Thread: really bad gas mileage

Tweet

I have an 88 formula with a 305 tbi recently rebuilt 2000 miles......... I have been tracking my gas mileage and noticed That I am getting 13miles per gallon. Used to get anywhere from 16-17 to 20-21 mpg. The 16-17 was when I had a bad map sensor. This is the worst I have ever had. I just put a new O2 sensor in. Me and my friend were playing with the tbi tonight because in drive I was idling at 1000 rpm now its at 500 which is a little low. But after reading the tech article I know how to set it. How ever when I hooked a computer up to the ecm up to it told me that at idle the map was reading 7ihq??? whic I am not sure on what this means. Is this a low vacuum reading because at idle my engine pull 21 pounds of vacuum...... well any way any help would be appreciated...... tonight I checked and i got 11 mpg which is un acceptable

any help would be appreciated
Kenny

Spark plugs and wires first, and follow the correct procedure to set the timing.

Originally posted by drumsk
I have an 88 formula with a 305 tbi recently rebuilt 2000 miles......... I have been tracking my gas mileage and noticed That I am getting 13miles per gallon. Used to get anywhere from 16-17 to 20-21 mpg. The 16-17 was when I had a bad map sensor. This is the worst I have ever had. I just put a new O2 sensor in. Me and my friend were playing with the tbi tonight because in drive I was idling at 1000 rpm now its at 500 which is a little low. But after reading the tech article I know how to set it. How ever when I hooked a computer up to the ecm up to it told me that at idle the map was reading 7ihq??? whic I am not sure on what this means. Is this a low vacuum reading because at idle my engine pull 21 pounds of vacuum...... well any way any help would be appreciated...... tonight I checked and i got 11 mpg which is un acceptable

any help would be appreciated
Kenny

drumsk, you should check the volts of you MAP sensor when you had the scanner on it. you should have full vac. going to it at idle and the volts reading should be around 1.5v idling, and as you idle the motor up the vac. falls and the v should go up to around 4.5 v. WOT. hi vac. will lean it out and low vac. will richen it. that thing should be running bad. sounds like to me you have temp. sensor(the choke) going bad. did you check that.

Any chance the converter has puked it's guts into the muffler and the clogged muffler is holding the engine back?

This one happened on my 89 Ranger 2.9 L, 4x4, 5 speed stick etc.
It was getting 20-21 mpg in mixed town & country driving.
Mileage went down to 17-18 mpg.

I'd done a smog test a few months prior and the converter was deemed bad.
That was replaced, but I didn't really realize the muffler was clogged until I towed my roadster over the Grapevine's steep five mile grade between Bakersfield and L.A.

Normally it would carry 45 mph in third and I ended up having to climb the grade in 2nd running between 30-35 mph.

Once the muffler was replaced, mileage went back to 20-21 mpg town & country and power went back to the normal dragging the roadster up the Grapevine at 45 mph.

the muffler and cat are brand new on 2000 miles on both of them..... I do believe the map sensor is bad because at idle it was only reading .93 volts and 7 ihg perhaps thats somewhere to start................. Also I noticed the cat was smoking last night and the car was given a new set of plugs and wire when I put the engine in........... kenny

.93 at idle should be ok ,thats lean, if you had idled the motor up that # would have gone up . dont think its the MAP.

check the vaccume lines and make sure that you on the right port for vac for your map,also you could check the knock sensor and make sure that it's ok, and you should check the fuel pressure and the fuel filter,