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Ask Dave Nova Your Own Question
Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19451
Experience:  ASE Master Certification. GM World Class Certification
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I have a 1998 K2500 4WD with a Vortec 454. I replaced the

Customer Question

I have a 1998 K2500 4WD with a Vortec 454. I replaced the plugs, wires and air filter. That caused me to get a rich code on both banks. Took it in to the Chevy dealership, where they found a lot of codes. They changed the injectors which they said 6 of the 8 was bad. Still had a slight miss, but no codes was showing up. They said I needed to change plugs and use AC Delco plugs. I installed the plugs with a .60 gap and still have what seems to be a rough / misfire condition and what feels to be a loss of power. Could this be caused by a faulty MAP? Do you always get a code when the MAP is going bad? What is the correct gap for my plugs? I have read to put them at .45 instead of .60.
Submitted: 1 year ago.
Category: GM
Customer: replied 1 year ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Dave Nova replied 1 year ago.

The spark plug gap should be .045. .060 is too wide and may cause misfire issues. If you have not done so, I would suggest that you replace the distributor cap and rotor, as these can cause issues as well.

Customer: replied 1 year ago.
I have replaced the rotor and the cap already. I'm going to adjust the gap to .45. I'm also going to test my plugs to make sure I am getting fire to the plug. If this doesn't fix the issue could it be the MAP sensor even though I am not getting a check engine light?
Customer: replied 1 year ago.
I have also replaced the MAF in the troubleshooting.
Expert:  Dave Nova replied 1 year ago.

MAP sensor is not likely to cause a problem like what you are experiencing. If the MAP sensor were far enough out of spec to cause driveability problems, you would have a lean or rich condition.

Customer: replied 1 year ago.
I put the plugs at a .45 gap and it is running worse than it was
Expert:  Dave Nova replied 1 year ago.

Is check engine light coming on?

Customer: replied 1 year ago.
No. The light has never came on. The plugs looked good when I took them out to regap them. The idle rpm has gotten steadier now but is still rough. I'm kind of at a loss. Thinking about getting a good set of plug wires, another set of plugs and starting from there. If tou are not getting any codes it's kind of like a blind fishing expedition. Even if the check engine light is not on, can you still get codes to know how the engine is performing and where a problem might be? I'm from the pre-ECM era and still have a lot to learn
Expert:  Dave Nova replied 1 year ago.

Do you have access to a scan tool that shows live engine data?

Customer: replied 1 year ago.
No. I'm going to call a local shop and ask them if they do. If nothing else, I guess I'll have to take it to the chevy dealership. I just got the truck out of the dealership and all they said I needed to do was change plugs to AC Delco. I would have thought they would have run a live scan. But I am thinking they didn't. At this point, I think I need to just bite the bullet, take it in to a place to have a live scan run on it and go from there.
Expert:  Dave Nova replied 1 year ago.

That would be best. Even if no codes are setting and no check engine light is on, the live scan tool data can show the various sensor readings, that way you could read a live misfire, or see if the engine is too rich or too lean on one of the banks, or see if the computer is pulling back timing due to a faulty knock sensor reading, etc.

Customer: replied 1 year ago.
Thanks for your help.
Expert:  Dave Nova replied 1 year ago.

You are very welcome.

Dave