Maintenance on my '94 z28 pic heavy

**Injuneer** · 11-05-2015, 09:52 AM

No need to be sorry..... large file provides a wide variety of operating conditions. Just making sure you understand why it may take a bit of time to look through it completely.

I looked at the range and average of the left and right O2 sensors while it was idling at the end of the file. That covered about 3 minutes. The right O2 sensor averaged 444mV, which is what it should be at (close to 450mV PCM bias voltage). The left O2 average was 373mV. While the O2 sensor voltage was lower than it should be, there was no measurable movement in the STFT's, which should have moved upward to compensate for an indicated lean condition. On the other hand, the O2 sensor response is pretty flat over the range of 350-550mV, so that might explain the lack of movement in the STFT. During that period, the right O2 covered a range of 40 - 852mV, while the left O2 sensor was 62-821mV. The left O2 seemed to be responding slower, hanging at low mV for an extended period of time, compared to the right O2.

I think it's enough to make the left O2 sensor suspect. One 0 cost approach would be to swap the O2 sensors side to side, to see if the behaviour follows the O2 sensor. Then run a log over 3 minutes of closed loop idle, and I can do a comparison to the earlier file.

**Mrmaroon** · 11-05-2015, 11:47 AM

Originally Posted by Injuneer

I think it's enough to make the left O2 sensor suspect. One 0 cost approach would be to swap the O2 sensors side to side, to see if the behavior follows the O2 sensor. Then run a log over 3 minutes of closed loop idle, and I can do a comparison to the earlier file.

I will do this after lunch when I check the cat. I'll get a good cold to closed loop and idle. Going to change passenger side wires too

I figured out the dip in the datamaster pic I originally posted. I was testing an injector to see if it changed the idle and unplugged it. That is why it dips then goes normal!

EDIT: I may have found something. I was researching how an o2 sensor worked. I watched this video

My left o2 wire had oil on it when I bought the car. It was leaking bad from an intake leak. In the video around 2min it shows outside air going inside the sensor body. If mine is full of oil that wouldn't work well. I will take it off and look at it today. I'll buy a new one too. Should I get the AC-Delco AFS75? Nobody around here carries them. Looks like I could pick up Bosch, Denso, or NGK around here.

**Injuneer** · 11-05-2015, 01:50 PM

Yup.... my wife's Grand Cherokee started acting up, code set for the O2 sensor and it had power steering fluid running down the wires. Ran like absolute crap though. You can even have problems if there is an exhaust leak blowing on the sensor body, altering the composition of the air surrounding the sensor.

Get AC Delco.

**Mrmaroon** · 11-05-2015, 07:28 PM

Originally Posted by Injuneer

Yup.... my wife's Grand Cherokee started acting up, code set for the O2 sensor and it had power steering fluid running down the wires. Ran like absolute crap though. You can even have problems if there is an exhaust leak blowing on the sensor body, altering the composition of the air surrounding the sensor.

Get AC Delco.

Thanks again Injuneer. I didn't have time today to switch them (daylight savings

), but I think its safe to say I may as well replace it. I was wondering if I could drive the car in speed density and listen to a change in idle. If I unplug the MAF, will I need to unplug the o2 sensors as well? It probably won't make a difference, since it seems to do it in open loop anyways.

I did get my transmission mount changed today. It didn't look terrible when I pulled it off - figured I wasted 10$. Once I got it on and started though the shaking went down a TON. I'm glad I changed it.

Here was the old one

I unbolted the cat-back and took a look at the catalytic converter. I hate to say it, but I was a little disappointed when I looked inside it - It didn't look bad at all. Was hoping that was my problem! Guess you didn't mention it, but I was curious!

I didn't get a total cold start and idle run in today or the plug wires changed. When I do get it logged I will upload it. I ordered a fuel filter and a Delco O2 sensor. They will be here Tuesday. I'll get the fuel pressure tested.

Thanks everyone for the help so far! I'm pretty good at troubleshooting and researching problems, but sometimes I can't figure it out. A nudge in the right direction helps a lot. I will keep working on it and posting.

**Injuneer** · 11-06-2015, 12:25 PM

I don't need a cold start. I need three minutes of idling in closed loop.

**Mrmaroon** · 11-06-2015, 10:40 PM

Here is the closed loop idle. I also added the oldest log I have. Should be about 2 weeks after I got the car. https://www.mediafire.com/?v7sm9iu4t...sg54owt89g9h59

**Mrmaroon** · 11-07-2015, 12:15 AM

Here is a spreadsheet I made of my L/R o2 data. This is way better vs datamaster.

**Mrmaroon** · 11-07-2015, 11:29 AM

@Injuneer

I found a nice list of what correct obd1 readings should look like. I can't find it again

. Was sure it said injuneer at the top of the list? Do you know the one I'm thinking of?

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**Injuneer** · 11-07-2015, 02:18 PM

Yes.... that's my Scanmaster writeup.

I can e-mail you a .pdf version. It was on my website, but I did away with the website a couple years ago. I think a couple of people have asked me for permission to post it on their sites, and I have allowed them to do it, as long as it still credited me as the author.

Send me an e-mail at InjuneerZZ@aol.com so I can reply with the attachment.

**Mrmaroon** · 11-11-2015, 10:23 AM

That is the one, thanks. That report and the check field manual are the two best things I've read.

i got around to changing the passenger side wires. Unfortunately this has made my rough idle worse. Before I could barely notice the pops, but now they shake the car. If I put it in 5th at 40mph and give it a little gas it jerks the whole car. The whole transmission jumps. I drove home and parked it. Pretty sure I must have a cracked plug somewhere.

Honestly and in all probability the idle problem is from something I did wrong somewhere. I'm borrowing my parents garage to figure it out today. I'm picking up the O2 sensor and fuel filter too.

Ill let let you know how it goes.