A funny thing happened when I took my 94 Z out to run a datalog: it died. The symptoms were very similar to what led me down the path to swap the opti. Had to tow it home. Did manage to get it started again, but it was short-lived, and now I'm back to 'crank, no start.' Argghhh!

But at least there's a datalog to review. It started out OK, but seemed to take a long time to reach the right idle; it took ~3.5 minutes to get to 800, and then down to ~600 when I actually started moving. By that time, my IAC count was down to 0. The data shows when I applied throttle, IAC went up, & when I let off, it dropped; I understand this could suggest a vacuum issue. It also shows odd values in the ST & LT fuel trims, esp on Bank1; they both get high, sometimes @ 160 (max). The MAF & MAP data are roughly what would be expected, altho MAF didn't get down to ~10gm/sec until idle was down to ~800, ~4mins into the scan. It also shows low values for the Bank1 O2 sensor, almost thru the entire log. Don't know if both O2s are the same brand, don't recall ever changing them myself. I just note the low values.

There are also quite a few DTCs, much the same as I noted before: they blip on a single line, and mostly don't set. Most of these a 'junk codes'--not listed in the FSM. For example, 87, 83 (I have an automatic), 92, 95, 96, 93, 62, etc. There are also DTCs that are valid, albeit brief: 70, 77, 21, 37, 29, 79, 45 (where the data actually shows a lean condition, rather than rich), there's a single 16, 22 (after a 21--odd), most of which are circuit-related. Then, after it died, I tried starting it again, and this time got a code that set: 51--eeprom programming error.

I'm not sure what's going on here. Given the many circuit-related DTCs, it looks like there's a short(s) somewhere, but when I do the diags, the values I get are normal. When I got it restarted in my garage (and it was rough), that scan shows 44 & 64, but it took a while for them to set (the data supports them). No other DTCs, and haven't gotten it started since.

I can retrace the wiring for any breaks, kinks, etc., but I also wonder--given the DTC 51--if I don't have a PCM issue. I know it's rare, but it does happen. For example, after replacing the IAC, I get values that are all over the lot--from very high to very low. And when I apply throttle, it actually drops, rather than rises, like before. W/ all the junk codes, I wonder if that 51 is telling me something. But I'm not sure at all.

Anyone experience this kind of thing, get this type of data? Or have symptoms that required a PCM swap? Any input is much appreciated.

 

What are you using to datalog? Code 51 usually means you are using something useless. Hope it's not mine ;-)

 

Of course I'm using Scan9495; I'm sure you've heard this many times, but it really is the best tool available, both in terms of the data collected & the ability to review it in, say, Excel. Fred's guidebook helps make sense outta what the data indicates.

While the manual testing/diags tend to indicate an Opti issue, I'm not so sure, all things considered. If nothing else, the data shows that the PCM is struggling mighty hard to adjust & maintain proper operating conditions; the DTC51 underscores it. The sensor data is troubling.

 

Getting near the end of my odyssey, but first, some thanks:

1. GaryDoug – for producing Scan9495 & making it available for free. Been using it for years now, but never to the extent I did here. Few of us have a Tech1, and this is the next-best thing, esp. since you can review & manipulate data in Excel. Also for making the FSM available for free; I understand that was also your doing. It really helped a great deal.
2. Injuneer, for producing the scan guide. It really helped make sense out of what I was seeing in the data, and ultimately pointed me in the right direction. While he no longer will interface w/ me (prob just as well in this case; it would only have frustrated you), comments made in other threads really helped & triggered the breakthru I needed.
3. Rob, for the Shoebox site. Didn’t use it much here—at least not directly—but that’s where I learned the basic diags to do most of this stuff. Much easier than looking it up in the FSM.

Without these things, would never have figured all this out. Still have some things to address, but it starts, runs reasonably well (despite lingering vac issues), good idle, no more codes, no SES, etc. Perhaps this will be of value to someone out there who is running into similar issues.

The data was telling me something, but didn’t recognize exactly what. Knew I had an elec issue, but didn’t know the source or how to address it. Confusing the problem was that the data was conflicting (in some spots it flashed both a rich & lean condition w/i a few lines of data), many codes flashed, but few actually set, there were plenty of ‘junk’ codes (not specific to a 94 LT1), the wiring & alternator/volt. reg. consistently tested good (still do), there were various misleading results & I got plenty of bad parts—the most difficult aspect, since some parts can’t be tested. That all this came after swapping the opti made it more confusing, but as it turned out, that was only coincidence. I needed the opti & there’s nothing wrong w/ the unit I put in.

Every time I resolved an issue, another came right behind it. Chris @ Petris suggested I go back to basics, so I did. I had spark, but when I ran a noid test (the FI wiring tested good), initially it blinked twice, then stopped. This seemed like a low-res pulse symptom, but no. Among the codes that set was 41; finally got a coil that tested @ ~8.3K ohms, so turned to the ICM & worked thru the flowchart in the FSM. It brought me to ‘faulty module’ or ‘faulty connector,’ so I figured WTH & replaced both. Didn’t realize it @ the time, but that was a turning point. A couple days later I went thru the diags again, and this time the noid test showed constant blinking. But still a no-start.

