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89 prelude misfire and viberation

 
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Old 01-30-2015, 01:39 PM
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89 prelude misfire and viberation

Iv recently had an issue wich has me boggled. My 89 prelude b20a5 has a slight missfie at idle and viberation at driving rpm's. along with a ticking upon acceleration or when engine is pulling hills. I have replaced the air filter, plugs,wires,cap and rotor button, pcv valve, new timing belt, set the timing dead on, checked valve lash. Plugs appear to be burning clean,engine uses no oil , no smoke at all...However all efforts have improved nothing... Heres the catch it doesnt do this all the time just randomly. One day it runs superb with no ticking noise next day it may have the same symptoms. Then fine again on and on...I need help before sinking tons of $ over a simple fix.
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Old 05-12-2015, 10:53 AM
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Re: 89 prelude misfire and viberation

It sounds like you're on the right track to sorting your issue, here.

Now... scary stuff - get it out of the way, 'cause it's cheap and easy to test. I highly recommend performing a warm engine compression test (wet rings), cold compression test (time for oil to drain from rings), and leak down test. You'll have to find the service manual for your specific model, for target values, but a good rule of thumb is 5-7% variance across cylinders is AOK. >10% = trouble brewing.

Per the work you've done, you can be fairly certain that your ignition system and intake side air handling are in good working order. The only other potential issues I can think of would be a goobered up MAP sensor or mis-gapped plugs (though both of these would typically be idle / low load issues)

Next thing to look at would be your fuel system. If you've got low fuel fuel pressure, especially at increased flow, you might start poorly atomizing fuel AND running lean. I would check / change fuel filters, and see if that helps. If filters don't solve it, check fuel pressure at idle (to test pump and FPR).

Once you confirm you've got the correct fuel pressure, try checking your injectors. You can do this by running for short periods of time on 3-cyl - pulling injector wires one at a time. (ideally, you'd just do this at idle, but it sounds like you'll need to put load on engine to diagnose). If the engine runs consistently on 3 cyl, the one you pulled is probably not the problem. If you run on 3, and intermittently on 2, then the injector you pulled is not on the problem cylinder.

There's more, but hopefully this should get the ball rolling again.
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