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Discussion Starter #1 (Edited)
Well, there I go again. I was trying to get some of the black fuel cloud to go away and blew the HG again. Glad it was the HG rather than one of my forged pistons. Steam and lots of it out the exhaust and a rough running engine. Pulled the plugs and found this. If the images don't show on line I will try to re-edit the message.

The middle 4 look good, #1 on left and #6 on right. The destroyed electrode looks like it was cut with a torch.
Closer examination revealed that the porcelain was broken on the #1.

Compression test revealed in order
#1 155
#2 175
#3 165
#4 150
#5 155
#6 140
Looks like my break is now accounted for.
pulled the head and found;

#1 and 6 obviously adding some heat and gasses to the coolant area.
Closer examination of cylinders revealed this in #1

note dings in head at top and both sides.
The piston fared no better.

Corresponding dings in head where pocelain was crushed to save Turbo from eploding(I hope).

I am not sure why these two cylinders were destroyed by detonation. It is quite a testament to the construction of the 7M, that I can blow up a plug without everything else being totalled. I did find that the ignitor clip for this pair had a cracked cover, but don't understand why that would drastically affect the fuel mixture. The black clouds of unburned fuel may be due to injectors choking on the fuel pressure. It was set at 45 while we were on the dyno with the 440s in it and I just didn't want to change too many things at once. This with the 18# of boost would give 63#, perhaps a tad much. I got no such clouds at 10# of boost. Well I sure want to have a warm and fuzzy feeling about what caused this before I boost it up again.

I ordered a new HG from titan (2.0 this time). They are local and I will have it overnight. I am going to try and clean the edges of the piston with a sharp tool and hope for the best.
I think I will put it back together as I cannot afford to be down for a long time right now.

Meanwhile I guess I will have my leftover block prepped incase I have destroyed any rings and don't know it yet. There is some slight scoring in a couple of cylinders I can see it but not feel it. Last time I took the engine parts to a machine shop it was a month or so before I could get it all back together.

Please chime in now if you have any helpful ideas that don't involve buying a race prepped engine for $7000, as like all MKiii owners I am somewhat budget constrained.

1.5JZ Turbo Supra
3,378 Posts

Moderator, l337 M0d3r4t0r
12,147 Posts
You know i had it even worse.. I had some nasty detonation.. but I dind't blow the HG but instead I blew the sparkplugs...

Anyways.. I found dents all over my pistons and head form the ceramic since I didn't pull the head off... I mean some nasty looking dammage but it didn't seem to affect compression or power.

So thats my 7m story ;)
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