[JoshF2005]

Looking for some guidance on troubleshooting an 2004 ZR5 that has a p0300 code and is misfiring on cylinders 1 and 4 at idle but at 1200 rpm it clears up and is steady. When driving it backfires and bucks on start of motion but with pedal feathering can get up to speed and run fairly smooth. We replaced the spider injector and numerous sensors but still no avail. you can tell by the smell that the truck is running rich but cant tell why. Compression checks were all about the same and during intake smoke check, no major leaks noticed. Any insight would be greatly appreciated.

 

[bk2life]

what do the spark plugs, sprak plug wires, and distributor cap look like?
when was the last time the distributor was removed and the gear inspected?

 

[JoshF2005]

We have had the truck for about 6 months and the previous owner replaced the distributor, the plugs, wires, cap and still had the same problem. When I looked at them they do not look bad or burnt. I have swapped them all around to see if there was a short in the wires or plug but did not change anything.

 

[oldeerslayer]

Have you done a fuel pressure and leak down test? What were the numbers?
If feathering the little pedal helps, that would point to a fuel issue. Pedal doesn't change timing.
Specifically what sensors are new and which ones are still original?

 

[chevymec]

If all the above has been done, I would switch to a leak down. Motor in my truck now had all the same parts replaced before I snagged it up. I felt like I knew the problem and bought it. Ended up having 1 cylinder with high leakdown and the cylinder beside it was creeping into the same %. A few bad valves.