meissen

Hey guys,

My dad's car has been acting kinda strange. When you let up off the throttle it pops. When you're cruising above 3k it feels like it has a miss -- you feel it kind of shuddering/shaking. The long term fuel trims seem high, too. We're just not sure what's wrong and don't want to throw parts at it.

http://meissenation.com/files/autolog001.uni

omega552003

Your timing is retarding up to 10* randomly. It sounds like a leaning issue, but im not seeing lean conditions that would cause knock.

I'd say the opti cap and rotor are starting to give.

Injuneer

The most noticeable problem is the right O2 sensor dropping to 4mV and staying there for an extended period of time. As an example, look at records 449-464 or 601-620. It stays at (or very near) 4mV for 3 and full seconds. The question is, is this due to a series of misfires dumping air into the right bank exhaust, causing the 4mV reading, or is the sensor voltage hanging and causing the misfires. My guess would be the misfires are leading to a false lean reading on the right bank, and causing the right bank BLM's to elevate. In almost all cells the right bank BLM is higher than the left bank.

The 4mV readings only happen on the right bank, and they are peppered throughout the data log. I would look for a problem with the right bank fuel or ignition.

Also interesting that in the idle Cell 16 and lower load Cells, the left BLM is also elevated, and in the same records that the right O2 drops to 4mV and hangs there, the left BLM is hovering in the range of 130-150mV for the same period of time. Now the question becomes is there defect in something that drives both banks - faltering fuel pressure would be another possibility. Or maybe the ICM or Opti causing misfires on both banks.

The 10* knock retard at record at record 1196 appears to be the result of the PCM's "knock count" calculation, where it detected a potential knock problem and retarded the timing, but not in response to actual knock. At that point in time, you are accelerating by opening the throttle rapidly, and the PCM has not yet entered PE mode, meaning it was still targetting 14.7:1 A/F ratio rather than the richer factory programming target value near 11.7:1 in PE mode.

meissen

Thanks for the help guys! I actually found the TunerPro sticky at the top after posting my thread and then went to Brent's page and grabbed a stock 95 M6 tune. We have a spare PCM so I threw the stock 95 M6 tune on the spare PCM and then data logged and we still saw the same elevated BLMs so at least we know it's not the tune.

My biggest worry is that the O2 wires were lengthened on the harness and I'm hoping it's not an issue with the wiring.

Could it be something as simple as a leaking EGR plug on the passenger header or a bad exhaust seal on the right side or does it seem like this is far more than just an exhaust leak? And since this seems to be centric to the right bank, is it a safe guess that this is not his optispark going out?


It's my dad's car, so while I did tell him to recheck his header bolts and what not I won't know his results for a few days.

meissen

My dad double checked the header bolts and he says they're all tight.

Today we swapped o2s to try and see if the 4mV O2 readings were because of the O2 being bad or if it was something else. The 4mV reading did not follow - it only happens on the right bank.

We ran the car on and off through the afternoon while we tried finding any sources of exhaust leaks. And just when we were about fully stumped, it happened -- we finally captured an old daemon while we were data logging.

The original issue that started my dad's problem a YEAR ago is he was driving home from a car show on a really hot day and the car started idling rough and eventually stalled. He ended up having to have it towed home. The popping exhaust / backfires started after I believe, but I'm not 100% sure, it could have been around the same time.

I was logging using TunerPro RT v5 and this is what we saw a few frames before it died:

Coolant temp: 177*
Left O2 mV: 44.40
Right O2 mV: 48.84
Left BLM (Long term): 160
Right BLM (Long term): 160
Left Int (Short term): 194
Right Int (Short term): 194
Left BPW: 8.93
Right BPW: 8.97
Airflow: 9.65
IAC: 55
Spark Advance: 24
Retard: 0.0

Here's three log files from TunerPro. It made us extremely confused. In the first example, the BLMs were very even, straight lines. In the second example, mayhem. In the last example, the car slowly loads up and dies while we're logging.

http://meissenation.com/datamaster/tunerpro/Run2.xdl
http://meissenation.com/datamaster/t...n4-NotSure.xdl
http://meissenation.com/datamaster/t...hatTheEff2.xdl

Injuneer

What do I need to open an .xdl file. I've never seen one before? Is there an option to export as .csv in TunerPro?

Was the temperature extremley high when you captured the data you posted above?

meissen

Sorry - .xdl is TunerPro's format. The outside temperature was only mid 50's to low 60's at best. Coolant temps never exceeded 180* in the Run7 when it started in open loop, went into closed loop, BLMs and INTs crept up to the point that it dumped enough fuel in there that it flooded and died.

Here's the exported XDL files to CSV. There's more columns in there than necessary - just didn't want to remove anything that could help.
http://www.meissenation.com/datamast...un2-Export.csv
http://www.meissenation.com/datamast...un4-Export.csv
http://www.meissenation.com/datamast...un7-Export.csv

PS - Greatly appreciate your help. I had your scanner readings article up the whole time we were data logging so I could understand what was going on.

meissen

OK - the tune that my dad's car has been running on seems jacked. Unfortunately, the "1995 Z28 A4 3.23 gears" LT1 file I got from Brent's page is jacked too. I was able to glean a 95 Z28 tune from a different site and now that I'm comparing the stock tune to the tune that was on my dad's PCM the more I'm questioning WTF is going on.

