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Engine knock after knock sensor replacement WTF??

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njdaewoo

10+ Year Contributor
167
1
Oct 19, 2009
Piscataway, New_Jersey
I just replaced my knock sensor because of my previous knock issues. I still have engine knock! My internals are all stock etc for my comp cams stage 2s. Is it possible that my stock valves are floating causing the engine knock in the 4000rpm range and higher? I have the BR8ES spark plugs and Im only running 20-21 lbs of boost on 93 octane. My timing is set at 8* in the 4000 rpm range (if i go any higher the knocking starts and about 2-4 degrees are pulled) The highest im able to take the timing in the 5-7k rpm range is about 9*. My A/F ratio is 11.3 and adding fuel or subtracting fuel has no effect on the knock. Im about out of ideas to try anyone have anything new to combat engine knock? BTW, the air temps in Sept. is about 77degrees... thanks for any coments...
 
There are several factors that can cause knock. Check for minor boost leaks, especially around the biss screw. By the way, what's your knock count? Or can you post a log...

At work right now, i will post a log tomorrow.. The biss screw and throttle shaft is leaking. I did a pressure test today. On my laptop how do i log knock counts? Im just recording knock using Dsm link ver 3. Before the summer came, I was running 16 degrees of timing with no knock at 20 lbs.My timing is dead on, It was checked twice by me and by a reputable shop
 
you are experiencing knock because youre engine is KNOCKING which means there is detonation and detonation is bad

Turn down boost

Wow. So constructive... :rolleyes:


You should be able to run that much boost and not knock. It's not valve float either. What you need to do is determine if this is real knock or phantom knock.

-First, try turning the boost down and see if you still get knock at the same rpm. You shouldn't get knock, especially with conservative timing and fueling.

-Next, just try free-revving the engine and seeing if you get knock.
If you do, it's probably phantom knock. Things like a loose exhaust heath shield may cause a false knock signal to be detected.

-If you don't get knock free-revving, try putting in some race gas in and see if you still knock.
If you do even with your conservative timing and fueling, it's probably phantom knock.


If you narrow it down to more than likely being phantom knock, do a search on here and see how people have solved the problem.
 
Wow. So constructive... :rolleyes:


You should be able to run that much boost and not knock. It's not valve float either. What you need to do is determine if this is real knock or phantom knock.

-First, try turning the boost down and see if you still get knock at the same rpm. You shouldn't get knock, especially with conservative timing and fueling.

-Next, just try free-revving the engine and seeing if you get knock.
If you do, it's probably phantom knock. Things like a loose exhaust heath shield may cause a false knock signal to be detected.

-If you don't get knock free-revving, try putting in some race gas in and see if you still knock.
If you do even with your conservative timing and fueling, it's probably phantom knock.


If you narrow it down to more than likely being phantom knock, do a search on here and see how people have solved the problem.

Thanks, I dont have acces to race fuel ,but I could mix some 108 octane booster with 1/4 tank of 93 octane. Should I leave the timing where it is (7-8* at 4k rpm and from 5k up the timing advances to about 10* max by 7500rpm)? Should I drop the boost down to 18lbs? or should I go lower?
 
Sounds good but I cant lower my turbo any more. The actuator must have a 20 lbs spring in it so im screwed. I have the mbc in the lowest setting and im still getting 20lbs.
 
Then at least try the free-rev (don't need to red line the thing) to see if you see knock.
The only issue with that test is that the engine ignores knock below a certain load based on rpm.

Since you mention a spring, I'm guessing the turbo is externally gated. Otherwise, you could have removed the actuator arm to keep from boosting.
 
Installed it myself, I removed it and then i wrapped the threads with teflon tape. I then thightened it by hand and gave it a little snug and i still got knock.

The turbo is internally gated. I will rev the car in neutral to about 4k rpm to see if i have knock and then I will see if i can find a lower spring pressure actuator and set the boost to about 17 lbs.. thanks for all your help guys.... Its raining in Jersey so im not sure when i can go out for a full throttle blast off!
 
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If the turbo is internally gated, you can take disconnect the wastegate actuator arm so that the flapper is just hanging freely. You won't build any boost (maybe just a little), but you should be able to get enough load on the engine to get phantom knock to register if it's present.
 
I did the free rev test and as soon as I tap the gas I get knock. If I gradually accelerate to the 5000 rpm red line there is no knock present. I have a couple of files that will show you what Im talking about.. I turned the boost down to 10-11 range and I was able to get the timing back up to the 16-17 degree range.

Im using DSM LInk Ver3:

One of the files is showing a 3rd gear with about 20-21 psi of boost with the extremely low timing...
 

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  • log.DWNSHIFT3RD2010.09.18-03.elg
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Sure the OP has solved it by now, but I'd like to add, I wouldn't run those plugs for that kind of boost. I'd swap to the 7's. Personally I tried the 8's a couple years back, threw them in a couple days before I went to the track. Did some runs & got knock where I shouldn't, kept on making thing less aggressive & still knock. Swapped from the 8's back to my reg 7's & everything was good again. At the time I was probably running 27psi or so & still didn't work for me. So at 20-21psi, the 8's are too cold of a plug.
 
you are experiencing knock because youre engine is KNOCKING which means there is detonation and detonation is bad[/QUOTE

I know this all too well haha. Just throwing this out there but is there a chance its phantom knock?
 

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At 7.038 seconds on the DWNShift log is that right where you downshifted? cause if you are just pushing the gas down then i would pull a little timing for that rpm/engine load range. But the full throttle log looks good so it does seem like PK. Try using diffrent oil if you have exessive valve tap, maybe see what your knock sensitivity is at?
 
At 7.038 seconds on the DWNShift log is that right where you downshifted? cause if you are just pushing the gas down then i would pull a little timing for that rpm/engine load range. But the full throttle log looks good so it does seem like PK. Try using diffrent oil if you have exessive valve tap, maybe see what your knock sensitivity is at?

Those logs were from 2010. I bet he figured it out.:p
 
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