I have a check engine light (with intermittant amber light and Restricted Performance warning), and codes P0171 & P0174 on my scanner. I don`t see any obvious vacuum leaks so far and the Mass Air Sensor does not look dirty. I`m in a 2003 XKR w/ 45000 miles. I`ve done a pre and post DTC trigger scan and the only glaring difference are the ST fuel trims. Fuel pressure at idle is 55PSI which may be a bit on the low side. Would it be a *BAD* idea to drive her 250 miles to visit my dad and use up the fuel in the tank and refill with fresh fuel? I don`t want to damage the engine and I surely don`t want to get stranded somewhere.

 

As you know, P1071 is bank 1 combustion too lean. The possible causes are:

1. engine misfire
2. air intake leak between MAF and Cylinder Head
3. Fuel filter / system restriction
4. Fuel injector restriction
5. IP sensor fault (low fuel pressure)
6. HO2 sensors (1/1, 1/2) harness wiring condition fault
7. EFT sensor fault (low fuel temperature)
8. MAF sensor fault (low intake air flow)
9. exhaust leak (before catalyst)
10. ECM receiving incorrect signal from one or more of ECT, MAF, IAT, IP, EFT or TP sensors

P0174 is the same for Bank 2.

You've already eliminated leaks and a dirty MAF. It's looking more like fuel restriction or a transient out-of-range signal.

If it was me, I'd pack the scanner, basic tool kit and go.

Graham

 

I had the same issue on my XKR. After trying to hunt the problem down for quite a while, it was remedied after I switched pumps to Chevron's 94 octane. No codes for me since.

 

Thanks for the input..appreciate it!

 

Those codes usually indicate a vacuum leak which may or may not be easily detected. I would not continue driving even though after a short while the computer will come out of limp mode and seem to be operating ok. I had the same thing happen with our X-Type (cause was the IMT O-rings leaking). It was winter and cold so I put off replacing until spring turned out to be a bad idea. Not very smart on my part since it was such a simple fix about 15 minute job. Any way I did drive it over the winter what was happening was the computer was doing all the adjustments to correct the lean air/fuel condition by adding more fuel so mileage really suffered and the added fuel apperantly really dirtied up the cylinders. After replacing the IMT O-rings it took several cans of 44K before mileage returned to normal again. So I would suggest locating the cause of the codes and fix it. IMHO.

 

I would be worried about ruining the catalytic converters.

 

Well...I did the drive and the restricted performance came on a few times but cleared itself. The mileage seems to be fine. Thanks for the opinions...I am going to investigate further for a vacuum leak or a bad MAFS. I read somewhere on this forum a post about using an *UNLIT* propane torch to search for a vacuum leak. Anyone know about doing this? Also...how do I perform a smoke test at home? I was thinking of lighting up my pipe (tobacco) and blowing smoke along the route from the air cleaner to throttle body and elsewhere.....

 

If a careful inspection does not turn up any intake leaks, I would lean toward replacing the MAFS. Get one at Advance Auto where they have a liberal return policy.

 

Is there any way to test the MAF sensor to know if it is bad? I`ll have to check, but I think my Actron scan tool gives a readout of the voltage from the MAFS.......

 

Intermittent MAFS problems will be very difficult to diagnose, especially if live data can't be gathered quick enough as the MAFS is sending out signals to the ECM. You may, or may not get lucky and capture a voltage change...or a delay in measurement -> transmission. If all vacuum leaks are ruled out, a quick swap of the MAFS is only logical.

 

Yesterday I decided to take a more careful look at my MAFS. It did look duller on the air filter side so I bought a can of MAFS cleaner and cleaned it. After reinstalling it I took a 20 mile drive and happily no codes or check engine light. Hopefully this was the problem. I love my car again!

 

This is a good point, cleaning the MAF is the first thing to do if it is suspect. It takes very little oxidized dirt on the MAF to degrade it. These units use a heated wire and this heat will oxidize dirt particles to the wire, eventually changing its performance. The particles are hard to see, so visual checks aren't helpful. I would never replace it before attempting a good cleaning. It is a very good idea to clean the MAF at air cleaner changes. Just good PM.

 

After replacing the MAFS Sensor, the P0171 and P0174 have returned . My fuel pressure is reading 55-56 PSI on an Actron Scanner. Is 55 PSI Fuel Pressure out of tolerance for this car? The JTIS says the fuel pressure should be 72 PSI on the 2003 XKR. My question is...would you all suggest that I replace the fuel filter as my next step? I sure hope it`s not the fuel pump...