I got my analyzer O2 working again- it was the sensor itself that went out; I got a new one and viola! .

However, does this make sense? I got the following numbers with the engine at about 180°F just before the cats lit up.

HC => 2108
O2 => 3.5%
CO => 3.18%
CO2=> 10.3%

As soon as cats lit up, it held steady at the below numbers all the way up to full operating tempearture of 200°F

HC => 50
O2 => 0%
CO => .08%
CO2 => 15.3%

This seems like the cats are doing all the emissions leg work masking some problem. Which probably explains why I still have a rougher than expected idle.

But if I had an issue, why would both side BLMs be exactly equal to eachother? I would think if one cylinder had an issue, the BLM's on that side would be very different than the other side...

EDIT: And I do have a mild rotten egg smell coming from the tail pipes. I guess that's a "running rich" signal. So the question is, with my O2 centering voltage set at .400, and my BLMs perfectly set at 128 on both sides, what would cause a rich condition like this?

 

Anybody?

 

from the first set of numbers your a little rich if you had a stock motor.
if i remember, around 1.2~1.5 CO is average for dead stock.
but then a ZZ4 cam isn't all that radical, is it?

i plugged the numbers into a Lambda calculator & it comes out to 14.36
how much did you try to lean it out when chasing the split BLMS & miss?
do you have AIR injection on it?
maybe play around with desired AFR or the O2 sensor & see if you can lean it out some but keep the 128 BLMs

the after cat numbers just shows how much a difference good cats really do make.

 

I'm actually running a cam slightly more radical than a ZZ4. 212/218° at .050.

When I was chasing the misfire, I had the fuel and timing all over the place trying to figure it out. But after I fixed the grounding problem that was causing the misfire, my tune was way off again since I had tuned around that misfire. My tune now is brand new.

One thing I was able to do today was to go around the engine while it idled and start disconnecting injector plugs one at a time. Remember during the miss the #2 cylinder wouldn't respond to anything? Well now it does respond which is good. However, with the other injectors, removing the plug will shoot the BLM's up into the 150-160 range. THe #2 will hit 142, but no more. It would seem to point to #2 as a problem, but the #2 spark plug looks just fine, a subsequent compression test showed all cylinders at 120±10 psi, and BLM's on both sides are precisely at 128.

Unless it's so rich it's spawning multiple cylinder misfires?

 

i don't think its rich enough to cause any noticeable misfire.

funny about #2 only going to 142, maybe try to swap it with an injector from the other side one more time now that you have the BLMs right & the miss fixed just to see if there is any change.

if you can, put it on the 4 gas & one at a time pull #2 & then one on the other side & see what kind of difference you get in HC & O2. it would probably be best if you can check both sides before the cats light off.

 

I'll have to try that stuff. I wish I didn't have that H-pipe cross over. The exhaust is mixing between the two sides unfortunately. That would have been very telling if could sample each side separately. Oh well....

 

Seems like you still have a misfire, with 3.5% O2 and high HC. On stock small engines, pre-cat, in closed loop, I typically see ~1%O2 and ~1%CO, and 14.7%CO2, and ≤≤200 HC for sure. 2100 HC is a definite misfire, in my experience, but I can't remember ever using an EGA on a cam with any significant overlap, but I wouldn't expect your somewhat small cam to spew soo much.

 

Thing is, when I had the misfire, it FELT like a misfire. It was a very noticeable miss.

But now, I'm actually surprised that it's running this badly (from an emissions standpoint), because it feels so much better then when I had that ground problem. It idles very steadily at 650 rpm, though there is still the mild roughness to it that I spoke of before.

Maybe the miss is still there, but the intensity has been reduced?

 

maybe worth going over everything that was done trying to diagnose problems in the past, and make sure it was all undone? for example, I seem to recall that you may have been trying different injector sizes in a cylinder or two, maybe worthwhile making sure all the injectors are back to equal sizes.

beyond that.. maybe post a datalog at idle? how stable is your timing at idle? if your idle spark adv/retard vs. idle speed error are fairly strict, you could be seeing a lot of idle spark change. just taking a stab/guess.

 

I'm back to 24 lb/hr on all cylinders.

One thing I was thinking about is the following: If the BLM's are only shooting up to 142 on a disconnected #2 injector, that would mean it isn't generating as much of a lean condition as when I disconnect other injectors which result in a 150-160 BLM. In other words, the #2 cylinder isn't moving as much air as the other cylinders. Otherwise it would also register a comparable BLM.

Now what could cause a descrepancy in air flow between cylinders?

My compression test was successful.

I'm going to run another leak down test.

Assuming the leak down test runs successfully, that could only mean a damaged intake lobe the cam, correct? Funny thing is, I changed the ZZ4 cam to this Comp cam after the misfire began several years ago. I suppose I'll have to do a valve-lift check with a dial indicator and see if there are any descrepancies between #2 and the other cylinders. I already changed the valve springs and adjusted my rocker arms (on numerous occassions) as well as inspected my pushrods for straightness. I also changed out the valve lifters a while ago as well (though if one of those went out, I'd very likely hear it).

Talk about confusing… There must have been a myriad of factors contributing to that misfire- the ground problem being one of them (resulting in a weak spark). If there's some remaining mechanical malfunction driving the #2 cylinder to fire differently than the other cylinders, that could explain what I'm seeing today. It'd have to be a minor malfunction because despite the very dirty pre-cat emissions, the roughness is nowhere near what it was before I fixed the ground.

 

Do you have the correct reach (length of thread) of spark plug in there? That bites a lot of aftermarket headed engines in a strikingly similar way. It's also a quick and easy check, just to be sure.

 

I'm not sure how I'd verify that without pulling the heads...

 

I would think that as long as you are running the plugs AFR recommends, you're OK.

What's your quench height? how much timing are you running? If you're starting the fire late (timing not advanced enough) and there is no quench (to promote a fast and complete burn) that could promote a high HC reading and a high O2 reading. probably not quite that high (unless the timing was really off/low); but still worth mentioning. If it's suspect, and you're running a stock damper, make sure the outer ring hasn't slipped on the inner ring.

one of those engine diagnostic scopes might help as well, it's possible you have a cylinder with a weak spark. enough to fire off and not feel a miss, yet not enough for proper/complete combusion.

just throwing out a few ideas.

 

https://www.thirdgen.org/forums/alte...rformance.html

About the spark plug reach question.

 

These are all things I've spent the last four years verifying and re-verfiying. I know beyond a shadow of doubt that I have fuel and spark. What's coming into question now is compression again. I thought I had checked that a long time ago, but this latest data seems to contradict that.