3800 Regal owners

[troy1]

What are you guys getting for gas mileage?

[maxwedge]

98 Lumina 3800, now when it is 10 degrees 18-19 short trip. 25 long trip, good weather 29 hway. at 135k now.

[troy1]

my 99 pontiac GP 3800 only can get 23.2 mpg should get better than that I would think kinda got me stumped. whats your Lumina got for gearing? my GP has the 3.29 regals have the 3.05 I think

[BNaylor]

'99 Regal LS (112K miles). Gets 22 - 23 in city. 28 highway. Over 450 miles on 17 gallons on a long distance trip.

The Regal LS has RPO option F83 which is 3.05:1 gearing.

[maxwedge]

Lumina LTZ has 3.29's, mileage difference with these diff ratios would be negligible, I also have aggressive sno's on in the winter.

[troy1]

Heck its 35*F here the only way I could get above 24 is if a strong wind is pushing me along. here is my post on the pontiac forum:

Mileage issue when I fist got to car was good been declining lately Its got a new Air filter plugs wires coil packs (terminals rusted) fuel filter new tires as of yesterday (plus one rim) new upstream Borg O2 sensor. PCM update. The only thing this car does on take off when say about 170/180*F you can feel the engine hold back slightly barely notice jerky acceleration. TCC locks up good and so on. Dang thing just should get better gas mileage than what it does. Even going 65 I can't hit 28MPG when I first got the car it was 30mpg. The only thing I can think of is maybe the cat is getting plugged. Gas I get it from a couple different stations so that shouldnt be an issue.

[oldreese]

'01 Regal LS, 29.8 highway, 24.2 city.

[BNaylor]

Originally Posted by troy1

Heck its 35*F here the only way I could get above 24 is if a strong wind is pushing me along. here is my post on the pontiac forum:

Mileage issue when I fist got to car was good been declining lately Its got a new Air filter plugs wires coil packs (terminals rusted) fuel filter new tires as of yesterday (plus one rim) new upstream Borg O2 sensor. PCM update. The only thing this car does on take off when say about 170/180*F you can feel the engine hold back slightly barely notice jerky acceleration. TCC locks up good and so on. Dang thing just should get better gas mileage than what it does. Even going 65 I can't hit 28MPG when I first got the car it was 30mpg. The only thing I can think of is maybe the cat is getting plugged. Gas I get it from a couple different stations so that shouldnt be an issue.

How many miles are on your car? Is the CAT convertor the original? At approx. 82K miles the gas mileage on our Regal LS got as low as 18 mpg city. The acceleration would surge (up and down) and feel jerky. GM's CAT warranty had expired. I replaced the CAT with a Magnaflow Hi-Flow CAT off of EBay. Cost was around $60.00 with shipping. Had a mom & pop muffler shop install it for $40.00. The gas mileage went back to what we were used to. Also, if you still have the u-bend get it deleted at the same time.

If you have access to a vacuum gauge (0 - 30 hg), run a vacuum test to see if you have excessive exhaust backpressure. You can tap into or tee in the lines off the throttle body feeding the purge solenoid. Run the rpms up to 1000 - 1500 and hold steady. If backpressure is abnormal the reading will gradually drop towards zero instead of stabilizing or reading steady. Another method is a low pressure test at the forward 02 sensor where a 0 - 5 psi gauge is connected. Backpressure reading with this method should not exceed 1.25 psi.

[troy1]

yes its the orginal cat 81K on the car its self. so how many inches of vac are we talking here? 60 bucks not bad for a cat. So what are you getting for gas mileage right now with your buick

also with a sanner what should your map reading be if you would bring the engine up to 1000-1500 RPM.

This what you got?
http://cgi.ebay.com/ebaymotors/GM-Ma...spagenameZWD1V

[BNaylor]

Originally Posted by troy1

yes its the orginal cat 81K on the car its self. so how many inches of vac are we talking here? 60 bucks not bad for a cat. So what are you getting for gas mileage right now with your buick

also with a sanner what should your map reading be if you would bring the engine up to 1000-1500 RPM.

This what you got?
http://cgi.ebay.com/ebaymotors/GM-Ma...spagenameZWD1V

Vacuum should be nothing less than 15 in.

I have two Regals, a '99 LS and '01 GS. LS gets 22-23 in city and 28 highway. The GS gets 20.5 in city and 29 highway.

On MAP I'd have to check the service manual specs.

On EBay link that is the Magnaflow Hi-Flow CAT but I don't recall if it was the same company but the price is reasonable. Hopefully you get the matter resolved.

[katana1981]

Well the only information I can get you, is that my Regal LS with 3800 cc 2002 does in city 20 mpg hot, normal or on cold weather. On highway, on summertime its about 33 mpg, during winter 27-28 mpg. the mix of both its about 25-26 mpg!

[troy1]

I'll test the Vac today hopefully, How fast has everyone been driving that has posted?

[BNaylor]

Originally Posted by troy1

I'll test the Vac today hopefully, How fast has everyone been driving that has posted?

On the highway 75 mph taching at 2100 rpms.

[troy1]

well no drop in vac runs 20 in hg at 1000-1500 had to unplug the purge vavle to steady out the gauge. any other ideas? I think at 75 I'm like 2300

[BNaylor]

Originally Posted by troy1

well no drop in vac runs 20 in hg at 1000-1500 had to unplug the purge vavle to steady out the gauge. any other ideas? I think at 75 I'm like 2300

Sounds good to me. I wouldn't rule out the CAT out but I'd defintely hold off on it based on the results.

What about 02 sensor? What brand are you using? If you can get the highway mileage figures up that would be better than nothing. The 02 sensors are critical in PCM closed loop mode which is cruising speeds and idling after proper engine warmup. Keeping the air/fuel mixture ratio at the ideal 14.7:1. For open loop mode the 02 sensors are basically out of the picture and the MAF sensor plays the key role in fuel economy. A MAF sensor that is out of calibration could cause poor mileage but I would say mainly the city mileage. Other than that I have no other ideas.

I know it must be frustrating but it sounds like you are taking the right approach and not giving up.