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prop7515
New User
Jan 31, 2006, 7:55 PM
Post #1 of 4
(3245 views)
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99 Cougar 2.5L codes p0171 & po174 checked for vacuum leaks at intake manifold, none present. Any ideas? Any known problems that would give these codes?
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DanD
Veteran
/ Moderator
Feb 1, 2006, 6:12 AM
Post #2 of 4
(3239 views)
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Re: 99 Merc Cougar
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With both these codes relating to both banks being lean and the adaptive fuel trim has reached it’s limits in trying to richen up the mixture. It has to be something that is common to all cylinders. Like you mentioned a vacuum leak, stuck EGR valve, low fuel pressure and the list goes on. It could be an internal vacuum leak as in the intake manifold gasket is sucked out and is drawing vacuum from the crankcase. Fords use to be bad for the power brake booster having internal vacuum leaks.
How does the car run?
It’s not likely both banks 1 and 2, O2 sensors have gone dead but you never know whether something has contaminated your fuel to kill both sensors.
I don’t know if you have access to a scan tool, which would be the easiest way to monitor O2 activity, if not a digital voltmeter will work. By back probing the signal return wire of the sensors one at a time and see what the sensors are doing. Cause a lean condition by pulling off a large vacuum line or a rich condition by restricting incoming air at the breather; see if the O2 react to these changes you’ve forced the engine to go to. The voltages should swing from .1 to about .9 of a volt; .9 is a lean indication and the computer should be dumping fuel to compensate and .1 of a volt is a rich indication and the computer should be pulling fuel away to lean the engine out. If everything is “normal” the voltage should be toggling above and the below .450 volts.
I believe the white wire on the right bank O2 connector is signal return and the white/red wire on the left bank. These are the O2’s that are in the manifolds. I use something like a paper clip or safety pin the back probe the wire connector. Carefully slide the probe up the back of the connector beside the wire until you touch the metal terminal inside the connector. Then hook up the voltmeter to the probe and a known good ground.
Dan.
Canadian "EH"
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way2old
Veteran
/ Moderator
Apr 10, 2006, 4:40 AM
Post #3 of 4
(3119 views)
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Re: 99 Merc Cougar
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Also check the Mass Air Flow sensor. If the hot wire is dirty, it will give a false air intake reading and cause the PCM to over compensate the fuel mixture. It is easily cleaned. Just be careful not to damage the wires inside. They are very fragile. Do as DanD suggested first. Then look at the MAF. There is a hertz reading that tells the vehicle the altitude. You will also need a scan tool capable of reading PIDS to access this information. Good luck.
Sorry, did not look at the original post date.
Being way2old is why I need help from younger minds
(This post was edited by way2old on Apr 10, 2006, 4:42 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 10, 2006, 8:27 AM
Post #4 of 4
(3112 views)
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Re: 99 Merc Cougar
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Don't worry about how old a post is. Folks are surfing for info that we never hear about and get the answers they need. It really helps when people post the make of the car on the subject line for others to find. T
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