[chuzz]

Probably a stupid question, but have you checked the air intake hose and filter to make sure some rodent hasn't built a nest in there? If that's okay, maybe a good cleaning of the throttle body would help. My 99 with the same drive train just rolled 190,000 miles Sunday and still runs great.

 

[ImperialCrown]

Fuel pressure sounds high. That would drive the PCM lean and set a fault code. Was the fuel filter/pressure regulator an OEM part?
If it is worse after a fill-up, the evaporative system/ORVR may still have a problem.

 

[A.j. Schreiber]

I agree with IC, Id start at the fuel system

 

[geekdad]

I think the fuel filter was aftermarket. It looked exactly like the one I put in which definitely wasn't OEM. The pressure regulator is in the tank on the pump. I'll see if the next fill up is any different. I'll have another look at the EVAP system too.

Oh, and I tried cleaning the TB out at the same time as I changed out the plugs and wires. It was due.

 

[geekdad]

Filled the tank today. Looks like its getting around 8.7 mpg right now - so its definitely flooding the engine. I talked to a dealer about the fuel pressure and he told me 58 psi +/- 5 was correct, so the pump should be working properly.

I'm going to look at the TPS tomorrow and look for any leaks in the EVAP system too.

 

[ImperialCrown]

It would be helpful to see what the O2 sensors are seeing in the way of an air/fuel mixture. A rich mixture fault or cat fault may take a long time to set. The previous P0172 rich mixture fault was probably real.
Do you have access to an OBDII scan tool?
If the catalyst is plugging or the fuel system is over-rich, the vehicle shouldn't be driven like this. Are the plug tips black?

P0172-1/1 FUEL SYSTEM RICH​

When Monitored: With the engine running in closed loop mode, the ambient/battery​

temperature above 20 deg. F and altitude below 8000 ft.​

Set Condition: If the PCM multiplies short term compensation by long term adaptive and​

the result is below a certain value for two trips, a freeze frame is stored, the MIL​

illuminates and a trouble code is stored.​

POSSIBLE CAUSES​

POSSIBLE CAUSES​

INTERMITTENT CONDITION​

O2 SENSOR HEATER OPERATION​

O2 SENSOR​

EVAP PURGE SOLENOID OPERATION​

O2 SENSOR SIGNAL CIRCUIT SHORTED TO VOLTAGE​

O2 SENSOR SIGNAL CIRCUIT OPEN​

TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED​

TP SENSOR SWEEP​

MAP SENSOR OPERATION​

ECT SENSOR OPERATION​

ENGINE MECHANICAL PROBLEM​

FUEL FILTER/PRESSURE REGULATOR (HIGH)​

PCM​

​

​

​

​

​

​

​

​

PO​

​

​

TEST ACTION APPLICABILITY​

​

​

​

​

​

 

[geekdad]

Thanks IC. I must have mis-typed in my first post - the dtc code was for a LEAN condition (I do remember the general description, just not the number), so it would have been a P0171 or P0174. I'm not sure of exactly which components what the PCM can affect, but my thinking is that the computer believes the engine isn't getting enough fuel and so tells the injectors to spit out more, flooding the engine under heavy acceleration.

Were you asking about the new plugs being black or the old ones? The old ones definitely were carbon blackened - all six of them. I have not pulled one of the new ones to check yet.

As far as the cat goes, I don't smell the rotten egg smell at all. I do have a neighbor with an OBD-II computer, but he is currently out of town. If he gets back sometime soon I will be sure to return with the fuel trim values.

 

[geekdad]

TPS turned out to be fine. I did discover a badly split hose leading to the EVAP purge canister. I replaced that section with new hose, but it apparently didn't solve the hesitation problem - I don't know if that would have affected the mileage or not. When it was running good it was around 24 mpg I believe. I might look at the fuel rail and injectors too. Is there any reason to not suspect a faulty O2 sensor?

 

[geekdad]

I went ahead and swapped the oxygen sensor - no more hesitation at all. The old one had some oily residue, probably due to the system running rich.

So now I'm curious which came first - a lazy O2 sensor or the rich system? I figure if the sensor was still fluctuating it's voltage it wouldn't trip the OBD code, but the range of flux could be limited to show it reading lean - thus the rich fuel mix.

Perhaps the bad EVAP hose introduced more air into the system causing the original rich mixture which eventually killed the oxygen sensor?

Either way, it appears to run normally again. I'll still have to confirm the mpg, but I strongly suspect it will be much higher now that the engine shouldn't be flooding any more.

 

[ImperialCrown]

The O2 sensor probably failed first and did not set an O2 fault code, but went straight to the 'fuel system lean' code. The PCM's only clue to rich or lean mixtures is through the O2 sensors. If it saw the O2 telling it that it was lean, it would have dumped more fuel in to compensate. A scan tool lean O2 voltage reading would have probably shown the O2 signal voltage pegged low.
If the split evap hose had opened the vapor-management system to air, it too would have eventually set an 'evap leak' fault code.
If you have fixed the mixture problem, it might be a good idea to disconnect/reconnect the battery to reset the fuel trim adaptives to center (neutral) and to erase the fault code if you haven't done so already.
If the engine oil smells of fuel contamination from the rich running, it might be a good idea to change that as a precaution as well.

 

[geekdad]

I pulled the battery cable after changing the split hose, but that was before I replaced the O2 sensor. I will reset it again to be sure. Thanks for all your help!