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Discussion Starter #1
I have a 1990 DeVille that is misfiring really bad especially on damp mornings. I drive up to get my morning coffee and shut it off get back in and start it up and it's fine. I took it to a local mechanic who said I have new plug wires etc. and he gave me some fuel injection cleaner which I have used with 2 full tanks of premium gas to no avail.

I am an old wrencher from back in the 350 big block days and I have the Chilton manual for the DeVille. Can anyone help me diagnose this misfiring as I live in Michigan and I need to get this vehicle in good shape for the upcoming winter as I am too old to be laying in a snow bank pulling motors with a come along under the oak tree

Thank you in advance!
 

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1996 Deville (sold), 2000 Mustang GT
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1,300 Posts
The first thing I would check or replace is the spark plugs, not sure if you replaced them when you got new wires, but if not, definetly start there. NOt sure if your car has coil packs or a distributer but that would be the next things to check. Also check the fuel filter and fuel lines, to make sure no water is getting into your gas. I suspect its electrical though.
 

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White Diamond '03 DHS (with DTS floor shift)
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I am with Misfit. If the plugs haven't been done, I'd replace them as well as the distributor cap. Also pull the codes if you haven't already by simultaneously pressing and holding the OFF & WARMER buttons.
 

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1996 Deville Concours
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805 Posts
The plug wires may be good advice. I have a 90, and I noticed they come pretty close to the exhaust manifold near the front. Make sure none are touching. I personally prefer using Accel wires which I can customize the length of the wires. If you go that route, you'll need to cough up another $25 or so for the crimper to put the terminals on the ends. Plug wires should be flexible and without cracks...If you have a multimeter you can test the resistance (in ohms). Longer ones will be a bit higher, but I'd say it's worth new ones if you're getting anything over 2000 ohms.

If you do the distributor cap, do the rotor as well. I actually found the rotor to be more the problem on mine.

The ignition coil is the real workhorse of the system. It's the cylinder-shaped doodad mounted right in the distributor cap. If you replace it, don't cheap out on this part.
 

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Discussion Starter #5
Thank you for all the advise fellas I will change the plugs, cap, rotor and wires even though the mechanic said I didn't need to as that was what I thought in the first place. I will let you all know the results
 

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1990 Sedan de Ville FWD
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I recently purchased a 1990 Sedan De Ville with 71k miles. It was just to clean and too good of a deal to pass up. The car has obviously been well cared for and garaged for most of it's life. I had to replace the BCM - which I knew was bad - due to the dash lights coming on and off - clicking sounds coming from behind the glove box. After replacing that, all blinking lights and clicking stopped. The car runs very well with the exception of a slight misfire under acceleration. I have changed all plugs, distributor cap and rotor. The spark plug wires look fairly new - still very pliable - no cracks etc. I have read several troubleshooting tips - and I am suspecting the ignition coil as possibly being weak. I see two small yellow hash marks on the coil - which makes me think it was replaced from a junk yard. My question is: is there a way to test an ignition coil without spending the $86.00 or so to replace it with a new AC Delco? I am also wondering if it might be something to do with the EGR valve. Any ideas on this one?
I have also pulled the codes and got an E52 and F30 and F31. Still researching those codes.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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Riopaloma- :welcome: please feel free to start a new thread when you have an issue. It's usually better than tacking one on to a 5 year old thread.

If start with replacing the wires. If they're original, their ancient.

You can find a link to OBD I code definitions within the "sticky" thread at the top of the FWD Deville/Fleetwood page.
 

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1993 Coupe Deville, 2009 XLR-V 1 of 6 Crystal Red
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I have also pulled the codes and got an E52 and F30 and F31. Still researching those codes.
The E52 is most likely from when you may have disconnected the battery. The F codes are BCM codes from when you were having problems with your BCM, they could be from your FDC also. I would delete or try to delete them and see if they come back. You can do that by entering diagnostic mode, wait for .7.0 and then hold down off and high until E.0.0 is displayed. That will erase the PCM modes, to erase the BCM, press and hold off and lo buttons until F.0.0 is displayed, the .7.0 will be displayed. Leave your ignition off for at least 15 seconds. None of those codes indicate a problem with a misfire unless you need to clean your battery connections and grounds. Might want to do that if you haven't already. Testing the coil, you need an ohmeter. Get a reading from terminals C- and B+, reading should be 0 or near zero. Even testing with an ohmeter if readings are ok, you can still have a bad coil. You also mentioned EGR. I wouldn't think you have a problem without codes, however it would be a good idea to clean the throttle body and the tubes in your intake manifold just below the throttle body. Get a gasket for the throttle body and the EGR, remove them both and clean up. Check all of your vacuum lines elbows etc. They get hard and crack with age. If you are planning on doing most of the work yourself, you might want to consider a FSM, ebay is your friend. Lots of good information in them. Usually you can usually pick one up reasonably priced. Here's one I wouldn't let go... http://www.ebay.com/itm/1990-Cadillac-DeVille-Fleetwood-Service-Manual-OEM-General-Motors-H-2714-Manual-/370590046322?hash=item5648e35872&item=370590046322&pt=Motors_Manuals_Literature&vxp=mtr
 
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