opinions please

[umina]

Hi, so my saga continues, but I've narrowed it down, rather I know what its not. I replaced my fuel pressure regulator to solve the problem of the car starting and then dieing and long crank times. I replaced the MAF, TPS, IAT, and IAC motor. Tonight I replaced all 6 plugs and wires using autolite double platinum plugs. No check engine light, car still starts and idles great, but runs and drives like crap until either

A. I unplug the MAF
or
B. I unplug the EGR electrical connector

Of course having either one of these sensors unplugged triggers the CEL in the car until plugged back in. I did fuel pressure test and it is correct at prime and when running. Also hooked up a vacuum gauge to the throttle body and vacuum is correct as well.

Is there some other sensor I'm neglecting to check that would control fuel mixture? With everything plugged in as it should be, CEL goes out, and when you step on the gas, there is no response from the engine when in drive. It makes this bogging noise, almost like the timing is being retarded by the computer, and accellerartes VERY slowly. Even if you floor it, the car will downshift and RPMs will go up but there is no power getting to the wheels. Once one of the two aformentioned sensors is unplugged it runs and drives normally. When the AC is on, it loses a chunk of power too so I know running rich is only helping it, but is not the solution. When load is placed on the engine it just gets no power, thought it never dies or stumbles.

What else can I check??

2001 Buick Regal LS, 141k miles.

[BNaylor]

Have you tested the CAT converter or ever replaced it?

[umina]

Whats a good way to test it? I did a vacuum test on the throttle body and and it showed normal. Is there a definitive way to test it other than that? I tried to disconnect the crossover exhaust pipe that goes over the tranny, but it would not seperate and only let a little exhaust gas out. I don't wanna shell out for a converter on a whim that it may fix it. I saw you can get the OEM part with complete pipe and bend for $160 + shipping off ebay and it looks like its just 4 bolts to swap it out. Or Ican go for a $50 one and have it welded in at a shop someplace. Whatcha think?

What about an O2 sensor, could it cause this and not throw a code?

[BNaylor]

Yeah that is a weird problem since it appears to be normal with either the MAF or EGR connectors off.

Best way to test the CAT is have a muffler shop run an exhaust backpressure test. They use a special fitting at the front 02 sensor and air. Specs are 1.0-1.25 psi. Nothing wrong with using an aftermarket CAT converter due to cost. I run one on my wife's '99 Regal LS. Came out to $90 with hi-flow CAT converter and install. It has been installed for about 50K miles now.

I doubt the front 02 sensor is the issue 'cause when you accelerate the PCM switches to open loop mode and disregards or inhibits 02 sensor input.

Did you check for any relevant ignition, PCM or emissions control fuses blown at the engine compartment and passenger side dash fuse boxes?

[umina]

hmm, havn't checked the fuse box, I'll look at that tomorrow. I noticed today that my garage smells like eggs/sulphur. This pretty much points to bad Cat I think. Or could it be because I've been running for a week or 2 with the EGR unplugged?

[HotZ28]

Do you have access to a scanner? The MAF you replaced, was it a rebuilt unit? I assume the loss of power happened after replacing the MAF, TPS, IAT & IAC? Did you replace all of these at the same time?

[BNaylor]

Could be a bad CAT. Also, a high sulphur smell can be the result of the brand gasoline you are using. What brand gas and octane level do you use? The 2001-2002 Regals do have a known issue with the CAT converter. GM sent out advisory notices to all owners. I received one for my GS. The CAT warranty was extended but based on your mileage you are out of the mileage window. See link below posted at our Tips & Maintenance forum.

Click here

You may have more than one problem but I would not rule out the converter.

[umina]

I began replacing the sensors to try and solve the power issue. I know the parts were good because I actually pulled them all off my 2000 Grand Prix GT that has half as many miles on it and runs great. I put all the Regal sensors in the Grand Prix and it still runs great. So at this point the only things I have not replaced are the O2 sensor(s). I pulled the one at the firewall when I did the spark plugs (had to to get the last plug out), and it was powdery yellow/white. Is this what it should look like? I get no CEL but an O2 sensor can still go bad with no CEL I think.

[BNaylor]

The best way to check the pre CAT 02 sensor is with a DMM or full function scan tool. Check the output at the purple wire. Look for .1 mV to .9mV and it will be changing. Make sure the engine has fully warmed up and the PCM is in closed loop mode. The other way is with a full function odb-ii scanner and check the short and long term fuel trims. An 02 sensor can be degraded or slow and not set any DTCs or trigger the SES/CEL light. The post CAT 02 sensor monitors CAT converter efficiency and may not trigger the P0420 DTC even if the CAT is clogged.