Z28Freak86

Hey guys, couple things about my car before I get into too many details. I always park my car for the winter. This year, before I parked it I noticed a popping sound from my exhaust on deceleration . These cars pop sometimes, but this was irregular. I've had this car for 10 years now and this is the first time I've hear this before. So I put the car away for the winter and March, I decided to dig into it a bit. The car has 165000 on the original motor so I figure it was time to do replace components anyways. A gm mechanic told me to replace the opti as that could be my problem, so while I was at it I replaced the water pump, spark plugso and wires, and the coil. The problem did no resolve itself. Instead it seems to have gotten worse. Now there's a miss/hesitation on acceleration and it pops even louder now, sometimes on acceleration and a lot more on deceleration. Obviously there's fuel getting into the exhaust. Are fuel injectors known to do this? I'm just stumped right now. So any help I the right direction would be great.

Z28Freak86

Its been a month since i posted this, but ive been doing alot of research and reading and cannot get to the bottom of this lean exhaust pop. since my last post ive looked for leaky fuel injectors (none), any vacuum leaks (only found charcoal pellets in the evap line, what a pain to clean out), replaced fuel pump due to bad check valve in the pump, and seafoamed through the intake using a drip bottle i got from my buddy. I been in the middle of backcountry wisconsin where there is no light for 20 miles and cannot see any arcing of the plug wires at all, and it seems like the lean condition only happens when the car warms up. Ive looked at the datastream on my car while its been running and my o2 sensors seem to be in normal range (as i have read other posts on 02 values, although they do change very frequently)

right now Im looking to entertain any ideas that anyone has at all on this. I am willing to test whatever and do have a actron 9190 that can do some data logging. I'll keep checking the data stream to see if i can find anything out of the ordinary. If anyone has had this problem before, let me know what ur solution was.

DelSoto

Just throwing this out there...leaky valve? Do a compression check if possible.

DelSoto

If it got substantially worse after opti, maybe you didn't get the opti indexed right. Did you get a cheapo opti? Some have been known to be bad out of the box.

Z28Freak86

Opti was a delphi from summit. Again im entertaining anything so ill get a compression tester and test that out when i can then ill do some checks on the opti. Any other checks i can do with the opti other than whats up in the sticky?

DelSoto

Depends. Do you have a scope? Willing to buy one? There is a member here that describes testing the signals with one. GaryDoug is his username. Might search his posts.

Z28Freak86

i dont have a oscilloscope, but i bet i have a friend who does. I love the out of the box thinking, that's exactly what i needed. Ill also get the compression test done this week.

raroz28

fuel pressure takes about 1 minute to check. When I had this exact issue, that's what it was.

I too wasted time replacing an opti that was fine. It was my fuel pump.

Z28Freak86

I just replaced my fuel pump last week due to a faulty check valve. But I tested it anyways and here's what I got... primed to 41psi, idled at 37 psi, when I rev the motor is stays right around 36-37 psi. I unplugged the vacuum to the regulator and got 45 psi.

Checked compression, all the cylinders were right around 160psi, plus or minus about 8 psi. I hope that sounds about normal.

Little update, I found that my problems are very much so based on outside air temperature, in that the warmer it is outside the more likely it is to start leaning out and popping out of the exhaust. This morning it was about 60 degrees outside and it didn't pop once coming to work. However if it's above 75 or 80, it'll almost certainly pop, more often if it's warmer. Also, the first couple minutes of my drive it won't pop at all, not until the o2 goes to closed loop will it start acting up on me. I'm going to attempt to data log a run within the first minute of me driving, then after it starts popping and see if there is anything that jumps out as strange. Any ideas on that guys?

Injuneer

Your premise seems to be the exhaust is lean. But you also indicate fuel is getting into the exhaust.... takes fuel and air to "pop". Wonder if its an injector partially plugged from sitting over the winter? PCM would see the unused air in the exhaust, figure it's lean, and add fuel to that bank. Now you have one cylinder sending unused air into the exhaust, and three cylinders on that bank running rich.

Just a thought.

What is the format of the Actron data log? Is it anywhere near as complete as Scan9495? In any case, if you post a link to the file I'll download it and take a look at it. Just can't be in an Actron based format with their own file extension. .csv or an Excel format preferred.

Z28Freak86

https://drive.google.com/file/d/0ByR...ew?usp=sharing

Above should be a link to a excel document with the data. I took 2 different shots of whats going on, one at idle, the other while i was accelerating. Today has been REALLY weird with the car. This could be a good thing, but it hasnt had an exhaust pop till i got back to my parking lot and it was idling. Now when i let off the throttle all seems normal. The weird thing is that now on acceleration something doesnt feel right at all. It feels like everything is running smoothly but i lost alot of hp and it isnt accelerating normally. Hard to describe, but it sounds like the motor is struggling now. So thats why i captured the data from idle and acceleration. see if you guys can spot anything

And fred a partially clogged injector is not a bad thought either. I have a set of 6 injectors laying around, i was planning on getting 2 more then sending them off to get cleaned and flow matched, the car has 170,000 on it now and it wouldnt be a bad thing to do soon.

Injuneer

What you posted was a single frame of data while idling, and a single frame of data while accelerating. Shows a few things that are meaningful, but not really useful for purposes of watching all the sensors and PCM parameters over an extended period of time, and seeing how they respond to changes and how they interact with each other.

A system like Scan9495 will log the data shown in your single frame, over a continuous period of time, and covering a wide variety of operating conditions. You can do a cold start, which the conditions that need to be met for the transition to closed loop, look at the LTFT's for all 18 of the "cells", make sure the O2 sensors are cycling rapidly (up to 9 times per second) back and forth between rich and lean like they are supposed to.

Looking at what you have, I noticed at idle the IAC shows as 0 counts. That means the valve is closed all the way, and it not able to adjust lower if required to hold the programmed idle speed. The target idle speed (Idle Req RPM) shows as 550 RPM - normal for an auto trans car, in gear, with the engine fully warmed up. What I couldn't find, and I sure looked for it, was the actual idle speed.

Some other anomalies.... appears that the data is truncated at the decimal point in some fields. Injector pulse width shows "0" in the idle data frame, and if the engine is running, that's not possible. The system is further suspect, when injector pulse width unit is labeled as mV (millivolts) when it should be labeled in mS (milliseconds). Pressure units are mixed, with barometric pressure shown in "Hg, while MAP readings are shown in volts..... impossible to compare the two readings without a lot of calculation gymnastics, and the calibration chart for a standard GM 1 bar MAP sensor.

I would look at Scan9495. You can also use TTS DataMaster, or FreeScan, but GaryDoug's Scan9495 is wayyyyy better.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Z28Freak86

Yea the actron just takes snapshots of the data every 1.1 seconds for a total of 15 frames. So when I record I have 15 sets of data but it's not really continous. I'll get on using scan9495 when I make the cable for my computer to scan cause I know what was specifically made for this year vehicle.

I just drove the car again for another 1/2 hour. Ran actually pretty well almost the entire time till I got to a town with a 30 mph speed limit, then it was popping almost every 2 seconds for the 3 minutes I was at 30mph. As soon as I accelerated again it didn't come back. Very strange

ToocoolZ28

My 95 Z28 acted like that, turned out to be the ignition control module. $90.00 from Rock Auto fixed it.

Z28Freak86

Icm is something, well one of the only ignition things I did not replace or test. I know auto places can test them, but js there a way for them to do so while it is heated up and worked a bit?

It's not popping as much when I let off the throttle. Instead now it's starting to pop and miss when I accelerate hard