So I finally got my new ignition coils, new cat converter, and new ignition wiring harness installed. So far I've been putting around to feel the car out. It definitely feels better than before replacing these parts, even though I haven't really wound it up yet. So today I had a chance to get some datalogs to see how the motor would behave at upper RPMs/boost. Here's my notes:

-I ran a couple of times at 11 psi and then a couple at 14 psi
-Each time I had very distinct "breakup" (felt like car hesitated a bit) above 5500 RPM
-It felt more prevalent at 14 than at 11 psi
-AFRs were somewhere between high 10's low 11's
-Timing/fuel map was not changed at all from before installation of new parts
-Knock readings on datalogs show clear spikes above 5500 RPM
-Knock curve was essentially flat (readings of ~1.0) until spikes above 5500 RPM
-I checked my plugs a month ago, and they appeared to be "OK", haven't put more than ~500 miles on the car since then
-I didn't check my plug wires, I assumed they would be fine with only ~20k miles on them (now I think I should have checked them)
-I didn't check the igniter (not sure how to do that, FSM calls out a special tool)

So what do you think? Is this what people refer to as ignition breakup? I think if it was detonation, my motor would be long gone I did five or six runs pretty much back to back, the motor still has a very happy idle, starts right up, runs nice and cool, no other obvious issues. FWIW, it still feels faster than before I replaced the parts, in spite of the obvious hiccups.

I attached some pics of the two datalog charts in addition to the datalogs themselves. Let me know what you think. TIA I'm going to pull my plugs and check my wires and check the igniter too, will report back findings.

Datalogs on same chart (14, 11 psi; boost, knock, AFR)


14 psi log


11 psi log

 

When my car had breakup it felt like it was stumbling. HKS twin power is a pretty cheap fix.

 

Sounds good to me, but I don't think I should be breaking up at 11 psi... hell my car ran at 12-13 psi for about 1.5 year w/o a TP and it didn't break up like this. Something else is wrong. But believe me, a TP is next on my list of stuff. After that I promised myself I wouldn't spend more money on this car, we'll see how that goes

What RPMs, AFRs, and boost were you breaking up at?

 

hmm... how is your grounding?

 

^ Eh, stock Maybe I should check that! It's usually the simple stuff that kills you, right

 

Check the plug wires (you said you hadn't yet). I had misfiring that turned out to be a burned plug wire.

Dave

 

Will-do captain From now on, anytime I take stuff apart, I will check everything while it's out. That's my new mantra

 

can you actually hear the engine misfiring up top?

 

Actually, no. I don't hear anything at all out of the ordinary. I can feel it, the power seems to suffer up top, before I get the hiccups, (from about 3-5.5k RPM), it feels perfect. After that it's just a couple of bumps and then all of a sudden I'm near redline. Like I said before, when I run lower boost it's less of an issue. I need to dig in more to this, as obviously I have not revealed the root cause in this issue...

 

Given that the AFR's look okay, it sounds like ignition to me, too. Especially since there is a correlation to boost; firing voltage goes up linearly with cylinder pressure. Because electrical current will find/take the path of least resistance, I agree with the suggestion to check the wires since they can fail in not-so-obvious ways. In my own experience, I've had a couple of episodes where I had a misfire and I thought it couldn't be the plugs because they had low hours and looked good--turns out I was wrong, and replacing the [offending] plug(s) fixed the problem.

The knock seems kind of weird; and if it is to be believed, perhaps it suggests that there is an ECU, timing or trigger issue that may be related.

 

If that knock is consistent I would be worried. Thats pretty high knock numbers under full throttle. The knock is also under peak torque which is when knock is most likely to occur.

Ignition breakup will often have lean spikes that show up where the mixture didn't completely burn and fresh oxygen is picked up by the wideband.

You should check the plugs again.. (what plugs are u running?), even pull them, crank the car and visually inspect the spark on each one. I had a huge pile of spark plugs that I tested and had several that appeared fine, but either wouldn't spark or were sparking within the plug rather then from electrode to ground strap.

 

Interesting that you can't feel the individual misfires, just a power loss. I had the exact same feeling. At first I didn't think it (the bad plug wire symptoms) were caused by ignition, because there was no loss of smoothness - just a severe power drop.

Dave

 

When you swap spark plug wires, don't forget to use dielectric grease on both ends (at the ignition coil and spark plug).

The ignitor gets grounded where it bolts to the chassis, it doesn't have a ground wire in the harness. Might be a good idea to unbolt it and make sure everything is clean. Might also be a good idea to double-check the grounding wire between the chassis and the battery since that is essentially the path the current will travel from the ignitor to the battery.

 

A very useful post that I want to underscore:

Absolutely. However, I would add: Is it really knock? Or is it reading mechanical noise when it drops a cylinder? I was warned about this....


Depends on the duration of the misfire(s) and the integration time of your wideband. You will likely not see an occasional misfire, however, you should see a long misfire; the kind that causes the motor to feel like it's laying down.

(BTW: It is this excess oxygen and fuel injected into the exhaust during misfire that is most destructive to cats.)


This mirrors my experience exactly: Thermal & mechanical shock to the nose insulator can cause crazing allowing the plug to spark down inside, where it cannot ignite the intake charge. I've also experienced plugs that glaze over with a coating (usually a grayish & shiny or glass-like) that is conductive that will shunt the spark to ground (meaning no spark).

 

'sure looks like something's up w the primary ignition what w the failure being in the peak Combustion Chamber Pressure range. an ignition breakdown. it is a bit weird your boost doesn't tail off too much which happens when an engine loses torque. plugwires, plugs would be the immediate suspects. i appreciate the data provided as it is a big help.

good luck,

howard