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91 fleetwood fwd
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1 Posts
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Hi I have a 91 fleetwood that has been running bad intermittently for a while. It has been stumbling and backfiring under light throttle. Yesterday it started running really bad and quit running altogether. Now it will turn over but not start and the code 31 trouble code comes up(map sensor short). I took the sensor to auto zone and they checked it and said it was fine. So far I have changed the fuel pump, all the filters, and the spark plugs. The engine turns but it is acting like it is not getting fuel. Does anyone have any idea of what could be wrong? Any help would be greatly appreciated.
 

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1992 Sedan Deville, 1984 Lincoln Town Car
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759 Posts
crank but no start can also be ignition failure. Common problem is the control module in the distributor konks out. Check for spark at your plug wires.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,738 Posts
Go back to basics, does it have fuel pressure? And what is the pressure reading? Does it have spark? Pull off an easy to get to wire at the spark plug, insert another old plug onto that wire and while its laying on metal. Does it arc ? Report back.
 

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1995,Cadillac Deville,HT 4900
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112 Posts
Have auto zone load test your ignition module make sure they load test it several times, if its bad replace that first. erase codes and see if PO31 returns.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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3,310 Posts
Backfiring is almost always ignition in my experience. I suppose a severely malfunctioning MAP sensor could cause that condition too. Since the code points to the MAP and since they do fail eventually I think it would be prudent to replace it since they are pretty cheap and easy to replace. I don't have a lot of faith in Auto Zone testing anymore. When I washed my engine my MAP sensor shorted out for a while but it came out of it. Done any engine washing lately?
 

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'85 Fleetwood FWD
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728 Posts
If it's back-firing up through the throttle body, it's also a sign of too lean a fuel mixture. Checking fuel pressure was good advice. The distributor module is highly suspect though. Autoparts stores don't always have the answers, with their equipment and people.
The fuel pressure regulator in the throttle body could also be a problem. MAP sensor hoses OK?? Vacuum leaks can sell a lot of parts for the parts stores. A thorough inspection of hoses is always a good move.
 
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