Help me!
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New User
Joined: Feb 2010
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Help me!
I just did head gaskets on my 99 expedition and I am getting codes for p0171 and p0174. I have checked all vacum lines and changed o2s but still have the problem and the idle is rough but as soon as I hit the gas all is fine. I just took the intake back off and the gasket look ok to me how ever it is not smashed down like the original one could this be my problem or does someone have any other ideas. Also the injectors and plugs and coils all check out.
Senior User
Joined: May 2009
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Well, I'm not sure that'll help now that I actually looked up the codes but it certainly can't hurt.
Some suggestions...
Clean the MAF with some MAF safe cleaner (I did this on mine and the code hasn't returned)
Clean the EGR valve
Check the voltage on the DPFE sensor. Those go bad a lot.
If you, by chance, installed a K&N filter (or other brand which is oiled) the oil might have gotten on the MAF. That was my problem. The odds of it being an O2 sensor are pretty rare. Unfortunately you already changed them but on the othe rhand, being that its a '99, it was probably time anyways.
Some suggestions...
Clean the MAF with some MAF safe cleaner (I did this on mine and the code hasn't returned)
Clean the EGR valve
Check the voltage on the DPFE sensor. Those go bad a lot.
If you, by chance, installed a K&N filter (or other brand which is oiled) the oil might have gotten on the MAF. That was my problem. The odds of it being an O2 sensor are pretty rare. Unfortunately you already changed them but on the othe rhand, being that its a '99, it was probably time anyways.
Logistics Pro
Joined: Jan 2001
Posts: 3,740
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From: Central NYS
If you can't find the leak/leaks, take it to a shop that has a "smoke" machine. They will block of the air filter and fill the intake with smoke and wait to see where it leaks out.
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New User
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Well it was either of those come to find out the timing was off. It was timed like an 05 and up 5.4 not the earlier years and that is what was causing the issue. Luckily it was off enough in time to bend valves. Plus I rolled it over by hand to make sure it was free before goin any farther. But I was wong and good thing I know some people who have done work on these engines.
