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Park Avenue Bad CAT? EGR?

I have an '01 Park Ave that recently hit the 220k milestone. On my way home from work yesterday, I was feeling random hesitation, as on the way to work and to lunch. The car died, and now it won’t start. A bit of backstory:
I’ve had P0404(EGR) and P0440(EVAP). I searched for that problem for like a year, but eventually gave up. It didn’t affect the drive, so I left it alone. During my attempts, I replaced the Electronic EGR with one from RockAuto. I learned shortly after that rockauto has a bad case on EGRs and my codes remained. No driving issues though. After last night’s hesitating episode, I scanned the car and found P0404,P0440, P0403(EGR), P1404(also EGR). I unplugged the EGR and it seemed to drive fine. In fact, it drove so well that I decided I would indeed take it to lunch today. All was well and then it died in the drive thru out of nowhere. Wouldn’t start back up. Plugged the EGR back in, still nothing. Diddly freakin squat. I looked at some other threads, and I suspect the CAT is plugged up. With work, I don’t have a whole lot of time to look at a million variables. Can anyone tell me what to search for? What to try? It seems to me that if the problem persists with the EGR unplugged, it must not be the EGR, right? Thanks!

Your car is telling you that there is a problem in the EGR circuit. Your symptoms match certain issues with the EGR. Please explain how you made the leap to the catalytic converter with absolutely no evidence.

https://www.obd-codes.com/p0403

Simple, I tried talking to other people and mechanic friends who mentioned that it could be throwing false codes. They also said the hesitation actually felt like back pressure when they rode in with me, and said to look into the CAT which I’ve never had to work on before. That’s why I’m asking how I should approach diagnosing this issue. No evidence? I’m trying to search for evidence. How can I determine if either of these are at fault?

Bad cat as in clogged? You could check for that by unscrewing the pre cat oxygen sensor, removing it, and test driving the car. The exhaust will flow out of the hole the oxygen sensor was screwed into. The car will be loud, but the power should be back if the issue is a restricted exhaust due to a blocked cat converter.

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If the EGR got stuck in the open position it could mimic the drivability problems you’d notice with a plugged cat. A fully stuck open EGR valve could prevent starting. The EGR valve on your engine isn’t just either on or off. It’s more like a garden hose valve, can open to provide varying amounts of flow. As you drive it is commanded by the engine computer to open whatever is needed to keep the internal cylinder parts from overheating and the nitrogen emissions within limit, while still providing good engine performance. Your EGR codes are saying the computer is commanding the EGR to open a certain amount, but its EGR position sensor (which the computer reads) is saying it is not opening that amount, but instead some other amount. If you want to try something yourself , replace the egr valve. It looks like a pretty simple job, but the part is somewhat expensive, $350 or so. There’s other possibilities, for example the valve is ok but there’s a problem in the wiring between the valve and the computer. With modern cars you can run out of money replacing stuff, because the average diy’er has more ideas of things to replace than they do money and time. The best way to solve this is to get an assessment from a shop having the Buick scan tool, one that is able to display the egr feedback signal as the valve is commanded to open to various amounts.

The evap code is probably unrelated to the egr codes. The computer tests the fuel tank to make sure no gasoline fumes are able to leak out and pollute the atmosphere. It does that by closing all the valves once in a while, and pressurizing the system to a fixed pressure, then monitoring the pressure to see if it changes over time, indicating a leak. There’s a remote possibility a vacuum in the tank is forming & preventing fuel from flowing to the engine, but that’s pretty unlikely. If the engine performs better w/the gas cap ajar, that could mean a vacuum is forming in the tank for some reason. More common causes for a large evap leak code is an evap hose that has sprung a leak or fallen off its fixture, or a problem w/the purge valve or a fuel tank valve. Faulty fuel tank valves seem to be the most common cause.

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They’ve got the egr valve listed for about $43 on A1 Auto. OEM (Delphi) looks to be around $100. It appears to be the same part as on my 05 Lesabre. Mine malfunctioned, and caused a check engine light and eventually caused a little off idle hesitation. I swapped in one from a junk car and it solved the problem, so I got lucky.

