Cadillac Seville No power

Tiny
  • MEMBER
  • 0 POST
  • 1991 CADILLAC SEVILLE
  • 126,000 MILES
I have a 4.9l engine that has had 3 injecters replaced i've replaced the plugs, ignition wires, dist. Cap and butten and the car still runs rough has reduced power and horrible gas mileage. Do you have any idea what might be the problem
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,873 POSTS
REAL common problem that affects mostly GM products. Chrysler is one manufacturer that buys their injectors from Bosch in flow-matched sets and problems with them are just about unheard of. Don't know about other manufacturers but GM, on the other hand, has a huge bin full of injectors that flow all different rates. They grab a handful on the assembly line and stuff them in. You typically don't notice the slight lack of performance or fuel mileage when the engine is new but after many miles and a little varnish buildup, or the fuel pump gets a little weak, and symptoms start to show up. The biggest red flag is you only replaced three injectors. That should never be done.

Depending on the year, model, and engine size, the injectors are all fired with the same "pulse width" or all of them on one side of the engine are fired the same amount of time. The time is the same for every injector, the fuel pressure to them is the same, but their flow rates are different. The one that flows the least will leave that cylinder a little lean, and that extra unburned oxygen will be detected by the oxygen sensor and reported to the Engine Computer. He doesn't know only one cylinder is affected and will respond by increasing the pulse width to command more fuel to either all of the injectors or all of them on that side of the engine. Most cars built before 1996 only had one oxygen sensor so all the injectors are pulsed the same.

To overcome what it thinks is a lean condition, the computer commands more fuel from all the injectors. That dumps unneeded fuel into the engine where it is wasted. In severe cases, that lean cylinder may still be lean even after more fuel is requested, and no matter how much raw fuel is going out the tail pipe, the oxygen sensor will still be detecting that unburned oxygen. (They don't detect unburned fuel).

A similar problem can occur when a cylinder misfires due to a spark problem. Raw unburned fuel and oxygen go into the exhaust system where only the oxygen is detected. The computer will try to correct that by adding more fuel to all the cylinders but there will still be that unburned oxygen from the misfire.

The fix for this is to buy a flow-matched set of rebuilt injectors. Do an internet search for "Jim Linder" in Indianapolis. He puts on real high level and expensive schools all over the country for engine performance specialists. His company rebuilds injectors and sells them in matched sets. He sells more injector sets for GM vehicles than all other manufacturers combined. Mechanics love them too because so many owners say their cars never ran so smoothly even when they were new. They buy used injectors too because they can't get enough to meet the demand.

To be fair, GM may have improved how they choose injectors on the assembly line in recent years, but they don't do anything unless they can make money on it.
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)
Tiny
LOLA1991
  • MEMBER
  • 1 POST
  • 1991 CADILLAC SEVILLE
  • V8
Car does not accelerate when you step on the gas. It does start though.
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)
Tiny
FACTORYJACK
  • MECHANIC
  • 4,159 POSTS
Does the engine rpm increase when you step on the gas pedal?
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)
Tiny
BUCKNUTDAVE
  • MEMBER
  • 1 POST
  • 1991 CADILLAC SEVILLE
  • V8
  • 2WD
  • AUTOMATIC
  • 110,000 MILES
Engine Performance problem
1991 Cadillac Seville V8 Two Wheel Drive Automatic 110000 miles

Please help my 91 Seville is running very rough and has oil on the passenger side under the hood near the serpantine belt. I have trouble getting up to speed and it stalls when idling rpm's are also running in the 2500 range. What should I do other than sell it to a scrap yard, just kidding we want to keep it it is in very good shape
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
When was the last tune-up?

For a start you can check the idle air control valve and throttle position sensor-
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Tuesday, December 20th, 2016 AT 10:40 AM (Merged)

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