Question about 1991 Cadillac DeVille

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My cadillic runs rich and rough when cold. Improves when it warms up. Mileage around town is terrible.

Not using oil but front plugs shows signs of running too rich.

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  • 180 Answers

Have the intake air temp sensor checked by a computer

Posted on Dec 01, 2012

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Posted on Jan 02, 2017

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SOURCE: starts good on a cold start. As it warms up, it

it can be engine temperature sensor, map sensor or oxygen sensor. what happen here is when your engine cold, it run on a limp mode. it ignores all the inputs from sensors but when it warm up to the operating temperature the computer will take over and at this time if one of your sensor is bad it will give the computer wrong data

Posted on Feb 25, 2010

  • 6982 Answers

SOURCE: rough idle after warm up

I'd take a look at the temp sender...the engines computer may be "thinking" the engine is still cold when it's not. That would cause it run rich (and rough) after it's warmed up. Generally the sender can be tested with an ordinary volt/ohmeter but you will need the specifications available in most inexpensive manuals. As with any complicated electronics system, I can only give you my best guess, without the luxury of doing any hands-on testing myself.
Good Luck!!

Posted on May 28, 2009

  • 113 Answers

SOURCE: 2000 catera cold start idles rough and dies. After

Did you have battery disconnected or dead recently?

Try to place ignition in run without starting engine for 3 minutes (shut off all accessories and lights etc..). Then shut it off and then start it. Should relearn the idle.

If this doesn't fix the problem, unplug the MAF sensor, if it runs fine with it unplugged, its the MAF sensor.

Exactly what happened on my wife's 01'.

Posted on Jul 25, 2010

  • 74 Answers

SOURCE: When my 1991 Deville 4.9 Liter Engine is cold it

The combination of heat and missing tells me that you have an ignition problem. Warm the engine as much as possible and take a water mister and mist the exhaust manifold with the water mist at each cylinder where the exhaust comes out of the cylinder. The cylinder(s) that doesn't evaporate as quickly as all the others is the one that's missing (no combustion = no heat out the exhaust for that cylinder). The next thing to do is to pull the spark plug. examine it for dirt built up around the electrode. If it's dirty then just replace all your plugs. If the plugs look good ( not worn - no contaminates around the electrode) then suspect plug wires. If all the cylinders evaporated the water pretty much the same, then your coil wire to the distributor cap or the cap and/or rotor itself is faulty. Examine the rotor cap and rotor for thin black lines running along the inside. If you find evidence of arcing (the lines inside) then replace the cap and rotor at the same time. The data you gave though sounds more like plugs or plug wires if I were to guess... For best results you should plan on replacing plugs/wires/rotor/distributor cap at the maintenance intervals suggested in the owners manual. But now that you're having these issues you should have some kind of concrete evidence before replacing these items - that is unless you've never replaced them ever before. In which case it's high time to have replaced them.

Posted on Oct 01, 2010

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1992 nissan maxima, hard start,runs fine until it starts puffing white smoke then its gutles as hell and wants to stall,before when i attempted to start it,it would sound like it would backfire or...


if it is puffing white smoke,you have lost a piston ring or broke it.the white smoke is coming from oil burning around the piston.your hard strating is due to the fact that you are loosing compreshion in the motor.take it into a mech.and have them run compreshion test on it.GOOD LUCK pretty spendy!

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Hard starting, rough idle when cold, then smooth running when warm


Need year/make/model/mileage of vehicle to provide a more specific set of troubleshooting steps.

When was the last tune up? Hard starts when cold are usually caused by fouled spark plugs, worn plug wires, or weak ignition coils. Fuel systems are not as effected by temperature changes as the ignition components.

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I have a 95 Ford F350 with the 460 motor. It started running fine when cold but after it warms up it starts to run rough, lose power, and runs REAL rich. I'm only getting a little more than 2mpg.


It Sounds like it is staying in the "cold start" routine. It also sounds like the diagnostic computer is not working right, because it must be rich and the O2 is not telling you a thing.

