1999 Pontiac Grand Am



January, 31, 2007 AT 2:59 PM

So. I've already had a question in here regarding my '99 Grand Am and its horrible fuel economy just over the past year.

I just had a few more question regarding things of possibility with this model of car. The following info I've taken from other sections of this site but was for different models of cars and I wanted to know if this was something that could be something to look into.

• Computer Controlled Engine Management System

• Catalytic Converter: " plugged" or restricted?

• Mass Air Flow Sensor. Heard somewhere this is only in the V6s, is that true?

• Fuel pressure regulator

• coolant temp sensor. How does this one relate to poor fuel economy?

• Spark plugs

These are all things mentioned for other models of cars and if anyone had any input on these regarding the Pontiac Grand Am that'd be greatly appreciated.

10 Answers


Service Writer

January, 31, 2007 AT 5:59 PM

Your still huntin huh? Good for you.
Did you have the oxygen sensor wave patterns checked liked Chris said?

Computer Controlled Engine Management System: This is what contols your air fuel mixture among other things. It consists of the Computer, inputs such as sensors and outputs like solenoids and valves. The inputs evalute or report tho the computer, the computer makes adjustmetns based their data and tells the outputs what to do.

Catalytic Converter: "plugged" or restricted? You will get a code if this is the case and the cel will be lit. A plugged converter will cause the motor to run quite rough.

Mass Air Flow Sensor. Heard somewhere this is only in the V6s, is that true? Some 4 cyls have them, not sure about yours.

Fuel pressure regulator - controls fuel pressure when vacuum is reduced to allow flow through injectors. Runability or codes would be expected to be set if there was problem.

Coolant temp sensor. How does this one relate to poor fuel economy?
This input sensor tells the computer how cold or warm the engine is. The engine wants to get hot as quick as possible to reduce emissions. This sensor reports it based on the coolant temperature. The colder it reads, the more fuel the computer gives the motor.

Spark plugs
Pull a plug and look at it. Measure the gap, either replace it if they look bad or clean and regap them. Replace the rubber boots at the same time regardless of which way you go.



January, 31, 2007 AT 9:14 PM

Yes! I am determined to find an answer to this!
It just frustrates me so much because I'll take it in and they all say if the computer doesn't find something then nothing is wrong but it is obvious to me that the fuel economy is off.

Where would I go to check the wave patterns of the O2 sensors?
For the post-catalytic, the check engine light came on, but I feel the pre-catalytic one (someone before mentioned this 2nd one) has something wrong but no light is on.

How would I find out if something is wrong with the CCEMS or is that not possible with a very noticeable problem?

Could bad spark plugs cause this noticeable of change in fuel economy?

It'd make most sense if it was something that regulated flow because it seems that when the engine is off to being turned on is when most fuel is lost, resulting in horrible city or short term driving.

When I had the oil changed this last time the receipt noted a few things that I was curious about as well and how important they are to be fixed ASAP.
1.) Recommend radiator flush (. Is this the coolant?)
2.) Recommend transmission fluid change.
3.) Rec. Fuel filter change. I just had this done last year and they said it was looking rusty already!
4.) They said it looked like my coolant (Dextol or something like that I think they said) was watered down.

I really don't know much about cars and I hope it is cool that I am posting all this, I'm just trying to see what anyone suggests, and the car runs and sounds great.



Service Writer

February, 1, 2007 AT 4:40 PM

If you go back to your original post, Chris mentioned this, as I was incorrect. A lazy O2 as he said may be the source of your fuel milage. An expenve scanner can read the wave pattern, It may be cheaper for you to just replace it however.


Service Writer

February, 1, 2007 AT 4:45 PM



How many miles since: plugs
transmission filter
coolant flush (& also last date. Of coolant flush that is.)

Dpn't worry about the fuel filter, do it another 30,000 since the last one.

" I really don't know much about cars and I hope it is cool that I am posting all this" It's very cool 8) As as much as you like and as often as you like. : D

Your car does have a MAF btw.



