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Discussion Starter #1
My 97 Deville Concours (300hp Northstar engine) has developed some symptoms my local mechanic can't diagnose and don't show up on a scan for trouble codes. It has quite high miles (over 150K) but the compression is decent. When it's running, it seems to run fine. However, it has become a little hard to start and apparently won't pass smog in its current condition. It has the typical oil leaks (probably from the case halves?) but no other obvious signs of problems. Plugs and wires and all oxygen sensors have been changed relatively recently. Worst case, I've been thinking of rebuilding or replacing the engine, mostly because of the miles and oil leaks, and now, because of this problem. but I don't want to do that if that doesn't address the other symptoms. Any suggestions? My next step is to try the dealer.
 

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2005 CTS-V, 1994 Infiniti Q45
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Sounds like a fuel pump related issue..... If the pump is overly noisy, then its going bad..... At 150k, it doesnt owe you anything.......
 

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Discussion Starter #3
elwesso said:
Sounds like a fuel pump related issue..... If the pump is overly noisy, then its going bad..... At 150k, it doesnt owe you anything.......
OK, I can check that. I don't recall it being noisy. I can understand how a bad fuel pump would make the car hard to start but I'm not sure I understand how it would affect the emissions?
 

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1968 Cadillac Sedan deVille, 1994 Chevrolet G20
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It's a bit of a stretch, but maybe it caused your car to run lean and cook the cat.
 

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DaveSmed said:
It's a bit of a stretch, but maybe it caused your car to run lean and cook the cat.
Another good idea to check on and I will. My past limited experience with bad cats is that once they are fried, they tend to clog up and noticeably affect both starting and running, at least until they cough up all the inerds of the cat out the tail pipe. Then, free of all restrictions, they turn into what my muffler guy calls a "performance cat."
 

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Usually when the fuel pump goes bad it makes the engine run really rough and misfire.....

If the O2 sensors are working halfway decent, the computer will lengthen the injector open time, so it wont run overly lean......

And usually, the cats fail when the engine misfires due to running too rich.......
 

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I've seen new cats make an amazing difference in emissions.
It would probably be worth it if everything else checked OK.
Did your mechanic do a compression test? Enough miles on engine to justify it.
 

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Discussion Starter #8
zonie77 said:
I've seen new cats make an amazing difference in emissions.
It would probably be worth it if everything else checked OK.
Did your mechanic do a compression test? Enough miles on engine to justify it.
Yes, the compression checked out OK. Also, I just talked to him and he checked the fuel pump and catalytic converter and both are fine. The car will drive down the highway without any problem at all but is missing and running a bit rough at idle.
 

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ianr57 said:
Yes, the compression checked out OK. Also, I just talked to him and he checked the fuel pump and catalytic converter and both are fine. The car will drive down the highway without any problem at all but is missing and running a bit rough at idle.


have you checked the fuel pressure regulator? have seen them go bad. would give you hard starting because fuel leaks past the diaphram and into the intake. high emissions beacuse of excess fuel. just a thought, hope you find the problem
 

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I agree..... Another good possibility........
 
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