Crandall

Yeah sorry I can' get signature to save right, it has cold air intake, kn filter, shift kit, long tube headers (pacesetter), off road y pipe, no cats, and a flowmaster muffler, I would love to know how to tune it for my mods if you have any suggestions that would be awesome, it has new ICM, optispark, and coil, I have a laptop and all necesary cables and hookups to be able to use my PCM

Crandall

Also I drove it everywhere today for hours and could not get it to run badly, as when it does it loses some power, idles rough, and kinda sputters and runs rich, so didn' bother scanning because the symptoms did not appear

Crandall

So do you think maybe that o2 sensor might be the issue

Injuneer

If the O2 sensor at times just hangs up and doesn’t move, could be the problem. I did look at the first of the two driving files attached above. The long term fuel trims for the most part are fairly stable. When they are in the range of +/-5% correction, usually not a problem. A couple on the right side are outside that range.

I still need to look at that file some more and the second one.

Crandall

Once again I am soooo thankful that your taking your time to help me out, this is the first time in my life I have had a car I truly love and I want it to be all it can be, as far as the fuel trim, I have read about people using that sea foam engine treatment, or like a good injector cleaner is that someth ing I should consider doing, i have read good and bad things about any kind of additive, and as far if we can pin point that o2 sensor being bad, I would like to be able to tune the car so I can get full benefits of the mods on the car, so if you have any info of what I should tune I would be super greatful

Injuneer

I don’t tune the LT1 PCM. I had lt1_edit back in the late 90’s, and played around with it. But when we built the stroker, I went to an aftermarket engine management system. A tune for a 300-shot of nitrous, on top of a 500 (flywheel) HP stroker was well beyond my capabilities. One of the top MoTeC tuners in the US did the tune, first on an engine dyno, then on a chassis dyno, and then on the strip. I have the ability to go in and tweak things, but that’s all I would even try. Unfortunately, the car probably has more dyno pulls on it than I have made trips down the 1/4-mile, due to some personal issues in the early 2000’s. Now I'm retired and getting too old to have fun with it. Probably be selling it in the future.

Your mods are not extreme. They mainly affect engine breathing - more air in, more exhaust out. The MAF system is fairly efficient with compensating for breathing changes. With your setup, just like a totally stock tune, the big gain is leaning out the "too rich" stock target A/F ratio in power enrichment (PE) mode - basically WOT. That's good for 10-15 HP on a totally stock engine.

LT1 tuners are getting harder and harder to find. Basic tune changes used to be available "mail order" from several sources. Of the two best sources, one stopped tuning LT1’s because he felt people were putting the tunes in poorly maintained cars, and then blaming him for poor results. The other apparently sold out the business to a partner or an underling who wasn’t qualified. Another top tuner, Ed Wright "retired" many years ago, but every once in a while he may do a tune.

Here's interesting sites with LT1 tuning info:

Adjustments for LT1 engines - tuning - Team ZR-1 Corvette Racers

LT1 PCM Tuning - Tips & Tricks for DIY Tuning!

Crandall

Thanks for the the info so I am gonna wait til I get my car to throw a code to post another scan and if you can let me know if you were able to check out that other scan that would be excellent, as if you see anything beside the slow o2 on the right. Once again thanks so much and PS your car sounds like a total beast

Crandall

Okay i have attached 2 scans now this is the same run but i know you said not to go over 20 mins so i did 2 scans, and like i said while going 45 or so when i gave it gas it seemed like it missed, it just kinda lurched forward very sluggish was not able to get it to throw a code, and idle was getting on the rougher side as well

Crandall

Yeah if anyone reads the scan in scan9495 the issues are at line 1384 to 1407 and 3411 to 3437 the MAP sensor voltage is very low as well o2 sensors seem to be on the low side .009 and .004 both kept jumping to those values

Injuneer

I downloaded both files. In the first one, I looked at the line ranges you mentioned. Nothing out of the ordinary, all normal. In the first range:

- you were moving at 52 MPH, engine at 3,623 RPM.

- you lifted off the throttle and it closed = TPS 0%.

- closed throttle decel at high RPM causes a large vacuum (low MAP), hence the very low MAP readings and MAP volts = 14 - 16 kPa MAP / .2 - .7 MAP volts

- with closed throttle decel, the PCM turns off the injectors = injector pulse width goes to "0"

- some air continues to bypass the throttle and enter the cylinders via the IAC being open to 55 counts.

