Now that you have gone thew all of this, have you checked all the wiring back to the PCM? I know you said that you replaced the Opti harness, I assume you are talking only about this section:




But what about this section the wiring from the PCM to that harness? Might want to check it all that wiring to be sure as well.


Then you might want to start checking resistances and signal along the ignition. Here is a schematic from a '95 for reference.

 

Thanks for the reply.

I checked all of the opti wires back to the PCM for continuity and resistance. I got good continuity and basically no resistance. I also checked for continuity between each wire to the others going to the opti. No interconnections (no continuity between other wires).

 

Fuel......which you say is fine at WOT
Ignition......you have changed everything possible
Compression..........at WOT (that would be weird) but I've seen it.

I've seen push rods rubbing on the back side of the heads causing the problem you spoke of.

 

I had a miss in that area once. It was a loose rotor button.

 

I am assuming that everything in the opti is fine since it was replaced with no change to the symptoms. I logged the low resolution signal again and it looked basically the same my past posts.

The other odd thing is that the car has LT4 valves springs that the seat pressure seems low. They are approx. 80-85lbs seat pressure. From what I have read they should be more like 100-105lbs. I would say the problem is valve float but as you can see in the dyno graphs the car continues to increase in RPM and make more power up to the end of the run...after the break-up stops.

http://s819.photobucket.com/albums/zz117/wilsoncd2/

so that would mean that the valve springs float but then stop floating after 5300rpm? That just doesn't seam logical.

 

thats not possible if the valves start floating and or bouncing off the seat you would start to see a jagged edge in your hp and tq curve and the the hp and tq falling off. valves dont start floating then stop . they will float and then get worse till they come in contact with the top of the piston .

if you kept making power beyond the miss /breakup .

i wonder if the optical encoder starts to wobble at a certain rpm and then smooths out after a certain rpm , kinda like the mythbusters thing about the cd exploding in a cd rom drive , if you whatch the vid it starts to deform at a certain rpm then smooths out then starts to distort/wobble again higher up in the RPM range.

i guess to try to find this out would be to take a opti and spin it with somthing and see if it ever starts to wobble , it just a therory but maybe im on to something. anyone want to do an experiment? lol

im having the same issue as you but mine comes and goes and get lower in the rpm range with the rise and fall of the coolant temp.


i wonder if it would be possible to goto a different type trigger system that would bolt to the dampner and use a hall effect sensor .

i belive your on to somthing with the messed up square wave at that rpm ,maybe the high voltage or maybe the resonance of the engine is screwing with stuff.

 

Bringing this back to life...

Since my last post, I have checked the following:
Logged PCM pulses to the ICM with a scope, pulses look fine. So it isn't opti.
Logged pulses to coil from ICM with a scope, looked fine.
Put and inductive clamp and scope on the coil wire to opti, no missing pulses.

With my timing light on any plug wire, it shows missing pulses, BUT when I put the scope on the same plug wire it doesn't show any missed pulses (at the same time the timing light does show missing spark). The logged data from the scope shows that some pulses are weaker (smaller amplitude) so maybe the timing light just isn't picking them up or the resolution isn't good enough on the light.

Still getting P0300.
Coil is new
Opti is new
Plugs and wires are new
All wiring checks out for continuity and no resistance
Connections seem clean and solid

Any other ideas?

Thanks,
Chris

 

Chris, I know you're struggling with this, and, have certainly replaced a lot of electrical componets in the process, but, your last post "quoted" above, gave me one more idea to try. Your comment about some secondary voltage/current pulses being weaker than others led me to thinking about trying this. Let's take some resistance out of the secondary wiring circuit and see if any difference is noticed. We all know that coil saturation time decreases with increasing engine RPM so let's try this.

Take off just your current coil wire and measure it's resistance. If it's typical "radio supression' wire it should have a resistance of between 2,500 and 4,000 ohms. Now comes the hard part ..... find a "mom and pop" auto store in your area that still sells "copper core" spark plug wire by the foot. Buy one(1) foot of this wire, and make yourself a "test" coil wire. Your "test" coil wire will have a resistance of less then 1/2 (i.e. .5) ohm, and by using it in place of the "radio supression" coil wire ....... you will immediately remove about 2,500 to 4,000 ohms of resistance from the secondary firing circuit. With the solid copper core "test" coil wire in place, now see and/or scope how your car runs.

 

Negative. I have seen plenty of cars(dyno graphs) that has one little hiccup, then straightens out and keeps pulling, with valve springs being the culprit.

 

I guess that can happen but, in general, what the untouchable describes is what happens. Valve float is essentially a spring harmonic that happens at some multiple of the oscillation rate of the spring. If the spring is light, that harmonic can happen at a relatively low rpm leading to uncontrolled valve motion ie valve float. It is easy overcome by using a heavier spring which, in effect, raises the harmonic to a higher oscillation rate than can be acheived in the engine.

I guess if you looked at it as a graph, you'd see the springs primary motion as a sine wave with a period of 1 and the first harmonic sine wave occuring with a period of 2. Sometimes the maxima of each will occur at the same time as will the minima. Sometimes they'll occur at different times and will interfere with each other. If you were to change the period of the first harmonic to a period of, say, 4, then you'll not see the interference very often. That's what you get when you use a heavier spring to control the valve......

 

Jasonisdn, yes I would really appreciate it if you could send me the link to the guy who sells just the Optisparks's optical sensor.

 

Here is another bit of interesting information.

While making a dyno pull, we watched the crank hub with the timing light (obviously made a mark on it for reference). The timing advanced up to 35Deg while the car was accelerating, BUT at the point where the miss started to occur the timing dropped way off... to about 15Deg. The logged data through Autotap said the timing was 35 Deg during the same time we saw it drop off to 15 Deg.

 

Yep.

90% of the ones I have seen floating are at 5800 rpms.

 

That sounds pretty important. The PCM doesn't actually know what the timing is...it knows what it commands. So it's commanding 35 degs of advance yet only 15 degrees of advance is being applied. Take a look at the circuitry for timing advance to see what can affect it as there isn't any mechanical mechanism fro applying advance....

 

pm sent i have received one from him so far but actually have not installed it yet.