Ok, replaced O2 sensor two weeks ago, was getting 13.5 MPG now getting 14 MPG wow big difference . The timing mark is about 3/4 of an inch counter clockwise (left) of the timing tab. not sure what that is. Put the comp into field service mode and checked the "check engine" light. would stay lighted for about half a sec then go off, and then it would randomly stay of for the whole second then go back to normal for a few more flashes then stay on again (when idling).. when i revved the engine to about 2000 and held it there, the light would go off completely, (lean condition?) and when i was driving around it would stay on for about half the sec. and also my fuel pressure fluctuates about +-3 PSI rapidly from 44PSI while idling. Have not yet checked to make sure cold start valve is closing.. But i noticed that when the temp guage was one mark past the 1/4 mark (175?). it was still in open loop mode. then i drove it around and rechecked it then it was finally in closed. I switch between regular and premium gas depending on how much it coast with almost no difference in MPG using each of them. vacumm is about 18 inches. but when i rev the engine, vacumm drops then when i let off it rises to about 20+. i can't remember if that is how to test for a clogged exhaust, or if it was if vacumm increased while revving engine. cap and rotor are new, wires are almost new, but are low resistance, plugs might be a little old.

edit: I have a 180 therm in. and in the mornings i drive about 2.5 miles to my off campus class, with the engine temp just reaching past the first 1/4 mark. then 45 min later i drive to school another 2 miles with the engine cooler, could this be contributing also if the engine were in open loop this whole time? would if be ok if i left the paperclip in A&B connectors while i drove the car around tomorrow morning, i dont want it to burn out on me anytime soon. also, i am running almost 100% water, would it warm up quicker if i put antifreeze in?

i think i included everything but if not then ask.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

http://www.geocities.com/david_angel_16

[This message has been edited by breathment (edited October 09, 2001).]

The fuel pressure shouldn't fluctuate noticeably at idle, so maybe check for a weak FPR spring. I'd more suspect an unsteady vacuum though, is it fluctuating at idle too or steady on 18?

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley module, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Streetdampr, Ruger P95DC, hot wife, new oil filter, !cats, !TBC, !AIR.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

its very steady

also, a clogged fuel filter wouldn't have anything to do with it would it? i don't know if its clogged, but it hasn't been changed in a while.


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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

http://www.geocities.com/david_angel_16

[This message has been edited by breathment (edited October 09, 2001).]

Watch the intake vacuum.

You say you have 18in/hg at idle.

Now increase the rpms (in park/neutral) to about 3000rpms.

What's the vacuum say now,while holding the engine steady at 3000rpm's?

If vacuum decreases fromt he 18in/hg, idicates a restriction in the exhaust. It should fall no lower than about an 1 in/hg if the exhaust is in good shape...lowr the reading, the more the restriction.

I get 12 MPG - Doh!

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1988 Jet Black IROC
5.7L W/ 64000 miles
Flowmaster Exhaust
Fully Loaded
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My IROC In Readers Rides
My IROC

Don not put a paper clip in the A&B outlets and crankt eh egnine. You will fry your ECM on the spot if I remeber correctly. Anywasy thats waht my friend told me and he seems to know what hes talking about.

-Max

"I get 12 MPG - Doh!" Something is severly out of what for you to be getting such terrible mpg. Have you done a tune up lately. I even got better mpg when I didn't have OD when I first got my car.

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"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

i put it in after i start it up.


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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

http://www.geocities.com/david_angel_16

Putting the paper clip in before starting the engine will not always kill the ECM. I did it once or twice by accident and it did nothing.

I am guessing that it dramatically increases the risk of a surge frying the ECM tho and hence it is not a good thing to do.

Dale

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1986 FireBird
2.8L MPFI
1/2 CAI
Gutted Cat, No muffler
Was 700-R4 --> Now T5
**** Great cars aren't bought, they're built ****

LoL It dosent seem bad at all. Im thinking I Had a miscalculation or a wrong number. Im gonna try again-lol

Car runs like a dream though


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1988 Jet Black IROC
5.7L W/ 64000 miles
Flowmaster Exhaust
Fully Loaded
------------------

My IROC In Readers Rides
My IROC

[This message has been edited by IROCThe5.7L (edited October 09, 2001).]

so would timming being really far advanced cause bad milage?

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

http://www.geocities.com/david_angel_16

Well...yes and no Too much advance could trigger the knock sensor, retarding timing and hurting MPG's.

But i'd think if it were so far advanced to retard the timing to constantly afffect your MPG's, you be hearing the pinging every now and then.

Now timing that doesn't advance at all, will destroy MPG's.

One other thing, you mentioned that the car is staying in open loop...this could be due to a bad CTS (being's that the O2 is new, should eliminate it as a cause).

Most likely driving around in Open Loop, MPG's would suffer as well.

well, it does stay in open loop, its just seems to stay in open loop until about 175*. a little past 1/4 on therm, unless the car is in open loop for a certain time right after u start it.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

http://www.geocities.com/david_angel_16