02 Honda Odyssey P1399 Random Misfire - What test have I missed?

You can easily do a relative compression test without an ampclamp:

Using one channel in volts DC connect the positive lead to engine ground and the negative lead to battery negative. Select a low voltage range so you can see the compression humps and crank the engine over.

Another way is to put the positive leads of one channel on battery positive and the ground lead to battery negative. Couple the scope to AC and crank over.
This way the compression humps are upside down because you're actually measuring the voltage drop and this one will be higher when the current flow is higher. If you wanted to view the compression like you see it with an ampclamp or the 1st way described you would just invert the signal on the scope or swap positive and negative leads.

The scope section of the Modis is the same as the Verus, no difference in sample rate.

I'll give that a shot. Thanks.

Regarding the MODIS, I just looked at some specs and your right, they are the same. Only difference regarding the scope is the screen

Vehicle should be back Monday. I"ll keep ya'll informed

POSITIVE UPDATE

Vehicle came back was the CEL on, I was expecting that. Figured it was for p1399 again. It was actually only on for an EVAP leak we have yet to deal with. No misfires in history and during a good 20 minute drive I only saw the ECU catch a misfire on cyl 5 once or twice but not enough for it to through a cyl specific code. Last time within 1-2 minutes I would have 4 cylinders misfiring.

I am thinking it is a flow problem through the injectors. I did put fuel system cleaner in the tank before they picked up the van so maybe this was a fix. We will recommend some more fuel system treatments to try and clear it up some more and see if that works. I am not a huge fan of fuel system cleaners but if it works, great.

I didn't flow test the injectors this time around only because I found out I don't have the right fittings for my fuel pressure gauge to rig it up to the fuel rail.

I did purchase a 60a probe so I did a current ramp test on the scope at each injector feed wire at a bulk connector and all the ramps looked good and each looked the same as the others.

Scoping the secondary ignition can tell you a lot about what's going on inside and even outside the combustion chamber.

Soooooooo, fuel system cleaner may have actually fixed something? :silly: Color me surprised!

Ya no kidding! I always avoid the stuff cause I never believe in it.

When I first scoped the ignition I used a spark extension lead from the coil to the spark plug so I had a secondary ignition wire to test and all I had was an alligator clip attached to the scope and clamped onto the outside of the spark extension lead to grab the secondary waveform. Problem I had with this is the old MODIS only goes to 50KV on the vertical scale so most of the waveform falls off the screen and I can't really see all the important stuff I wanted to see. I need the shop to order an attenuator for their scope and proper ignition lead as well.

These coils, the way they are design, you can't get the secondary ignition by back probing the primary. I was really hoping I was going to have a successful waveform test and see possibly lean misfires, bad plugs etc.

graywave wrote: Ya no kidding! I always avoid the stuff cause I never believe in it.

Agreed. But hey, as long as the PCM is happy, I'm happy. :lol:

Nice job sticking with it.

graywave wrote: When I first scoped the ignition I used a spark extension lead from the coil to the spark plug so I had a secondary ignition wire to test and all I had was an alligator clip attached to the scope and clamped onto the outside of the spark extension lead to grab the secondary waveform. Problem I had with this is the old MODIS only goes to 50KV on the vertical scale so most of the waveform falls off the screen and I can't really see all the important stuff I wanted to see.

If you really had a waveform where most of it went off screen while in the 50 kv display mode then you would have had a HUGE problem....

Actually Ithink this is almost impossible, with a complete open in the secondary and an extrem potent coil you MIGHT get a seconday peak voltage off screen but then there wasn't no spark kv or burn time to be analized. What part of important information of a waveform takes place beyond 50kv?

The kv settings on the old modis and the not so old verus as well are the same, stepped into 5, 10, 15, 20, 30 and 50 kv ranges. Using a 10x attenuator in the highest range would give you a 500 kv limit to be displayed. Now think about this; would there be ANY detail left?

I didnt have the proper capacitive pickup for the secondary ignition so using an aligator clamp could mess with the results im guessing. I havent done to much ignition scoping in the past. I will need to pick up the proper leads.

Basically, it was as if the signal was too amplified. Even the burn time was even off the screen. My test was not a very valid test i will admit

Graywave,

without the dedicated probe you can use the lab scope function to get a better result and not the ignition scope.

Then you would select a DC voltage range and adjust it accordingly to your needs in order to obtain a meaningful waveform. The absolute readings will be off but you can compare to a known good cylinder just to get an idea about the relationship.

With most COP coils you can just use the regular test leads. Negative to ground and positive placed on top of the coil or on it's side and you'll get an interpretable secondary waveform as it will capacatively pick up the signal. You may want to put a short protection on your signal lead though, just in case the coil secondary was leaking. This you should have done anyway in your described scenario with the extension lead as well.....

!KEEP ON SCOPING!

Most ignition systems I have scoped I was able to back probe the primary of the coil and get a nice clean waveform that way. So scoping only secondary for the first time with only what I had on hand seemed to be a little difficult at the time

I will certainly be playing around more with secondary ignition systems on the scope to get a better handle on it.

I am following this thread with interest it is a real puzzle I have never seen compression test pressures over 200 psi on petrol engine.

My offer still stands on the injector flow test. I can post pics of the spray patterns. That wouldn't explain the high compression though.



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Welp the boss didn't want to put more time into it since it wasn't throwing any misfire codes so it was kicked out the door before I could verify some other things and recheck compression.

Maybe it will come back

I did take it out for another drive before it left though and feel the issue is still lurking underneath. After awhile on the way out, the computer reported "yes" for misfire on cyl 5 and on the way back I shut the engine down, and cycled the key which seems to reset the misfire data, drove it back to the shop and the computer reported cylinders 2,3,4,5 misfired. No Codes though. Cyl 2 is a new one to misfire. Never felt it and drove much better. I have a feeling it is fuel injector flow related or bad fuel as I heard it sits a lot.

Trying to convince the big boss to buy a master fuel system test kit with all the fittings I would ever need.

The compression I would have liked to verify. Who knows if the compression gauge was even accurate. At those compression pressures I figure that starter would be working overtime. Seemed the crank normal and quick to me.

There is an EVAP issue that they may want to get resolved so it may come back.

Until I see it again, there won't be anymore updates

just wondering have you attempted a crank shaft pattern clear and relearn? your scanner should be able to do it. i had an 05 accord in the shop p0301 p0305. fixed it with the relearn

I did reset all adaptive values. There was no "crank/cam relearn" offered in the scanner, only ECM/PCM Adaptive Reset