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05 Cadillac STS4 V8
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Discussion Starter #1
Synopsis: random powerloss, backfires. Caddy Techs don't know the cause of the issue. Codes point to Cat and rich fuel mixture in the odd cylinders. They want up to $5700 with a 50-60% chance of fixing the problem.


Story:

The other friday I was going home from work when I realized that as I was pressing down on the gas pedal I had a sudden loss of engine power (cruising on the highway). After a few seconds the power came back but it lasted a short bit of time until it happened again. It was intermitted back and forth between full power and loss of power when I finally had to come to a complete stop at a stop light. I noticed my car was shaking, so bad it was actually shaking my body, but the RPM gauge showed that it seemed to be idling normal. I didn't drive it all weekend until I had to go to work on Monday with the intent that I would be dropping it off at the dealer at somepoint during the day. On the way to work the symptoms returned after the engine seemed to have warmed up to normal opperating temperature. I noticed that when I was experiencing the loss of power that the engine light was blinking instead of staying constantly on. Looking in the rearview I also noticed a little smoke coming out the back. Needless to say I figured that I was lucky enough that it kept moving so I took it straight to the dealership. While I was in the parking lot waiting for them to open their door the car finally killed and shut the engine off. I was able to immediate restart it and as I was pulling in the could here it was backfiring.

When the techs were finally able to get to it the following monday they weren't able to pinpoint exactly what was going on. The services manager told me that the engine was feeding a rich fuel mixture and that was hurting the cat. He said that without tearing apart the engine they wouldn't be able to pinpoint what was causing the issue. I've owned the car for a year but he said the previous owner had warranty repair work that had been done previously and possibly there was a link between what was done and what is happening. Long story short GM said they won't cover under warranty (I'm out of warranty) and they wouldn't be able to tell me the repair work that had been done because that would be a breach of customer privacy with the previous owner, although I don't see how that works since I would recieve no previous customer information. The dealer I'm working with seems hesitant to even do any repair work as they aren't certain what the issue is. The other day he told me that the odd number cylinders are running lean (which contradicts what he told me earlier, possibly he's confused) and the cat needs to be looked at but he thinks its some other piece thats the root cause. Regardless today he presented a quote of $4900-$5700 to fix what the tech thinks is the issue but would only be 50-60% confident that the repairs would fix the issue. I'm not wanting to fork over that kind of money with that little of a chance that it will be fixed. Anyone have any ideas?
 

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Formerly 06 STS-V, now 13 XTS
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536 Posts
I'm far from being an expert, but the first thing I would check based on what you are saying is the oxygen sensor. A very similar issue happened to my grandmother's Oldsmobile a few years ago, and it was the oxygen sensor. Her car would buck, backfire, alternate between full power and limited power.
 

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2005 Cadillac STS V8 Luxury Performance Package RWD
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121 Posts
This could be a HUGE long shot, but from working on OLDer cars, like carburetors and such, when a car warms up and starts acting like that, alot of the times, the spark plug wires are breaking down and letting the fire "jump"..... so the fire never makes it to the cylinder like it should..... just a thought.
 

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05 Cadillac STS4 V8
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7 Posts
Discussion Starter #4
One of my buddys said it could be a coil pack which I might bring up to the dealer. I'm hoping its something simple but I'd think that the dealer would check out those options first. They really seem to want to tear apart the engine to try to figure this out. If anyone else has any ideas, even if they are a long shot, I'll bring it up to see if its a possibility. The only thing that leads me hanging is the fact that the odd number cylinders are the ones that are lean/rich (depending on when the service manager talked to me) so I'd think that it would be effecting all cylinders.
 

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2005 Cadillac STS V8 Luxury Performance Package RWD
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121 Posts
I had a friend whose old Crown Vic had the same issue and it was the coil pack. Granted, it was just running like crap, missing big time. Coil pack fixed it. Good luck man!
 

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Sedan de Ville, CTS
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4,764 Posts
Shut the engine off. If you do not have the coils on the individual plug wires, pull the coil wires off the coil packs one by one. Look at the chrome nipples on the coils. On the Buick 3800 engines, the plug wires nearest the engine (by less than 1/4 inch) corrode. The other plug wires do not. Get some sand paper to remove the corrosion as a temp fix. Then go to a GM parts retailer and purchase the necessary coils and plug wires. Do not pull multiple wires off at once--easy to mix up wires. It will then take you 2 days to straighten wires out.

Or simply bad plug wires, as someone stated. Moisture gets inside the valve covers where the plug wires sit. Then wires start arcing.

I find it hard to believe you have an engine problem. Those engines are bullet proof.
 

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06 STS AWD V8 09 Escalade ESV
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111 Posts
I would agree with these guys. It sounds like the "COPS" problem on the 02-05 T-Birds as well. Engine is probably fine since it run ok when cold.
 

