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Possible causes of a shaking engine?

@“Honda Blackbird” Wires were one of the first things I went through, replaced all of them after I found the one that had burned through, sorry I had forgotten to mention that they were all replaced.

@jmcarc has a good suggestion. I’ve done this many times to verify shorting plug wires or a bad plug wire.
You can watch the light and see if you have any spark…or double spark from a shorting wire or bad cap.


Update: thanks so far everyone! I just had a chance to do the compression test, I believe I’m in range on where I should be, cylinder 5 was at 135-140 but I’m firing there, cylinder 1 where I’m not firing is 145-150. Leaving me with injector or ecu at this point, one step closer.

Update again: it’s running on magic somehow!

Glad to hear you are back to running on all cylinders.

Maybe a plug wire popped off the end of a spark plug and doing the compression test… you put the plug wire back on tight.

Or just pulling the plugs left all the bad JU JU leak out!!!


I’m still leaning towards injectors, she still has a random shake here and there so taking then to get cleaned Monday. New problem is a bad shudder whenever I turn right, seems more on the engine side than suspension.

bad shudder whenever I turn right

Sometimes wires or vacuum hoses can get pinched during turns b/c the sway of the body changes the geometries. Differential problems can cause this symptom too. Suggest to have your differential fluid level checked.

Okeedokee…Good! But it still shakes? I hope you did the plugs as well?

If no codes are present then it may be time to do a good Ole Compression test… If its not fuel or ignition…its time to compression test… Hell…It may have been time all along… But we all like to start with the usual and less expensive suspects first, so the troubleshooting is as far as Im concerned is going its usual course.

Like I said…if no codes are present…it leads a more direct path toward a comp test being needed.


I hate to burst your bubble but those compression numbers you mentioned are not good.
The engine will run on them and they’re not the cause of your cylinder specific misfire but they’re tanking.

A wet test should be done to see if the numbers jump upwards considerably. If so, that would point to piston ring issues.

An engine in great condition should have 185 and up on compression. An engine developing wear over high miles will hopefully be in the 165 or better range.
When you’re in the sub 150s there’s a problem.

Oops…duh…maybe I should read before I post… LOL… Sorry… Yeah not sure what the spec is on the compression numbers…have to look that up.

The problem with looking specs up is that many manuals are wrong in this regard. Why they do this I have no idea unless the manuals are put together with a group of people in which not one of them has ever actually run a compression test and they’re operating on theories.

One manual I have here states that compression is fine if it is 115 PSI and to make matters worse the manual also states that it is acceptable to have 115 on one cylinder and 150 on another.
That is all total BS.

The rule of thumb on compression is to multiply 20 X the compression ratio.

The only low pressure engines that I’ve ever seen in which low is considered normal are air-cooled VWs, sidevalve auto and motorcycle engines, and aircraft engines.
Compression ratios are usually low (6:1 or less) and aircraft engines are a whole nother kettle of fish so to speak.

One practical problem with your suggestion @ok4450, it can be difficult to determine the designed compression ratio of the engine, esp for diy’ers. That number usually doesn’t appear in diy’er manuals like Chiltons and Haynes. I looked my truck’s compression ratio up in a book about Ford small block V8 engines I found at Barnes and Noble, and for that model year (the designed compression seems to vary quite a bit year to year in that era) it’s rated at 8.3, so your 20X number is consistent with what I measure as the compression, about 165 psi.

The reason I’m a stickler on compression is for the following. I’m schooled and licensed as an A & P aircraft mechanic. Compression checks are required about every 100 hours on aircraft engines; maybe more often if a problem is suspected.

At the dealers where I worked compression tests were a way of life. Those tests were done during tune-ups or major maintenance services all depending upon era, whenever performance issues exist, during routine used car inspections, and so on.
Even if a car was as new with 30k miles on it compression tests were always done even if the engine was running like a Swiss watch.

I can’t say how many compression tests I’ve done but it has to be in the thousands. Do enough of them and the trends are obvious.
Some of the smog era Big Three cars would have lower than normal compression (say 165-175) compared to others but that’s mostly due to retarded camshaft timing.

If one took an identical, low miles, same make and model as the OP’s car and ran a compression test more than likely one would see 185 or better during the test.

I do not suspect the shake is related to the lower compression. There are a number of possibilities even down to and including new spark plugs which can drop dead at any time.
The point is that the compression is abnormal and thought should be given to the future.
If the car were mine I’d run a quick wet test and see if those numbers jump up; meaning ring issues if they do.

My old 94 H22 Honda Prelude engine that i installed into my Accord had 220 psi in every cylinder. Man did that thing RUN… You would notice the xtra 100 Hp and the 8200Rpm Redline every time you drove it… Installed a Close Ratio LSD manual 5sp too. I miss that car…the kid who bought it probably blew it up by now.