First, a little history of where my problems started: Front passenger side tire belt broke while driving down the road. When tread came off, it tore out the wheel well and snatched my ECM wiring harness.....HUGE MESS! Replaced ECM, reconnected all wires and replaced bad places. Car still wouldn't start. Thanks to someones advice, I finally found my fuel pump fuse ( Chevrolet dealership couldn't even tell me where to locate it) and sure enough, it was toast. Replaced it and she started up. The only thing is, she was running really rough. Have put on new spark plugs and wires. After that, she has run a little smoother. Did test and got codes 22, 34, and 45. You can tell she's running rich just by the smell. So we replaced the TBA and MAP sensors. No further improvements on the running condition. I have to hit the gas easy or it's like she's flooding out. Idling at about 400 RPMs. After replacing sensors, still reading same codes. 1990 RS 305 TBI. Any help or suggestions about what to check next would be greatly appreciated. Only 99000 miles. Clueless!

 

Scheff,

Still getting the error codes after part replacement?

Is the TPS voltage within the normal range on start-up?

Vacuum line connected to MAP? Have you checkd the MAP reference and output voltages at the sensor?

 

Any luck on checking that sensor output?

For your DTC 34 -

Your Manifold Absolute Pressure (MAP) sensor should be located on the intake near the throttle body, or on the firewall. There should be a small vacuum hose routed to it, and the three-wire electrical connector.



Of course, the hose connecting the sensor to the intake manifold needs to be intact, free from cracks, leaks, splits, or kinks. The electrical connector needs to be clean and tightly seated.

The MAP sensor can be checked with a vacuum source and a digital voltmeter. Turn on the ignition without starting the engine. Connect across the 'A' and 'C' terminals to be sure there is a 5VDC reference voltage available to the sensor. The sensor should output a 0-5VDC signal at the 'B' terminal. The output voltage is based on absolute pressure (opposite of vacuum) at the hose connection. The sensor should output full voltage (5.0VDC) when there is one BAR (barometer, or atmosphere) of pressure applied. This means there is basically no vacuum (0" Hg) and the Absolute Pressure is at 14.7 PSIA.

When the Absolute Pressure decreases (due to vacuum) the voltage output on the 'B' terminal should decrease as well. Test the sensor down to about 20" Hg of vacuum, or 0.33 BAR (4.9 PSIA), where the output voltage should be around 0.8-1.2 VDC. The voltage should vary in direct proportion to the Absolute Pressure, or amount of vacuum applied.

If you don't have access to a vacuum pump, you can start the engine and use normal engine vacuum to test the sensor. At normal idle vacuum of about 17" Hg, the sensor should output about 2.0 VDC. Anything close to that value should be close enough.

If the MAP output "jumps" or "sticks" at a given point, the sensor bridge circuit or the mechanical diaphragm is failing. Since there is no good way to repair a MAP sensor, replacement would be indicated.



For your DTC 22 -

Your Throttle Position Sensor (TPS) is located on the right side of the throttle body. Again, turn on the ignition without starting the engine. Check across the 'A' and 'C' terminals for a 5VDC reference voltage. Check the 'B' terminal to ground for an output voltage. The voltage should start at about 0.8 - 1.0 VDC when the throttle is closed. As the throttle is slowly opened by hand, the voltage should increase at a near linear rate. Peak output voltage should occur at wide open throttle, and be above 3.9VDC.

The DTC 45 is a rich exhaust condition, which is no doubt being caused by one of the other problems. Once the initial problem(s) is solved, the '45' should not recur.

Let us know if all those items check out, or if there is a problem.

 

OOPS! I forget the TPS sensor location (item 31):

 

Thanks for the help Vader. We'll check all that too. About the EGR valve, according to the diagram under the hood, I found the EGR valve. The Haynes book says that you should be able to push up on the diaphragm. I can't. Don't know if I have the wrong part or not. Hose J comes from in front of the throttle body and goes to the EGR selenoid with another hose coming back toward you (standing in front of car) and goes to a metal, round thing on the back side of the throttle body. Is this my EGR valve, and if so, is it bad since I can't push anything up. The hose (J) was not on all the way. Pushed on all the way and it seems to run a little better, but not much. Stills seems like it's flooding when you hit the gas more than easy. It does have a little more power now. Thanks for all the help.

 

Sheff,

This is a cutaway of a typical EGR valve:



The diaphragm is somewhat shielded, so you'd have to stick a finger through one of the openings on the underside to lift the diaphragm.

Chances are that the EGR is O.K. The only time you'd have an issue with it at idle speed is if it were stuck open.