Fuel Issues

[bd]

Disregard code 32.  Code 32 set because the EGR vacuum hose was disconnected during diagnosis.  Following is a direct quote from the 1987 GM driveability manual:

     "The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off vacuum to the EGR valve diaphragm. With the EGR valve closed, fuel integrator counts will be greater than they were during normal EGR operation. If the change is not within the calibrated window, a Code 32 will be set.

The ECM will check EGR operation when:
     • Vehicle speed is above 50 mph.
     • Engine vacuum is between 40 and 51 kPa.
     • No change in throttle position while test is being run."

FWIW - Randomly throwing parts at a problem is both expensive and generally nonproductive.  Determine the actual "cause" before changing any more parts and possibly introducing a "new" problem.

[VileZambonie]

The suggestion was to simply unplug the vacuum hose from the valve and plug the hose. If the valve was hanging open intermittently due to a sticking solenoid, then the problem would go away as long as the valve is fully closing. If no change, then it's not your issue.

[gunrac]

I guess I missed the part of plugging the hose.

[gunrac]

Quote from: VileZambonie on January 19, 2017, 01:40:00 PM
The suggestion was to simply unplug the vacuum hose from the valve and plug the hose. If the valve was hanging open intermittently due to a sticking solenoid, then the problem would go away as long as the valve is fully closing. If no change, then it's not your issue.

Moving on. I did not swap out solenoid as it does not seem to be the problem. I got 12.5 mpg this last fill-up. I'm not a hot shot driver by any means. I don't get in a all mighty hurry to hit freeway speeds, but I do run them. 65 to 75 mph are normal speed limits here in TX. My curve is around 80. Going to hook up the solenoid back up today.

I've read somewhere that the IAC and TPS can be adjusted. What is your take on this? I replaced both, last year. I don't remember doing any type of adjustments.

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..

I tried the test on several occasions, I didn't see or notice any differences in rpm's. Would not having the EGR solenoid hooked up affect the test?

I'm wanting to check adjustment the TCC brake switch. Can you relate the procedure? Is there a proper way to check it w/a  multimeter, to make sure the switch is good? 

Or, do I need to go another direction first?

[bd]

Don't expect outstanding fuel mileage at 80 MPH.  I researched the brake switch for your '94 - unfortunately, it is nonadjustable (see image).  It either works or doesn't.  Check TCC function using a scanner.  The TCC solenoid inside the transmission receives fused power through the brake switch, but does not energize until the ECM completes the TCC circuit to ground.  The ECM uses engine temperature, road speed, transmission gear and changes in throttle position to determine whether TCC is appropriate. 

Make sure that no fuses are blown and that engine temperature climbs above ~150° F, at minimum.  Use a scanner or fabricate a jumper that allows you to connect a DVM to the TPS leads to monitor TPS function.  The three leads of the TPS provide 5-volt reference from the ECM, ECM ground, and ~0.5 - 5 volts signal return to the ECM.  The TPS signal voltage is dependent on throttle position.  Using your scanner or DVM, monitor voltage changes across the TPS as you slowly open and close the throttle, idle to WOT to idle, several times through.  Voltage change should be very smooth and gradual, virtually linear.  If the voltage signal is erratic, replace the TPS.  The TPS is virtually nonadjustable on TBI throttle bodies and should measure ~0.5 volt at idle, <5 volts at WOT.  Using a scanner while road checking on a empty rural street, monitor TCC function above 30 MPH in 3rd and 4th gears, lightly depressing the brake pedal at times.

Use the emissions and driveability manuals in the Technical Pages for reference.

[gunrac]

Don't expect outstanding fuel mileage at 80 MPH.  I researched the brake switch for your '94 - unfortunately, it is nonadjustable (see image).  It either works or doesn't.  Check TCC function using a scanner.  The TCC solenoid inside the transmission receives fused power through the brake switch, but does not energize until the ECM completes the TCC circuit to ground.  The ECM uses engine temperature, road speed, transmission gear and changes in throttle position to determine whether TCC is appropriate. 

Make sure that no fuses are blown and that engine temperature climbs above ~150° F, at minimum.  Use a scanner or fabricate a jumper that allows you to connect a DVM to the TPS leads to monitor TPS function.  The three leads of the TPS provide 5-volt reference from the ECM, ECM ground, and ~0.5 - 5 volts signal return to the ECM.  The TPS signal voltage is dependent on throttle position.  Using your scanner or DVM, monitor voltage changes across the TPS as you slowly open and close the throttle, idle to WOT to idle, several times through.  Voltage change should be very smooth and gradual, virtually linear.  If the voltage signal is erratic, replace the TPS.  The TPS is virtually nonadjustable on TBI throttle bodies and should measure ~0.5 volt at idle, <5 volts at WOT.  Using a scanner while road checking on a empty rural street, monitor TCC function above 30 MPH in 3rd and 4th gears, lightly depressing the brake pedal at times.

Use the emissions and driveability manuals in the Technical Pages for reference.

I'm not expecting to gain a whole lot on MPG. I just think I have issues that need corrected.  Unfortunately, I don't have access to a scanner. Also funds are a bit tight right now. I still see no difference when I lightly apply my brake peddle.

I did check TPS w/a DVM. Ref. signal 5.04.....at idol .59 WOT 4.60

 

[bd]

I did check TPS w/a DVM. Ref. signal 5.04.....at idol .59 WOT 4.60

The idle and WOT voltages are fine, but how smoothly did the voltage transition and was the voltage repeatable across the sweep?

[gunrac]

The idle and WOT voltages are fine, but how smoothly did the voltage transition and was the voltage repeatable across the sweep?

Seemed to be smooth......no jumping back and fourth. I worked it several times

[VileZambonie]

Check the MAP sensor hose and voltage key on engine off and at idle. You really need to get a scan tool to get any real help with this. You can buy a cable and use a laptop too

[gunrac]

Check the MAP sensor hose and voltage key on engine off and at idle. You really need to get a scan tool to get any real help with this. You can buy a cable and use a laptop too

Can you suggest what I need to get set up with a tool? I know nothing about them an see a lot of options.