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Strange engine drivability issue

buickman104

buickman104

New member
My car has 207k on the clock. Maintenance is all up to date. A few months ago I started with a weird issue where I would be at cruising speed 40 to 50 MPH and suddenly the engine started feeling rough and I got a vibration from the engine that would lightly even rattle the dash. I let my foot off the gas and then lightly get the rpms back to speed and back to normal. The problem was pretty rare, but started becoming more and more common about 2 weeks ago.

What I noticed on my aeroforce is that as I am cruising and as the vibration/roughness develops my timing advance drops into the single digits and stays there until i take my foot off the gas. I get 0 degrees of KR throughout this process unless instead of taking my foot off I put my foot down to try to accelerate. Then I get a over 9 degrees of KR. I also have been getting the p0300 code for random misfires. My vacuum lines are all good, played musical coils and ICM is good. The only thing I can imagine is that my fuel pump is dying out as the issue has become more prevalent as of late. I would like to know if any member has had a similar issue or has a better idea of what the issue might be. My worst fear is that I change the fuel pump for an OEM Delco unit and I still get this issue. Please let me know what you guys think.
 


How are the plug wires? I'd look to see if anything is hitting, that's a pretty easy area to get vibration in based on being in 4th with lockup.
 
The plug wires are brand new. I've played with switching them out between my prj and brand new Napa set, with no change. I also thought it might be a vibration stutter. So I have played with the shifter manually putting it in second and 3rd gears and it still does that weird thing with the timing and vibration.
 
I thought about that too, but I have been monitoring missfires while driving on the aeroforce and don't get any while the timing is in the single digits. Also took a listen with a stethoscope and they sound fine at idle.
 


I've had this before but not on a W-body. Turns out it was a trans issue/shudder. Think the trans was on the way out and it was slipping while shifting up or the T/C was having issues. Never heard the resolve on it other than the guy replaced the trans. I know you said you tried manually shifting it but thought I'd throw it out there.
 
Yeah, in the back of my mind I had a feeling it was either a trans or a fueling issue. I am not getting any transmission codes. The fluid level is fine and it doesn't smell burnt. Are there any tests or parameters I should be looking at with a scanner to confirm it is the trans?
 


Just wanted to update on this issue for the collective forum knowledge. When I bought the car in 2011 I changed the fuel filter. I decided to change it again because my fuel pump was pretty loud.

The old filter was clogged and now this problem is resolved and my fuel pump is quiet again.

Spark notes: if you are having some driveability issues and your fuel pump is loud; then change the filter!
 
I haven't had this problem (yet?) but thank you for updating us! That's a simple solution to a difficult-to-diagnose problem.

Thanks again!

P.S. It took me a 4 foot breaker bar with an additional 4 feet of OSHA-approved torque multiplication tube (rusty steel pipe lol) to break my old fuel filter loose back when I replaced mine :D
 
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