Rough running 7.4 Vortec

[stutaeng]

This is a good article to goes to the basics: https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-troubleshoot-a-no-start-1

Most likely Items 1.) or 2.), but also look into 3.) and 4.)


Says 4.3, 5.0, 5.7, but also applies to the 7.4, all Vortec series engines

 

[Carlaisle]

Is this the same start then immediately die thing you mentioned before or something different?

 

[TexasAggie]

Same thing. I left the key on for 15 minutes until the security light went out and she fired right up. Looks like that black bear tune will come sooner than later. Worth it to disable the passlock nonsense!!

 

[TexasAggie]

Ok, back to looking into the rough running motor... I contacted BlueDriver and they say that Chevy PCMs don't support the Mode6 misfire counter until 2008. Direct quote - 'Unfortunately GM did not have a mode 6 misfire counter until they adopted the CAN protocol (roughly 2008). This data may be available through enhanced/manurfacturer live data.'

How are folks diagnosing misfiring with the basic scanners that are out there? I had an Innova, but couldn't find the option there, and now on the BlueDriver it isn't available either.

 

[Schurkey]

My '97 K2500 7.4L 4L80E has misfire history. #8 had a bazillion misfires when I was looking at it pre-purchase. Turned out to be a broken (cracked) spark-plug porcelain.

Fixing the misfire ALSO fixed the lack of torque-converer lockup. The computer won't lock the converter if it detects misfire.

This is why I bought a used, ancient PROFESSIONAL-GRADE scan tool (Snap-On MTG-2500 with software to 2006) instead of brand-new consumer-grade junk. My scan tool body is probably older than plenty of people on this forum. One of these days, it's going to quit working and I'll have to buy a much-newer, used, professional-grade scan tool (probably in the Snap-On Solus/Solus Pro/Solus Ultra series.)

 

[Fishon]

More updates - went out to try and run the diagnostics again and left the key on for a long time while I fiddled with the scanner. Turned it to start and it fired right up and stayed running. Went and drove around for 20 minutes to try and collect data and now I can't figure out how to read it from the scanner app. Turned the truck off and started it again with no issue.

Checked fuel pressure before my ride and it was a steady 52psi at idle and jumped up to 60 when I would hit the throttle in the driveway.

No idea what caused the no start condition all day.... need to figure it out though before it leaves me stranded.

The next time it doesnt start pull #3 plug wire and try to start. Yes I know sounds crazy! I didnt believe it until it worked for me. If it works go buy a GM rotor and cap. Even if yours is only two omonths old like mine was... good luck

 

[TexasAggie]

This is why I bought a used, ancient PROFESSIONAL-GRADE scan tool (Snap-On MTG-2500 with software to 2006) instead of brand-new consumer-grade junk.

What did you give for it if you don't mind me asking? Also, what's the best way to identify if an older tool will work for me? I'm fine using something from the early 2000s as long as it does everything I need for the Chevy (I also have a '96 Ford that it would come in handy for).

 

[Schurkey]

What did you give for it if you don't mind me asking?

I bought the thing 15+ years ago. What I paid then is not what the current prices are on eBay. It was not new even then--probably made in the 1990s sometime. It came with some cables 'n' adapters for OBD-1, the adapter for OBD-2 and a handful of OBD-2 keys; paper manuals, carrying case, and software good to 2003 Domestic and perhaps 2002 Asian. No European software at all. The "rechargeable" battery wasn't worth a crap when I got it, It's not even installed now. I HATE HATE HATE rechargeable batteries.

Today, something similar might be ~$400, maybe less. The MT-2500 which doesn't include the graphing feature of the MTG-2500 would maybe be half that price. But support for the '2500 series ended with 2009 software, the thing had been discontinued long before that. Any of the 2500-series "Red Bricks" are antiques now.

