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I'm trying to diagnose a specific drivability issue with my 94 Firebird V6 that only happens after I've started out driving the car, once I get over about 5 mph, it just runs a little rough after that. It resets when I turn the car off, and the issue returns once I start out driving again, over about 5 mph. So it seems to me like it starts happening once one of my emissions valves opens, like maybe the Vapor Can Purge Valve. It's not displaying any SES lights, and I don't think it's storing any codes (because of the former problems with finding a scan tool for 94 OBD1 Firebirds, I just got a scan tool, GaryDoug's SCAN 9495, for it, and ran my 1st scan today. I've previously replaced a ton of parts trying to stop it from happening. Those replaced parts are....

Ignition Control Module, All 3 Coil Packs (Spark Plugs and SP Wires), EGR, all EGR system Gaskets, PCV, all PCV Grommets and Seals, PCV Harness, both O2 Sensors, Engine Coolant Temp Sensor, Air Filter, Fuel Filter. I've also gone through and cleaned all the main computer connectors, and the power and ground connections.

Before running today's scan, I was strongly suspecting my Vapor Canister and Purge System since that the only system that hasn't been touched. Except I did confirm my Purge Valve is working by unplugging it, then testing it with an outside power source. The only reason I haven't gone through and tested all the other Vapor Can parts is they're really hard to get too.

During today's scan, two things jumped out at me that may be a, or the, problem. It said.....

Injector Failure this Run. Every time I turned off, then restarted my car, and started driving it, this Injector Failure this Run would show up. But the car seems to be firing on all cylinders

It also said,...

CAM Signal Missing. Does this mean my PCM isn't getting a signal from my Cam Sensor...?

Does anybody have any idea what might be causing my car's issues?

Thanks
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Attach the data log file so we can download it and look at it. I've never seen a file from a V6, but I've been reviewing files for people for close to 15 years.

If you have an injector fault, and/or cam position signal missing, it should set DTC's. Where did it tell you the cam position signal is missing, if not a DTC?
 

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Discussion Starter · #3 ·
I'll record it now. Post in a couple hours.

It said "CAM Signal Missing" in the box at the lower right side of the engine tab. I don't think the V8 tab has it there as I saw the V8 engine screen in my manual, and didn't see it there.

According to my Carline 94 Service Manual,.... Camshaft Circuit Error is a code that should have been stored. But it doesn't show up a SES, just stores the code. I didn't see it anywhere.

Be back soon with a datalog post soon, I hope...

Thanks Fred
 

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Attach the data log file so we can download it and look at it. I've never seen a file from a V6, but I've been reviewing files for people for close to 15 years.

If you have an injector fault, and/or cam position signal missing, it should set DTC's. Where did it tell you the cam position signal is missing, if not a DTC?
Just got back from driving around, doing multiple scans. Every time I stopped, and stopped a scan, my PC said "Windows has encountered an error, and needs to shut down SCAN9495". When that happened, I restarted the app, and the scan. When I started driving again.

I checked properties of the datalogs, and it said they open with MS Notepad (I hadn't loaded any office software on this PC yet, and I guess none was on it when I bought it the other day. So I just installed a old copy of MS Office 2000 I had. That automatically changed the datalogs to Excel Files. But when I opened them, they still don't look like what I saw when I was doing the scans.

I'm finally figured out how to upload those three datalogs onto this post. Hopefully they'll come out looking correct after I do that.

If not, could somebody please help me figure out what's going on, and how to fix it? I seem to be having back luck right along with this project.

Thanks
 

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Quick peek on my iPad and they look like they are supposed to. I'll open them in the morning on my PC w/ Excel. In one when I looked at DTC's, there are 2 stored in history. It takes me about 15 minutes to set these up the way I like to look at them in Excel.... grid lines on all cells, freeze the top line of labels, add max, average and min calculations for each column, hide unnecessary columns, define limits for cold start enrichment/open loop, closed loop, and power enrichment. The V6 version appears to be missing the status flags that are so helpful in the V8 version.
 