It would appear making a block off plate to block the ports off where the valve mounts would be pretty easy. You could probably even use just thick paper gasket material temporarily. Basically make a gasket for the egr valve, minus the holes for the port(s), remount the egr valve over the portless gasket, and leave the valve unplugged. If the car runs well with the egr valve unplugged and blocked off- you know the driveability problem lies within the egr system. Nobody else here probably does hack stuff like that, but I’d like to be certain before laying out the cash for the part. You won’t hurt anything by temporarily deleting the egr valve for testing. All it does is allow exhaust gas back into the intake to re-burn during certain portions of the drive cycle. Failing open, it will allow too much air into the intake at the wrong time, like at idle. This will be similar to a vacuum leak. If it failed closed, you’d probably never notice anything but the check engine light.

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Before your cat would clog up, you would have been getting a P0420 and/or P0430 codes. If you didn’t get those, your cat is OK.

$100 for an EGR valve that is indicated by the codes and symptoms plus an hour of labor vs over $1000 for a new cat with no evidence that it needs one? No brainer to me.

Do I have to do this “evidence” crap with you again? Turns out my head gasket blew so bad my car won’t start. Codes can be false, but they leave a trail. “No evidence” doesn’t mean no faults. Geez, guy!

He was asking for evidence pointing to a possibility of cat failure. There is no evidence in any of your posts of cat failure. This quote you gave gives no such evidence as you can’t isolate cat failure by “feel”. Please calm down. People here are only trying to help with only the information written.

How did you determine that?

I had used the information that the nice guys gave me, but I couldn’t find anything wrong yesterday. I gave in and went to a mechanic who had some spare time. I showed him the post, he said “f*ck Keith” and is doing the job no labor charge. He found that the coolant was low and mixing with oil, I must’ve been burning it for a while. See, it doesn’t take evidence to draw a suspicion. Don’t treat your OBD like an honest mechanic.

I had an EGR code on my Olds (at the great car lot in the sky now). So the shop put in a new $500 EGR. Same problem. Had it to the dealer and they tried to clean the passages but said to go any further would require pulling the transmission to get at them. So for the last three years or so I just had it unplugged. Ran fine but the engine light was always on. If I plugged it back in, the engine would run rough for a few miles, then it would shut the EGR off and the light would come on. Not worth fixing but it was the passages that needed cleaning out not the EGR valve itself.

It seems odd that a compromised head gasket would result in an egr pintle position error code. But if the head gasket’s blown, that has to be fixed before other diagnosis can ensue, so OP is correct to get that work done.

Just curious OP, why is your mechanic willing to replace the head gasket with no labor fee?

Isn’t it odd? I can only think the coolant smoke would have something to do with it but even then. When I removed the egr, it seemed completely fine. Pintle moved with ease, it wasn’t really even that dirty. I would hate if after all this, I still had an EGR code.
Honestly I’m not sure. He quoted me a week on repair. I’ve been to him a couple of times, but usually been scouting other shops(if I’m not working on it myself). Maybe he’s just trying to bring a customer? Wouldn’t know. I’ve had tire shops do that for me before. If this guy does a good job and I don’t see any “rig-to-die” like I have in the past, I might just start seeing his shop

I hope you have the work order in writing because I can’t see anyone doing this kind of work for free .

For sure. This one shouldn’t be too bad, I’ve personally done a head gasket on a 3800 before as well. I just don’t have the time now with my current job

Here’s a word of warning.

If you don’t know how long the coolant has been mixing with the oil, then it might be too late.

I’ve repaired engines under these conditions, and more often than not, the engine failed a few months later because of bearing damage.

And yes. I warned the owners.

Tester

I’ll keep that in mind, thank you. I should find out soon if I destroyed it already. Hopefully not. Otherwise, I do have another Park Avenue for a while for work. If I had to, it’s open for me to buy from my buddy. It was a project of ours last summer, so I know if it’s condition, and it’s got decent miles

Is there a way I can inspect it for that kind of damage?

Drop the oil pan and remove the bearing caps.

But that doesn’t tell you the condition of the cam shaft bearings.

Get it?

Tester