I have a 1998 Sierra 1500 with 5.0 vortex, 181.750 miles, it has been running great. It has been parked inside my garage for a week, I backed it out yesterday to work in the garage and it ran great. Went to back it out today and it spit and sputtered and acted like it wanted to stall, very rough idle, the cel came on. I drove it 25 miles to Autozone to get a reading and during this drive the cel began flashing. The Autozone codes are P0135, P0307, P0102. When I returned home I checked the #7 plug and I have spark. While the truck was running I disconnected the MAF and the truck stalled. Then I shut off the truck, disconnected the MAF and then started the truck it started but idled rough. I have no problem in starting the truck at all but once started it runs very rough and then when I put it in gear and hold down on the brake it really gets bad, much worse than when it's just running while in park. I usually drive this truck to work but have been laid off for about a month so it hasn't been driven much lately however last week I had an appointment and drove it for 60 miles with no problem. No problem until the second time I backed it out of the garage. I sprayed carb cleaner could not find any leaks, no rotten egg smell from exhaust. Any advice you can provide would be really appreciated.

 

I would check the fuel pressure first. When is the last time it had a fuel filter changed?

 

I have a throttle body, I changed the fuel filter about 2 years ago. I thought I should buy new wires tomorrow and start there as the code said misfire on #7 and I do have spark there but I don't know if I do under load.

 

That is a possibility - maybe swap the #7 wire with another one and see if the code follows the wire. I would try the free/easy stuff first. Fuel pressure takes 2 minutes to check. Let us know what you find.

 

Thanks, your ideas made much more sense. I checked the compression and it was good at 170. I swapped the #7 wire with #5 and it still showed the code that something was wrong with #7. Then switched #5 and #7 plug and it still showed the code that #7 was misfiring. The #7 plug was wet when I swapped it out. The #7 plug has more of an orange spark and I once heard it should be more blue. I ran a can of MAF cleaner through the MAF and that didn't make any change. So I still don't know what is wrong.

 

If it was wet then I would be leaning towards the spider injection. They are infamous for leaking and can cause this issue, but before I spent the money on that I would pull the cap and see if number 7 contact looked different than the others. You could also get a multimeter and check resistance of that contact in comparison to the others. If that checks out then it sounds like another spider injection issue IMO.