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'05 STS4
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668 Posts
It's hard to imagine a dealership saying "you should spend @5K and we think there's 50-60% chance that will fix it" :D

As others have said Move On..... find yourself somebody who's actually competent at automotive repair
 

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Cadillac Owners Troll
2019 CT6 Sport 3.0TT,2015 Luxury ATS , 2016 ELR, and Volt
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It's hard to believe a GM dealer could be that blatantly crooked these days--that's way over the top!! Anyway, I doubt this is a base engine issue but rather an ignition or fuel system problem. The engine diagnostics should be able to lead right to the cause(s). It almost sounds like it is going into "save" mode as if it is overheating--they will continue to run but fire alternate cylinders to protect itself. It may not be overheating but a faulty sensor could trigger that mode. I suppose it could be something more serious such as a cam phasing issue, but once again, good diagnostics should lead to the root cause. BTW, depending on what really is going on, there may be a chance the the emmision warranty may cover it.
 

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06 STS-V & 06 STS 4 (sold 2016)
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I would definitely find out what work was done before. If it is related, you might have an argument that that work should have a warranty. But for sure find a dealer who cares and knows what they're doing.
 

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05 STS-4 1SG
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11 Posts
I would agree with what others are telling you.

At cold start until the car hits operating temp, it runs in closed loop where fuel and timing are controlled differently. Once it heats up, the car runs open cloop and depends on all of the sensors like the 02 sensors for tuning.

GM cars usually determine if a cat is good by a set of front and rear 02s. If the rear 02s see a mixture that is too rich, they tell you the cat is bad. If the front 02 sees a mixture that is too rich, it tells the computer to add less fuel by bank.

I would definately take the car somewhere else. For $5700 you should be able to absolutly everything replaced under the hood. I think they are trying to pull something over you.
 

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2005 Cadillac CTS 3.6L VVT
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1,062 Posts
do you know what was the code from the dtc? if its all in one side, it will help. I didn't see any code on this post.
 

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05 Cadillac STS4 V8
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Discussion Starter #17
I finally got a repair history and called all the dealers (that are still open) and asked for the codes and symptoms. Here is a synopsis.

Current dealer where the car is:
P0171 - lean bank 1
P0174 - lean bank 2
P0300 - random misfire


Previous Dealers:
P0315 - This showed up twice and they reprogrammed the PCM
P2119 - This showed up twice and they reprogrammed the PCM as well

PCM Replaced 9/21/07
PCM Reprogrammed 11/28/07
PCM Reprogrammed 12/11/07
PCM Reprogrammed 02/28/08
PCM Reprogrammed 04/03/08
I believe the car was sold/traded in shortly after until I bought it in Sept of 08.

At this point I am going to pick it up from the current dealer and take it some where else to get a second opinion. If they have no clue, or want an absurd amount of money I don't know what I will do.
 

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05 STS-4 1SG
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Whatever that dealer was charging 5700 for is not causing your issues. I'm a bit surprised they reprogrammed the pcm to trouble shoot or fix that issue.

If you are getting both left and right bank issues I would look at you MAF sensor. The P0300 can be set by detonation caused by the lean issue. I wouldn't worry about fixing it until you have the lean codes fixed because it can be caused by the issue making those codes happen.

When you pick the car up I would bring a bottle of MAF (mass air flow) sensor cleaner. Try the easy cheap things first. The can costs 6 bucks at any parts store. Pull the covers off the engine bay and get to the MAF sensor which is in the intake tract after the filter and before the throttle body. Disconnect the battery (which will allow the codes to reset) and unplug the MAF. Spray the elements that stick out and look like little exposed wires with the cleaner and let it dry. Put the sensor back in the car and take a minute to look for a vacume leak AFTER the MAF. Another thing that can cause those codes is unmetered air that is getting in behind the MAF so the car can't compensate for fuel.

Look at the intake tube and connections into the throttle body which will be on the front of the manifold under the silver engine cover. Look for tears, rips, disconnected tubes etc. If you find anything, fix it, if not put the sensor back in the car and connect the battery. See if it is running better after 10 minutes when the car hits operating temp and starts reading the MAF sensor. This will require basic hand tools like a screw driver or 10mm/8mm sockets etc.

I wouldn't assume your problem is 02 sensor related because both are setting the code and that almost never happens. If the codes come back look on EBAY for a MAF for the car (most MAFs from a given year from GM are the same even if they don't say so).
 

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05 sts
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I agree with all the above try all the fixes and if still does not work properly go on ebay and buy a new or slightly used engine for 1500.00 to 2500.00 and drop it in for about 700.00.Its less than 5700.00.
 
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