altitude induced sputtering in Club Wagon engine?

I've got a 98 Club Wagon with a 5.4L V8. Has worked flawlessly since I bought it new in '98...until October 2004. Car has spent most of its life at sea level, but in October I took it above
7000 feet for a week or so. A light on dash came on, saying "Check Engine Soon." I ignored it and everything was fine, until I returned to sea level.
This is why I ignored it... Because 5 years ago, I took it above 7000 feet, and the same thing happened. I was alarmed, stayed over an extra day, so I could go to the Ford Agency on a Monday morning. They told me to forget it. So I returned to sea level, that light stayed ON for a month or so, with no symptoms. After a month, the light went out, never to return until our October 2004 incident.
So in October, 2004, upon returning to sea level, I noticed a "sputtering" of the engine, especially noticeable when the engine is cold. I still suspect the engine is "lean," with the fuel mixture being stuck at a setting appropriate for high altitude. I changed the air filter, with no improvement.
So here we are, three months later, and the light is still on. If I get one of those code readers from a parts dealer, will it tell me anything?
Any suggestions, other than the obvious one to take it to a dealer?
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Jerry opined in

Clean the MAF sensor according to instructions found about anywhere through a google search. Except DONT use Windex!
The sputtering should disappear, then the light go out in a few driving cycles.
--
- Yes, I'm a crusty old geezer curmudgeon.. deal with it! -

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Thanks, boss. Any suggestions as to where that nasty sensor would be? I expect to be lifting my van for some preventative maintenance pretty soon. Seems that nearly nothing is accessible from the petite hood. I did recently buy a CDROM describing the details of the vehicle...but it is so vertically integrated as to make it very, very tedious to use. Thanks again for your excellent suggestions!

through a

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I'm digging. Thanks to you and Google, and some diligent folks who shared their experiences! http://www.dantheoilman.com/maf /
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I took the air cleaner housing out, and looked at the MAF sensor. I could see the tiny electrical elements there, and they looked clean. I didn't spray them, even though I bought CDC QD Electronics Component Cleaner. A friend supplied a code reader. We restarted the engine, after putting the air intake assembly back together. We got a "0401" code, which translates to an exhaust gas recirculation problem. My friend thinks the EGR valve is a problem. It makes sense to me.
Do you have an opinion on the EGR valve, or its controlling devices? EGR valves are subjected to harsh treatment, unlike the MAF sensor. Furthermore, this car gets lots of short-mileage trips, so that probably adds to the EGR stress.
Thanks for your opinion.

through a

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P0401 would be insufficient EGR flow. Could be a clogged EGR valve, clogged EGR ports in the throttle body, pinched or broken EGR vacuum lines, or bad DPFE sensor (or equivelant sensor/actuator on this model Ford).
Do a google search on P0401, very common engine code. You should be able to find enough info to clear the code on your vehicle by fixing the problem, so long as you know how to troubleshoot EGR issues.
Matt
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I have replace the PCV valve, which I failed to replace according to the maintenance schedule recommended by the manufacturer. Sure enough, it was a leaker. I put my mouth on it and verified air could easily flow in either direction. The new PCV valve allows flow only in one direction; away from the rocker cover and towards the intake manifold. The car seems to work fine now. I haven't run it up to temperature, but the sputtering problem was at its worst at low speed, cold operation anyway.
Prior to replacing the PCV valve, I removed the EGR valve and examined it. It was a bit sooty inside, but worked fine. I used a vacuum gun to actuate the valve; it worked fine. I squirted some gasoline in it, with the valve shut, and it held the gasoline. When I pumped the gun ever-so-slightly, the valve opened and the gasoline poured out.
Hmmm...it seems those fault codes must indeed be taken with a grain of salt. No EGR faults observed. When I started the car, after installing new PCV valve, I knew that the EGR valve, itself, was good. So, to test the EGR's controller, I put a vacuum gauge on the vacuum control line leading to the EGR valve. It read no vacuum, as I would have expected, upon turning the engine on. The engine was dead cold, and I had read that the EGR valve is not supposed to be active when the car is cold. I suppose the EGR should be most effective when the car is at operating temperature, while stuck in traffic, idling, etc. The idea is to reduce NOX. I suppose EGRs have to be rather effective at high speeds, also, or we'd all be living under a brown blanket of NOX. Catalytic converters do nothing to remedy NOX!
Thanks for your reply.

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It's not just the egr valve getting vacuum or being bad enough not to hold vacuum, there are also the egr ports in the intake to consider. If they are blocked or constricted this might cause the engine code to be stored. Also, if your vehicle has a DPFE sensor or equivelant apparatus, this may also be failing, preventing the valve from opening when the computer says to.
Again, our 2000 taurus wagon has this P0401 code and I found a wealth of info on google on how to troubleshoot, etc. I think most often a new DPFE sensor for about $70 is in order. That or the egr ports are cleaned.
Matt
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Jerry opined in

YOu are probably right that the EGR is the problem, rather than the MAF. However, the thing can look clean to the eye and still cause a problem.
Best is to remove the sensor itself, spray and lightly brush it.
That said, you may still have more than one problem.
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Thanks for your reply, but I disagree with your advice to attempt any cleaning of the MAF sensor, in absence of conclusive evidence that it needs cleaning. The environment of my MAF sensor is very clean. The MAF sensor is delicate and expensive.

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Jerry opined in

It is not "delicate"
Ask a component engineer. I worked with the same components and others like them for years.
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