I'm back for another time. 1995 Camaro Z28 A4. Stock internal, shorty headers, EGR and AIR delete. Transmission rebuilt with updated servos and a shift kit for 1st to 2nd.
I have replaced the optispark multiple times and finally have a 100 % guaranteed rebuilt MSD Opti with the help of Injuneer. The problem started out with not being able to shift from 2nd-3rd. I would bounce off the REV limiter at my tach showed 6300 RPM, but I dont know if I believe it. I began to get a shudder around 45-60 MPH when under load and not down shifting, (I believed this to be the Torque Converter Failing). I took it to the local transmission shop and they claimed it to be an engine issue because it started to back fire through the intake when hitting the rev limiter in 2nd. Now the intake backfire is becoming more consistent at WOT around 4500-5000RPM in 1st and 2nd gear. I have 9495 scan and have uploaded two scans. One is just WOT to 2nd gear, the second is WOT until I hit 3rd gear. I dont know if this is fuel, ignition, timing, or transmission issue, since hitting the rev limiter typically kills fuel.
I have checked fuel pressure: At Idle 35 PSI, with the vacuum line off 45, at WOT 43.5 PSI. Opti, plugs, wires, MAP, TPS, Coil are brand new.
Any help would be appreciated.
***As a side note, I did have the PCM tuned by LT1 tuning, for the files attached, I changed it back to stock tune in case it was the tune, I can submit files with the current tune if needed.

 

I would suspect the MSD Opti. High RPM stumble is what I experienced with mine. Sent it back for "rebuild" and then sold it. Injuneer has spent a great deal of time and effort on MSD issues and it appears they are a lost cause now.

Backfire through intake is a very common opti fail symptom.

Maybe someone can analyze your scan data to advise further on what the issue is

 

I'm a bit confused.... last I heard from you in a PM in March, you had finally reinstalled the rebuilt MSD Opti, and the engine would not start no matter what you did. What changed? I have been telling people to avoid the MSD Opti like the plague based on the fact your rebuilt unit did not work after they sent it back.

This is actually one of the MSD Optis on which I discovered the erratic high res signal from the module, with brief spikes indicating RPM as high as 7,000.... while the engine was actually idling (although surging like crazy because of the erratic data from the optical moidule). The Scan9495 data from this unit was among those I sent to MSD engineering, through an MSD service rep that posts on ltxtech.com, that enabled them to track down the need to modify both the optical module and the cap design.


The two scans are very short - 15 seconds and 21 seconds. Do they both include the backfire?

 

This is accurate, I called MSD and complained, they told me to send it back, they rebuilt it incorrectly the last time, the sent it back to me, I installed it and it finally ran. I have had it in since the end of April/Beginning of May. The car seemed to run fine, but then these weird transmission issues started happening. Then the back fire.
Yes both have the back fire, when the RPM gets up around 4500 -5200 upon acceleration thats when it happens in those logs.
For these logs, the stock tune was reinstalled so that It would be accurate.

 

 

Yes to both, i Have a feeling its going to come back to the opti again.

 

Looking at the data logs, it's hard to see the cause-and-effect relationships, because the scan rate is so low. You are running 2 frames per second. The PCM is processing data at 5X that rate. I know Scan9495 can run faster than 2 frames per second.

In the limited places where it's actually idling, and it's in Cell 16, your LTFT's are 108 on both sides. For some reason it's pulling out 15% of the fuel to try and lean it out, and prevent it from running rich. To me, the MAF reading (~7.3 gram/sec) looks high for an engine idling at about 550 RPM. I would expect something in the range of 2 to 3 g/sec. I went back to the earlier data log from February - the one I sent to MSD - but with the idle jumping all over the place due to the MSD, it's hard to find a point where it's idling anywhere near 550 RPM for more than a single frame of data.

At idle, MAP also looks a bit high. Again, you have about 40 kPa, where I would normally see 35 kPA.

As far as the rest of the LTFT's, in any cells where you appear to have driven for a reasonable period of time, the LTFT's are all low - Cell 10 114/115. Then there are the mathematically derived cells, that are weighted averages of the closed loop cells. Cell 18, used in open loop when the engine is under load, and some other closed loop situations is 108/108. Cell 17, used primarily for decel (closed throttle) is 108/108. Appears for some reason, the engine is running excessively rich, and the LTFT"s are trying to lean it out.

Just to clear thing up, as I understand it, the backfire through the intake manifold occurs at WOT? If that's the case, this would not appear to be the "lean backfire" suggested in post #3. That entire post is directed at closed throttle decel, and that is not where you are getting the backfire. To me, everything looks normal on decel.

