Restoring MPg

[Yonkerse]

Hey Guys,

Let me start off by introducing myself...I am a proud owner of a 2005 Pontiac Bonneville SLE with the 3800 Series II that I have been tricking out ever since I purchased it 18 months ago. I have done routine maintenance to it including LIM, coolant flush to Prestone mixes with any, tranny flush and many other mods.

Within the past few months, my girlfriend picked up a 2005 GP SE with about 74000 miles on it. Recently, she has been complaining her gas mileage has been dropping off. What she explains to me, is she's now getting about 300 miles to a tank, instead of 400 like she was getting before. Her driving is always consistent (same routes) and she drives pretty mildly.

I have plans to replace her spark plugs and wires (any suggestions?), fuel filter (if in-line) and also replace her front O2 sensor. Now when I would propose these questions to my Bonneville buddies, they would always recommend the best brands, and the brands to stay away from (for example: Bosch). So, could you guys please chime in and give some recommendation of brands, and other things to replace to help her MPG get restored?? The car is now approaching 80K.

Also, I have Aeroforce Scan Gauges installed in my car which I plugged into her car to scan for any issues. The car didn't throw any codes which please me, but when checking throttle percent, at idle, the car was reading 8% throttle. My car is drive-by-wire, but shows 0% when idling. Is 8% throttle common for drive by computer cars? This seemed high to me...are there any issues here or anything I should check?

Thanks guys and appreciate any comments/suggestions/replies!!

[Fivefingerdeathpunch]

a good tune up should do wonders.

go with ac delco stock replacment plugs and ac delco wires or a autozone lifetime warranty brand.

New air fliter would help if its old.

And becuase yours is DBW I would strongly recommend you take the throttle body and clean the living crap out of it and make it shine.

If the trans fluid has never been done, I would do that aswell. Drop the pan, put a new filter in and bolt it back up and fill with 7-8 quarts of trans fluid.

If your going to replace the o2 sensor go with ac delco or denso

[NegativeOne13]

In 2005, they only made the base, gt1, gt2, gtp, and gxp.... no SE. So I take it SE as in base? But, plug wires, just pick up a set from autozone, lifetime warranty. In '05, the inline fuel filter was spotty, some were inline, other were built into the fuel pump. Just check under the car to see if there is one, if not, then its in pump. The o2 prolly wouldn't hurt since your getting up there in miles, but probably not essential. Though, o2 sensors can go bad without throwing codes. Check the air filter.... could replace it with a K&N panel filter. My car at idle is usually around 4%-8% idle so I don't see that being an issue. Tire pressure, if they are around 33psi it usually tends to help fuel mileage out some. A canned tune would help benefit some mpg.

In my personal experience, no matter how I drove, I always got about 300 miles before I got to the yellow hashes. Highway miles I'd see maybe 330 miles.

[TLSheff]

If keeping stock, stick with AC Delco. I say that as a GM Parts guy and as a regular user too, they are better. The 3800s do not like Bosch or platinum.

Plugs are recommended (ACDelco #41-101) (IRIDIUM)
Wires same (ACDelco #746DD) *IF N/A L36
-----------(ACDelco #746EE) If L67 (Supercharged)

Fuel Filter (ACDelco #GF578)
O2 Sensor (ACDelco #213-1553)
Air Filter (ACDelco #A1096C)

Should really help, may also consider cleaning the Throttle Body and MAF Sensor while your doing all that, just to be safe

[NegativeOne13]

If keeping stock, stick with AC Delco. I say that as a GM Parts guy and as a regular user too, they are better. The 3800s do not like Bosch or platinum.

Plugs are recommended (ACDelco #41-101) (IRIDIUM)
Wires same (ACDelco #746DD) *IF N/A L36
-----------(ACDelco #746EE) If L67 (Supercharged)

Fuel Filter (ACDelco #GF578)
O2 Sensor (ACDelco #213-1553)
Air Filter (ACDelco #A1096C)

Should really help, may also consider cleaning the Throttle Body and MAF Sensor while your doing all that, just to be safe

The walking talking ACDelco rep... lol just playin. If you come to KC meet... I'm so gonna ask you a part number for a random part......


better study up.

[TLSheff]

The walking talking ACDelco rep... lol just playin. If you come to KC meet... I'm so gonna ask you a part number for a random part......


better study up.

Not sure If I will be able to make it, but if so... I will accept your challenge

[blueguy]

If he comes to KC...he better be bringing Shawn Larsen with him

[Odi]

acdelco plugs are NGK plugs with a different brand name on them.

[TLSheff]

acdelco plugs are NGK plugs with a different brand name on them.

True, depending on where you buy them depends on which is cheaper too.

Just recommending the part #s and factory recommendations.

We all know there's better performance wise, but if its staying a factory DD then he just needs good quality parts and I feel the factory OEM parts would be the best to suggest.

[Yonkerse]

Thanks for all the replies and part numbers!! Really appreciate the support the forums show for these cars!!!

