SRX cold start misfire

It's your engine, transmission, driveline
kevm14
Posts: 13935
Joined: Wed Oct 23, 2013 10:28 pm

Re: SRX cold start misfire

Post by kevm14 » Sun Mar 15, 2020 12:34 pm

Since I have 1 new coil in a box, I ordered 7. And 8 plugs even though they aren't that old.

Total: $379.79

There is a $2/plug rebate so that'll be $16 back. $363.79 after rebate...

I have a feeling this is wasteful but then if it doesn't fix it, I guess something else is going on...

And maybe if it does fix it, that could be an indictment on my methods...oh boy, bad news either way. In my defense, I am still juggling multiple variables so it's still not going to pinpoint exactly what the issue was.

kevm14
Posts: 13935
Joined: Wed Oct 23, 2013 10:28 pm

Re: SRX cold start misfire

Post by kevm14 » Sun Mar 15, 2020 6:39 pm

Already submitted my $16 rebate online. Cool.

kevm14
Posts: 13935
Joined: Wed Oct 23, 2013 10:28 pm

Re: SRX cold start misfire

Post by kevm14 » Mon Mar 16, 2020 7:03 am

So this is dumb. The firing order is NOT the order of cylinders in that misfire graphic. I have no idea why they are ordered that way.

The actual firing order is: 1-2-7-3-4-5-6-8.

I feel like depending on the exact nature of the misfire, misfires in one cylinder can show up occasionally on a cylinder after that one in the firing order (nowhere near enough to light the MIL though). I have no idea why the list wouldn't be in firing order (it should just be 1-8 then). But here are the hits reformatted for firing order from the last scan:

1: 1 hit (pass side)
2: 3 hits (driver side)
7: 6 hits (pass side)
3: 9 hits (pass side)
4: 0 hits (driver side)
5: 1 hit (pass side)
6: 1 hit (driver side)
8: 1 hit (driver side)

So it is possible that some "soft misfires" (my term but call it incomplete burn) on #7 could in fact be coming from #2. And the hits on #3 could be coming more strongly from #3 and that coil came from #7 which did have quite a few hits on the last P0300. Also #5 and #7 are NOT next to each other in the firing order, and those two were clearly misfiring before. This is less scientific than I'd like but maybe the point is I am more trusting of misfire reports from non-adjacent cylinders (in terms of firing order). When it is that clean, I believe the results. In fact, a light was set. Pretty concrete. The pic I just posted is not clean at all, by comparison (no light/codes).

Now I could just ignore it and say...if I don't get a light, I shouldn't chase problems. But that's probably not the right answer given the history here, and long term incomplete burns (and occasional non-light-setting misfires) are not good for the cats. Or fuel economy.

The good news is, I will do plugs and coils and that should hopefully baseline those items. The thing is, neither the plugs nor all 4 coils on the pass bank should have anything wrong with them. And if they do, then do I 100% trust new parts? That's why I am reading the misfires rather than just throw parts at it (or why I have been doing that until now).

Still, you could say that if I did not have a Tech 2, maybe I would have just done all coils as soon as one seemed to be failing. I am still not convinced that would have been a 100% solution because it still seems like I have more early failures so even if I did all 8 originally, I'd still be faced with buying more right now. In fact it would probably just be the opposite situation. I could have bought all 8 before, and when I had early failures on certain cylinders, I may have specifically targeted the replacement rather than buy 8 MORE. Net coil purchases: same.

If on the other hand, in the very unlikely scenario that all of the unreplaced driver side coils are causing ALL of the hits on the passenger side, then I admit defeat. I doubt that is the case though. And I will never know the answer because I will be doing all plugs and coils...

I guess the only thing I could really do is replace the driver side coils and plugs and run it for a week and see what happens. Probably not going to do that. The available evidence does not support that theory.

kevm14
Posts: 13935
Joined: Wed Oct 23, 2013 10:28 pm

Re: SRX cold start misfire

Post by kevm14 » Wed Mar 18, 2020 9:18 am

Coils and plugs came in...all I have to do is install them.

kevm14
Posts: 13935
Joined: Wed Oct 23, 2013 10:28 pm

Re: SRX cold start misfire

Post by kevm14 » Sat Mar 21, 2020 3:44 pm

Installed them. Everything looked good that I took out. No oil on anything. Plugs looked good and gap was good.

It seemed to be doing the same thing off a cold start but it maybe was a little smoother at least (minor, occasional shakes in park, nothing in drive). Drove it around and it was pretty damn smooth. I think whatever this is seems to happen right off a cold start so I will have to be more targeted in my diagnosis.

I still think I had a max of 2 failing coils and I don't think there was anything wrong with any of the plugs. So that was kind of a waste. However, this may have been a necessary step if something like this happens again. And worst case, if it needs more coils down the road, I have at least 6 that are probably good. I labeled all of them and even stuck the plugs in the ends.

Further theories would be something like a vacuum leak or leaking intake manifold gaskets. I can try retorquing the bolts (after it cools).

There was something blocking the rear of the intake manifold so I was not able to feel the PCV breather hose (the one that caused lean codes on my STS). And that's the thing. I drove around and fuel trims were fine, less than +10% on both banks. Now an individual cylinder vacuum leak like an intake gasket wouldn't show up as well on the whole bank so that's something but otherwise I'd expect other codes before I just get a couple random misfires. On the STS, I don't recall any misfires when I had the lean codes, in fact.

Jury is still out I guess. Needs more time/driving. Feel like I wasted money though...

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