1985 Grand Marquis stalling

[ajg]

Hi everyone,

Bought a 1985 Grand Marquis (white, 351 'Windsor' engine, ~50,000 KM) last August and it has been a great car to drive, much admired by many. Until today has run with little or no problems, only:

- when cold (after priming) starts immediately, stalls after a count of 3, but then runs fine on restart.
- on one occasion last year, sounded / felt rough when started, as well as making a noise that (from inside) sounded like a sort of shhhhhhhhhhhhh sound. Although not running smooth, got the car out of the drive, but it stalled when I came to a stop at the first set of lights. Nearly stalled at the next set, but once I opened it up on the main road, it ran fine. Never repeated this problem. Occasionally the 'sssshhhhh' would return, but would disappear after shifting among P / N / D a few times, or moving the shifter about a bit.

Today, I headed out early to the store. No problems, started fine, drove smooth. When I went to leave, the car started fine but sounded rough and then quickly stalled. The 'sssshhhh' was back with a vengeance, and is now permanent! Tried several times: same result - starts immediately but soon stalls, whether I shift it to drive or leave it in park. I could keep it alive by giving it a bit of throttle. I could get it moving by putting it in drive and giving it some gas (not exactly smooth driving) - it would seem ok when the throttle was open, but as soon as I took my foot off the pedal it would start to feel rough (even at speed) and would stall whenever it came to a stop (unless I slipped it into N and kept a little gas on). If it did stall it would always start up again immediately. This made for an interesting drive home - luckily the roads were still very quiet.

I've been out for a look this afternoon and the problem is still there. Starts ok, 'sssshhh' noise begins, idles rough, stalls. At one point it kept going long enough for me to get round to the engine bay but I couldn't ID where the noise was coming from. When inside the car it almost sounds like it is coming from just behind the dashboard. It was revving a bit high so I tickled the gas pedal and it dropped back down to normal... and then immediately stalled. Fluids ok (power steering a bit low, but I doubt that would making the car stall), transmission fluid a bit discoloured (a light beige-y red) but plenty in the system.

New to these cars, don't have much knowledge of automatics generally, and all my tools are thousands of miles away in Europe (temporary resident in Canada) - so I will be taking it to a shop regardless, but would like to try and get some idea of what is going on (and so some idea of what it might cost us to get it sorted...) - so would be interested to hear any thoughts.

All views appreciated.

[EaOutlaw1969]

sounds like a vacuum leak either at the Vacuum booster for the brakes or the parking brake vac release if your car is equipped with vac release parking brakes but my first guess is what i would check first. by disconnecting the large vacuum line from the brake booster and blocking it off with electrical tape or large rubber plug then starting the car to see if it runs and sounds normal.

If the car starts and runs normal you will need a new booster and possibly a master cylinder ( check the back side for leaks ) best to replace both at the same time anyways.

Do not try to drive the car with the booster vacuum line disconnected as it will feel like a brick is under the pedal and it will not stop good at all.

[gadget73]

vac leak is my thought as well. If its big enough to cause running problems and audible inside the car I'll vote for brake booster.

[ajg]

Thanks. A vacuum leak seems plausible given the noise.

I've just been out and tried your test. It didn't have any effect. The car still starts but will only run if I give it a little throttle. As soon as I take my foot of the gas it dies. Worth noting: when I disconnected the hose from the booster at first, it gave an audible hiss, suggesting it was not having any problems holding vacuum.

Before doing the test the car idled high on its own briefly so I was able to have a quick listen. The noise is louder at the rear of the engine bay. It seemed to be coming from the area behind the engine. It's getting dark so I couldn't have a proper look.

[gadget73]

are you sure its not an exhaust leak? I believe these have air injection to the back of the cylinder heads as well as a tube down to the catalytic converter. If either rusted out you'd get exhaust noise out of the hole. Thats all that comes to mind at the back of the engine.

Should be some other vacuum lines but I'm not really familiar with exactly what lives where on a 351 car.

[ajg]

I've just been out to check, and she was considerate enough to hold an idle for me for long enough to have a quick look round.

There are definitely some (!) exhaust leaks, so exhaust repair / replacement is definitely on the cards, but I'm not sure they're the source of this particular problem. The noise definitely sounds like it could be a vacuum leak, coming from somewhere at the back of the engine bay toward the centre, possibly just behind / below the carb, but is much less audible from under the car. I had a bit of a poke around and couldn't localise the source or get anything to change by pinching lines etc. - not much more I can do without any tools, and it's a bit of a nest of cables and lines back there. I've managed to get a spot in a local shop Friday morning, so lets see.

Thanks for all your suggestions.

[gadget73]

bit of rubber line as an "ear sniffer" might be of some help there. Could be the carb base gasket is bad, or maybe just the carb bolts are loose. I've seen that before.