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post #1 of 7 (permalink) Old 05-10-2017, 07:42 AM Thread Starter
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Question for the experts

I have been on this site for a while and I know there are some really knowledgeable guys here. I am having an issue with 97 Bird 4.6 with 201,xxx miles. DTC codes P0172 and P0175 occurred just after 200K and I have been chasing this problem for quite a while. So far I have checked for vacuum leaks and corrected a few minor ones. A friends scanner indicated fuel trims over -15 to 25 range when the engine was hot and noted the hotter the engine got the worse the furl trims got. The cooling fan seemed slow to come on so I replaced the ECT and IAT sensors. I swapped the purge solenoid and still no improvement. I then had a "professional" scan which indicated the MAF was "slightly" out of spec so I replaced the MAF. Fuel pressure was found to be within range. The professional exhausted his list of items to check and ended up with fuel injectors as the problem and suggested using a cleaner to possibly free a stuck injector. Done with no improvement. Lastly, I just swapped out the CCRM from my other 97 Bird to see if the temp issue could be the cause. After 3-4 restarts the CEL was back and so was the P0172 code. No doubt if I drive some more the P0175 will return.

I have read many posts on this site and others and I believe I have checked or replaced all the suggested causes, except for replacing the O2 sensors (which do not seem to be the problem according to the websites) and replacing the injectors.The car runs good with no performance issues although gas mileage does seem to be less than normal. I am not a novice mechanic but not an expert either, especially with all the computer controls on these models.

Any suggestions would be appreciated. Sorry for the long post but I thought more info the better.
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post #2 of 7 (permalink) Old 05-10-2017, 05:09 PM
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Replace the o2 sensors, and check the intake manifold for a leak.

A leak at the exhaust manifold will also show lean.

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post #3 of 7 (permalink) Old 05-11-2017, 10:20 PM
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the o2 sensors should have been the first item to be replaced, more than likely that's your problem

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post #4 of 7 (permalink) Old 05-13-2017, 07:48 AM Thread Starter
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Thanks for the replies(2). I am somewhat surprised by the comments regarding the O2 sensors as most of what I have read indicate the O2 sensors are usually not the cause, only the device that signals the problem. What are your opinions about the engine temp affecting the fuel trims as indicated by one of the scans? And how would the O2 sensors affect ECT?

And the comments about the leaking manifold causing a "lean" condition does not seem applicable as there is a "rich" condition on both banks.

I just don't want to change parts trying to find the problem.
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post #5 of 7 (permalink) Old 05-13-2017, 10:35 AM
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Have you tried using a vacuum gauge to determine if there is a leak upstream of the cylinder heads? At 200k, you should have replaced the upstream O2 sensors 140k miles ago.
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post #6 of 7 (permalink) Old 05-14-2017, 06:51 AM Thread Starter
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So if I should have replaced the O2 sensors at 60K does that mean I need to change them 3 times? (hehe) The curious thing is there had not been any issue in engine performance and no CEL until after 200K. Regular maintenance- oil, filters, lubes, etc but no other issues engine wise. It's like a switch went on at 200K but performance is still OK.

Where would you suggest I use a vacuum gauge upstream from the cylinder heads?
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post #7 of 7 (permalink) Old 05-14-2017, 07:02 AM
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Brake booster line is a good place to grab vacuum from IMO.

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