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Discussion Starter #1
Mileage on my car is less than 100,000 original miles. I'm having an acceleration problem. The mechanic couldn't pinpoint the issue. We've looked at plugs and wires. They're fine. Not sure where to start but I don't want to beat my car up. Suggestions please?
 

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Super Moderator SEMPER PARATUS
2003 DeVille Base
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4,439 Posts
Welcome to the forums! Let's move this to the correct Deville page and you'll get more specific help there.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,864 Posts
Mileage on my car is less than 100,000 original miles. I'm having an acceleration problem. The mechanic couldn't pinpoint the issue. We've looked at plugs and wires. They're fine. Not sure where to start but I don't want to beat my car up. Suggestions please?
573871
 

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Super Moderator SEMPER PARATUS
2003 DeVille Base
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I think what Basscatt is trying to tell you is we need a lot more information
 

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White Diamond '03 DHS (with DTS floor shift)
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86,242 Posts
Yeah, you need to define "acceleration problem". Is it misfiring? Is it sluggish? Is it not shifting?
 

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Discussion Starter #6
Sorry. There may be a minor misfire. It shifts but it's extremely slow speeding up. As long as I'm really gentle with it, it drives but it used to have a lot of GO. I havent been taking it on the freeway because it's so gradual getting up to speed.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,864 Posts
Sorry. There may be a minor misfire. It shifts but it's extremely slow speeding up. As long as I'm really gentle with it, it drives but it used to have a lot of GO. I havent been taking it on the freeway because it's so gradual getting up to speed.
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hmmmmmmmmmmm -
I don't have the manual for a 1990 Deville but I do have one for the 1993 -
I assume the 1993 would be very similar -

almost sounds like half of the fuel injectors aren't firing -

there is a FUSE / RELAY box up under the dash near the glove compartment -

in this fuse box are TWO 10amp fuses for the fuel injectors -
one fuse powers injectors 2-3-5-8 - the other powers 1-4-6-7-

use a stethoscope - or similar - to listen to EACH injector while the engine is running -
there SHOULD be a very distinctive SNAP or CLICK - every time the injector fires -

no SNAP = no injector = no fuel = no power
 

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Super Moderator SEMPER PARATUS
2003 DeVille Base
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if you don't have a suitable steth, use a long screwdriver with maybe a plastic bottle attached to "listen" to your engine. The injectors have a very definitive sound. As for cats, crawl under and whack the cats with a mallet. You'll hear the rattle if it's bad.
 

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in some GM vehicles, a bad throttle position sensor can be replaced by Manifold Absolute Pressure as an indication the driver wants more power. The ECM does this automatically, diagnosing sensor failure. The MAP sensor tends to be a slower responding device.
One other possibility is on older vehicles, carbon deposits can break loose and move around in small intake manifold passages, slowing the response of the MAP sensor. Depending on where the PCV valve vents into the manifold, that is the source of the carbon/coke.
 

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70 Deville 78 Seville 92 Deville 03 Deville
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That gradual getting up to speed sure sounds like a clogged cat. That's easily verified with a vacuum check and seeing low vacuum. It costs nothing to check the fuses that Bass mentioned.
 

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I would test each fuel injector. They are known to go bad on those engines. Especially once the car has sat for a period of time and moisture has accumulated in the fuel. I suspect this could be the case considering the mileage. My 1990 had similar symptoms and it turned out I had 5 bad injectors.
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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767 Posts
Yep, when I got to two bad injector, started to feel the sluggishness. Replaced the whole set bosch upgrade (reman'd and balanced)
 

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Look at the simple stuff before you start throwing money at sensors. My 93 sat before I bought it from an elderly woman's son, I'm currently experiencing the same issues, and have spend over a thousand dollars replacing parts, just to find out the inside of the tank is rusted out. Humid climate, impurities in low grade gasoline and letting it sit will give you tons of problems. Check spark and fuel, if you're getting over 12v to your plugs, and 21+ psi to your fuel rail, move next to distributor cap and rotor and fuel filter, then finally move along to fuel tank/pump and injectors.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,864 Posts
Look at the simple stuff before you start throwing money at sensors. My 93 sat before I bought it from an elderly woman's son, I'm currently experiencing the same issues, and have spend over a thousand dollars replacing parts, just to find out the inside of the tank is rusted out. Humid climate, impurities in low grade gasoline and letting it sit will give you tons of problems. Check spark and fuel, if you're getting over 12v to your plugs, and 21+ psi to your fuel rail, move next to distributor cap and rotor and fuel filter, then finally move along to fuel tank/pump and injectors.
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if you're getting over 12v to your plugs, and 21+ psi to your fuel rail,
move next to distributor cap and rotor and fuel filter,

correct fuel pressure at the fuel rail is 39 to 45psi -
it MIGHT run with 20psi - but certainly NOT well -
 

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2004 Deville base
'05 SRX N*/AWD, Vetts/Birds/Trucks
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360 Posts
"if you're getting over 12v to your plugs"
??
Please...clue up...K?

"Spark plugs usually require voltage of 12,000–25,000 volts or more to "fire" properly, although it can go up to 45,000 volts."
 

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70 Deville 78 Seville 92 Deville 03 Deville
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I think most of us assume it's 12 volts to the distributor. Almost everybody knows spark plugs take mega-volts.
 
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