I would start by looking for a temperature sensor. You may have 2, with 1 being for the dash and the other being for the engine controls. You want to replace the temperature sensor for the Engine controls. This will help get it out of "cold start" routine.

Change your thermostat. The onboard computer does not monitor operating temperature.

Fuel pressure regulator. Have pressure checked.It could be forcing too much gas in each time an injector opens.

If you can not do this yourself, tow it in. At 2 mpg it may be cheaper to tow it than to drive any distance for repair. The Mechanics are going to need some gas left over in it to work on the engine.

Also turn on ignition and energize the fuel pressure, check for leaking fuel lines. Put on fuelcap locks if fuel drops when parked.

For this much of an extreme problem, I would like to know what you find wrong with it. I hope my solutions help.

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Rough idle,tps,iac,fuel pump and filter replaced,was running great,then all of a sudden,started running bad at idle,runs ok going down the road...any thoughts?


does it run rough after warm up??or cold too,,u mite have a vacuum leak,,,take some injection cleaner spay,,carb or brake cleaner spray,,seen many different spays used,,,but spay around air intake,,around base,,see if engine will stumble,,also seen temp censer problems,,where its tell the ecu that the motors cold,so it rich-ens the fuel,,injector,,hoped it helped,,

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Hello. my 2000 4runner v6 has been running rough. when i start it, it runs fine untill it warms up. then it begins to miss. have replaced spark plugs, and battery but didn`t make a difference. diagnostic...


Change your oxygen sensors - they're responsible for feedback that the computer uses to determine the air/fuel mixture. They usually are good for about 60k miles and then start to go downhill. When they get to a point that the computer won't trust them, it ignores them and runs on preprogrammed fuel maps that run excessively rich (too much fuel) to safeguard the engine. You've probably seen a decrease in fuel mileage as well. And the O2 sensors have to be up around 900 degrees before they'll work - the car ignores them until then. That's why you run fine after a cold start but run rough once the car is warmed up.

The O2 sensors you want to change are in the exhaust system between the engine and catalytic converters (the "pre-cat" sensors). There are O2 sensors after the cats as well, but those are used comparatively to determine how well the cats are functioning. The primaries are the ones used for fuel mixture. If it's been this way for a few weeks or so, I'd put new spark plugs in as well - rich fuel conditions can foul them and contribute to the rough running.

Dec 09, 2009 | 2000 Toyota 4Runner

1 Answer

Starts dicent when cold but when it warms up it starts running so b ad it wont accelerate and will finally die


Do you see black smoke coming out the back at all, once it warms up? To me, it sounds like your oxygen sensors are going bad. If you have a 1996 or newer, change the oxygen sensors between the engine and the catalytic converters. If it's a 95 or older, you'll only have one set. Change them out.

The O2 sensors determine what the fuel mixture for the engine will be. They are ignored when the engine is cold, as they have to be up around 900 degrees to work. Once it warms up, feedback from the O2 sensors is used to determine how much fuel is needed. When they fail, the car defaults to a rich-running condition, with excess fuel being dumped in. This is because the computer doesn't trust the sensors, so it adds extra fuel. Running rich fouls spark plugs over time, and causes hesitation and bogging and bad gas mileage, but it's better than running lean (too little fuel) - that blows engines. So the car is programmed to err on the side of caution and richen the mixture. Change the O2 sensors and the spark plugs, and you should be good to go.

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Sounds like your automatic choke is giving you problems. Check to make sure the choke is operating correctly. If it ins not backing off as the engine gets to operating temp it will cause a rich condition and excessive black smoke out the tailpipe and extremely poor fuel mileage.

Feb 18, 2009 | 1984 Ford F 150

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Check emission light


Have you seen poor fuel economy? Does it run rough when warmed up? If so, chances are you have a bad oxygen sensor - it'll cause the car to run rich, which will hurt fuel mileage and cause rough running. You might also want to change the spark plugs - if they've been in there too long, they're probably covered in carbon and not firing as well as they should be, which will also cause issues with the smoothness of the engine.

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And letme know. If you feel any diference. ok.

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