The Snap-On Solus series (Solus > Solus Pro > Solus Ultra > Solus Edge) replaced the '2500 boxes. The OTC Genysis and it's clones sold by Mac and Matco were competitors to the Snappy '2500 and Solus tools--I've never used them, but they're also Professional-grade.

Also, what's the best way to identify if an older tool will work for me? I'm fine using something from the early 2000s as long as it does everything I need for the Chevy (I also have a '96 Ford that it would come in handy for).

The TOOL isn't the issue--the software revision is. Buy a tool that comes with the software new enough to work on whatever you own, or expect to own in the near future. You could get GM-only software, "Domestic" , (GM, Ford, Chrysler, Jeep) Domestic + Asian, or Domestic + Asian + European. More coverage = higher prices.

The prices are based AT LEAST as much on the software version as on the actual tool. Newer software = more expensive. And make sure what you buy has the battery-charger, DC "cigarette lighter' power adapter, and all the OBD-1 connectors you're likely to need. With Snappy, OBD-2 also requires an assortment of "Keys"; for example K-9 is very popular for GM applications.

I can't help you with what might be needed if you went with an OTC Genysis, or the GM "Official tools", the Tech 1 or Tech 2. Never worked with any of those. I worked with an OTC Monitor 4000 (?) but it was decades ago, I hardly remember it.

 

[TexasAggie]

Are these tools self contained or do you need to hook them to your laptop in order to fully utilize them? How easy/difficult are they to work with?

 

[HotWheelsBurban]

I bought the thing 15+ years ago. What I paid then is not what the current prices are on eBay. It was not new even then--probably made in the 1990s sometime. It came with some cables 'n' adapters for OBD-1, the adapter for OBD-2 and a handful of OBD-2 keys; paper manuals, carrying case, and software good to 2003 Domestic and perhaps 2002 Asian. No European software at all. The "rechargeable" battery wasn't worth a crap when I got it, It's not even installed now. I HATE HATE HATE rechargeable batteries.

Today, something similar might be ~$400, maybe less. The MT-2500 which doesn't include the graphing feature of the MTG-2500 would maybe be half that price. But support for the '2500 series ended with 2009 software, the thing had been discontinued long before that. Any of the 2500-series "Red Bricks" are antiques now.

The Snap-On Solus series (Solus > Solus Pro > Solus Ultra > Solus Edge) replaced the '2500 boxes. The OTC Genysis and it's clones sold by Mac and Matco were competitors to the Snappy '2500 and Solus tools--I've never used them, but they're also Professional-grade.


The TOOL isn't the issue--the software revision is. Buy a tool that comes with the software new enough to work on whatever you own, or expect to own in the near future. You could get GM-only software, "Domestic" , (GM, Ford, Chrysler, Jeep) Domestic + Asian, or Domestic + Asian + European. More coverage = higher prices.

The prices are based AT LEAST as much on the software version as on the actual tool. Newer software = more expensive. And make sure what you buy has the battery-charger, DC "cigarette lighter' power adapter, and all the OBD-1 connectors you're likely to need. With Snappy, OBD-2 also requires an assortment of "Keys"; for example K-9 is very popular for GM applications.

I can't help you with what might be needed if you went with an OTC Genysis, or the GM "Official tools", the Tech 1 or Tech 2. Never worked with any of those. I worked with an OTC Monitor 4000 (?) but it was decades ago, I hardly remember it.

Part of the expense on these things is the software licensing fees. Like when you get a tune, it's licensed for 1 VIN, 1 use, if I've been told correctly. That's how software developers make a lot of their money, licensing their "intellectual property ". Same thing with movies/TV shows and music. The $$$ is in the licensing.
I knew a little about this from musician friends, but learned a lot more when my brother took entertainment law in college. He also ran the HCC Stafford computer lab for a few years while continuing his education. Part of his duties were helping other students, but mainly he was supposed to be sure no one was pirating the software (they had a lot of expensive digital movies/music stuff for production and editing).