1991 4.9

[DSkrab]

Hi folks I'm new to your Cadi forum, thanks for your time.
I have a 1991 Sedan Deville, 150,000 miles. It was running fine, then one day on the way home it started to sputter like a sensor just went, and lose a little power. it has been getting progressively worse.to the point now where it has no power at all. Ive changed the egr valve, fuel pump, fuel regulator,plugs, wires, cap, catilitic converter. Ive gone from 20 mpg down to 6 mpg. The car starts right up but put it in gear and it just has no power. Any help would be appreciated. Thank You.

[Sevillian273]

http://www.cadillacforums.com/forums...x-engines.html (OBD I codes for 4.x Engines)

[AMENCADDY]

Check your codes as suggested for clues. but if the car has no power there you may have a blown head gasket or worse. Compression check might be in order. Do you have any smoke, black, blue or white from your exhaust? Could even be transmission problems. How's your T fluid, clean or black?

[DSkrab]

Originally Posted by AMENCADDY

Check your codes as suggested for clues. but if the car has no power there you may have a blown head gasket or worse. Compression check might be in order. Do you have any smoke, black, blue or white from your exhaust? Could even be transmission problems. How's your T fluid, clean or black?

I checked the computer codes. I'm not blowing any smoke, no water in the oil no oil in the water, It doesn't smell like it's running rich. I did a compession test on the front four cylinders 150 to 170 psi {I think I may have to break down and check the back 4, but it was startig to run bad when I changed plugs and they looked good}. It I need to no where the plug is that I have to jump to do the timing. The car idles
very uneven now rpms up, rpms down. Trans fluid is down half a quart but is vert clean. The car doesn't run fast and not go antwhere, if a load is put on it the motor just has no power.

Thanks

[cadillac_al]

It gets 6 mpg and no codes? Maybe it's the ECM.

[Sevillian273]

The plug you are looking for is the #1. It is the first plug wire from the left when standing in front of the car. Look under the p/s pump.

I agree with al, it sounds like the ECM is dying. I heard that when they overheat they revert to zero timing and rich fuel.

[AMENCADDY]

Are you sure you got the firing order correct when you changed the plugs? Also, you mentioned a new EGR valve. Did you clean the stack tubes from the throttle body intake ports at the same time? Might also want to check fuel pressure, even thou you have NEW parts. (NEW means Never Ever Worked!)

[Notaguru]

I'm no guru on these engines, but on others of the same age those symptoms point to a MAF sensor failure, and some failure modes involving leaks can occur without a code.

[Sevillian273]

These engines are speed density. They dont have MAFs. They have a MAP sensor but it should set a code. I think they can be tested at auto parts stores.

The engine will run and drive fine with zero EGR flow. I have proven this with my own vehicle by using a block-off plate for a few thousand miles. Theoretically there is some risk of detonation but I have experienced none even with 4 deg advanced timing and 95+ degree Florida driving. Most EGR related driveability problems are caused by the valve sticking in the open position, allowing too much exhaust into the combustion chamber.

DK says it started sputtering and getting progressively worse so that rules out a firing order issue, otherwise it would have run bad from the get-go.

A healthy ECM will advance the timing as rpm goes up. If it has a problem and is not applying the spark curve, the motor will run at base timing(10deg) throughout the rpm band, which would explain a loss of power under load. Thats just one way it may have failed. Maybe it's applying ridiculous amounts of fuel... its hard to say, but with all the new parts and no codes, My money is on a bad computer.

[AMENCADDY]

Don't forget about the trans possibility for the "no power" problem. With 150K, how's the T-fluid?. If it is not clean pink, that would not be a good sign. - but then where oh where is all that fuel going? 20mpg down to 6mpg might be leaky fuel injectors or just a faulty FPR (even though it is new- u didn't happen to buy these NEW parts at Autozone did you?)

[revdowrong]

What spark plugs did you put in the car? And when you worked on the car did you disconnect the battery? Oh and also check your fuses especially the ones behind the glove box, chances are you might have blown the fuel injector fuses.