Hey all,
I'm on my 2nd 93 fbody. First was a z28 that ran great, but had to sell to move across the country.
Now I've got a 93 trans am with a t56 and it's being weird.
The knock count is increasing by the thousands, rolling over at 65k, constantly. It's causing the computer to retard the timing, and killing performance to the point it's almost undrivable. I've pulled logs using Scan9495.
I've replaced the knock sensor, and while I was down there, saw the pig tail had some exposed wire. I replaced the pigtail, and no change.
The weird thing is it increases while the key is set to run, but the car is off.
So, following the FSM, I tested voltage at the pigtail, 5.21v. Over 6 it says replace ecm, under 4 replace wiring.
I ended up putting an extra ground cable from the battery to the rad core support when I was troubleshooting some issues with the wiring the previous owner did for the headlights. I tore most of it out and ended up just rewiring the headlights. Those work perfect.
I also grabbed an ECM from a 92 vette, it just happened to be that the ECM was a rebuilt one, and is in perfect condition inside the box.
With the vette ECM and EEPROM chip plugged in, it does not count up while off and ignition set to run. But, if I crank it up, it fires and immediately dies, and counts up in spurts and then stops.
When I swap my tuned EEPROM chip with a Moates adapter over to the vette ECM, there's no change from the original issue.. it counts up like crazy. I even replaced the adapter.
And now the backstory of the car from the last year I've had it.
I bought it with a reman engine from Jasper, had ~3k miles on it.
Ran fine, except it would overheat. I replaced the heater core, heater core hoses, thermostat, rad hoses, etc. No more issues with overheating. I had it on a dyno and it pulled 298hp/405tq to the wheels, but cut out at 4200rpm.
So I replaced the opti, it ran great after. I moved, installed long tube headers, full 3" exhaust, and wired up heated O2 sensors from a 94 fbody.
I've had one sensor die on me (I used Denso at first, and the replacement I got was AC Delco). I re-wired it properly this time and it's reading again.
I've also had the OE fuel pump give up its guts (232k miles on the car itself...) so I replaced it with a fleabay walbro, it died within 2 days. I replaced that one with a racetronix walbro, and it seems to be randomly getting weak. I suspect it's getting clogged. I just got the racetronix fuel pump wiring kit, I plan to pull the pump and confirm it's clean when I do the install (hopefully this weekend.)
Bar that, the car sounds amazing, and was running great.
I just don't get why the knock count is freaking out, or where to go from here. Voltage shows fine based on the FSM diagnostic criteria, I've replaced the ECM, I've replaced the adapter, the only thing I've yet to do is try an OEM EEPROM chip (as I don't have my original one anymore... it got tossed when I moved) or another EEPROM chip.
I've uploaded the latest logs from testing a few days ago after I tried the new eeprom adapter.
I love the car, but I am almost ready to give up and get rid of it. It's certainly cemented no more 93's in the future for me.

Any suggestions?

Thanks everyone!

 

The Corvette LT1 has dual knock sensors, wired in series. F-Body LT1 only has one sensor. How did you address that?

 

I didn't, I just swapped the ECMs to see if the knock count would steadily rise like with the fbody ECM.
Mainly bought it so I could swap the EEPROM chip to verify the ECM itself wasn't the problem. (There is some corrosion in my original ECM.)

 

The resistance of the 2 sensors in series would be different than the resistance of 1 sensor. The would change the base voltage between the sensor pin and the block when the harness is connected. No idea if that would screw up the ECM response to the signal, with respect to knock count accumulation. Just threw that out as something that may need to be sorted out.

Apparently there was little impact if the only change when you went from your “corroded” F-Body ECM to the Corvette ECM, other than not accumulating knock counts when the engine was not running with key on.

A problem I haven’t run across before in my 25 years on this site.

 

Well, let me re-walk through this one..
Original ECM, tuned chip (from Solomon). Knock count increases like mad.
Vette ECM, vette chip, does not increase.
Vette ECM, tuned chip, knock count increases like mad.
Original ECM, vette chip, does not increase.
No difference between the Moates G1 adapter and the tunercat G1 adapter.
I did not test voltage with the vette chip in, just with the original ECM and the pigtail.
I went to move the car today, and found the battery was so dead it wouldn't even start to charge. So I jumped the car and let it run for about 20 minutes, with scan9495 running and idle set to 1,000rpm to help charge the battery back up.
I turned it off, turned back on, was fine. I've got it on a trickle charge now, but suspect I need to find another place to run my power wire for my heated O2 sensors..
It's a base trans am, I don't even have the fog lights... Any suggestion on what fuse to use? I ran it to cig/accy on fuse 11 in the fuse box in the dash by the driver's door. I suspect it's maintaining power and that's my draw as I've never had issues with the battery dying before.

