[insite94]

Hi All -



In trying to chase down a recurring detonation problem at WOT (Hall sender recently replaced, central warning light now extinguished), I started with the basics by running a compression and leakdown test in anticipation of installing a variable fuel/air mixture device.



I had certainly noticed a recent increase in oil consumption to about 1 quart every 1500 miles, but still within tolerance. However, I was not prepared for the following outcome:



#1 - 180, -12%

#2 - 187, -20%

#3 - 175, - 8%

#4 - 170, -28%

<img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" />



Those are not typos. Plugs confirm the condition, esp on the #4 cyl. Source of the leakage is both valves and rings based on listening for air in the intake, exhaust, and crankcase. At 185K miles, she's getting tired. She's my daily driver and I'll drive her until oil consumption gets down to 500 miles per quart.



So I thought I'd solicit the list for ideas and options. I think I'd like to have the motor rebuilt, but have no idea what that means in terms of $$$. What other "while you are in there, you might as well..." stuff should I consider? I don't think I want to spend the $$$ to convert to correctly dialed-in (dyno'd) turbo. Maybe mild super charger if I can keep the A/C? Normally aspirated John Miledge motor? Or just rebuild the stock to factory spec?



Bullet proof and longevity are the keys. It's not a track car, but I still like to have fun on PCA tours and enthusiastic drives. I intend to have this car for along time. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />



All thoughts appreciated.



TIA,



Buzz

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[Greimann]

So what are the percentages you list based on? Usually you compare the high and low and if they are within 10% you are not in serious problems. 186K is a lot of miles though and you certainly would have a significant bump in HP with a valve job. The oil leakage is most likely the cause of the detonation.



The extent of your repair is really dependent on how deep into your wallet you want to dig, but rampant detonation for a long period of time is not doing your engine any good.

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[insite94]

Dave -



I wasn't sure of the answer so I called my mechanic. He said it was a gauge that actually reports a percentage differential right on the dial. The dial is denominated in percentages rather than a PSI reading requiring paper math thereafter.

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[insite94]

Oh, and the stock chip goes back in the car since the performance chip seems to be the source of detonation in the engines currently degraded condition.



By the way, that 's not a slap at the chip. It's just fine in healthy motors. But in my less-than-healthy motor, it seems to exacerbate destructive behavior <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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[Greimann]

[quote name='insite94' date='Nov 16 2005, 11:23 AM']Dave -

  He said it was a gauge that actually reports a percentage differential right on the dial.  The dial is  denominated in percentages rather than a PSI reading requiring paper math thereafter.

[right][post="12459"]<{POST_SNAPBACK}>[/post][/right][/quote]

I am not familiar with that kind of gauge, sounds fancy. Anyway, if the PSI numbers are accurate, the readings are still within 10%, but like said, I think the oil leakage is the cause of the detonation. Oil dilution reduces the effective octane number. It is only going to get significantly worse if you wait 'till 500 miles / quart.

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[flash]

hmmm - still don't think the chip would cause any issues, as long as the knock sensors are working - they should help the DME which should pull back the timing if it gets to that point, regardless of which chip - granted you wouldn't see the performance gains, since the timing woud be getting pulled back in such a motor, but it shouldn't make anything worse

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[insite94]

Only a guess Bob, but per Dave's comments above, oil could be the issue. As it relates to the performance chip, the timing advance curve must be jumping out too far under WOT, or is somehow exceeding or ignoring the limits of the stock chip/knock sensors and it's interaction with the ECU??? Honestly, I'm making this up as I go along. But I have no code lights and no pinging at all with a stock chip.



The chip does seem make a diffence on this engine and ECU, but I don't know why. The performance is way better with the chip, and as long as I lift slightly over 5500 RPM(but still accelerating), I avoid pinging. Go figgur' <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" />

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[flash]

i suppose it's certainly possible - it makes sense - since there is a minumum octane requirement of 90 RON+MON/2, it's possible that the lower levels are exceeded, and the system is only capable of retarding so far, but i would think your compression numbers would be a lot lower - i tested an engine here, which runs fine with a performance chip, and has numbers close to yours - the oil mix thing may be playing in on yours though



if the ECU were advancing the timing unchecked, certainly a performance chip would exacerbate the problem - however, normally, the timing should be retarded (or not advanced as much) the instant the knock sensors tell it there is a problem with detonation - whether the cause is low compression, low octane fuel, or whatever, it should still step in and take care of it, and not be affected by the particular chip



even though you have no indicators showing fault, have you had your knock sensors checked? somebody else recently had one that was failing, but not showing a fault code yet

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[insite94]

[quote name='flash' date='Nov 16 2005, 12:47 PM']...even though you have no indicators showing fault, have you had your knock sensors checked?  somebody else recently had one that was failing, but not showing a fault code yet

[right][post="12474"]<{POST_SNAPBACK}>[/post][/right][/quote]



I haven't had them checked, but that would be a good idea.

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[flash]

just a thought - may not help you at all, and you may very well have just too soggy a motor to handle it, but i would think it can't cost much to check them for the peace of mind

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[lyonlance]

Just a quick question; what should the PSI look like on a compression test? When I ran one on my car, they all came up to the 185 range.

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[flash]

cold, with 8 revolutions, anywhere above 180 is fine - 190 plus is a tight motor

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