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More Than One Way Find That Misfire
Posted to Technical Theory Forum on 9/29/2014 32 Replies

Good Evening Fellas (and Ladies)..

Last-week, I was presented with a 2001 ACURA INTEGRA DOHC 1.8L (B18C1) exhibiting an intermittent misfire. The customer told me, the misfire is more noticeable during a steady-state cruise/70mph, although I can feel the misfire right in the workshop, but very infrequently. Surprisingly, "snap-throttle/brake-torquing" could not flush-out an ignition-misfire so out came the FLS/lab scope.

The 2 traces revealed a misfire intermittently occurring on cylinder #4, as seen in this trace.

[2001 Acura Integra GS-R, Engine/Propulsion Waveform]

I switched to an ignition-scope because it was the next logical/easy general-test to help guide me down a diagnostic-path. A "paraded" acquisition quickly revealed some secondary-leakage on #4.

[2001 Acura Integra GS-R, Ignition Waveform]

So an inspection of the "fairly-new" ignition cable was conducted. Nothing stood-out as a potential leak-point for a spark-deviation so the plug was removed as well.

The #4 spark plug was fairly oil-fouled. As a result, the porcelain insulator had cracked and allowed the spark to short intermittently (very-surprising, given the excess KV-DEMAND of the snap-throttle/ brake-torquing couldn't reveal the problem initially...his complaint was at a steady-cruise!!!). I was informed by the owner that he was aware of the oil-consumption and he planned to have the valve-guide seals replaced soon. A new set of plugs was fitted and the vehicle ran flawlessly. The car was returned to the owner and he experienced no more issues....for 2-weeks...

The vehicle returned today with a more steady-misfire at idle, although not as bad at higher RPM. A vacuum gauge revealed a slightly bouncing-needle. Again, the ignition-patterns were analyzed and #4 revealed an issue, however nothing like it did before! The ignition pattern appeared to have a very turbulent burn-line and when paraded, #4 Firing voltage was far-less amplitude then the remaining cylinders.....ugh-ohh.....this feels as though we are heading towards a mechanical-issue!( see the ignition-patterns below)

[2001 Acura Integra GS-R, Ignition Waveform] [2001 Acura Integra GS-R, Ignition Waveform] [2001 Acura Integra GS-R, Ignition Waveform]

I interfaced the vehicle, first with : *CH1(YELLOW)- #1 IGNITION-SYNC *CH2(GREEN)- FLS ON THE INTAKE MANIFOLD *CH3-(BLUE)- RELATIVE-COMPRESSION The engine was cranked and the info was captured. The waveforms were exhibiting an obvious compression-loss on cylinder #4. There was definitely a disturbance evident in the intake-trace. Rather than analyze the capture, I chose to simply move the FLS from the intake-manifold to the tailpipe. A very-evident issue was present in the exhaust stream as well. I uploaded the waveforms to PC so I could apply an overlay and begin to put all of the puzzle pieces together. ...SEE THE ATTACHED BELOW!

[2001 Acura Integra GS-R, Engine/Propulsion Waveform] [2001 Acura Integra GS-R, Engine/Propulsion Waveform]

There is definitely more than one way to skin a cat. Ive learned this from Greats like Albin Moore...As he says, he is always looking to put "THREE ARROWS IN THE TARGET". I realize that the diagnostic-path I chose with this vehicle was not necessary to draw a conclusion but I more-so wanted to demonstrate multiple-tests that backed-up my data to help me put the diagnostic-puzzle together. The more I use what I have learned from others in regards to ignition/pressure/vacuum-waveform testing, I can feel myself becoming more confident in my diagnosis'. The connection between the results of my testing and engine-dynamics is also far less of a gap. With a bit more practice, I can see these techniques becoming replacements for the more traditional testing that has served me well for years. As always I welcome all questions/comments/criticism...every opportunity for anyone to learn is what Im trying to generate with my posts...Thanks Fellas! -BRANDON-

Brandon from Indiana

Files Referenced:

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car Vehicle Data

2001 Acura Integra GS-R 1.8L

Engine1.8 L
Trans5-speed Standard

car Vehicle Data

2001 Acura Integra GS-R 1.8L

Engine1.8 L
Trans5-speed Standard