LT11996

Hey guys so I just got my ALDL cable in the mail today to use on my 1994 Z28. The car has basically lost a lot of power in the 2 months I've had it and won't even try to spin the tires if I put it in 1st gear and mash on the gas while holding the brakes. But it doesn't have a CEL.

I honestly dont have hardly any experience with computers so at first, it was a bit confusing trying to work Scan 94/95 with my dads laptop I borrowed. So I'm still learning on it. I only got two different logs to save to the laptop the first time I connected it to the car. The second time though, no matter how many times I tried saving each new scan, every time I would try to review that scan, I couldn't find it in the folder where the first two were saved. So I'm not sure what's going on there.

I was disappointed to see no DTCs popped up the first 20 minutes of idling, nor after a few WOT pulls down the road and back. So I shut it off and went in the house to read up more about all the readings I was seeing, then came back outside and hooked it up again, and within a few minutes of idling, DTC 16 code popped up. But the car has no issues idling or trying to stay running. I cleared the code and drove it again making a few WOT pulls hoping that it would save those logs, but of course it didn't work still for some reason. But that code never came back afterwards. So I'm wondering if I could get away with replacing the opti harness first before having to buy a new opti.


Guys on Fb told me my fuel trims are way off and the car is running way too rich with trims showing around 108. And they said from the data that the bank 2 o2 sensor is reading bad. The dip in rpms on the graph was from when I reset the IAC while it was idling




Sorry for the awful pictures. As I said, I'm computer dumb and only know how to do stuff with my phone lol but I just wanted to show the data I had after letting it run for awhile and the o2 graph after I figured out how to show those. I'm sure there's another way to get screenshots from the laptop to here but with the scans not saving for some reason, I just haven't messed with the laptop since then earlier today

Injuneer

Screenshots have limited value, but yours show serious problems with the A/F ratio. You need to record a full data log, cold start, warmup through transition to closed loop, then drive it normally, with an attempt at a full-throttle high RPM pull.

But given the O2 sensors indicating a serious rich condition, avoid the full-throttle step, and just drive it for a couple minutes. If it's really running that rich, fuel could be washing down the cylinder walls and diluting the oil. Pull the dipstick and see if it smells like gasoline.

LT11996

Alright I just figured out the scans were saving under a different folder after the first two for some reason so I just went out and made another datalog how you asked, from start up to closed loop, then I drove down the road and back about two miles and went WOT on the way back.

But now, how do I go about posting the datalog here? Would it be okay to go through mediafire like others I've seen on here have?

GaryDoug

You should be able to post it as is like this one.

LT11996

http://www.mediafire.com/file/ubl7ba...PXR2110943.csv

I tried uploading it as an attachment as you did Gary, but after 5 minutes of it saying "uploading-please wait", a Database error pops up and exits out of it. Did that twice. So I hope posting this link works instead for you guys.

By the way, I'm sure you've heard it a million times by now in the last 3+ years, but thank you for making Scan 94/95 and completely free on top of that. Its really given me the motivation to work on this 1994 and not let it become another lawn ornament like my 1996 z28 has been for the last 5 years lol.

The only problem I've had with it is that when I select trans to scan along with engine, anytime I save that scan and then try to review it after its finished, it says "Index error" and wont open. So the above datalog is just with engine selected

GaryDoug

Your file is probably larger than their file size limit here.

Reading back the transmission log file is not supported.

Injuneer

It isn't unusual for DTC 16 to show up once in a while. Sometimes seems to set while cranking, while the PCM looks for the pulse signals from the Opti.

Since you cleared it, and it hasn't come back, I wouldn't do anything, other than inspect the Opti short harness at both ends for corrosion or damaged pins. If DTC 16 is an "active" code, it shuts down the fuel system, killing the engine, but does not turn on the SES light. If it's a "stored" code, it doesn't affect anything.

I downloaded the file, and will try to take a good look at it as soon as I can. Definitely a problem with the left (drivers) bank of the engine. The PCM is pulling out 15% of the normal fuel at idle. Could be excessive fuel from the injectors, or a faulty O2 sensor. Appears you cleared the PCM before you ran this log, and that resets all the long term fuel trims to 128 (0% correction). I have to look at each of the 18 fuel trim cells to see if they are fully developed, since they only "learn" when you are actually operating the engine in that cell (a grid defined by RPM and engine load, as measured by MAP).