When you go WOT, the PCM goes to Cell 15. It does not appear you have driven much in Cell 15, since the LTFT's are 128/128. And of course the PCM locks the STFT's at 128/128 in PE mode. But, if the engine was running rich, necessitating the 108 LTFT"s, it would appear rich at WOT in PE mode. Your O2 readings are in the 0.950 volt range, with the right bank running a bit richer than the left bank in both logs. Using the stock narrow-band O2 sensors at the A/F ratios GM targets in PE mode (~11.7:1 stock tune) is not a precise method.... the narrow-band sensors are simply not accurate at those rich A/F ratios. The difference from left to right bank could easily be explained by minor differences in the two O2 sensors, or a temperature difference from side-to-side.

In both logs, you are getting significant knock retard at WOT. In log 1 you get 6-degrees, in log 2 an 8-deg retard, it recovers and at the end a single frame of 12-deg. This could be a response to any vibrations caused by the backfire. Does not appear to be because of a lean condition or too much timing. It does run a bit hot at 215-degFcoolant. The fans go to high speed, which may be the PCM reacting to the knock.

In log 2 the RPM peaks at 5,726 RPM, and I don't think that is enough to hit the rev limiter.... as I recall stock limit for both the A4 and M6 are over 5,800 RPM. Right after it peaks at 5,726 RPM, it's clear that it shifted because RPM dropped to 3,728 while the MPH continued to increase and the TP% remained at 100%. When it did shift, there was a strange MPH reading.... it had peaked at 42 MPH, immediately after the 5,726 RPM peak the RPM dropped to 4,496 but MPH jumped to 59 MPH, then immediately dropped to 50 MPH and continued to increase speed. Maybe you lost traction on the shift?

It seems to me that if you had a backfire through the intake, there would be a pressure spike in MAP, and that does clearly happen in one instance, and possibly in another. In log 2 with the throttle still at 100%, at the same instant it pulls 12-degrees of timing, the MAP goes from 92.27 kPa to 99.65 kPA, actually above the 97.81 kPa barometer.... that could be the point of the backfire. Note that the O2 sensors are still at ~0.950 volts, so it's not leaning out. Again, some of these thing may not be recorded with the slow scan rate. In log 1, there is a MAP peak that approaches barometric pressure, and you are at 100% throttle, and immediately back off.

Looking at the complete record of what happened in a single frame before the MAP spike, there was the peak knock retard of 6-degrees. in log 1. In log 2 the knock retard occurs immediately after the MAP spike. But again, the knock retard may have actually occurred in the 1/2 second between the previous frame of data, and the frame where the MAP spiked.

Is you EVAP plumbing hooked up and functional? When you go WOT, the EVAP duty cycle goes to 31%, so it's possible that there is something related to that causing issues. Maybe a saturated canister, maybe a vacuum leak, but neither of those conditions seems to show up in the O2 sensor readings.

Are you absolutely sure you have the cam dowel pin in the correct hole in the back of the Opti? Erratic timing due to movement of the pin being in one of the large clover-shaped openings could be causing both the knock retard (too much timing advance) and the backfire (spark while the intake valve is open). Incorrect timing could also explain the high MAP at idle. Crossfiring on the plug wires could also cause the problems you are seeing. The fact it is getting worse with time could indicate the plug wire insulation is breaking down, causing more cross firing.

About a month or two ago, I went through a situation where an OBD-2 LT1 had a constant code for the crank position sensor. The CKP code was setting because the CKP sensor reading was offset an excessive number of degrees from the cam position readings from the Opti. Guy was sure he installed the Opti correctly, but when he checked after I ruled out every other possibility, he found the dowel was too short and had gone into the clover-shaped hole, not the correct index hole.

 

I am 100% positive the distributor is installed correctly, I use the method of taking the cap off and verifying the location. I was curious if this could be a PCM failure? That's pretty much the only thing I have not replaced and with the computer only getting two frames a second seems off. Other than that, I'm not sure where to turn.
The EGR system was reactivated when I put the stock tune back in, the non-stock tune has the system deleted so that canister would normally not be activated. If needed, I can do another log with the non-stock tune in it.

 

 

 

We think we have found the problem, we finally got the car on the dyno and the guy believes the transmission valve body is sticking/failing causing it not to shift. Originally I would hit the rev limiter and now it back fires. What are your thoughts, sorry to bring back an old thread, but finally had time to do something. This is from him "Attached is the shift graph we discussed. AnVlt3 is the voltage across the 2-3 shift solenoid. The other line is engine speed, measured at the crankshaft. As you can see, shift solenoid voltage overlays very well but the shift point of the 2-3 shift varies. I didn't have a recording of the worst offending shifts where it just bounces off the limiter, the black line just barely hit it."

 

 

Is your rebuilt MSD still working? I sent one to get rebuilt at MSD.