February, 2, 2007 AT 12:10 AM

Hmm, that is interesting about the Mass Air Flow Sensor because my dad had bought this book and it said only the V6 model but who knows. Lol

oh, and with CCEMS I meant to say Computer Controlled Engine Management System ; ) sorry about that.

And I never knew about a transmission filter, will have to look into that.

I've never done a coolant flush while I've owned it since 2003, to my knowledge. ; )

Thanks for all this continual info, hopefully in the end there will be an anwser to all this. : )


Service Writer

February, 2, 2007 AT 2:55 AM

Generally if there is a problem with the computer sytems, a performance problem or cel will come on. There is a data stream that can be monitored with the more expensive scanners. One who is up on this can evaulate what is going on to narrow down or find causes. Such is the case with you oxygen sensor wave form. This form should be "jumpy" versus straightline. The coolant flush on yours should be done every five years with dexcool. Dexcool is the coolant that gm uses and is a long life coolant. Should any green coolant (older tyep) be added, then you can have it flushed and refilled with the green, but now it is a 2 year coolant. Anytime a lower rated coolant is combined with a longer life, the coolant bcomes reduced o the lower common denominator.

If you decide to do the tranny filter:

Call a parts store and ask for a mass air flow sensor and see what they say. Can't believe everything you read :wink: , including here. The MAF is an input to the computer and evalutes how much air is coming into the throtle bore. This has nothing to do with fuel economy, it is more for preventing acid build up that eats away at the internals such as the heater core, removes or at least reduces hardened particles that can cut the seal on the waterpump, and replenishes the cooling and freeze/boil protection qualities needed for the motor.

Again, I would focus on the upstream o2 sensor, sense the rear was replaced.



February, 2, 2007 AT 10:25 AM

Yeah, that O2 sensor seems like a great place to start.

Oh, and I went on Google to look up "Dexcool, " mainly because I wanted to see what color it was supposed to be and I found some not so pleasant results.

But then I read in another article that color is meaningless and it is used just to help find leaks. I suppose I can believe that more. ; )

Are transmission flushes a complex thing to do, I seen this at the bottom of an article you posted on another thread and it said "Never, EVER, get a transmission flush unless you have the money to buy a new transmission." Just scared me a little bit, lol


Service Writer

February, 2, 2007 AT 2:16 PM

Let me get this otta the way first. : Oops: Your engine does not have a MAf sensor, perhaps 4 cylinder GMs do not. I know others such as ford and Dogde do however. My labor give.4 to change the MAF that you car doesn't have : roll: As far as the dexcool. It does form a sludge around the radiator cap area this should get cleaned out. I have no proof otherwise. Early years of dexcool 95-98 there seemed to be a higher incidence of the coolant getting muddy-ish. I couldn't tell you why, but I don't see it much anymore. It has nothing to do with finding leaks. If you can't find florecent green, yer sure as hell not going to see purple.

This you referred has some filtered information. The chevy 3.1, 3.4 and 3.8 motors have flaws that are inherent in them. Poor designed intake manifold that can't handle the heat, poorly designed gasket that require an upgraded design. The coolant doesn't eat up gaskets. I have read more articles on coolant than I care to reflect on. I use dex-cool on a car that came with it. There are guys that drain it out and put the green in as soon as possible. I'm okay with that too. I had to research the coolant again today on a chevy Aveo that has blue coolant. The dealer didn't have an immediate answer for me, suggested consulting the owner's manual, cause it has to be in there. It wasn't, just reflect to use the " proper coolant". The only info I found was it has to meet astm 1825m standards. : Evil: Please post the transmission post, that doesn't sound like something I would " never ever" say. The exception may be if it was a lincoln that had 100,000 miles or more than had never had a filter put in. Can't think of any other instance. :



February, 2, 2007 AT 4:08 PM

Sorry, meant to say that you didn't say it, it was in an article posted by you... near the bottom of this: http://autorepair.about.com/od/otherodddiyjobs/ht/trans_filter.htm

I think I am pretty much confused by what all liquids and filters there are, I probably should go through my manual and that book that I have that is targetted at Grand Am's.


Service Writer

February, 2, 2007 AT 4:56 PM

W : D e'll be here

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