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Surging update


PAUL T

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To update everyone, On my 94 Concours, I have a surge or chuggle on light acceleration. I have change plugs and wires, fuel filter, air filter, cleaned the phenolic plates, replaced a cracked vacuum hose, checked the EGR valve, checked the fuel pressure(not while running), checked the FPR, misted the wires, all to no avail. The only codes I have been getting is P074 occasionally and P071, never at the same time. I have checked all the grounds except the one on the passenger side on the engine next to the firewall, I have not figured out how to get to it. My next plan of attack is to clean the EGR and the throttle body. Should change the MAP sensor? could it be causing the problem or is it a false reading due to something else? Am I doing something wrong? I plan on checking the plug wire resistance when the weather breaks. I have read about a service bullutin about changing the PCM? This is really frustrating me to the point that I am leaning toward trading her off for a newer Deville, but I really can not afford it right now.

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... I have read about a service bullutin about changing the PCM? ...

Can you please give a refference or link about PCM change service bullutin?

I don't think your problem some how connected to bad PCM. I fixed other problem on my 94' STS by PCM changing, so I'm interested to know if that was a famous problem.

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For a little more on the diagnostics side, I have placed a couple of the service manual pages for P071 and P074, on my web storage site. (see below for link)

For P071 you will need a way to apply vacuum to the MAP sensor after removing the intake COVER; a small hand pump with gauge is all that is needed.

For P074 just use the diagnostics from the dashborad.

Diagnostic pages for P071 and P074

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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I have always attributed surging to a vacuum leak. Just a thought here but you didn't mention the PCV. Is the seal tight where it plugs into the cam cover?

I have check the PCV lines and the PCV. I thought it too may be a vacuum leak. I was worried when I cleaned the phenolic plates that maybe I did not get them seated right but I pulled the intake manifold and rechecked it 4 times, finally I added black RTV to the gaskets for piece of mind. I also thought maybe I pulled a vacumm line loose when taking out the intake, but I have checked and double checked and can not find an unhooked connection. I have used the trouble shooting charts in the manual to the point that I am capable of checking, but can not get one to tell me to change something, they just keep me searching for another chart. I am leaning toward a bad (new) spark plug wire. I have checked the routing of the wires more than once. It is really frustrating.

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