- air and no fuel leaving the cylinders via the exhaust = dead lean condition = very low O2 sensor volts.

- as soon as you hit the throttle again, MAP, injector pulse width and O2 readings return to what you were seeing before the decel.

Not the cause of or a symptom of your problem. The problem occurred when you got on the throttle.

I'll keep looking. But these are large files, and it does take time to go through them.

Crandall

Yeah that' exactly right I was coasting and when I gave it gas very little mind you it chugged it felt very much like a miss, and it seems if I am going about 45 plus is when the car acts up, and how it was acting is how it acted when like my orignal post, when coming home from an hour drive at like 60 most of the time, when it threw the ses it was just like this however more extreme and the idle was like it wanted to die and like super loss of power

Injuneer

Are you saying it stumbled and ran poorly immediately after those coast downs, when you got back on the throttle?

Crandall

Yes, it didn' stay running poorly but here is the situation I was coming to a light and was some distance off and the light ended up turning green so I went to give it gas again and it stumbled, just enough throttle to speed back up so I let off gas again and pushed the peddle down again, more this time and it stumbled again but kinda smoothed out as I kept gas on this time to try to i.guess you could put it ,work through the stumble. So it seems if I cruise at over 40 for a few mins and try to give it just a little gas it has stumbling and acceleration issuesx like example if I go down a road that lets say 30 for half mile and I give it small amount of gas it has a certain amount of pick up after reaching 30 miles an hour , the same for 40+ , but if I do the 40+ for let' say 5+ miles at a constAnt speed and try to slowly build speed it will not have the pick up, as it would if I went shorter distance. Lol here let say normal sound is like bawwww constant, when it stutters its like baw baw baw then bawwww. I know silly example but I think you will get the idea

Injuneer

What is the elevation above sea level where you live? What octane fuel are you using?

In the first of the two logs you posted above in #23, there are three instances when you hit the throttle hard enough to put the PCM into "power enrichment", or PE mode. When that happens, the PCM has recognized that you want power, not low emissions and fuel economy. So it richens the A/F ratio to produce that power. At part load the target A/F ratio is 14.7:1. That gives you decent fuel mileage, and is the "stoichiometric" A/F ratio, where, in theory, there is exactly enough oxygen to combine perfectly with the amount of hydrogen and carbon in the fuel. And that's where the A/F ratio needs to be for the catalytic converter to function correctly.

In PE mode, the PCM calculates a new, richer target A/F ratio, based on engine RPM and coolant temp. That typically ends up at 11.7:1. When that happens, the O2 sensor readings will generally exceed 900 mV. On your engine, the right side does exactly that. Averages anywhere from 906 mV to 975 mV. the 975 is a bit on the high side, but the stock, narrow band O2 sensors are not real accurate at these rich A/F ratios. A temperature change to the sensor produces larger variations in voltage than the O2 content. But in general, your right side is pretty much where it needs to be.

Problem is the left side. In the three cases where you went into PE mode, the right side averaged 583 mV to 766 mV. That is relatively lean for PE mode, and I would have expected to see some knock retard..... but there is none, leading me to believe you may live a bit above sea level. That becomes important, because we need to know if the low O2 readings in PE mode are actually because the injectors are not supplying enough fuel, or maybe because something happens to the O2 sensor.

Looking at the injector pulse widths when in PE mode, the left side is actually staying open a bit longer than the right side, due to the 132 LTFT on the left and 128 LTFT on the right. So, the injector pulse width is where it should be, but the left side doesn't appear to be supplying enough fuel.

This gets a bit clouded by the fact the left bank O2 sensor averages less mV than the right side over the entire data log, and the left O2 max reading in the log is 830 mV while the right side is 1,030 mV. I don't think it's an O2 problem. Right side O2 sensor still seems to react slowly at idle, at least. How old are the O2 sensors?

And the big question.... is when it went into PE mode that you were experiencing the rough running problem? the ranges of the two longest PE excursions are lines 1357-1381 and 3997-4009. I know that isn't any easy question to answer.

Crandall

I live 879 ft above sea level and I use shell N+ nitro 93 octane, it' just the premium octane, but I only use 93 octane and as far as your second question is the reference lines, your refering to when I put the gas down enougt to put it in pe mood, it' likely but I can certainly do another test and keep track of exactly when I give it alot alot gas, let me know what I should do with next test. I can note things when I do them