teddie300c

Hi I have a 93 z28 I have changed plugs and wires, put brushes in the alternator, a new seal on p\s pump, motor mounts and tranny mount. just got this all hooked up and was wondering if someone could take a look at my scan. Should I just take one idling in the garage or what would be the ideal scenario be. It ran real good after changing the plugs and wires but has slowly gotten a little rough. I had a bad injector and replaced it which helped tremendously but I still feel like it could be smoother thanks.

NOTE FROM MODERATOR - This thread starts with 13 posts that were made in another forum, and were moved and merged with a newer thread. I apologize for any confusion, but this topic works better in the "LT1 Based Engine Tech" forum.

Injuneer

Is it driveable? If so, do not clear the ECM. Cold start, let it idle/warm up for about 4 minutes. That's usually enough for the PCM to go into closed loop. Then drive it for another 5-10 minutes under varying combination of RPM and throttle position. A WOT pull is also helpful. Try and replicate the conditions that produce the times when it is not "smooth". Do you have misfires, stumbles, surging?

To do a meaningful review, I would also need to have an accurate list of all the modificatons (if any) to the engine, whether it has a non-stock chip in the ECM, etc.

teddie300c

I'll go do it here soon. It has had the ac compressor removed and I think it had an egr delete. All help is appreciated

teddie300c

Hey I'll do that tomorrow first thing.

teddie300c

hey i think i got an ok scan. its raining so it was kinda hard to get a WOT. i drove around town and got on the interstate at the end.

Injuneer

Downloaded, reformatted, and it's not very useful - other than to tell you your O2 sensors are not working at all. Almost looks like they are not connected. One potential problem with a 93 is that it uses single wire (unheated) O2 sensors, and if you have headers, the sensors may not get warm enough to work (600-degF). But usually there is some sign of life, even if they run cold at idle, and only warm up under some sort of engine load. But your driver side goes +/- 0.03 volts. Passenger side shows some sign of life, but it could just be a false reading. Check to see if they are plugged in. If it turns out the engine has headers, particularly long tubes, it would be a good idea to convert to heated O2 sensors.

As a result, the ECM cannot go onto closed loop, and fuel trim learning is not enabled. No way for the ECM to correct the A/F ratio if needed. Didn't actually drive it much - speed did not go over 15 MPH, throttle never exceeded 38%., RPM never got over 1,658, 90+% is closed throttle/0 MPH.

Other quick observations:

- do you have a thermostat - took a while for the coolant to warm up (started at 65-deg, took 6 minutes to hit 140-deg, 10+ minutes to hit 180-deg))

- inlet air temp OK

- barometric pressure - OK

- MAP at idle - OK

- TPS voltage - OK

- EGR has not been programmed out

- Idle air control (IAC) seems OK

- system volts - OK

- spark advance at idle seems normal

teddie300c

Well I just went out and on my way home it set 3 codes. 13, 28, and 64. On the scan I sent earlier I got into the interstate and was going about 80 at one point. You think there's anything wrong with scanning or the version of the program. I'm trying to replay it and it shows when the new codes set but they don't show up in the dtc tab. I have a toggle set up in the obd plug and that's how I got the 3 codes. Which version should I use. I'm using the v2-0-0 with 93

teddie300c

Oh and yes I think it does have headers after googling some pics. I figured they were stock cuz of a vehicle I had before but can't remember what it was.

teddie300c

How can I go about getting better info for you. And what should I do about tuning the egr out.
Thanks again so much

Injuneer

DTC 13 is an open circuit on Bank 1 O2 sensor. Consistent with your data log and my analysis. DTC 64 is not consistent with the data log I reviewed. At no time did the Bank 2 O2 sensor indicate a lean condition. It wasn’t dropping much, if any below the 450 mV reference voltage supplied by the ECM. It would be more likely to see DTC 63 which is an open circuit on Bank 2.

There is no point doing another data log until you fix the O2 sensors.

Apparently you are not aware of all the mods. That just complicates the problem. If your speedo was reading 80 MPH and the ECM is indicating 15 MPH, there's something wrong with the way the signal from the vehicle speed sensor (VSS) is being handled. As I recall correctly the 93 has a different VSS distribution than the later models. I'll have to check the 93 factory service manual, when I have time.

I'll ask GaryDoug if he can address the discrepancy between the seeming errors in the RPM and MPH data in the log.

Injuneer

I'm going to see if I can move your initial post and our follow ups to a new thread. This thread is not intended to be a place where data logs are reviewed. This should have been posted in “LT1 Based Engine Tech”.

teddie300c

teddie300c

Whoops just saw where you said something about moving my posts

teddie300c

I was talking to injuneer and I think I have this in the right place. I recently got the scan9495 hooked up and asked him to look at a scan for me. I just got done putting heated O2 sensors in because it wasn't going into closed loop. Well after installing the second one it runs terrible at idle and I have to feather the gas because it cuts out. It pours the smoke when I pull it back in the garage and it's driving me crazy.

Injuneer

What does Scan9495 tell you the O2 sensors are reading?

Sounds like one of the heated O2 sensors may be wired incorrectly, or shorted to ground. Did you follow SHOEBOX’S guide:

http://shbox.com/1/heatedsensor2.jpg