3800 Regal owners

[troy1]

Originally Posted by bnaylor3400

You forgot the banghead smilie..lol. Seriously, if I were in your position I'd probably run that vaccum test while on the road. I did a similar test with a fuel pressure gauge and taped it to the driver's side wiper.

There is one other test that can be run on the exhaust system to test for backpressure or CAT acting up but it is a real hassle. The dealers normally have the test fixture or check with any mechanic friends. One can be fabricated if you are willing to go through the trouble. The test is run with a 0 - 5 psi low pressure gauge. A connector (tee) is needed where bottom is male thread 18mm X 1.5mm pitch and the top is female 18mm X 1.5mm. It has to have a fitting to connect the gauge. The fixture is threaded into the front 02 sensor bung and the 02 sensor is threaded in at the top. Engine is warmed up and brought up to operating temperature. Then rpms are taken up to 2000-2500. The gauge should not read greater than 1.25 psi.

The CAT is still a possibility and under "poor fuel economy" it is near the top of the list in the GM service manual, especially with all the other tests passing.

You said the CAT was near the top of the list what other things are at the top with no SES. oh by the way I ordered a downstream delco O2. oh I got 24MPG today 137miles round trip 5.7 gals at fill up thats on 55 & 65 mph roads 20 miles of 80mph on the interstate 25*F.

[BNaylor]

Originally Posted by troy1

You said the CAT was near the top of the list what other things are at the top with no SES. oh by the way I ordered a downstream delco O2. oh I got 24MPG today 137miles round trip 5.7 gals at fill up thats on 55 & 65 mph roads 20 miles of 80mph on the interstate 25*F.

02 sensor(s)
EGR valve
ECT (Engine Coolant Temperature) sensor out of calibration - thermostat
Dirty or clogged fuel injector(s)
Spark plugs and/or wires
Torque Convertor Clutch (TCC) operation
Vacuum leak
Fuel pressure
Air intake system leaks
MAF sensor
Ignition control, timing, and knock sensor
A/C in full time operation
Engine compression

It doesn't differentiate with or without SES light.

[troy1]

Originally Posted by bnaylor3400

02 sensor(s)
EGR valve
ECT (Engine Coolant Temperature) sensor out of calibration - thermostat
Dirty or clogged fuel injector(s)
Spark plugs and/or wires
Torque Convertor Clutch (TCC) operation
Vacuum leak
Fuel pressure
Air intake system leaks
MAF sensor
Ignition control, timing, and knock sensor
A/C in full time operation
Engine compression

It doesn't differentiate with or without SES light.

EGR valve >>>>>>>>>>>>>>>Checked operated correctly

ECT (Engine Coolant Temperature) sensor out of calibration - thermostat

Checked new 195*f stat>>

Dirty or clogged fuel injector(s) >>LTFT/STFT were ok super junk added to fuel tank

Spark plugs and/or wires >>NEW NGK plat. plugs/delco wires/delco coil packs

Torque Convertor Clutch (TCC) operation >>I would of felt dumb

Vacuum leak >>>>>>>>>>>>visual and propane check

Fuel pressure >>>>>>>>>>>>In specs

Air intake system leaks >>>>Tested with propane around UIM

MAF sensor >>>>>>>>>>>>Checked dont know what they did to it

Ignition control, timing, and knock sensor Did not check timing/Ignition module

A/C in full time operation>>>>Not in full time operation

Engine compression >>>> Did not check

O2 sensor (s) >>>>>>>>Said were OK
HUH

[troy1]

Got a new toy on the way! backpressure tester! So it should be no more than 1.25psi BEFORE the cat?

Troy

[BNaylor]

Originally Posted by troy1

Got a new toy on the way! backpressure tester! So it should be no more than 1.25psi BEFORE the cat?

Troy

Great. From what I understand no greater than 1.25 psi but that is an upper end tolerance. A lot lower would be better. The Regal will have a different result because it is single exhaust all the way out to the tailpipe whereby your GP GT has the split duals after the resonator.

Let me know how the test fixture works out because I might get one. I'd like to do some testing for more exhaust modifications in my GTP. Good luck!

[troy1]

Originally Posted by bnaylor3400

Great. From what I understand no greater than 1.25 psi but that is an upper end tolerance. A lot lower would be better. The Regal will have a different result because it is single exhaust all the way out to the tailpipe whereby your GP GT has the split duals after the resonator.

Let me know how the test fixture works out because I might get one. I'd like to do some testing for more exhaust modifications in my GTP. Good luck!

Will do I got it through a local parts store if I like it I'll give you the brand name.GP should have less PSI thanks to the dual exhuast I would think. If its above 1.0 PSI the CAT is going in the scrap pile.

