Got my ‘86 Grand Marquis about a month ago and it has been running smoothly. car was pulled out of storage and has not been driven that much for 6-7 years. Anyway, thought I’d service the thing and gave it a new cap and rotor, new wires, new plugs ( Champion RS14LC gapped at .050 ) after I replaced these things it has developed a tendency to buck here and there. Only when the car is coasting. On top of this I’ve noticed the mpg seems to plummet momentarily… Cruising along at 55, mpg says 22-23, suddenly it goes to 6-7 for 30 seconds, then back to normal. During those 30 seconds, the engine seems to run fine although maybe not as crisp as otherwise. I noticed the connector on the coolant temperature sensor right next to the distributor has broken off. It will slide over the two pins but it’s not fitting very tight. I suspect this maybe the culprit… the sensor looses connection and the mixture gets pretty rich ? needless to say, I’ll fix this. Does it sound right, that this sensor loosing circuit will cause mpg to drop THAT much? on a side note: how loud is the fuelpump supposed to be, when running?
First, the fuel pump is supposed to hum when running; you should not hear it unless you step next to the gas tank. If you hear it while sitting behind the wheel, you should check running pressure (30-45 PSI, depending on if there is vacuum at the FPR). If the pressure is lower than spec, or if you have no idea when the filter was replaced, do so. Second, one way to find out if the ECT connector pins are not making good contact is to start and heat up the engine, then shut it off. Pull both pins and use a piece of 16ga. Wire to short them together. This effectively tells the computer the temp is 273°F. Tape up the connection so as not to allow a short, then test drive. Monitor the Tripminder, and power will be down a bit because of what the computer 'sees,' but if it no longer bucks, it's the connector. Get a new pigtail and repair the connector anyway, but at least you'll know if that is the cause of the bucking. As f
Got a replacement filter in the mail, I'll replace it tommorow regardless. So you mean I should pull the connector off of the temperature sensor and short the two pins in the connector itself and by doing so telling the computer, that the engine is at maximum temperature? 273F jeez... that's alot. Should this manuever turn on the coolant light in the dash? Say, whats the normal operating temperature on these engines? around 200F or so? I can definately hear the fuel pump humming when I turn the ignition on. Idont really hear it when the engine is running or when I'm driving. It does not seem to change pitch... I mean, the humming stays constant all the time.
the sensor broke the plastic socket around the pins and got it glued back together as a better-than-nothing temporary sollution. I guess I can check the resistance in the sensor, to check if the sensor itself is good?
Yes, I just had to do this for another member, but shorting the terminals together after the engine's hot will at least tell you if you have a connection problem.
Have you tried reading codes? I cannot remember if your car has a check engine light or not, but you can check them if you have an analog voltmeter and some wire.
So, yes, the pump has a gerotor ("gear rotor") in the pump, and yeah, they're noisy. They get noisier the emptier the tank is, and the longer a fuel filter is left on. Those should be changed every 10,000 miles, to keep the pump's stress down. An engine should be in the neighborhood of 210-235 degrees, when a 195 degree thermostat is installed. But don't put in a cooler thermostat, unless you live in Arizona or the Sahara Desert. It fools the computer. Also, when you short the ECT wires together, you're only telling the computer it's 273°, not actually making the engine run at 273°. Same as unplugging the ECT, the computer just thinks it's -40°, when the engine isn't actually at -40°.
I havent pulled codes yet. Gotta get a test light. Tried the regular way and the engine light never blinked, so I'm assuming my car is too old to have a working CEL. Actually I think my pump got a little less noisy after replacing the fuel filter. gotcha on the 195 thermostat.
Yeah, no CEL till 1989 model year. My friends' '88 Colony Park doesn't have one, but my '89 Colony Park does have one.
Actually, do the KOEO. Doing the KOER is difficult without a scan tool with the proper connectors and software.
