Fuel Issues

[gunrac]

94' 305 TBI, extended cab, 2 wheel drive. Completely stock truck, minus the cat. I haven't paid much attention to my fuel milage on this truck until recently, while making a 1,200 mi. run. 12 MPG. at best.

Thought it was because I was running pretty hard, 75 to 85 MPH, 90% of the time. After making my destination, it never got any better after running a couple more tanks of fuel thru it.

Before leaving, I had a fella replace badly corroded fuel and brake lines. With nearly 90,000, and corrosion on the sending unit, decided to replace fuel filter, unit and pump.

After paying more attention after this work. I do not pump gas pedal. Starting up w/a cold engine,  my tach reads at idle, 1100 RPM, after a min. or 2, it will drop down to 900 RPM. After it meets 180 degrees, it drops to 250 RPM. Once in gear, foot on brake, I'm at 150 RPM.

At cold start you can smell it running a bit rich, w/a semi rough idle. It does smooth out after reaching 900 RPM. Idle, seems a little on the low end to me once I meet 180* I done a valve job w/a complete tune up less then 4000 mi. + a yr. ago.

Does this sound correct? It doesn't to me. Hoping to get a little info on my scenario.

[zieg85]

I am surprised it will run a 250 rpm so no that isn't normal.  I know nothing about a TBI system other than how it is suppose to run.

[gunrac]

It was down there,  before I switched out pump an filter also. It has never died. A few days ago, I had to stand on brakes to avoid a car that pulled out in front of me. It still stayed running.

[VileZambonie]

I don't believe your tac readings. Nevertheless unhook the EGR hose, see if it makes any difference. Also check for vacuum leaks at the TBI base gasket.

[bd]

In addition, verify that the TCC engages properly.

[gunrac]

I don't believe your tac readings. Nevertheless unhook the EGR hose, see if it makes any difference. Also check for vacuum leaks at the TBI base gasket.

I unhooked the at EGR, sprayed all around baseplate an vac hoses, no changes in engine RPM. EGR was replaced a yr. ago. Did seem like injectors was a bit heavy on fuel....BD, I need to read into the TCC more.

[bd]

The torque converter clutch is easy.  Just take it out and drive it.  At highway cruise lightly depress the brake pedal, but not enough to engage the brakes.  You should feel the TCC disengage and RPM jump slightly higher.  Remove your foot from the brake pedal and RPM should drop as the TCC reengages.

You ought to verify fuel pressure too as one of your early diagnostic steps.  High pressure will cause it to run rich.

[gunrac]

For what it's worth, I did have issues coming down. Code read O2 Sensor. Replaced a donut gasket on the passenger side. Reset. No codes after that. This was Dec. 31.

[gunrac]

The torque converter clutch is easy.  Just take it out and drive it.  At highway cruise lightly depress the brake pedal, but not enough to engage the brakes.  You should feel the TCC disengage and RPM jump slightly higher.  Remove your foot from the brake pedal and RPM should drop as the TCC reengages.

You ought to verify fuel pressure too as one of your early diagnostic steps.  High pressure will cause it to run rich.

BD.....Just checked fuel pressure between filter an TB.....11 psi    Is this the correct way? I read somewhere that you should block off return line. I did not do that.
Also, I did as you said, on checking TCC. I did not notice any difference, working your procedure. I changed out filter and fluid in tranny, but not the torque convertor about 2 months ago. I believe I have the 4L60E trans. After a bit of reading, I understand there are 2 solenoids located inside of tranny. Could this be my issue? You mentioned braking without applying. Got me wondering about another scenario.
Quite a while back I had my emergency brake cable freeze up. I cut the cable. Never replaced it. Not sure if that would have anything to do with it, but wanted to share this info.   

[bd]

You checked fuel pressure correctly and it measured within specs.  Eleven PSI reflects the fuel pressure regulator (FPR) calibration, which is the crucial fuel pressure parameter.  Pinching the return line defeats the FPR and tests maximum fuel pump pressure.  However, leaving the return line pinched will damage the pump, so pinch the line momentarily only for diagnostic purposes and only if necessary.