Cylinder Volume is set to 0.0
Injector Flow Rate is set to 793.46 lbs/hr
Speedometer Scalar is set to 549
Speedometer Scalar, Fraction is set to 9.86
Time Between Pulses for "Stop" is set to 1.53

I'm not as concerned with the speedometer, but injector flow rate of almost 800lbs/hr? Wouldn't that jack something up?

meissen

Just an update - it appears we were fighting two gremlins. For one, we had a corrupted tune. Whether it was corrupt when the tuner uploaded it to our PCM or somehow our PCM changed the values, I don't know.

Either way, we found a good stock tune and customized it so it wouldn't DTC for the EGR, AIR, EVAP, etc and had the right speedo calibrations. Uploaded the tune and instantly the popping that we were experiencing went away. Before, you could hear the popping/backfiring 10 houses away it was so loud.

As we drove the car around and got it heated up, the 2nd gremlin set in which I believe was the original gremlin we faced last year when this all started. The car was hot, it started misfiring, and the PCM started loading up the engine with fuel to the point that the engine floods and dies.

At this point we think it's the optispark. We're going to swap the optispark tomorrow and will update with results in case anyone else searches and finds this thread while trying to diagnose their own problems.

meissen

I think this car is possessed by Satan himself.

Replacing the optispark did not entirely fix the problem, although it *appears* to have helped.

Prior Condition: On a cold start, the car would run fine. Once it went into closed loop, the BLMs would go to about 160 but the Short Term Fuel Trims would fluctuate while it idled. When the car would warm up after running for about 30 minutes, my dad and I would notice the car started misfiring and the Short Term Fuel Trims would start climbing up (lean condition). In response, the Injector BPW would also go up to dump more fuel in the car. It got all the way up to 8+ and the car would flood and stall out. This would only occur after it ran for a good 30 minutes or so and the car was really warm.

The only thing we changed was the optispark and the blaster coil (my dad wouldn't listen to me about removing the ICM before removing the waterpump and optispark - he learned his lesson when the wrench hit the blaster coil and broke the plug right off).

Current Condition: From a cold start the car runs fine in open loop, but once it hits closed loop, the Short Term Fuel Trims immediately start climbing to 194. What's different than the previous condition is that the Inject BPW stays steady around 3 to 3.5. The PCM does not dump more fuel in the engine and the car is able to recover - it spits out Lean O2 codes for Left and Right banks and the car goes back into Open Loop and continues running. This can all occur in about 5-10 minutes, it just can't handle closed loop because of how lean the O2s read.

We replaced the O2s thinking when the optispark was crapping out and flooding the car that maybe the O2s got too gunked up with carbon deposits. Sure enough they were black as could be, but when we started the car with the two brand new O2s it still does the same thing as the Current Condition states.

What we've replaced or swapped:
MAF
ICM
Blaster Coil
IAT
PCM
Tune
Both heated O2 sensors

What we have ruled out:
MAP sensor - MAP readings in comparison to BAR look OK in the datalog
TPS sensor - looks OK in datalog

What we haven't tested/checked:
Spark plugs
Fuel Pump


Is there anything else anyone can recommend us to check? We're borrowing a fuel gauge on Tuesday to test the fuel pressure -- we're just confused on that because prior to the optispark replacement the car would completely flood out which made us think we definitely had enough fuel flowing into the combustion chamber. Now it seems we don't. Just confusing.

meissen

Here's the TunerPro datalog taken yesterday.
http://www.meissenation.com/datamast...riginalPCM.xdl

meissen

Well - that was embarrassing. Apparently the vacuum line for the EGR (which has been deleted) was completely exposed. We found the rubber plug we had used and there was a crack running all the way from tip to head. It must have been allowing air in prior to the optispark swap but it was a small enough of a leak that the PCM could compensate.

When we did the optispark swap, I replaced the optispark harness and I must have knocked the rubber plug completely off the vacuum port and never noticed - the plug was sitting in the valley between the intake manifold and the valve cover.

Spraying carb cleaner around the engine bay exposed the issue real quick - as soon as I sprayed by the throttle body it became quite apparent that's where the issue was and then I realized what my dad and I both thought was a loud alternator whine was the damn vacuum port sucking air.

Lmao -- needless to say, damn embarrassed that we didn't catch that sooner.

Since the issue started last year - these are all the items that we found which were contributing to the problem:

1. Corrupt tune telling the PCM that the injectors were flowing 700+ lbs/hr.
2. One fuel injector was out of calibration by 15%
3. Bad o2 sensor
4. Bad optispark
5. Vacuum leak at the EGR port in the TB

Pretty nuts that we had all 5 of those gremlins that we were fighting all at once... no wonder we were so stumped that every time we thought we found the fix and there was still something wrong.