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Discussion Starter · #6 ·
Wow,... that's very cool Fred. Looking forward to seeing what those stored codes are. I thought I clicked on the DTCs tab and saw an empty box there. Guess I'm looking at the wrong thing.

I also swear I saw a status button or tab or something.

I'm looking forward to your analysis.

If there's anything I can do to make the scans more effective for diagnostics, please let me know the specifics and I'll certainly do it.

Thanks for everything.
 

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All windows computers have a notepad built in, at least as new as win7 does. If that won't open the scan file try craigslist for a used copy of microsoft office.
 

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The last three columns show DTC info - # stored in history; # active; the actual codes (but this may only be the active codes - you are correct, there is nothing in this column).

But at no point is there anything other than "0" in the column for RPM derived from the 24X (high res crank position) sensor signal.

Looking at the 94 factory manual, there is no DTC for injector circuit failure on the 3.4L V6.

When you ran the large data log, did the engine exhibit its typical rough idle after warmed up, and reaching 5 MPH?

Engine takes forever to warm up. After 6 minutes, coolant is only up to 104*F. 10 minutes to hit 150*F. Have you verified there is a thermostat installed? Is it possible the fans are running continuously? The LT1 software has flags to indicate when the fans are actuated.

Looking at the first 10 minutes, the EVAP operates seldom, duty cycle is low. It shuts down when your TPS goes to 0% (closed throttle). In the 11th minute, EVAP DC goes up over 50%. During that time, the O2 sensor voltage average is very close to the "neutral" 450mVolts. I don't see a connection between EVAP and anything else.

Your idle long term fuel trims (Cell 16) are 124 left/122 right, indicating the PCM is not making more than a 5% adjustment in fuel calculations. Cell 4 (low RPM/low engine load) is similar. But cell 8 has a 153 left / 131 right LTFT. That would indicate the engine is running 20% short on fuel on the left bank using the "normal" calculation, and is making up that shortage by raising the LTFT. But the right side has no real issue.
 

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Ramblin' Wreck
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I keep suggesting this but nobody seems to hear it. Apache Open Office is available for free online. It is compatible with Microsoft Office earlier versions and has programs that are almost identical to Excel, Word, and Access. It can open any csv file and display it just like Excel does.

https://www.openoffice.org/
 

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I keep suggesting this but nobody seems to hear it. Apache Open Office is available for free online. It is compatible with Microsoft Office earlier versions and has programs that are almost identical to Excel, Word, and Access. It can open any csv file and display it just like Excel does.

https://www.openoffice.org/
That's a really great tip GaryDoug. But it's a non-issue as I did install a copy on MS Office 2000 directly after doing my scans, doing that install automatically converted my datalogs to Excel Files. It was very cool.

The last three columns show DTC info - # stored in history; # active; the actual codes (but this may only be the active codes - you are correct, there is nothing in this column).

I'll do another scan tomorrow and see if I can find any stored codes on that tab.

= = = = = = = = = = = = =

But at no point is there anything other than "0" in the column for RPM derived from the 24X (high res crank position) sensor signal.

OMG Fred !!!! You're right,.. there is no readings at all on my 24X Crank Sensor ! That could be, and probably is, my whole, or at least part of,.. my misfire problem,... right? I can't believe I didn't notice that.

= = = = = = = = = = = = =

Looking at the 94 factory manual, there is no DTC for injector circuit failure on the 3.4L V6.

When you ran the large data log, did the engine exhibit its typical rough idle after warmed up, and reaching 5 MPH?