 

Okay, more troubleshooting, still no change.
Car off, Ignition to Run.
Using Scan9495.
Set to 93, connected, scanning.
Knock count increases by the thousands per second.
New knock sensor pigtail (2nd new one).
New wire from ECM to knock sensor.
New oem equivalent 4ga ground from battery to the top post on the back of the alternator.. (I figure that's a good 'nuff extra engine ground.. ya?)
Knock sensor unplugged? Count still increases, and throws KS error (as expected..)
New (reman) ECM from the vette.
New tunercat adapter.
New EPROM chip from lt1performance (Solomon).
Everything has been replaced. I just don't get it.
I even added the Racetronix fuel pump wiring kit as I figured maybe the walbro255 isn't quite getting enough power.
I ran the power wire for the O2 sensors to the air pump fuse in the fuse block under the hood. Fully charged battery.
Once it hit 160, went into closed loop, it started popping as if it's too rich/lean. I did *not* smell gas, and Florida can be stinky at night, but no sulfur smells..

Car as it sits for what's been done other than the above info:
Jasper reman engine at 220k mi (I do have the pamphlet from the previous owner showing it was done... with warranty info from 2016) Car is at 232k mi.
New Cardone Opti 21 miles ago
New plugs/wires about 1000 miles ago
New heater core, heater core hoses
New 160* tstat about 1000 miles ago
New Trick Flow CAI with K&N filter about 1000 miles ago.
Long tube headers into 3" y-pipe, 3"9" generic cat converter, 3"x6" flex pipe, 3"x12" resonator, over rear axle into y-pipe split to 2 bullet style mufflers. All mandrel bent. Sounds great.. when running right.
New walbro255 pump about 80 miles ago.
New O2 sensor (ASF75) with about 300miles ago for driver side (Denso) and new O2 for Passenger side (GM OEM) 21 miles ago. (I wired the passenger side heated O2 wrong.. burned it up.. got a new one and wired it right this time.)

I have 2 new ASF74 3-wire heated O2's coming to simplify wiring..
But bar that.. damn thing is driving me nuts.. knock count goes up, retards timing if I hit the gas at all.. and now the backfiring..
2nd 93 Fbody, first one to have weird issues like this. And nothing seems to come up online for this issue.

Edit: 2 YT videos of me testing tonight.. both under 1m long each:

 

Not much more I can contribute here. In the course of 20+ years I have reviewed upwards of 1,000 data logs for people. I have NEVER seen anything even close to what you are experiencing on knock counts. Looking at the log, a couple things stand out:

- the O2 sensors response is EXTREMELY slow. They will hang up high "rich", or way down low "lean" for anywhere from 4 to 9 seconds. They are supposed to be moving rapidly back and forth between rich and lean about 9 times per second.

- the timing at idle seems higher than stock - maybe that's Solomon's work. To get the program value you have to add the indicated advance plus retard. Where the stock advance at idle is typically in the range of 18-20 degrees, yours is as high as 28 degrees.

Lean O2's + high advance may be setting off the knock counts..... I don't know. Coolant temp, inlet air temp, MAP all look reasonable, so they aren't likely to be triggering knock counts.

Have you asked Solomon for any input on this?

At one point I was thinking maybe some high voltage interference on the knock sensor wire, but that wouldn't explain the counts increasing when the engine isn't running.

That's about the best I can do. Who knows what the mix of the Corvette PCM, an F-body EPROM and an adapter (that I am totally unfamiliar with) is contributing.... sort of a Frankenstein build. I believe on the early Corvette applications, the Opti harness had a wrapped shield wire to eliminate high voltage interference on the Opti signals.

 

Yeah, I have new O2 sensors coming, switching from 4 wire AFS75's to 3 wire AFS74s...
I have a feeling I likely wired them up wrong.
Hopefully.. that solves the issue.. but, I guess we'll see. I've never heard of knock count going nuts like this.
I only used the vette chip to really test and confirm if it would increase while off..

Anyhow.. I've asked Solomon to tune out the KS since they're useless with this issue anyways..
I'll cross my fingers, put the new O2's in when they get here this weekend, and hope to hell that solves this.. otherwise.. I give up.

 

Well now I feel like a ditz. Unfortunately I can't test my theory out yet..
I didn't realize that when you add a tuned chip, you still have to toss on the original chip onto the adapter too.. I event sent pictures showing it not plugged in..
Unfortunately I threw the original memcal chip out when I moved, but.. I have the one with the knock part in it from the vette..
I tossed it in and tried to fire up the car last night, but looks like my fuel lines leaked and I ended up with an engine fire. Got it doused, but. now I gotta figure out why the lines leaked.. probably bad oring.. then I gotta make sure nothing was too damaged.
Ugh. One thing after another..

 

That's what I meant by “Frankenstein build” in my last post. Tuning out the KS makes no sense at all. It is not “useless”….. it does a great job of protecting the engine from damage due to knock. You also might want to try another tuner.

 

Nah, not the tuner's fault, my fault for not realizing the memcal was required to be added to the adapter as a piggyback chip.
On the plus side, the 92 vette knock module in the memcal works fine. Car runs like a champ, and as I suspected, orings went bad. Replaced them, replaced the fuel pump strainer, car runs like a beast again. With the exception of some exhaust pops.. but I suspect that's from the heated O2 sensors not being wired properly. I just got 2 AFS74's in a couple days ago, plan is to wire them in this weekend, and see what that does. At least for now I can drive the car again.

 

"It is not “useless”

Yet another case of Fred prodding the member to think about the problem and focus on the resolution. Member left off an essential part for no apparent reason. Good for both of You!