Check engine light flashing

[bikernut]

I have a 2003 GMC 3500 4x4 with a 6.0 engine. Problem: when plowing snow, hauling a small Kubota tractor or just driving down the road when the engine RPM gets to about 2200-3000 the check engine light starts flashing, I let off and reduce RPM and it stops flashing. What I have done so far is replaced the knock sensors 2 times, changed all 8 coil packs, 8 spark plug wires and 8 spark plugs all GM products no aftermarket stuff. I have gone to the local service station and had the scanner installed and driven it to the RPM and it says misfire in about 4 cylinders. When the light flashes it won't set a code just flashes and this is about to drive my crazy. The engine idles nice and smooth and when the light starts flashing at the RPM there is no roughness to the engine at all. Anyone have any ideas?? I have even gone and disconnected both batteries for a 24 hour period. Do I need to go to the GM Dealership and have the computer erased or re-flashed?? I'm at a loss, truck only has 45,000 miles.

[hatzie]

Have you checked the output from the MAF when it's misbehaving?

[bikernut]

how do you do that when driving? thanks

[hatzie]

Log it. Torque Pro on Android phone or tablet with a good Bluetooth OBDII adapter or any number of PC based OBDII packages will let you graph sensor output.

This is someone doing it on an S10 with Torque Pro on an Android tablet...

http://www.youtube.com/watch?v=KXwnhjbXY74

[bikernut]

I will have a problem then as I don't do any smart phone or android thingy & my pc is so old it can almost vote, but thanks

[hatzie]

There's so much old laptop hardware out there now it's almost free. I bet you can probably find an old working Toshiba or Dell or HP with lithium batteries from 2003 or 2004 that's running Windows XP for free.
OBD II software isn't real demanding of processor power or memory resources and most of it will still run on Windows 2000 say nothing of XP or Windows 7.

My creaky old 2004 vintage HP NX7400 running Windows XP is almost old enough to be steam powered and it'll run Memory Card Explorer to burn Tech 2 Binaries to Linear Flash cards in the PCMCIA slot along with most OBD II software and all of the PC based ALDL software packages. I just can't connect it directly to the internet anymore for fear of it getting an infection and and attempt at installing Windows 7 is not likely to be a fruitful endeavor.

I have several of my old work laptops that I beat to death on transit coaches working on embedded control systems. Most of the still kinda work but the cases are really quite beat up... screen hinges snapped off and the like.
If I didn't have three nearly complete NX7400 parts laptops in pieces on the office closet shelf and three more modern HP 8560W Elitebooks in pieces I would go for one of the fully working $100 Dell D620, D630, D820, & D830 laptops you see all over evilbay.
Those Dell laptops are plentiful and they make great el-cheepo garage PCs. They're the antithesis of your garden variety ancient laptop. They are old old old but they are tough as hell and they will run 32 bit Windows 7 with Dell drivers for all the internal goodies. They have a Real RS232 DB9 serial port with a real DOS addressable 16550 UART alongside more modern USB 2.0 ports and even a PCMCIA/Cardbus slot to program Tech 2 linear flash cards. Batteries are cheap and easy to find. Power paks are cheap and easy to find. Not as heavy duty as a Panasonic toughbook but they don't have that Toughbook pricetag either. They're still tough as hell and cheap enough to buy one or two more as backups JIC you drop one and kill the screen or motherboard.

You can get cheap $50 Chinese Android tablets as well. They're cheap but if the only thing you're running on them is Torque Pro or some other OBD 2 package that's not a big deal.

You have new enough trucks that a laptop or at least an el-cheepo Android tablet is going to become a necessity to do your own work.

[bikernut]

wow all the pc talk took my breath away as I understood none of that, but I did know what OBD II was don't know what it means but I do know where the hook up is in my truck. I will see if any of my old buddies understand any of what you said. my pc is about the 2001 time frame and is so slow that sometimes I wait about 15 minutes for it to start, and being retired on a fixed income here in New England and handicapped I need to save money not go out and buy something I know nothing about as this has been doing this for a few years now so I might just leave it and hopefully some day it will stop and throw a hard code so I can finally fix the problem. I thought this might be a cheap fix but it sounds like $ now that I don't have. thanks

[richards72chevy]

The check engine was flashing on my 02 Silverado because it had a clogged catalytic converter.I think it happened because I let a leaking intake manifold gasket go on for to long.Crazy thing about it my truck made a horrible noise when I would take off.Sounded like a very neglected serpentine belt or a bad ujoint.It drove me crazy looking for that noise and it ended up being mt catalytic converter.

[TKCR]

I have always had the understanding a flashing CEL (Check Engine Light) is something serious to be concerned about. A blinking CEL indicates that your vehicle's engine is misfiring, which could severely damage your catalytic converters. ... Engine misfire is a severe condition that requires immediate attention to avoid expensive repairs or even a car fire.
I just thought it was common knowledge that an engine light on is something that needs checked out, but a “flashing” engine light, means it is more serious. The vehicle should not be driven when the light is flashing.

