I am getting about 8.5-10 MPG with my car. I would rather spend $200 and get this TBI fixed, then spend $500 and do a full carb conversion, but I am fixin to go carb. My car is running really rich, bogging all the time. I have replaced my O2 sensor and that didnt do a thing. What can I do/replace before I take my car into the shop. Also the car's spark plugs and wires are new. The fuel filter is about 3000 miles old. Help is very much appreciated.
Thanks,
Brady

 

Hmmmm, quite a prob you've got here. Check the fuel pressure regulator. I think when that diaphram goes bad it make the mix really rich. Anyone?!?

 

FPR is new AC Delco. Also when the car is cold the injectors dont prime the engine although the pump turns on and builds pressure. I have to start the car with starting fluid when it is cold, all summer long i didnt have this problem till the cold fronts started hitting a few months ago. anyone?
thanks,
brady

 

Just for yucks, check the gap on the plugs... I was having similar problems w/ mine. The mechanic had timed it wrong and installed plugs w/ a gap of .06" rather that .035" (i think thats the proper gap). Fixed it and it made a world of difference. Check the injectors to make sure they're not clogged/leaking and check the diaphram in the pressure regulator too. All kinda stupid stuff but then again, the stupid stuff is what was causing my problem.

 

lol... hard cold starts are a problem here too.

 

gap is at .035" and the fuel pump relay is new

 

I have the same problem. I have replaced the O2 sensor also it worked for a while now it's back again....

 

I was getting about 14 MPG then I changed O2 sensors and I now get ~9MPG

 

are you getting any codes? ive had some trouble getting my car to start when its cold out but so far i havent had to squirt starting fluid in it

 

Check:

Spark plug wires make sure they are good (check plugs for fouling) just because they are new doesn't mean anything, you could be running on 7 cylinders
Cap/ Rotor
Timing
Thermostat 180 degree min. for a daily driver stock is 190 or 195 can't remember exactly. hotter is better fuel economy/emissions.

Your mileage is horrible car is running rich and/or the timing is off.

I would average 18 mpg in city/highway driving

also that other guy who's now getting ~9 mpg AFTER changing th e o2 sensor... that is horrble. Something else going on there.

reread your post...
Also try putting the stock air filter housing with heat stove back on for winter use. This will help the car warm up quicker. (better mileage)
your ecm is tring to add more fuel to compensate for the much colder ie / denser air, the stock 305 really can't do anything with it. Your car is running "fat" for too long until the intake air gets up to temp.

 

I am gonna look for carb swap parts now. This FI has never ran right in over a year. It hasn't started right in over a year. And it hasnt got 13 MPG for over a year. Anybody got any Holley 4 barrels or intakes for sale or distributors of FPRs?

 

I keep thinking it might be the coolant temp sensor. Did you replace that?

 

havent tried that, how much do they go for?

update: now the car stalls for no reason, it seems to do it only on fast turns and sometimes slow ones, but not on hard straight line braking. WTF is up with that?

 

where does the CTS go? Where do i install it?

 

The coolant temp sensor is in the front of the intake manifold. It's a gold color and there will be wires running to it. So now it stalls in corners? have you replaced your fuel pump?

 

fuel pump is "supposedly new" i had it replaced in feb. '01. i got a new CTS and i am going to install it right now. thanks

 

CTS is installed. anybody got anymore suggestions?

 

You can also get a bad O2 sensor straight off of the shelf. May want to try another since that's when your MPG took a dive.

Steve

 

check the float setting... j/k

Too many problams to diagnose over a PC

First steps you should do is check that the basics are working correctly

Air
Spark
Fuel


A dirty air filter will affect gas mileage and driveability
Faulty ignition components will affect gas mileage and driveability
Weak fuel pump, dirty fuel filter, bad gas, clogged injectors, will affect gas mileage and driveability.


If the basics check out then it's time to diagnose sensors, faulty sensors however should trip the SES light. Sensors have a range of acceptable values once they deviate from this range the ECM registers this as a error.

Every computer controlled car I have owned over the years has never had a bad sensor. The problem was always rooted in the 3 basics. The only sensor I really ever replace is the O2. since it sees the most abuse.

Example, years ago I had a weak fuel pump. The car drove fine but after hard acceleration it would trip the SES light and go into limp home mode. The car would drive horrible, not accelerate, hard to start etc. seems that the fuel pressure was weak enough trick a sensor and register an error. (lean condition)

to make a long story short, after decoding the trouble code and changing the 02 sensor the car still ran bad. BUT after testing fuel pump pressure and seeing it PLUNGE when accelerating in park. well there was the answer to the mystery. It was also a good excuse to replace the fuel filter and clean the injectors at the same time.

Good Luck

 

i dont know what i am doing with this car. i just want to throw a carb and stuff on it, but my dad wants to take it to a dealership to get it fixed. the CTS didnt do much, it doesnt stall on turns anymore but that is a mysterious problem that came and went i guess. i dont know

edit: will a dealership make a big deal out of the fact that i dont have a smog pump?

 

I am having the same problem with my 89 L03 with the T-5, I only get about 10-12 mpg. And I have replaced the distributor, cap/rotor, wires, spark plugs, fuel pump, fuel filter, tps sensor, map sensor, egr valve, air filter, cleaned out the tbi (took off and "rebuilt"), new fpr, cleaned out the cat, and it is still getting 10-12 mpg... anyone have any ideas on this one?

 

The problem could be your right foot...

Also how are you checking your mileage? The only accurate way to do it is to top off the tank (fill it up all the way to the cap). Otherwise you NEVER know exactly know much gas you used between fill ups.

 

I am keeping my foot off of the gas as much as i can, and every time i fill up the tank i check the milage, which is every 5-7 days, depending on how far i drive, i only get about 160-170 miles on about 13 gallons, even if i use cruise, but most of the time i am in the city. I think i might see if i can pull a tbi off of a car at the junk yard, those things are harder than you think to find in Omaha. If i can't do that, i'll see if i could build up a 350. But if anyone has any more suggestions, i'd be happy to take them.

 

UPDATE: took the car to a dealership to get it fixed. they found that the fuel pressure was low coming right out of the tank. they replaced the fuel pump in the tank and the car starts right up and runs good. i can here the pump turn on when i turn the key to "on"
hopefully my MPG will go up

 

so did it effect the MPG?!!?

 

Damn, that was a while ago.... I really don't remember, sorry.