Yes Fred! it did exhibit the expected the rough running, under load, after starting the car and exceeding about 5mph (it's not really noticeable at idle). But this day it wasn't quite as bad as it usually is, and can be. Sometimes the symptoms are worse than at other times. The symptom seems to be extra bad when it real wet out, and raining (which we are famous for our rain up here is Greater Seattle

= = = = = = = = = = = = =

Engine takes forever to warm up. After 6 minutes, coolant is only up to 104*F. 10 minutes to hit 150*F. Have you verified there is a thermostat installed? Is it possible the fans are running continuously? The LT1 software has flags to indicate when the fans are actuated.

I always warm up my car at least 3 minutes for my 1st drive of the day. But, for the 1st scan/datalog, I did warm it up 6 minutes,.. at least. It was also very cold outside, close to freezing. Then, after I drove out of my parking stall,... I coasted my car down a long hill, for the next minute or so,... then was caught at a freeway traffic control/on-ramp stop light,... and had to wait my turn (at least two more minutes) to get on the freeway. So those driving conditions may have contributed to the strange datalog readings. Normal driving didn't start until I was in 4th gear, and doing 60mph on the freeway, but even then,.. I was stopped more then once by lousy drivers, cutting people off, and causing traffic problems.

I do know, for sure, that I have the correct thermostat, and the PCM turns on my fan at the correct temperature. I had the coolant system gone over by the local GM Dealer a couple years ago, and the ECT Sensor is fairly new, and was bench tested before installation. The coolant was flushed and refill with Dexcool about 15 months ago with 50/50 coolant/water

= = = = = = = = = = = = =

Looking at the first 10 minutes, the EVAP operates seldom, duty cycle is low. It shuts down when your TPS goes to 0% (closed throttle). In the 11th minute, EVAP DC goes up over 50%. During that time, the O2 sensor voltage average is very close to the "neutral" 450mVolts. I don't see a connection between EVAP and anything else.

So it looks like my EVAP system is not a problem...?

= = = = = = = = = = = = =

Your idle long term fuel trims (Cell 16) are 124 left/122 right, indicating the PCM is not making more than a 5% adjustment in fuel calculations. Cell 4 (low RPM/low engine load) is similar. But cell 8 has a 153 left / 131 right LTFT. That would indicate the engine is running 20% short on fuel on the left bank using the "normal" calculation, and is making up that shortage by raising the LTFT. But the right side has no real issue.

When you say "Right Side" you mean the passenger side,... right? Could these readings you see there be caused by one or more bad injectors?
Thanks so much Fred. I have to tell you,... I am a complete novice when it comes to all these sensors, PCMs, fuel injectors, etc. In fact, almost all of what I've learned was in the last 3 years since this problem raised it's ugly head. I have replaced a ton of parts, and have done tons of reading in manuals, how-tos, and forums, but mostly my Carline shop manuals. It's been very educational,.. but I still have a lot to learn. I'm not real great at interpreting what this data you point out actually means. That's why I need to ask if what I think it mean, is correct...? Please bear with me.

What should I do next? Have my 24X Crank Sensor replaced (or replace it myself).

Thanks GaryDoug and Fred !!!
 

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Ramblin' Wreck
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I just uploaded a new trial version of this app that logs all the other data shown on the engine tab (the ones at the bottom also). It is rev 1-1-0. You can just put it into the folder with the other one and run it the same way. Everything should work the same but the datalog file will have more data.

On the subject of DTC's, make sure you also have the DTC section selected to scan, otherwise there will be none listed on the DTC tab or in the log file.
 

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Discussion Starter · #12 ·
I just uploaded a new trial version of this app that logs all the other data shown on the engine tab (the ones at the bottom also). It is rev 1-1-0. You can just put it into the folder with the other one and run it the same way. Everything should work the same but the datalog file will have more data.

On the subject of DTC's, make sure you also have the DTC section selected to scan, otherwise there will be none listed on the DTC tab or in the log file.
Oh,... I see what you're talking about. I didn't even notice the section where I can check the boxes for different scans.

So,.. I'll be able to check more than one of those boxes and run several types at once Is that correct...?

