I have a 96 4 door 4x4. The codes I have now are po175 po300 po440. I have replaced the IAC valve, injector assembly, plugs, wires, cap, and rotor. Fuel pump is a little over a year old.
It runs rough to very bad, intermittently. Sometimes it runs perfect, others it is barely noticeable. It just now started with the po300 and po440. I need some serious help. I would be pulling my hair out, if I had any.

 

Welcome to the forum!

If that's the order the DTC's were retrieved.... P0175 indicates a rich fuel mixture on the passenger side. P0300 indicates a random misfire, which can cause a rich condition. P0440 is an EVAP problem not related to the running of the engine.

P0300 is almost always caused by a fault in the secondary ignition system: spark plugs, plug wires, distributor cap, rotor, and ignition coil. These engines are real fussy when it comes to those parts, especially the plugs, cap & rotor, (use AC Delco only). Fuel pressure issues and incorrect camshaft retard can also cause both of those DTC's to set.

Start by checking fuel pressure and leakdown, it's free & easy. Ignition ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi. It must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results.

 

In the process of checking the cap and rotor, I found that the distributor shaft seems to have excessive vertical play in it. I am going to compare the play in the shaft to a new one.

 

DTC's must be diagnosed and repaired in the order they are retrieved. As mentioned above, the P0175 could cause the P0300 to set. After each repair, clear the DTC's and perform a General Motors Driving Cycle to confirm the repair, then move on to the next DTC, (if any still exist). Gotta start at the top and work your way down

Did you check fuel pressure and leakdown? What were the results?

It's perfectly normal for the distributor shaft to have ~3/16" axial play. When the engine is running, the gears will pull the shaft down and keep it down. Radial distributor shaft play is unacceptable.

 

I haven't yet purchased a fuel pressure tester. I did find out today that the evap line and return line were swapped at the fuel pump. I haven't had a chance to take it on a long drive, but the service engine immediately turned off after correcting the lines at the fuel pump. I might add that all the codes and running issues started after the fuel pump was replaced. I will post the results of this after I get some drive time.

 

That's tough to do, the return line is 5/16" and the EVAP is 1/4".

 

I drove it today for about 80 miles. Mixture of city and highway driving, but mostly highway. The service engine light did come back on, but there are no noticeable driving issues. I will get the codes checked tomorrow or Monday.

I will add that when I corrected the fuel lines, I checked the evap canister. I disconnected the lines on it and got about 2 cups of fuel out of it. I am hoping that this has corrected the drivability issues. Maybe I will be able to move on to the next project: 4x4 issues.

I will post my findings soon.

 

The purge canister needs to be replaced. It is designed to handle fuel vapor only. The PCM will continue to set EVAP DTC's until it's replaced.

 

It seems that the fuel lines were the problem. It is still running good. No misses or extended cranking, and no DTC's. I would like to thank Captain Hook for your instructions.

 

I misunderstood one of your posts. The purge canister is probably fine. More than likely what was happening, was the fuel return flow was restricted trying to go through the 1/4" fitting on the pump module, causing fuel pressure to increase, which caused the P0175 and P0300. The P0440 was set due to incorrect purge flow. Anyway, glad you got her fixed. Thanks for posting back.