The TCC not locking up will impact fuel mileage above ~30 MPH.  If you have a scanner, monitor TCC actuation while driving >30 MPH.  It will cycle ON and OFF, modulated by the ECM, depending on inputs from VSS, brake switch, CTS, TPS, MAP and gear.  There is a 12-volt solenoid inside the transmission that controls TCC actuation.  Energizing the TCC solenoid blocks the TCC exhaust passage, which builds hydraulic pressure and applies the TCC.  If the TCC solenoid doesn't receive a voltage signal (the most common scenario), or the solenoid is faulty, or debris is fouling the valve or its passage, TCC will not engage and mileage will suffer.

Check the adjustment of the TCC brake switch.  It is a common problem to inadvertently pull the switch out of adjustment by catching the brake pedal with one's toe and pulling up on the pedal.

The e-brake cable issue will have no effect as long as the brakes aren't dragging.

[VileZambonie]

I don't believe your tac readings. Nevertheless unhook the EGR hose, see if it makes any difference. Also check for vacuum leaks at the TBI base gasket.

I unhooked the at EGR, sprayed all around baseplate an vac hoses, no changes in engine RPM. EGR was replaced a yr. ago. Did seem like injectors was a bit heavy on fuel....BD, I need to read into the TCC more.

It's not the EGR itself that is problematic, it's the solenoid that sticks allowing the valve to open at idle. The result is poor idle stability, loss of power brake assist, harsh exhaust fumes and it's intermittent. You should disconnect it for a few days and drive it to see if any improvement just to rule it out.

If you do have a scanner, look at fuel integrator and block learn.

[gunrac]

I don't believe your tac readings. Nevertheless unhook the EGR hose, see if it makes any difference. Also check for vacuum leaks at the TBI base gasket.

I unhooked the at EGR, sprayed all around baseplate an vac hoses, no changes in engine RPM. EGR was replaced a yr. ago. Did seem like injectors was a bit heavy on fuel....BD, I need to read into the TCC more.

It's not the EGR itself that is problematic, it's the solenoid that sticks allowing the valve to open at idle. The result is poor idle stability, loss of power brake assist, harsh exhaust fumes and it's intermittent. You should disconnect it for a few days and drive it to see if any improvement just to rule it out.

If you do have a scanner, look at fuel integrator and block learn.

 Disconnect the vac. line only from solenoid to the EGR or should the power connection on the solenoid be disconnected also?
I do seem to have all the symtoms you described.

Even as the brakes go, I do have a good brake, but it still seems the peddle goes down a bit more then it should. I just put new pads an rotors on and adjusted the rear shoes out just a bit before my run down south. Shoes have around 4k. Drums were still pristine. Hand adjusted shoes out till I could barely slip drums on. Then I done the reverse gear and slam, to make sure they were fully adjusted.  Right or wrong, that is what I was taught.

As mentioned before, at cold start, seems to have a fuel overload for a couple min. Idle would then drop to 900 rpm and smooth out. Seem to act more carbed. then fuel injected. W/O air cleaner on yesterday, there seemed to be a sneeze each time I shut off , this is after it reached full temp.

I do know there was a issue w/EGR before I swapped out last yr. by checking the EGR. uninstalled. The solenoid, was not replaced.

I'm thinking it's best to rule out  the EGR solenoid, before getting into the TCC possible issues. Besides, it seems easier.......I don't have the scanner.

[bd]

I agree with you.  Basic engine malfunctions generally have much greater effects on drivability and fuel mileage than TCC.  Some engine malfunctions may temporarily defeat TCC.  Once the engine basics are handled you can revisit TCC, if needed.

[gunrac]

I did unhook vac. line from solenoid to EGR. Didn't undo power source tho. Run around 30 mi. today......guess will see.

[gunrac]

I did unhook vac. line from solenoid to EGR. Didn't undo power source tho. Run around 30 mi. today......guess will see.

I ran another 20 mi. errand. Just before I made the 1st. 10 mi., check engine lite appeared. I left a couple hrs. later, no lite appeared. After checking a bit ago, I retrieved a code 32 ....32- egr circuit (fuel-injected models)

Some may remember, around the 1st. of the month, my check engine lite came on and it popped up, I had a O2 sensor issue. Fixed an exhaust leak. Reset, I had no issue after that.

Cold start today, the idle seemed a bit smoother. My tach reading are still all the same. Did seem like the brake had a bit more attention running yesterday, but not so much on the cold start I had this morning.

I did pick up the a EGR solenoid a couple days ago, does it seem problematic enough to go ahead and install?