I'll download the new version then run and post new scans tomorrow.

Thanks
 

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Just do the engine and DTC scans for now otherwise it slows down. When you want the fastest scan and don't need the DTC's, just do the engine by itself.
 

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Have I offered to send you the pdf file called "scanner readings and what they mean" It will help you to understand. Private message me with your e-mail address if you wish to get the file.
 

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Discussion Starter · #15 ·
Just do the engine and DTC scans for now otherwise it slows down. When you want the fastest scan and don't need the DTC's, just do the engine by itself.
Thanks for the reminder, Gary. Will do.

Have I offered to send you the pdf file called "scanner readings and what they mean" It will help you to understand. Private message me with your e-mail address if you wish to get the file.
I don't think I remember reading a post like that,... but I've read quite a few.

That would be really helpful,... thanks Robert !!!

GO

Seahawks !!!!!!!
 

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Looking at the first 10 minutes, the EVAP operates seldom, duty cycle is low. It shuts down when your TPS goes to 0% (closed throttle). In the 11th minute, EVAP DC goes up over 50%. During that time, the O2 sensor voltage average is very close to the "neutral" 450mVolts. I don't see a connection between EVAP and anything else.
I forgot to reply to this comment....

The 1st scan, my engine displayed no rough running until the 11th minute at least,.. because...It was the 11th minute after start-up before I did any real driving, using the engine. I had a 6-7 minute warm-up,...then around 4 minutes coasting down a hill, mostly in neutral,... and then waiting for my turn to get on the freeway at one of those damned freeway on-ramp traffic-control stop lights.

In about the 11th minute I pushed my car up to about 50-60mph entering I-405 (that was when the rough running symptom started), and was on I-405 for about 5-6 minutes before driving another few minutes on stop-and-go city streets.
 

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Have I offered to send you the pdf file called "scanner readings and what they mean" It will help you to understand. Private message me with your e-mail address if you wish to get the file.
Is this my Scanmaster document? If so, it is focused on MAF applications, and may be confusing to someone running scans on a speed-density application like the 3.4L V6, at least with the concept of A/F control. The V6 scan also appears to utilize a different LTFT Cell grid and numbering.
 

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Yes, that's the one. I usually recommend it for lt1 cars, but except for maf readings, most of the info should be helpful for learning how to interpret scan data.

Didn't realize it was your document as I didn't know your last name.
 

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You really need to be patient. We've invested a lot of time helping you so far, and we are not all here 24/7.

The ECM uses three sensors to determine where the crankshaft if in its rotation - 3X crank position sensor, 24X crank position sensor and cam position sensor. The ECM need to know which cylinder is approaching top dead center, and whether that cylinder is on the compression stroke or the exhaust stroke. That way, it can time the ignition spark and fire the injectors.

The engine can run without the 24X crank position. It get's adequate info from the 3X sensor to run the engine. But the 24X signal is called "high resolution" and the ECM can more accurately time the spark and injectors. It uses this primarily for idle, and below 2,000 RPM. I would expect a tiny change in the smoothness of the engine, but it's hard to see how this can be major, but it can affect the sequence of the injector firing, and uses a waste-spark ignition (one coil fires plugs on two cylinders at the same time. I have run my LT1 engine with only a crank position sensor, keeping the sequential injection, but using the waste-spark coils. It was possible for the PCM to synch the sequential injection 1 crank revolution out of phase (which would naturally occur 50% of the time). The only time I noticed any difference in the way the engine ran was when it was cold. There would be a slight stumble, probably the result of the injector firing against a cold, closed intake valve. Once things warmed up, I could not detect any roughness.

It is possible that absence of the 24X signal could make the engine operation seem rougher at low RPM. But I have no experience directly with this engine, so I don't know the magnitude of the problem. In any case, check the wiring harness connector. There is also a diagnostic procedure in the factory service manual for this DTC.
 
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