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Discussion Starter · #1 ·
I decided to change the head gasket on my 87 Supra Turbo with 80,000 miles because the engine had low compression in cylinder #5 (115 #), and leaking valve guide seals. I also thought I had a blown head gasket but as it turns out it wasn't blown. When I reassembled the engine it wouldn't start and I believe I traced the problem to the ignition system. I connected the #5 plug wire to a spark plug, grounded the base of the plug and cranked the engine with no spark. Does anyone have any idaes on what the problem may be or how to test the components. I was very careful when reassembling the parts and am fairly certain everything is installed correctly. I have a volt/ohm meter and oscilliscope available to test the components.

I also checked the compression in cylinders 5 & 6 to make sure the compression was good after the valve job but to my surprise #5 was still bad (still 115#). I put oil in the cylinder again but no help. If it isn't the valves or rings what could the problem be?

Confused in Florida
 

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i would try swapping some wires out - maybe you have a bad one. Did you check out all of your cylinders for compression after you reassembled it? Also, how much different is the compression from the other cylinders?
 

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Discussion Starter · #3 ·
The plug wires are new as are the plugs. As for the compression readings before the repair, they were all around 150# except for #5 which was 118#. After the repair I only checked #5 & #6 because they were easy to get to.
 

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are all of your valves adjusted correctly? ive seen the camshaft ride on the shim when it should have been off altogether. If your valve seats were cut they may stick out farther than before. if its not your valves, and you say that the head gasket is well torqued and in good shape, rings could be the only other culprit. Maybe you should try a higher viscosity oil when you do your compression check.

As far as the spark goes, ive seen and heard of faulty cam position sensors, ignitors and coil packs. Did you try a different spark plug, switching the source of the spark plug wire, and did you check all of the quick disconnects? In addition, there are two different q/d that are exactly the same. One plugs into the ignitor and one plugs into the coil pack. If you have them mixed up, you wont get a spark. Check all of your quick disconnects very carefully for loose and pulled out wires. This included the q/d on the CPS. Give it a wiggle.
 
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