So I looked at the fuel system anew. I noticed @ KOEO, didn’t hear the fuel pump ‘whiiirrrr’ you should hear, so tried it @ the prime. Pump ran & fuel went in the rail; tried to start it, and…zoom. Only ran a few seconds, but confirmed the pump was good. Checked the vac line @ the FPR (dry, no fuel smell), and that left 1 option: the FP relay—another elec component. Tested & it was dead. Picked up 2 diff brands, swapped it & resolved the ‘no-start’ condition. This was when the pattern started to emerge.

Everything was elec related, but wiring/circuit issues didn’t explain it; every reading I took showed as good. Took another dataset & went back to addressing the DTCs that actually set. Next was a 48 (MAF); the MAF readings were high @ idle (~11-13gps), and had been for a while. Before I had pulled the elbow & MAF, reseated everything & the code went away. Not this time. So I worked the flowchart & ended @ ‘faulty MAF’ or ‘faulty connector’ again. I got both, replaced the connector first and—despite the wiring testing out—it turned out to be the problem. There wasn’t any corrosion or anything to suggest a bad connector, but like w/ the ICM, you can’t dispute the results. I learned that simply because the wiring tests out doesn’t exclude a bad connector—even if it looks fine.

In every dataset I took, noticed the IAC counts were low; it suggested a vac issue, but I was still focused on the elec problem. Didn’t know what caused it (still don’t), just had the oddball data. Each scan showed improvement based on what I addressed, but still indicated problems (like high LTFTs) & I still got invalid/flashed codes. Then I saw a thread where the OP had similar issues & had supplied his data, which looked similar to mine. Injuneer noted those were anomalies, perhaps the result of some sort of electrical interference. That’s when it clicked; those goofy flashed codes were an effect, rather than a cause. I needed to stay focused on the codes that actually set.

What the data supported was some sort of power surge that apparently jacked up the ref. voltage to the point where it fried various sensors & elec components, and perhaps the connectors. It explained a lot of the problems I was having, including the scan data. I discounted the DTC51 as an effect (it never returned) and moved on to the next issue, DTC44--Bk1 O2 sensor. Checked the FSM, and combined w/ the IAC data & the high LTFTs @ Bk1, this led me to the vacuum issue. The intake elbow was torn & frayed around the edge, so replaced it & started checking the vac lines. Right away found the little “C” hose (PCV to manifold) was bad; when I removed it, it disintegrated in my hand. Had some hose handy & replaced it, and noticed improvement both in the IAC counts & the LTFTs—better, but not yet optimal. Also noticed the elbow from the TB to the evap solenoid has cracks, but you gotta make that yourself (or find an old spark-plug boot)—it’s been disconned for many years.

Before continuing w/ the vac hunt, drove it ~5 miles, and when I went to leave, it wouldn’t start (argh!). Found the new FP relay (a Standard Ignition) was bad. But I found a BWD sitting on my shelf, swapped it and voila, started right up. Ran a new dataset on the way back and noticed the Bk1 LTFTs were coming down. Two things I learned: 1) bad parts abound, and it sucks (among the bad parts I got were multiple TPSs, ICMs, a couple coils & the FP relay), and; 2) the PCM needs stable runtime to adjust to changes that affect things like LTFTs.

I’m still working on the vacuum issue(s) (haven’t checked @ the evap canister yet) & watching the data. The IAC counts are still low & the LTFTs are still off, but not nearly as bad as before. The O2 sensors are also showing wild fluctuations (already checked the wiring), but the 44 hasn't returned. I’ll work the vac issues and see where I am. Found I need a tranny mount, so can’t try WOT just yet. I also seem to have a minor elec issue; the chimes you should hear initially @ KOEO (like when you start Scan9495) aren’t sounding (the 2 fuses are good), so need to trace that down. But I seem to be heading down the right path, anyway.

 

An update...

Made signif headway w/ the vac leaks. Found a Dorman part to swap the evap elbow; it's a 2-pc deal, pn 46021CD. If you don't want to use the little "U" hose, some 1/4" works well--good tight fit. Btw, if you need the CCV hose (also disconned), reference Autozone pn C80405; need to cut it down to size, but it's a good fit.

Took a new scan, did the calcs and idling in park (650 target) show 20.05 vacuum. However, in gear (550 target) am high @ 18.19; it should be closer to 10-12, as I understand.

While I haven't had a chance to really drive it--just took it up & down the street, enough to get data in a few diff cells--it has positively affected the trims. In cell 16 I now get 136/120; still not optimal, but a big improvement over previous scans. Cells 17 & 18 still show signif. variance, but LBL is well below 160, at least. Cells 1, 2, 5 & 9 look good--little variance from 128--but 6 & 10 are still high on LBL & low on RBL. I'll need to see what it looks like when I do a true test drive.

The O2s still vary considerably from one side to the other, as noted above. Individually they seem to be operating correctly, but while I'm swapping the trans mount, will switch them & see what happens. Based on what I'm now seeing, plan to put it on a lift & see if there are exhaust leaks ahead of the O2s, esp. on the left side. The IAC is still low, dropping down to ~4 @ idle. The confounding thing is that it runs reasonably well--no hesitation, misses, rough idle, etc. But the data doesn't lie.