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need help figuring out what the problem is 2000 Deville

10005 Views 29 Replies 3 Participants Last post by  Ranger
My Deville just recently went over 100,000 miles and now the "service engine soon" light comes on. Not only that, but the car started like stalling anytime I accelerate from a complete stop. Then the "service engine light" starts blinking. ( Keep in mind I'm not mashing it). I took it to the shop and got the following codes:
Po141-o2 sensor bank 1
Po154-o2 sensor bank 2
po155-heated o2 sensor bank 2
po3000-random misfire
po507-Idle speed high

I got the spark plug replaced, but I didn't get the car scanned again yet. Do the o2 sensors need to be replaced? Or is something causing them to get a bad reading? Where are the fuses for the o2 sensors located? Is all of this related?
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Yes, a flashing SES light means severe misfire detected.

A clogged CAT would present driveability problems at higher speeds and RPM's as the engine would have trouble exhaling, so to speak.

I don't trust Bosch parts and that causes me some concern.
Still haven't made any progress on fixing my issue, but I've been doing alot of reading and getting the opinions of other mechanics that live near me. At this point I'm going to rule out a clogged cat. I think all of my problems are coming from the p0300-Random misfire code. All of the sensor codes have come and gone and I'm convinced I was only getting them because the car misfires. I still get the p0155- Bank 2 sensor 1, but I noticed it only happens when the car misfires. And after a while the service engine light will go off and when I pull codes the o2 sensor codes are gone.

Pep boys and my neighboor both thought that I needed new ignition coils. Well over the weekend I replaced the rear ignition coil and my car is still misfiring. I looked at the front one and it looks like an aftermarket brand (Delphi) and it doesn't look old or worn. (spring is still springy and no carbon tracking). What else could be causing the misfire? Should I check for a vaccum leak again? If so exactly where do I spray the TB/Carb cleaner?
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Have you ever checked for a ripped plenum?
No, I haven't but I was looking at this post titled "2000+ Northstar Plenum Duct Replacement steps" which showed the steps. Some of the steps I couldn't follow because of my inexperience such as "bleed of pressure from fuel rail pressure relief valve".Also I couldn't find was how to test the Plenum Duct.
OK, you know that the plenum duct is the rubber coupler between the TB and the manifold. It usually develops a rip on the bottom where it cannot be seen. With the engine at idle, spray some Brakleen or such under the plenum while flexing it with your finger to open the rip (if there is one). If there is, the RPM will increase.

The fuel rail remains under pressure once the engine is shut down for quick starts. Look for the schreader valve on the fuel rail (looks exactly like a tire valve). Remove the cap, hold a rag over the service port and bleed off the pressure (just like letting the air out of your neighbors tire). You may get a about an ounce of gas out of it.
I'm going to test it as soon as I get off. If there were a rip in the plenum shouldn't I be getting a lean code like P0171 - Fuel Trim System Lean Bank 1?
Am I supposed to remove anything other than the vanity cover to test it? I sprayed some throttle cleaner under it but I didn't get a reaction. Thing is I'm not able to get my fingers underneath it to open the tear if it is one. What do I do?
Improvise. Use a screwdriver, dowel rod, anything that will flex it a bit.

Usually a ripped plenum will set a P0171 & P0174.
The plentum checked out ok. So I took it to the Cadillac dealership and they told me my problem was coming from a loose fuse in put for the oxygen sensor fuse location. Basically he told me that due to the p0155 code that I kept coming and going that the information was recieved by the ecm and the ecm was compensating for the code which some times resulted in a misfire. They also checked the pressure of the block because I was getting a low coolant message combined with misfires so they considered my hg was going bad. But the pressure checked out ok. Thoughts?
If you are talking about a cooling system pressure test, that will rarely detect a bad HG unless it is already so bad that it is so obvious that a test is not needed.
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