[hatzie]

Originally Posted by bikernut

wow all the pc talk took my breath away as I understood none of that, but I did know what OBD II was don't know what it means but I do know where the hook up is in my truck. I will see if any of my old buddies understand any of what you said. my pc is about the 2001 time frame and is so slow that sometimes I wait about 15 minutes for it to start, and being retired on a fixed income here in New England and handicapped I need to save money not go out and buy something I know nothing about as this has been doing this for a few years now so I might just leave it and hopefully some day it will stop and throw a hard code so I can finally fix the problem. I thought this might be a cheap fix but it sounds like $ now that I don't have. thanks

You're in the Keene area?

I bet there are some folks local to you that can log data that could give you a hand.
A serious misfire like the one indicated by a flashing MIL is not something you can ignore. You really need to find out what's wrong with it or you'll be buying a replacement soon because it died.

[bikernut]

about 30 miles from Keene and when I feel like moving around I will see as my arthritis in my knees plays hell with me moving around a lot. thanks

[richards72chevy]

I don't have a fancy scan tool and I don't consider myself a mechanic.So I know this may seem archaic to some.You can remove your o2 sensors in front of the catalytic converters if your lite quits flashing then more than likely you have a plugged cat.But I've been told cats just don't plug up.In my case I think it was a leaking intake gasket that I let go for way to long.I replaced it myself it wasn't to bad but nowhere as easy as replacing an old sbc intake.

[bikernut]

I have changed all the O2 sensors and as I mentioned changed the knock sensors twice so along with that is the intake gasket but thanks

[hatzie]

People seem to think that OBD II scanners are super expensive...
You can build a 7" Android tablet based OBD II scanner for $135 or a 5" phone based scanner for $105.

The 8gb Amazon Fire 7 tablet is $50. You can get a 5" Android cell phone at Wal Mart for $20-$30. No cellular data plan needed on either. The build quality of the Fire Tablets is much better than the ElCheepo cell phones. You don't need to connect either of them to anything but WiFi and you only need that long enough to connect to Google Play or the Amazon app store and download Torque. You can do that on free WiFi. I use ElCheepo brand $20 Walmart Android phones for Bluetooth DRO displays on my Lathe and my Milling machines and they're not connected to any cell network at all nor have they ever been.

Software cost? Torque is free... Torque Pro was under $5 IIRC. Not super pricey for the full version and it's a lifetime license.

You don't need GMLAN CAN capability so you can find a good old fashioned J1962 (OBDII) bluetooth interface. It's the most expensive part of the tool. You can buy the cheap Chinese ones that might work or just get an OBDLINK MX for $80 on Amazon that will work every time you plug it in and won't screw up your PCM.

If you figure you can't afford to buy one think about how much it'll cost to pay to have the vehicle diagnosed or to swap a bunch of parts you don't need to replace til you fix whatever is causing the problem.

[richards72chevy]

Originally Posted by hatzie

People seem to think that OBD II scanners are super expensive...
You can build a 7" Android tablet based OBD II scanner for $135 or a 5" phone based scanner for $105.

The 8gb Amazon Fire 7 tablet is $50. You can get a 5" Android cell phone at Wal Mart for $20-$30. No cellular data plan needed on either. The build quality of the Fire Tablets is much better than the ElCheepo cell phones. You don't need to connect either of them to anything but WiFi and you only need that long enough to connect to Google Play or the Amazon app store and download Torque. You can do that on free WiFi. I use ElCheepo brand $20 Walmart Android phones for Bluetooth DRO displays on my Lathe and my Milling machines and they're not connected to any cell network at all nor have they ever been.

Software cost? Torque is free... Torque Pro was under $5 IIRC. Not super pricey for the full version and it's a lifetime license.

You don't need GMLAN CAN capability so you can find a good old fashioned J1962 (OBDII) bluetooth interface. It's the most expensive part of the tool. You can buy the cheap Chinese ones that might work or just get an OBDLINK MX for $80 on Amazon that will work every time you plug it in and won't screw up your PCM.

If you figure you can't afford to buy one think about how much it'll cost to pay to have the vehicle diagnosed or to swap a bunch of parts you don't need to replace til you fix whatever is causing the problem.

I didn't know you could use an android phone.That's the phone I'm using now.I know amazon sells a cheap little scan device that you plug into your port and transfers it over to your phone.I know harbor freight sells what looks to be a decent scan tool that shows live data.But I'm a little nervous about plugging up that scanner to my truck.

[hatzie]

Originally Posted by richards72chevy

I didn't know you could use an android phone.That's the phone I'm using now.I know amazon sells a cheap little scan device that you plug into your port and transfers it over to your phone.I know harbor freight sells what looks to be a decent scan tool that shows live data.But I'm a little nervous about plugging up that scanner to my truck.

The real cheap Bluetooth interfaces are a crapshoot.
The Harbor freight scan tools actually have some good press. They seem to be moving away from the super cheap crap and into some ok entry level tools. Some of their stuff is still super cheap crap tho. Look up some reviews of that exact sku and decide for yourself.

This is the Bluetooth OBDII/CAN interface that's lisyed in the Torque FAQ. I use it on my 09 Impala & 05 Silverado. It won't screw up your ECM. https://www.amazon.com/ScanTool-OBDL.../dp/B006NZTZLQ
If you use the manufacturers app from the Google play store it'll update the interface firmware to the latest release. It also gives you access to raw Mode $06 data. This app only works with their interface yes it's free but not to use with another obd tool.