Edit for type-o 2.0 change to 1.0

[katana1981]

Since I changed the CAT, at average speed of 65 mph, my car is doing 34 mpg on the road and 27 mpg in the city

[BNaylor]

Originally Posted by katana1981

Since I changed the CAT, at average speed of 65 mph, my car is doing 34 mpg on the road and 27 mpg in the city

Man, I love success stories.

[troy1]

Thats great! I hope I find out whats wrong with mine soon 22-24 sucks for all hiway.

also is 1.25psi based on the regal Bob?

[BNaylor]

Originally Posted by troy1

Thats great! I hope I find out whats wrong with mine soon 22-24 sucks for all hiway.

also is 1.25psi based on the regal Bob?

I hope so too.

That figure is directly out of the GM Grand Prix Service Manual.

Good luck!

[troy1]

Well got the gauge today backpressure barley comes off of zero, needle shakes alot while testing. One thing I did notice was I have oil sitting down on the lower intake by the injectors on the firewall side of the engine. UIM/LIM problem? or just the valve cover leaking. Took a trip out of town this weekend going there couldn't get to 24.5mpg @ 80mph reset the trip computer with out filling (not completely accurate) on the way back dumb thing never got less that 26.9mpg @ 80 mph all the way. usally it drops like a rock to 22/24 at stays there. Keep inmind that I do not rely on the trip computer just using it as a "gauge" and I always calulate it out. My average is probably 18/21mpg but thats alot of intown driving. Tried using the whole tank I tried some BG 44 fuel system cleaner @ $18 a can. I'll I have to say is HUH!!

Troy

[BNaylor]

Originally Posted by troy1

Well got the gauge today backpressure barley comes off of zero, needle shakes alot while testing. One thing I did notice was I have oil sitting down on the lower intake by the injectors on the firewall side of the engine. UIM/LIM problem? or just the valve cover leaking. Took a trip out of town this weekend going there couldn't get to 24.5mpg @ 80mph reset the trip computer with out filling (not completely accurate) on the way back dumb thing never got less that 26.9mpg @ 80 mph all the way. usally it drops like a rock to 22/24 at stays there. Keep inmind that I do not rely on the trip computer just using it as a "gauge" and I always calulate it out. My average is probably 18/21mpg but thats alot of intown driving. Tried using the whole tank I tried some BG 44 fuel system cleaner @ $18 a can. I'll I have to say is HUH!!

Troy

Was the gauge a 0 - 15 psi? It sounds OK to me even with the fluctuation.

When you get that oil sitting in those spots it is normally a valve cover gasket even though it may look like the source is the manifold. I've had to replace the valve cover gaskets on both the GTP and Regal LS for similar plus seeping down the block. The valve cover gaskets start heading South around 70K miles.

Did you ever get and try the 02 sensor? 26.9mpg @ 80 mph doesn't sound that bad now. That's about 457 miles on a tank of gas which is pretty close to normal.

[troy1]

I've got it but no time to install ! Filled the car up today after running that can of junk through it 293.1 miles 14.16 gals 20.6MPG 106miles are hiway. Maybe I got some bad gas this all happed after Katrina and it gummed stuff up I think the gauge is a 0-5 psi its got marks a 0 1.25 2 & 3 but it shakes so rapidly kind of weird. I guess I'll see what this tank does. right now its 21.6. It does not seem that I have to have my foot into it as much.

Oh its a STAR brand gauge

[troy1]

Well I'm almost convinced that I had dirty fuel injectors. Its been a few days now, going 70 the computer says 28.2 mpg which is excellent. I have not had a good long trip yet but the results so far are good. Also I did get the new downstream O2 installed also but the mileage was on the way up before that. So If anyone wants to try what I used it was BG 44K fuel system cleaner $18 a can. I will keep everyone posted for a while with my mileage. Just maybe it will help some else with crappy MPG.

Troy

[BNaylor]

Originally Posted by troy1

Well I'm almost convinced that I had dirty fuel injectors. Its been a few days now, going 70 the computer says 28.2 mpg which is excellent. I have not had a good long trip yet but the results so far are good. Also I did get the new downstream O2 installed also but the mileage was on the way up before that. So If anyone wants to try what I used it was BG 44K fuel system cleaner $18 a can. I will keep everyone posted for a while with my mileage. Just maybe it will help some else with crappy MPG.

Troy

Probably more than that. The BG 44K also cleans all the carbon off the valves and combustion chambers. I've heard people swear by the stuff but most claim about a 1 -2 mpg improvement which in itself is better than nothing.

Our local Indian Tribe sells BG products at their convenience store chain. Better price than the dealers that carry it. I'll try some in my wife's Regal LS. Maybe I can get it up to 30 mpg highway.