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Old 09-08-2009, 08:55 PM   #1
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Question KR - how much is too much???

Just finished replacing my BCS and am finally getting full boost. However, I am now getting some KR. At WOT, I start getting about 1 degree of KR at around 2.5 psi of boost, and it peaked out at 5 degrees of KR at around 6.5 psi of boost. Engine coolant temperature is 199.4 F, and air intake temperature is 98 F. Outside temp is around 80 F. Road speed is around 60 MPH and engine speed 3,940 RPM. Ignition timing is between 9 and 10 degrees. (the conditions I am listing are at the max KR of 5 degrees)

I have new spark plugs and wires. Just put a new air filter in. The fuel filter has not been changed in some time. I am still running the stock thermostat (190 F???). The car has 175,000 miles on it. I am the original owner, and although I drive aggressively, the car gets good routine maintenance.

There is no KR below 2.5 psi boost.

Is this level of KR a concern? If so, what should I do to correct it? I am pretty sure you are going to tell me to use a 180 Tstat, but I am not sure I want to do that. Winter is coming, and the car does not run well, or heat up enough for my tired old bones, with anything lower than the 190 Tstat.

As always, your comments and advice are welcome. I can scan for other parameters if it would help to understand what is going on.

Roy
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Old 09-08-2009, 09:37 PM   #2
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The fuel filter shouldn't be causing the issue, and you should be able to keep the 195F which is the stock t-stat, I'm not familiar with SC engines but seeing only 9 or 10 degrees of advance sounds low, I'm used to 25-30 degrees on my NA, 5 degrees of KR seems a bit high

what octane gas are you running?
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Old 09-08-2009, 09:38 PM   #3
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Any KR is bad KR. Running 9 to 10 degrees of timing is really low, you should be holding a good 18* Is that still the stock pulley? If so then that'* really bad KR. Start by listing for noise in the supercharger. I just did a swap on a car that I couldn't get better then 12* of timing. Dropped on a known good supercharger and he now has 16*. A cold air intake will help a bit, as will a 180* thermostat. Anything to drop intake air temps.
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Old 09-09-2009, 05:55 PM   #4
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I am buying 93 octane, but am getting my gas at the duty free gas pumps at the Windsor/Detroit border. Its at least $0.40 per gallon less than gas prices anywhere else, but I wonder if the gas is good quality. I will try Shell or some other name brand for a couple of tanks.

I will get my handy dandy stethoscope out and see if I can hear anything out of place in the supercharger.

It is the original factory installed pulley. I am the original owner of the car, and I have not changed the pulley.

Thanks for the input.
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Old 10-08-2009, 11:21 PM   #5
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I am still getting as high as 3* of KR. I start getting KR at around 2 psi boost and it peaks out at around 6 psi boost. Timing is dipping down to around 12* when there is 3* of KR.

I stopped buying the cheap duty free gas at the border and am most of the way through the 3rd tank of BP 93 octane. I wanted to rule out bad gas as a contributor.

Changed my fuel filter, no improvement.

Listened to the supercharger with a stethoscope and I don't hear anything out of place.

I am running the original pully.

I want to mod, but not if I can't get this KR cleared up with the stock setup. Any suggestions?
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Old 10-08-2009, 11:29 PM   #6
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You could have a bad knock sensor. Check the plug and wires. Check for 5 volt Using a DVOM, check voltage between engine ground and terminal at KS.
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Old 10-08-2009, 11:40 PM   #7
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Quote:
Originally Posted by Danthurs View Post
You could have a bad knock sensor. Check the plug and wires. Check for 5 volt Using a DVOM, check voltage between engine ground and terminal at KS.
Plugs and wires are new. I changed them about a month ago when I had the misfire issue that turned out to be an injector.

When checking for 5 volt between ground and the KS, what do I physically touch the probe to... dig into wire, push into KS...? I will take a look on Saturday to see if the answer is obvious.

Would a bad O2 sensor be a possible cause? I only ask because I have 175,000 and the original O2 sensor.

Thanks Dan.
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Old 10-08-2009, 11:56 PM   #8
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Unplug the KS, I believe the 5volt wire is dark blue bank 1 and light blue bank 2. Put one probe there, and the other on a engine ground.

A bad O2 would make the engine run rich. I've seen a few 2000+ that run lean all the time. This causes knock. But with you having that much knock at such low boost I suspect a bad KS or problem with one. Or a problem with the tune. A good tune will change how quickly a KS pulls timing, as well as how fast it returns the timing.
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Old 10-09-2009, 12:07 AM   #9
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Our favorite on-line parts store has knock sensors for $40 if I need one. I will check it on Saturday and post the results. Thanks again.
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Old 10-11-2009, 12:17 PM   #10
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Checked the front knock sensor and it is getting 5 volts. I can't get at the connector on the rear one because the sensor is turned so the release catch in not accessible. How on earth do you change that rear sensor? There'* not much clearance between the tranny and the engine. You would need a deep socket to give clearance for the connector but I don't think a deep socket would fit in there.

I think I will change the front sensor because it is so easy to get at. If the problem doesn't go away, I will have to figure out how to get that rear sensor out.

Does the cooling system have to be drained to pull these? (I think yes)

There are two sensors, but only one listed at the parts stores. Are both sensors the same part number? (I think yes)
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