Costly Repair?

Asked by Barry Jan 20, 2019 at 03:35 PM about the 2005 Mercury Grand Marquis LS Premium

Question type: Maintenance & Repair

Suddenly started running (sounding like) a motorcycle at idle. Used dongle
to run fault codes which follow:

PO109 Powertrain Manifold absolute pressure/barometric pressure circuit
intermittent

PO 316 Engine Misfire

PO355 Ignition Coil "E" Primary/Secondary Circuit

PO 622 Generator Field "F" Terminal Control Circuit

I had absolutely no idea what any of this meant so googled these faults and
had absolutely no idea what any of that meant. You may have surmised that
I am not a mechanic though, to my credit, I have learned in my 75 years to
open the hood and spot the battery right off - on some cars, anyway.

Before I am compelled to just turn the car over to a mechanic and say, "Fix it,
please." perhaps one of you fine fellows might offer some guidance.

Thanks, Barry

5 Answers

41,865

Ford 4.6 an excellent design... This is basic and not an expensive repair less than one hour. be aware DTC's do not indicate the cause of the problem Example P0109 MAP (manifold absolute pressure) sensor is commonly misdiagnosed, your vehicle doesn't have one! when the problem is the EGR valve or an intake manifold leak... based on your description I would have the EGR / exhaust gas recirculator valve serviced. component cost $40, labor and or diagnostic $150 Correct this clear codes and scan again

Thank you for your quick response. You said "service" and not "replace" (which I would much prefer to do since valve cost $190) but what does service mean/entail? Thanks again.

Found out that engine blew out a spark plug which collided with the coil. Replaced plug and coil and back in business. If you have any knowledge of why an engine would blow out a plug I'd like to know. Hasn't happened to me before. And why would that dongle have given the readings it did? Shouldn't it have noticed that a plug was missing and the coil was not doing well? Thanks for your efforts to help.

41,865

First a dongle cell phone interface type of code reader is typically very basic / generic compared to the Ford OEM IDS-VCM search online to see this tool. The 4.6 is not known for ejecting spark plugs unlike some other Ford motor engines...I suspect it was not torqued properly when last changed. Finally any freshman tech should be able to detect the sound of a loose or missing spark plug confirming this with a quick visual inspection. I'm no longer surprised by things people may not notice or sense.

Thanks again for your answer, Mark. At least I know now that faults discovered through the dongle are questionable. Still think the thing should have been able to notice a missing plug and ruined coil. Those things would have jumped out at me if I were a dongle. You're a good man for providing help.

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