- Joined
- June 17, 2004
- Messages
- 24,497
- Reaction score
- 5,099
- City, State
- Knoxville, TN
- Year, Model & Trim Level
- 98 Limited AWD 302
Andy, have you checked the fuel pressure with the engine running on gasoline? I just finished changing my fuel pump after having codes P0171 and P0174 for several months. Just recently I discovered that my fuel pressure was low. I had 55psi at idle, dropping below 50psi with winging the throttle.
The 99+ fuel pressure should be 56-65psi, mine has been just on the edge, so I have had random times when a code would appear. If you have a 99 truck, you need a 99+ PCM, if that is the problem. There are no mid year PCM's, don't go looking for a 99 PCM made in 98, forget that waste of time.
The bottom line is that you should baseline your engine. You need to get it running properly on gasoline, before diagnosing things which are different with LPG. The symptoms you are getting with LPG will likely cloud the troubleshooting, experts can help get the gas system running correctly very fast. Get the truck running with gasoline first, find and fix the problem, then switch back to LPG. Check the fuel pressure, good luck.
The 99+ fuel pressure should be 56-65psi, mine has been just on the edge, so I have had random times when a code would appear. If you have a 99 truck, you need a 99+ PCM, if that is the problem. There are no mid year PCM's, don't go looking for a 99 PCM made in 98, forget that waste of time.
The bottom line is that you should baseline your engine. You need to get it running properly on gasoline, before diagnosing things which are different with LPG. The symptoms you are getting with LPG will likely cloud the troubleshooting, experts can help get the gas system running correctly very fast. Get the truck running with gasoline first, find and fix the problem, then switch back to LPG. Check the fuel pressure, good luck.