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1990 Deville - poor acceleration

6K views 28 replies 11 participants last post by  basscatt 
#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?
 
#7 ·
==========================
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
 
#11 ·
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.
 
#12 ·
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.
 
#14 ·
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.
 
#16 ·
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.
 
#21 ·
12 v to the coil, which could be in the distributor. The coil is a design similar to a transformer but based on magnetic fluctuations. The 12v in the coil creates a magnetic field. Remove the 12v, the field quickly collapses and induces a high voltage current on the output.
 
#29 · (Edited)
I've installed spark plugs and wires, distributor cap, map sensor, , all filters are new. Installed oxygen sensor today. Seems that I have more acceleration. But I kinda hear a sputtering noise when the windows are down.
How do I thee above 2 methods?
Resistance test & cylinder balance test.?
=====================
firing the PARTS CANON and HOPING something "sticks"
is NEVER the right answer and the MOST EXPENSIVE method -
PROPER DIAGNOSIS - followed by actually FIXING the problem RULES!

rather than me typing out instructions - hit GOOGLE and YouTube
 
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