98 Expedition pings while pulling a load

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Jun 21, 2005 | 04:05 PM

ebraunusa

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98 Expedition pings while pulling a load

Hi all,

I have a 98 Expedition with a 4.6L. It has 112K miles and I had a tuneup at 100K that replaced the plugs and wires.

When I am pulling a load (2500 pounds or better) and if I stomp on it, I get a pingging noise and it sounds like it is coming from the catalytlic. Also, the check engine light goes on. However, it runs fine if I don't stomp on it and it only happens with a trailer attached of many people in the truck.

I did an engine scan and the codes were

P0171 System Too Lean - Bank No. 1.
P0174 System Too Lean - Bank No. 2

The parts guy at Checker said it was the oxygen sensor before the catylitic. Is that right? I have been reading comments about the MAF sensor or pvc valve being the issue. Any ideas?

Thanks

Jun 23, 2005 | 10:33 AM

Hoosierdaddy

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From: Valpo, Indiana

My guess would be o2 sensor-this could cause engine to run lean or rich.
PVC valve would not cause pinging or lean running motor, but is cheap to replace.

Jun 23, 2005 | 10:49 AM

PaulC

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Clogged EGR passages may play a role as well.

Jun 23, 2005 | 11:14 AM

scholzee

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From: Grand Island, NY

Code readers can be confusing, it does not mean the O2 sensors are bad just that they reported a lean condition and turned on the check engine light. If the light is off the condition is not present anymore. I know you said a tune up was done, did the fuel filter get replaced ? My guess is with the trailer and truck under load it is not getting enough fuel causing ping and O2 sensors to show lean condition. It would be good to get a fuel pressure gage hooked up and the hose routed under the hood by the base of windsheild. you can watch it with hood closed and towing. If pressure drops out of spec during pinging fuel filter first, if still out of spec when pinging then fuel pump. If fuel pressure is in spec when pinging then maybe MAF or another sensor is bad. I believe the O2 sensors are showing the result of a problem not the cause.

Jun 23, 2005 | 11:52 AM

ebraunusa

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They did replace the fuel filter. That was about 15K miles ago. IF I remember right, I did have the pinging before they replaced the fuel filter, but not positive.

I did not change the O2 sensor. I checked the pcv hoses and they look pretty good. However, the MAF sensor was looking black and I cleaned them up with electrical cleaner. They are nice and shinny again. It seems to drive better, but I haven't hooked up the boat yet. I'll do that this weekend and will have to see if that helped.

Jun 23, 2005 | 01:57 PM

pitrow

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From: Cornelius, Oregon

Quote:

Originally Posted by Hoosierdaddy

PVC valve would not cause pinging or lean running motor, but is cheap to replace.

Now, correct me if I'm wrong here, I believe that the issue with the PCV valve is that the hoses crack (or maybe that's only a problem on the 5.4L?) and cause a vacuum leak. A vacuum leak would certainly cause a lean condition and a lean engine runs hotter and is more suceptible to pinging.

Then again I have been known to be wrong before.

Jun 27, 2005 | 09:03 AM

ebraunusa

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Mass airflow Sensor was the culprit

After cleaning up the MAF sensor, the truck runs like brand-new. No more pinging!

For what it's worth, the 2 wire coils in the sensor was dark-brown/black. After spraying the electric cleaner on the wires, they were a bright silver color.

Thanks