Hi all, new to the Forum and this '99 Bonneville. Actually it's my son's car.

Just started having drivability issues which we half cured with a new fuel filter. It would chug and hesitate on acceleration to the point it was undrivable. Sort of like when an O2 sensor goes bad. It still hesitates a bit but at least it's drivable now.

The problem is that now there's no power... for a supercharged car it should and used to have all kinds of power. More than a 16 year old needed at the time.
He called me the other day from the expressway saying it would not "go". Floor the Go-pedal and nothing. He admitted that it started when he turned on Performance Shift.

So a day later I drove it and it was OK. No coughing, bucking....but NO power. No downshift when it was floored either. The car just accelerated like an 80hp Honda. Then after a couple miles it bucked and coughed and almost stalled. We replaced fuel filter and that issue seems to be gone but it won't downshift or accelerate like it should anymore. While he was driving I shifted it from D to 3rd and there's no difference. He says it never did but I expect at least a little RPM change.

So, I'm chasing a ghost. Is it the tranny, fuel pressure regulator, clogged injectors, etc. There is no coolant or fuel in the oil. It doesn't use coolant. I get no codes other than the destroyed catalytic converter P0420. The car has always had that code for more than a year
I can't help but think that the trans has an issue now that he played with Performance Shift. Solenoid bad, etc.

I guess I'm not allowed to attach pictures...bummer. There's two ports on a sensor at the right, front of the engine. One has a vacuum hose going to it on the left side, the other port directly above it has what looks like a sponge filter over it. The sponge is gone now after 190,000 miles. Did or does the other port get a vacuum hose? Or is it just supposed to be filtered with that sponge crap?

And where the heck is the fuel pressure regulator?? Is it at the right\rear of the engine protected by a metal can, or is it at the front on the fuel rails somewhere?

We haven't driven it enough to set anymore codes. Maybe 10 miles. The P0420 should set soon. I'd think there would be an O2 sensor code if it was that. Maybe I'll take the MAF off and clean it next. I don't have a noid light.

Thanks for any tips.

It could be that the cat is clogged or your fuel pressure is low because of either the fuel pump or regulator.

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WHITE WHINE - 1992 SSE Supercharged 236.26 ci (.040 Over) 15.090 at 90.2 MPH on old engine w/ slipping trans & melted O2 sensor - Gen 3 M62 and matching TB, Gen 2 Pully, Zillamotorsports Ported LIM, YT 1.72 Roller Rockers, SII FPR & Injectors, Hypertech Thermomaster chip w/ 160 Thermo, TransGo Shift Kit, Infinity/Pioneer Speakers & a 10" Alpine Type R Sub, all the watts, 140 amp Alternator, Ricepipe CAI w/ heatshield, Pilot Angel Eye Foglights, Clear Corners, '02 17" Chrome Bent 5's, Magnaflow F-Body Muffler and Hi-flo Cat, Ceramic Coated Ported Exhaust Manifolds, Fan Override, Monroe Reflex struts, red calipers
2009 G8 GT - Sport Red Metallic, loaded, SOLO Axlebacks, Rotofab Intake, Tuned, autodim mirror, removed intake manifold cover, HSV GTS triple gauge pod, two tone red-hot shifter and HSV SuperSport steering wheel, GXP rear sway bar and diffuser, 3.45 diff and various Camaro suspension bits, LED Taillights