. I see afr in the 12's. AEM gauge type or inline? I see a correction factor pulling 4-6% fuel at wide open throttle. Targets are 10.8( too lean IMO set it to 10.4.-10.5) You have selected WOT fuel of BLM 150 correct(+17%)? Are you seeing the same? My PL is set up for SD and may be screwing up my reading of your log.
Make sure your Powerlogger and AEM are reading the same.
Does your AEM go full lean KOEO?
Oh...Too much alky too. Turn it back to 6.5 start at 20-21 psi and go from there.
 
It's an AEM in-line wide band! I'm not sure if that will change any of the questions you ask about though! I appreciate you taking time to look at it for me, thanks a lot...
 
It appears to me that you may be too lean like was said?

My first thing to do would be add some race gas and see how and what that does at the same boost levels with the added octane.

The installation of the DW pump should provide additional fuel which you probably need at 23 psi to keep it from going lean?

Does the chip have the ability to add fuel with the added boost?

You cannot just add alky for more HP, you also need more fuel, or more octane, or both at some level.
 
This car is local to me. I have had a feeling that the Walbro pump currently in use is dying. If you look at the fuel pressure on the log it is very jumpy and doesn't reach the 1:1 pressure rise that it should. A few weeks ago we had to raise the wot correction to 150. I feel that it shouldn't need that much correction based on the combo. The alky pump is new and the AFR isnt too terribly lean BUT why wouldn't the knock be heard but not picked up by the sensor? I think the DW pump will help a lot.
 
10.7afr should be plenty rich. Overall fuel pressure is maintaining. If it was starving I would think the trace would go down hill and afr's would rise. The fp transducer mounted on the rail could be why we see such erratic trace. I show the same on my logs. I plan to try and isolate the sensor with a hose. ;)

My guess here is bad fuel. Get some fresh and see what happens.

RL
 
scrobbyd said:
I verified knock sensor about 6 months ago when I installed audible.
Click to expand...

This is where you start. If the sensor is working it should pickup the knock. 6 months ago means nothing when your having problems "today". Once you have a working knock sensor that eliminates that part of the equation.

for 22 psi the gain should be 6-7 tops. If your running on 8 and leaning out.. your trying to compensate for a fuel issue=bad pump/bad reg/bad wiring/etc to the fuel pump.

Fix air fuel with fuel. Fix knock with alcohol.

HTH
 
Okay so yesterday I put a long extension down on the block near the knock sensor with the key on, not started I wrapped on the end of the extension a few times with a hammer. My audible started beeping right away. So i assume my knock sensor is okay, but possibly not torqued correctly. Anyway I drained all my gas from the tank today with the anticipation of a new DW FP being here and installed on Wednesday or Thursday. Another thing is I've been kind of leaning towards bad gas myself. I've always run Exxon 93 oct. but about a year or so ago I started running Conoco no ethanol 93 gas. But for the convenience about 3 months ago I switched back to Exxon gas at new station that I pass daily. Thanks for the responses guys!
 
Is it possible this detonation sound could be coming due to mufflers issues? So far I've replaced my fuel pump with a new Deatchwerks, put a brand new Alky pump on. I have no signs of knock on Scanmaster or power logger but still making a detonation noise. So I pulled waste gate rod off of WG puck and went WOT and I'm still getting the same noise but not quite as loud as with WG connected. My hooker exhaust system is about six years old still looks good (no rust) but don't have any idea of where else to point the finger. Any more ideas?
 
Is it possible that the spring in your tensioner is getting old/tired, or your tensioner pulley is going out? The assembly could be bouncing around and sounding like knock; try revving it while looking closely. (Mine was doing something like this.)
 
Chuck Leeper said:
While chasing the issue, let's see what the plugs look like......................
Click to expand...
What Chuck said... The spark plugs will show whether real detonation is occurring or not. Little black specks on the center porcelain is from detonation. Little silver balls among the specks is pieces of piston and is a really bad sign.

RemoveBeforeFlight
 
Cut the threads off, and look at the base of the insulator. Do this with a fresh set of plugs. Looking at old plugs is a waste of time.
 
Might be valve float at high boost. The exhaust valves need a good spring on them to keep them from bouncing under high boost. What seat pressure are you running? Measure a few exhaust springs and let me know.
Also put race gas in it and see if it is in fact detonation. If you are not up to speed on plug reading.
 
Chuck Leeper said:
Cut the threads off, and look at the base of the insulator. Do this with a fresh set of plugs. Looking at old plugs is a waste of time.
Click to expand...

How is cutting the threads off of a brand new set of plugs going to tell you anything if they've never been installed... You want to see the plugs that were IN the car, don't you?
 
Turbo6Smackdown said:
How is cutting the threads off of a brand new set of plugs going to tell you anything if they've never been installed... You want to see the plugs that were IN the car, don't you?
Click to expand...

HUH??? I made no mention of cutting up plugs that have never been in an engine.........
The point I made: Don't read plugs that have been run for an extended period of time...Fresh= put in a "brand new" set, make a pull, or maybe 2, read them..
Cutting the threads off allows one to see the base of the porcelen.
An otoscope is a nice plug reading tool. Get 1 off the bag, w/ a 10x magnification, and a hi intensity LED lite.. Bout $30 for a good one.
[Otoscope = what the dr looks in your ears with.]:D
http://www.mopedarmy.com/forums/read.php?7,2959417
 
Ah, I see. I always understood "fresh" to be "uninstalled" A fresh pair of tires is a set that hasn't been run. Or putting in a fresh magazine for a pistol isn't a magazine that has a few rounds missing out of it already. Got confused.
 
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