1999 Cadillac Deville Loss of Power

CADMAN703

MEMBER
1999 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
116,000 MILES

I have a 1999 Cadillac Deville Concours currently with 116,000 miles. A little less than a year ago I took it to the dealer to check out some engine codes I had and diagnose its rough running. It was showing P340 so they did repairs on the crankshaft and camshaft sensors. The codes did not clear and the car continued to run rough. I brought it back a couple months later to see if they could do anything. One of the techs said the gear probably wasn't set at the right angle. That change did clear the code but a new one for electrical pulses appeared. It continued idling rough as well with faint vibration and up and down rpm at rest. Also continued to have a problem of locking when I would try mash down to pass or go for hard acceleration. I would have to let off the gas a little to get a "release" feeling which I could pick up speed afterwards but still slowly at that. Recently my transmission broke down and my car was immovable. So I got it repaired and it still had the symptoms mentioned earlier but seemed to run a little worse even. Less power and acceleration ability than before. This shop told me I need coil packs. I'm worried that this might not solve the problem. I'm also curious as to whether the problem could be simple spark plugs or wires since it now shows a code for pulses, and if that "locking" feeling with hard acceleration could be a clogged cat converter, or even something. I am trying to avoid spending any unnecessary money on this car. Any ideas? Thank you for your time and cooperation.

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

I am a little misunderstood of your terminology, particularily 'locking' and 'pulses'. You say you have a code for electrical pulses, what is the code number? That may provide me a clearer understanding of what you are describing. You mention you get a release feeling, and I can only imagine misfires under load, that as you ease the pedal decreasing the load, it stops misfiring and running smooth. That kind of feels like what can be described as a release. If someone can show you the coil packs, and the secondary terminals are corroded, then yes you should have them replaced, they can be causing misfires. Also the plug wires are corroded as well, on that end. A clogged converter will not give you an intermittent fault. Sometimes they can be a bit unnoticed at lower rpms, but as exhaust pressure is increased, the loose particles get to moving around and can clog. Often once they are lifted off the bottom of the cat, exhaust pressure keeps them there.