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1991 Deville sedan runs rough, intermittent stall, low fuel pressure

3150 Views 16 Replies 5 Participants Last post by  sefiro
Fuel Pressure very low. (10-15 psi) Replaced fuel pump and filter but no change. I swear fuel pressure 20-25 psi before I changed pump. What else would cause pressure to be so low when checked from fuel rail? Any other tests to track it down without throwing parts on it? All fuel lines look great.

The CHECK ENGINE and SERVICE ENGINE lights come on. Its not throwing codes besides an F32 from the onboard diagnostics. Are there hidden codes that can only be read with OBD?

The cooling fans kick on with key turn no matter what. They are not waiting for the temp to go on, they turn on from start. Going to throw an engine coolant temp sensor at that. Fuse for cooling fans looks fine, I assume relay is good. Should I throw at thermostat at it? Read 4.9s had issues with coolant containers, radiator cracks, stuck thermostat.

Running rough. I rodded egr tubes which seemed to help a little, they were pretty gunked.

Vehicle starts fine everytime but when it is put in to drive on a flat surface the vehicle does not want to move until you give it gas. Is this odd? Reverse it will move on its own.

There seems to be decent amount of water in muffler. Normal or have headgaskets blown? I've read on here it's pretty rare for 4.9's to have head gasket problems, maybe an intake but not head. A steady stream came out the tiny hole in muffler when I jacked it up. Mild precipation from exhaust when running.

Overall she's pretty clean, grabbed her from auction. One owner Missouri/Texas, only 101,000 miles.

To Do/Check/Throw Parts at:
Secondary Air Injector
Crankshaft Sensor
Fuel Injectors

Would clogged Cat choke it to death? How often to Cat's clog? If the EGR tubes are that gunked, is everything gunked? Do I really have to go through the plugs/wires/rotor?

Link to Exhaust Video/Sound

Thanks in advance.
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Probably a short or loose connection.

Per the 92/93 FSM, the fan relays control signals are switched on off by switching the ground leg inside the pcm based on input from the temp sensor.

If the fans are on, then the pcm ground is in good working order.

There are a pair of wires linking the bcm and pcm. Check the wire harness at the pcm to make sure they are tight and dry.

You can further diagnose which wire and possible cause via the 6th post

Once again, this is all based on 92. The 91 should be the same though.
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