My check engine light is blinking

Tiny
ROBC1985
  • MEMBER
  • 2000 GMC SIERRA
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 193,000 MILES
Over the last 2 to 3 days my service engine light has begun to blink. I installed new plugs and wires about 6 months ago. As well as the 8th ignition coil. The only info I can find online so far tells me the issue is a misfire in which sunburned fuel is getting to the catalytic converter and potentially causing damage to the catalytic converter, or the catalytic converter has been too damaged already. I don't care about the catalytic converter. The whole exhaust is in bad need of replacing. I pulled out and cleaned all 8 spark plugs. From what I can tell the white residue on the plugs was from too much heat or possible chemical deposits. I can't provide a picture but I'll find one online to show what I can. Cleaning the plugs changed nothing. Should I change the crank seal? The truck has performance loss but that's not new. Honestly the only thing new is the light blinking non stop about 5 minutes into driving. Nothing else from what I can tell has changed. It lost some power over a year ago and has been a bit slow starting and sometimes will cut back off but that's very rare. All those issue aren't new only the light blinking. Please inform me of any and all possibilities and level of severity.
Friday, February 5th, 2021 AT 4:11 AM

4 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
The first thing to do is to scan the truck for the misfire code(s) that are causing the check engine light to blink. They can be caused by the plugs but also from many other causes. White deposits could be chemicals or coolant. Without seeing them it's hard to say. However the first thing is get the codes. Then you at least have a target. I also would not keep driving it until you at least determine what is actually wrong. I would worry about damaging the converters as they are not a cheap part, the ones for the 4X4 version are between $350.00 and $700.00 each and it uses 2.
Once you know if it's a single cylinder miss or random multiple misfire then you can go farther. The reason is that a random multiple miss covers all of the cylinders and could be anything from a vacuum leak, low fuel pressure, plugged fuel filter, bad pressure regulator while a single cylinder misfire could be a bad plug, coil, or internal to the engine like a damaged valve or injector.
Getting the codes isn't hard, many of the chain parts stores will scan it for free, or you can buy a simple code reader even in places like walmart.
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Friday, February 5th, 2021 AT 5:22 AM
Tiny
ROBC1985
  • MEMBER
  • 20 POSTS
The codes are misfire 8th cylinder 2nd bank that's all I ever get from the AutoZone near me. That's it. Even after I replaced the wires plugs and coil pack to that cylinder.
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Monday, February 8th, 2021 AT 5:38 PM
Tiny
ROBC1985
  • MEMBER
  • 20 POSTS
And unplugged battery overnight.
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Monday, February 8th, 2021 AT 5:38 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
P0308 would be the code then. With a single cylinder misfire you look at the ignition and fuel to that cylinder first then compression. For spark the easy way is to put a spark tester on that wire and make sure it is actually firing. Next I would do an injector test to be sure it is actually working. For that you need a fuel pressure gauge and an injector tester. To use it the pressure gauge gets attached to the test port and the tester goes to the injector. Then it's a process of turning the key on, write down the pressure and then pulse the injector. Next read the pressure. Move to the next injector and repeat the process. After doing a couple cylinders start the engine just to remove the excess fuel before doing the next pair. What you want to see is that the pressure drop is the same for each injector. So say you have 55 PSI, you activate the tester and it drops to 40, if all of the injectors drop to say 39-42 PSI they are all working. However if one or more drops to say 30 psi, those are failing and are adding excess fuel. If on the other hand the pressure only drops to 50 then that injector is plugged.

Next thing if they all test in the same area is a simple compression test. It is possible it's a bad valve and compression testing may show that.
https://www.2carpros.com/articles/how-to-test-engine-compression
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Monday, February 8th, 2021 AT 7:28 PM

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