LT11996

Yeah I cleared that dtc 16 code after it came up at the request of an LT1 Nation member to see if it would come back up but it didn't. I did let it run for at least 30 minutes straight and drove it several miles afterwards though. But the driver side has a new o2 sensor. Couldn't get to the passenger side as it's above the Y pipe but I had the new o2s laying around for my 1996 and wanted to see if replacing that one at least would help it run any better because it originally had a very bad exhaust leak on the driver side manifold gasket until I replaced it.

Would you recommend that I let the car idle for a little bit longer or drive it a couple more miles to let it learn what it needs to then take a better log?

Injuneer

Let me look at the log some more. But it doesn't match the screen shots you posted. In the screen shots the Bank 1 long term and short term is down to 108, as well as the Bank 2 long term. In the graph, appears both sensors have reading close to 1 volt, which is about as high as they can go and very rich. In the data log, only the Bank 1 long term is bottomed out at 108. Bank 2 is closer to normal.

If you do another log, do not clear the PCM. Seems to take a bit longer than normal to go into closed loop. That's because the engine seems to warm up very slowly. I think instead of the usual 206 seconds it took something like 350 seconds. So let it idle for two minutes, drive it moderately for another three minutes to make sure it's in closed loop, then start driving with a wide variety of throttle position and RPM.

Don't worry about a full throttle pull. Something is causing knock retard. Does the exhaust or anything rattle on closed throttle decel? That's when the knock retard starts, and then increased as you rolled into WOT.

LT11996

I wish I hadn't cleared it lol but the screenshot posted above is from the very first scan I used and it was before I originally reset the IAC, fuel trims, and cleared the PCM.


But I was thinking it may have taken longer to warm up because it was around 40 degrees outside when I cranked it. Also, the car does pop and backfire upon closed throttle deceleration. Nothing crazy loud but it's there. I haven't noticed any rattles or anything like that from the exhaust though

LT11996

Here is another datalog I just made. After I let it warm up, I drove a few minutes and made sure it was in closed loop, then kept it in certain gears and drove at different rpms. I wish I could take a longer log or a farther drive, I'm just afraid that the car will die again and leave me stranded like it already has twice lol. One thing ive noticed between the logs and the tachometer, the tach is way off. When the scan shows 900ish rpms idling, the tach shows 1100-1200. And then while driving, it could show as much as 500-1000rpms higher than what the scan actually shows it at.
https://www.mediafire.com/?er75q5o8ama7hs2

I guess I should make a quick list of what I've done to the car so far. Note that some of these parts have been swapped over from my 1996 Z28 when they were in known good working order.

SLP 160* Tstat
MAF meter and sensor from 96
IAT sensor from 96 (swapped the elbow)
Ignition Control Module from 96
New AC Delco driver side o2 sensor
New AC Delco Ignition Coil
New MSD coil wire
New HFP 255lph fuel pump

Lastly, the car came with one of those junky Hypertech tuners so I made sure that it had the stock tune on the pcm, and just put in the info on it that it now has a 160* tstat

LT11996

Bump. My plans for tomorrow are to swap injectors side to side and see if anything changes in the scan. After not cranking it for two weeks, I fired it up and took it down the road tonight while it was still in open loop and it seemed to have more power than usual.

Update:
I just swapped the injectors side to side. Each of them were pretty rusty and nasty looking on the bottom side. I guess that's normal for a 152,000 mile LT1? Also, after swapping them, I propped the rails up on a piece of cardboard and turned the key to ON to see if any were leaking, but none of them leaked.

I read that to check for an injector not firing, I could unplug one injector while the engine is idling and see if anything changes and if the car starts idling badly, that means that injector is working. But if nothing changes in the idle after disconnecting one, then that injector is bad.

So I went through that process on all 8 injectors, and each time, the car idled worse and dropped down some except for when I unplugged the cylinder #4 injector on the passenger side. I went through the process twice, shutting the car off and re cranking it after plugging back in each connector just to make sure that it was firing again. And both times, disconnecting the #4 injector didn't affect the engine at all even idling for another 20 seconds or so.

That injector was originally on the driver side this whole time. So if it hasn't been firing this whole time, could that be a big part of my problem?

Injuneer

Somehow I missed the post of the data log from 02-19. I just tried to download it, and I got this message (Norton):

timnfxr

That links works here...

LT11996

Thats strange. I clicked on it in your quote on my phone and laptop and both opened the link and downloaded the file just fine