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

3176 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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Well, if you have low fuel pressure you either got a bad pump or a bad gauge. I can't remember if the fans are supposed to come on when your climate control is set on defrost or not. A lot of vehicles are like that.
Ok. Brand new pump in there now. Will try different gauge. I check defrost. Nothing else is on in CC.
Clogged fuel filter?

IS the A/C on? Fans run when the A/C is on.
Changing the thermostat won't help.

Unless you are using coolant and having to regularly top it off, it's probably just condensation.


Not often, but on a 28 year old car, I wouldn't rule it out.
This may help you diagnose it.
Fuel filter is brand new. So dont think thats the culprit. No A/C not on. Nothing on in CC. Will try the link. Thanks.
That exhaust sounds pretty rough. We used to have some simple instructions for retrieving codes in the engine section but it doesn't seem to be here anymore. You will have to try to get the codes with whatever sticky you can find. If you find a 4.9 section it's in there. There should be some code making the light come on. Oops, found it.

As rough as it sounds, if you are going to throw money at it I would start with new spark plugs and a cap and rotor. It's hard to find spark plug wires as good as the originals so if the originals still look good they probably are. Then I would check the vacuum to see how healthy it is. It could have a simple vacuum leak causing running problems. The cat doesn't "sound" clogged but it is always a possibility.
Yeah the only codes I can pull is an F32 'loss of communcation between ecm and bcm'. Which I found on here the fix is

1. Bad ground (check battery negative cable and connection, clean and retighten)
2. Loose or corrupt data cable between ECM and BCM. (Remove and reseat)

Will go after the plugs and vacuum. Thanks!
Replaced all plugs. Lots of carbon build up on plugs. No real difference in running condition though. Carbon on 02 sensor too. Tested back pressure. No issue there so Cat must be fine, right?
Replaced thermostat and coolant temp sensor. As well as water inlet, part of it corroded off. Fans still turn at key turn.

What's the baby food looking goo in radiator?
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Well good news, she passed CA Smog!

All in all, I replaced:
Fuel Filter
Fuel Pump
All 8 spark plugs
Water Inlet (Over Thermostat)
Coolant Temp Sensor
and Flushed the Radiator

Fuel Pressure is back up.
No stalls.
No service or check engine lights.

Now on to the drivers window and a/c. But she's purring nice now. Not to mention CA legal.
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Well she's back at it. Very odd.
Couple different scenarios happening:
Fans on with key turn to Aux.
Service Engine and Check Engine will come on at start.
Kind of a putt idle.
Put into Drive or Reverse she wont move unless given gas.
It stalls out.
Upon restart, no fans on at aux, no engine lights on, she moves in drive or reverse without gas applied and all is fine.

Fans on with key turn to Aux.
Service Engine and Check Engine will come on at start.
Kind of a putt idle.
Run for a bit to warm at highway speeds, engine lights turn off and shes fine.

She starts, runs fine on highway, no lights, then all of a sudden check eng and serv eng pop on but no difference in engine or running noise.

I can sit there and turn the key from off to aux. If the fans go on, I know its gonna run rough. If the fans dont go on it will run fine.

All circumstances the only code pulls are F32 (BCM to ECM).
I tried unseating and reseating the bcm connectors, but did not fix.

Bad Ground?
Bad BCM?
Bad ECM?
Something else entirely?
Some other sensor?

It seems entirely electrical because its so intermittent and finnicky, like I said it can run perfect sometimes and rough the others.
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