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Discussion Starter · #1 ·
Would appreciate someones help on a technical issue. Have a 1992 240SX. The first cylinder up front, or I assume #1 is not firing. Engine has 94,000 original. Took compression and results were thus: #1 - 230 psi, #2 - 200psi, #3 - 196 psi and #4 - 194 psi. I assumed these engines should be somewhere between 160 - 200 psi. This was a dry test with all plugs removed.

I'm puzzled at the 230 psi for cyl. #1 and why it will not fire. It is getting spark, but still why so high compression. There are no knocks and engine does not smoke. Also, are cylinders numbered from front to back in ascending order. I understand the firing order is 1342. Thought maybe the wiring order was wrong. Appreciate any guidance.
 

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Discussion Starter · #3 ·
3 hole

KA23-

Appreciate the comment, but why just the #1 cylinder and the remaining are around 194 psi?

Also, is the cylinder ID on this engine one, two, three, four starting in the front?

Thanks
 

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Yes, starting from the radiator to the firewall 1-2-3-4 Firing order 1-3-4-2. I'm not sure why you have that amount, but a lot of carbon would have to build up to bump compression almost 50-60psi. Make sure your cams are set correctly and re-check compression.
 

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Discussion Starter · #6 ·
3 hole misfire

Ka24e: Thanks for the info. I'll change out the timing belt and recheck, although seems odd that only one cylinder would carbon up. Hopefully, the timing problem is causing the one over pressured cylinder. Thanks again.
 

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Couple ideas:

Could be your cam timing is off one tooth allowing a high VE at cranking RPM and your #1 cylinder is good and all the others are a little weak. As I think about it, I would guess that an intake cam advanced by 1 tooth might cause this scenario. This is assuming that valve to piston interference is not taking place, obviously. But then also your engine would probably lope at idle in this case as well.

Another thought, I've always notice my #1 plug is always the most white and the plugs get gradually darker or more tan as I go back to cylinder 4. I've always thought this had something to do with the coolant outlet being molded into part of the #1 intake runner and heating the air in that runner more than the others. This may or may not have anything to do with your problem though. Just a couple $0.01's.
 

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Discussion Starter · #8 ·
3 hole firing

BMoses

Appreciate the feedback. Checked the cam timing. Its good. Also, do you agree if the cam timing was off, the other cylinders would have fired intermittently? This is what I was told prior to checking the cam timing. Now, I think it may be the fuel to that cylinder. I should have checked the basics first. This would explain the miss on #1, but not the high compression. I'm stumped, but hope to find out. When I do, I'll share with you. take care.
 
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