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Discussion Starter #1
I replaced the HG I blew last week with a Titan MS 2.0mm. 2 days waiting for HG, 1 day waiting for no rain day. and 1 day to replace it. I replaced the plugs, coolant, oil, and switched to a spare ignitor. The other ignitor had a cracked connector and I thought it might be misfiring causing lean condition in the #1 and #6 cylinders. Drove it around for a few days and decided to check it out again.
Ran the compression test and it looked bogus, then I read a post about compression readings mentioning the throttle being closed(DOH!). Yay for the forum again!
Ran compression test again and it looks to be within spec as noted on the pic. Lower than before, but I expected that with thicker HG.

The #1 and #6 plug porcelain are much darker in color than the other 4. This is after about 200 miles with no more than 10psi of boost. I sure wish they all looked the same, but am not sure if I am in trouble or not. My idiots guide to Supras(Haynes) sez that brown to grayish is normal and there is no visible wear yet.
I want to go to the dyno, but last pass I was blowing lots of fuel at high boost and it looks like these cylinders were not burning it. They leaned out and blew the HG later. So none of the A/F readings from last time were accurrate, as they read all 6 cylinders together.
I am thinking about boosing up it up in fourth and watching my A/F closely for any inkling of lean. If that is good, I will boost in second and see if I still get the black cloud. Then off to the dyno if not.
Any one want to give me a good opinion on whether this is normal? I really don't want any more down time now, but it is hard to enjoy driving at low boost all the time. Where do I go from here?
 

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S.T.A.R.S.
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260 Posts
It's actually 142 but that's not the minimum. What you look for is the difference between the cylinders as long as there is not a difference larger than 14psi accross the board you have nothing to worry about. Now that the 145 is sort of low compared to the others I would do a wet compression check on that cylinder. Might just be a bad ring. Get an SAFC and tune it out!! I would say as long as your not blowing smoke or running rick you should be fine. But it doesnt hurt to double and triple check. Hope this helps you out

John R.
 

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Discussion Starter #4
I installed a thicker HG which means less compression, not sure really how much, but I have heard 10-12 psi less mentioned.

I did a wet test last time and the low ones came up about 15psi, so yes there is probably some ring seal damage, but not enough to stop using the car just yet. It is not smoking or using oil to any appreciable extent. Rings are lots more trouble than a HG to replace, so I will have to wait till I have a few days off to replace them.

I run a haltech fuel comp which gives me pretty complete control over injector duty cycle vs. rpm and boost. It is applied to all 6 cylinders equally, as you would expect. I would like to feel certain that I am getting a good burn in all cylinders before I rely on a wideband which reads the output of all 6 mixed together.
Perhaps checking it every couple of weeks is all I can do for now.
 
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