Log in

View Full Version : Weird running condition.



Sully008
05-30-2023, 12:33 PM
Hey everyone,


Not sure how to explain this, but I’m having an issue with my car that popped up late last year before I put it away for winter. It’s come back now that I’m driving it again.


Usually, when I first start the car, everything’s fine. Fuel pressure is good, oil pressure good, temp good, idles fine.The car sounds and runs great. But after driving for ~10-15 mins., the exhaust note changes, it gets deeper, the car feels sluggish, and it almost sounds like there might be an exhaust leak happening. Also a bit of rattling from somewhere under the car that I haven't been able to pinpoint. Doesn't matter outside temp either (started doing it late fall, still does it now with warm weather).


All vital signs engine wise still appear normal (as noted above). The engine itself sounds fine. No weird noises, no stumbles, misfires, etc.


I’m leaning towards bad/plugged catalytic convertor, or bad o2 sensors, as the car is exhibiting some of the symptoms of those, but I’m not sure…

I did maintenance this spring (new plugs, changed oil, filter, cleaned air filter, cleaned MAF sensor). Did a full change of transmission and rear gear oil about 3 years ago.


The car’s been s/c’d for the last 13 years, almost 95K kms. on it. Magnaflow hi-flow cats have been on for at least 10 years, original stock o2 sensors.


I have the Xcal3 that came with the Trilogy that I could data log with, but what should I be monitoring? If you need more info, please don't hesitate to ask.

TIA,

mustangeddie
05-30-2023, 03:50 PM
Without seeing it judging by the noise & exhaust tone you've probably melted the cats & they are coming apart inside causing the rattling.

Sully008
05-30-2023, 07:45 PM
Thanks for the reply. Forgot to mention there's no check engine light. Yet. I've decided to garage her again until I get this sorted out. Hopefully I can get it to the shop in the next week or so.

rkk
05-30-2023, 08:46 PM
Not sure if this is your case but when I had an exhaust note change around 82,000 miles, my right rear axle went south. Although when this happens you would see differential fluid in the wheel fender well. This was an issue with early 2003 models as the "soft axle issue(s)". Are you 2003 or 2004?

Sully008
05-30-2023, 09:07 PM
Car is a 2003. I had the axles looked at when I first got the car.No fluid in either wheel well.

burt ragio
05-31-2023, 05:16 AM
Maybe while in storage a rodent nested in your exhaust.

Sully008
05-31-2023, 08:01 AM
Maybe while in storage a rodent nested in your exhaust.

Possible, but it started last fall before putting it away for storage.

1Marauder
06-02-2023, 04:13 PM
Clean Maf, check all intake, look for any leaks on intake? Fuel filter-pump?

Sully008
06-02-2023, 08:42 PM
Clean Maf, check all intake, look for any leaks on intake? Fuel filter-pump?

I cleaned the MAF, and reconnected all clamps. Fuel filter was changed a few years ago. Stock pump still. Fuel pressure good at around 40psi. No drops.

Sully008
07-24-2024, 03:21 PM
Hello everyone,

Just wanted to update this thread. I finally brought the car down to the shop to have it looked at. What they found was the nuts/bolts connecting the headers to the cats worked themselves loose and there was a gap. :rolleyes:

New hardware, installed new O2 sensors while it was up in the air, and we're back in business. Not sure why I didn't see the loose hardware when I was under there changing the oil. Oh well, I'm just happy it wasn't anything major.

1Marauder
07-26-2024, 01:38 AM
Great news. Thank you for closing the loop and letting us know!