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Discussion Starter #1
My father as a 93 deville with around 80k miles on it. It has the 4.9 engine & has a misfire all the time even at idle. You can here the putt, putt, putt out of the exhaust. It is very rhythmic patternl. With the help of this board so far I have:

1. listened to all of the fuel injectors with a stethoscope and they all pretty much the sounded the same.
2. Checked the fuel pressure regulator nipple for leaking fuel (there was none).
3. checked fuel pressure with a gauge & got 40psi at idle.
4. cleaned the egr tubes with a wire.
5. checked for a bad engine ground by turning on all of the accesories while at idle and the idle did not change, nor did the car try to stall. I also used a jumper cable connected to a engine bracket as an "extra" ground. The idle never changed.
6. Installed plugs, wires & new rotor. (when I plugged the plugs all looked good. None soaked in fuel or white)
7. scaned for codes and got an e90-something about a vcc. (dont think this would be related to the problem)

I think something is bad in the distributor like a coil or there is something wrong with a valve, spring, pushrod, etc.

Next tests will be with a compression gauge or off to the shop.

Any help would be appreciated
 

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White Diamond '03 DHS (with DTS floor shift)
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Replace the cap. The contacts get eroded over time and thus the gap increases causing a misfire.
 

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93 Sedan Deville 4.9L
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Could try seafoam, Or other cleaner in through the throttle body.

May help clean the idle up some, Did so for me, Their is a "seafoam experience" thread with good tips and directions in the 4.9/4.5/4100 forum
 

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Discussion Starter #5
Did some more tests this evening on the car.

1. tested the fp again got 35psi & 42psi with the vacumn hose off of the regulator

2. examined the regulator when idling for fuel leaks & found none.

3. pulled 3 of the 4 front plugs & they were all carboned up & smelled of fuel.

4. checked for spark on each wire with a timing light. They all were firing.

5. examined the wiring going to the distributor & coil for cracks. (found none)

After the tests tonight I dont think it is bad fuel injector or mechanical damage to 1 cylinder such as pushrod, burnt valve, etc.

Can a ignition module or pickup coil cause it to run rough at idle?

Although there is spark can it be not "hot enough" to light the cylinders off?

Can bad oxygen sensors cause a rough idle, hestitation, etc.?

What are the symptoms of a power steering pressure sensor or map sensor?
these can up while searching, but note I have not got any codes indicating either is bad.
 
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