knocks like a diesel when hot
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Joined: Jul 2010
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knocks like a diesel when hot
ok guys i was sent here by a member from corvetteguru so don't shoot me. here is my deal 93 corvette washed engine bad mistake. fried opti . changed opti with richport technology opti from local part store. car started but gave 36 code.pulled opti got another same kind.installed no code but runs good cold but when hot sounds like diesel it spark knocks so bad. new coil new knock sensors new taylor wires installed correctley (checked 3 times)this has been going on for a month now sow all moisture problems should be out of the equasion i have made sure everthing is dry.need some advice please
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Joined: Jun 2001
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From: Detroit area
There is only so much that controls the timing. Did you get the PCM wet? Bad gas? I am sure Injuner will chime in. He is a wealth of knowledge. I dont know much on the 93's. And welcome aboard, anything with an LT1 is welcome here.
Last edited by joeSS97; Jul 11, 2010 at 07:34 AM.
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From: Hell was full so they sent me to NJ
I think Rob/Shoebox got it right... Opti is not indexed correctly to the splined shaft. Contrary to the advice you got on the Corvette site, it is very possible to index the shaft incorrectly, and without a lot of pressure.
You also need to get a genuine GM Opti, not the junk they sell at parts stores.
For anyone who needs a good read, here is the original post from the Corvette site:
http://www.corvette-guru.com/modules...post_id=131112
You also need to get a genuine GM Opti, not the junk they sell at parts stores.
For anyone who needs a good read, here is the original post from the Corvette site:
http://www.corvette-guru.com/modules...post_id=131112
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Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
To actually hear spark knock, you would have to have more than 15-deg too much advance. The knock sensors pick up the knock before you can hear it, and the PCM can retard the spark up to 15-degrees to eliminate the knock.
Other possibilities that can contribute to knock:
-low octane fuel. What grade are you using?
-high coolant temp. What is your coolant temp while you hear the knock?
-excessive air intake temp.
-oil entering the A/F mixture
-cross-firing on plug wires.
-excessive carbon builup in the heads, piston crowns.
-too high heat range spark plugs.
-incorrect MAP sensor reading putting the PCM at the wrong location in the spark advance tables (a grid of RPM vs. MAP).
-high voltage pulses (e.g.- from ignition wires) interfering with high res pulse signal from the Opti. Does your tach ever dance around when it should be holding steady?
Other possibilities that can contribute to knock:
-low octane fuel. What grade are you using?
-high coolant temp. What is your coolant temp while you hear the knock?
-excessive air intake temp.
-oil entering the A/F mixture
-cross-firing on plug wires.
-excessive carbon builup in the heads, piston crowns.
-too high heat range spark plugs.
-incorrect MAP sensor reading putting the PCM at the wrong location in the spark advance tables (a grid of RPM vs. MAP).
-high voltage pulses (e.g.- from ignition wires) interfering with high res pulse signal from the Opti. Does your tach ever dance around when it should be holding steady?
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Joined: Sep 2004
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My Vortec truck engine does it when my intake gaskets leak coolant into the cylinder(s). I know they have gone bad when I start it up and it sounds like a diesel. Only lasts maybe 20 seconds then goes away as it warms up. Then I check the coolant level and sure enough it's gone down.
I know it's opposite to your problem, but my point is, coolant leaking can and usually is the cause of a gas engine sounding like a diesel.
The only difference between hot and cold (open loop vs closed loop) is essentially the amount of fuel. So to eliminate the fuel issue, unhook an O2 to force it into open loop all the time. Even after it gets hot and see if it still does it.
My money's on it will still do it and it is not from the fuel or ignition.
Check your coolant.
I know it's opposite to your problem, but my point is, coolant leaking can and usually is the cause of a gas engine sounding like a diesel.
The only difference between hot and cold (open loop vs closed loop) is essentially the amount of fuel. So to eliminate the fuel issue, unhook an O2 to force it into open loop all the time. Even after it gets hot and see if it still does it.
My money's on it will still do it and it is not from the fuel or ignition.
Check your coolant.
Last edited by Guest47904; Jul 12, 2010 at 03:43 PM.
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From: Hell was full so they sent me to NJ
I mentioned the fact that the PCM can pull 15* of timing, because if the timing it off by more than 15*, its going to audibly knock. If you can hear knock, you have a MAJOR problem. You are probably doing serious damage to the engine.
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From: Hell was full so they sent me to NJ