Her car needs a little work cosmetically as the previous owner (older lady) had the mentality to pull forward until she felt a tap..haha, so the front bumper cover will eventually get replaced...and also needs a new left (Drivers) headlight...so if anyone has one..let me know!!

But since she had a few bumps..she got the car at an awesome price ($5500) with new tires!! Can't complain about that! Will work on getting pictures of it up.

And wasn't aware the "SE" wasn't a trim package for that year..im really a noob in the GP department. I would assume its a base since her DIC is VERY limited and only shows Odometer and trips...no temp, trans temps, tire pressures, oil life, etc. Which brings the question to mind, could I get a DIC from a different model (say GT1 or 2) and simply plug into her car...or is her car also lacking all the sensors to read values?

Thanks again for everything!!

[iamsam2010]

If keeping stock, stick with AC Delco. I say that as a GM Parts guy and as a regular user too, they are better. The 3800s do not like Bosch or platinum.

Plugs are recommended (ACDelco #41-101) (IRIDIUM)
Wires same (ACDelco #746DD) *IF N/A L36
-----------(ACDelco #746EE) If L67 (Supercharged)

Fuel Filter (ACDelco #GF578)
O2 Sensor (ACDelco #213-1553)
Air Filter (ACDelco #A1096C)

Should really help, may also consider cleaning the Throttle Body and MAF Sensor while your doing all that, just to be safe

ok just out of curiosity was told ngk had a higher spark or w/eand i have used them in cars just not a gp,usually i use the acdelco rapidfires,but wondering would the NGK irridiums be an ok change?and if so would they help the car any?
i have a 99 gt with 143,000 i drive it daily as i am a home health aide and it seems to be getting worse and worse mileage(starting to only get like 280-290 per tank with heavy accel.)never thought about the front 02 sensor,always been told if its not throwin the code,don't fix it,and dude told me 2day to clean my maf cause i got a ram air and mufflers on car but seems my car tries to hard to suck air in at start up and sometimes hesitates and dies...


sorry long winded i know :-( still trying to get used to this site and the features,and all the tech help from current and previous gp nutz like myself!~ on my 7th gp and lookin for my ultimate fire engine red gtp

thank you guyz for listening and any and all input would be greatly appreciated

[Scottydoggs]

a bottle of injector cleaner in the gas tank never hurts.

i just dumped a bottle in last week and with in miles i felt a difference in power and im getting better mpg on the highway.

and cleaning the throttle body never hurts either.

and a tune up will do wonders as well. im all stock so i got the iridiums spark plugs,(ac i think) and stock wires from auto zone. been working just fine for the last year.

[Yonkerse]

Hey Guys,

Got around to working on her car a bit this last weekend. Installed AC Delco Iriduium Plugs, Beldon plug wires, Denso O2 Sensor and an AC Delco air filter. The car seems to be running much smoother, and we'll see if her gas mileage comes back.

All in all, I think the parts cost around $120 for everything, and took about 2 hours to install everything with just a few scrapes and bruises from stretching around the back side of the motor.

Had an interesting find when I took out the old air filter, found about a half dozen leaves sitting in there. I'm sure this is where her MPG issue was coming from, most of the air cleaner was blocked and not letting air pass. Is this common for debris to get into this air box?

Thanks for the help guys! Will chime in after she gets some more miles on her to see if anything changes.

[Scottydoggs]

leaves in the air box are common, I've pulled leaves out of every stock box, on every car i've ever had.

[TLSheff]

...Had an interesting find when I took out the old air filter, found about a half dozen leaves sitting in there. I'm sure this is where her MPG issue was coming from, most of the air cleaner was blocked and not letting air pass. Is this common for debris to get into this air box?

Leaves, dust, dirt, bugs, a very pretty butterfly, and once... part of a bird and some feathers...

Schmitz happenz ya kno

[Yonkerse]

Yea, I will make sure I check hers often to make sure its clean and clear...

She still says the car doesn't catch sometimes and stalls when trying to fire..was hoping the tune up would have fixed this...Any other suggestions?

whats the best method to a TB and MAF cleaning? Is there a techinfo article on this?

Thanks!

[Fivefingerdeathpunch]

take the air duct hose off and remove the 3 bolts holding the TB on and unplug the DBW connector and any other sensor on the TB then brake clean the living piss out of it and wipe it good, then use maf cleaner on the maf and bolt it back together.

[iamsam2010]

is there a tech article?i was told that i should clean my tb and went to do so and took the top round sensor off and undid bolts wires etc and the sensor was BLACK as night with ALOT of buildup,but there is a black bracket in the way of getting the bottom tb nut off???how do i go about getting this crap off?

[Scottydoggs]

http://www.grandprixforums.net/how-c...ody-48650.html

[Yonkerse]

Thanks for the link. I really hope this cures her issue where the car wont catch when starting sometimes. She's always nervous that it will act up more serious and the car will keep stalling out and never start...