I have a 1997 ford ranger. check engine light code PO303. I've changed the plugs and wires (really needed to anyway) tested coil packs and amde sure the EGR port is not clogged. how do I test the EGR vacuum solenoid and how do I know it's working or not. Chilton's is totally contradictory about when solenoid works.

 

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A code 303 is a miss on cylinder #3, below is a list of possible causes.

What engine do you have?

Possible causes:

Ignition System.
Fuel Injectors.
Fuel Pressure.
Evaporative Emission System.
EVAP Canister Purge Valve.
Base Engine.
Running out of fuel.

 

Thanks, Ken...I have a 2.3L engine. I hope your list will help. TO update: when I took out the EGR vacuum solenoid to try to test it I cleaned it, don't know why but that seems to have helped. Engine WAS missing all the time, now it's only missing on the first start of the day then when it warms up it's fine. I clear the check engine light and it stays off, and the engine runs fine the rest of the day. I've been running injector cleaner through the engine (I've just started the 3rd tankfull).
Peter

 

Without a code it's hard to pick the appropiate test(s) but these seem to be what your looking for....

HE24 CHECK FOR EGR FLOW AT IDLE WITH EGR VACUUM REGULATOR SOLENOID CONNECTOR OFF
Key off.
Disconnect vacuum hose at EGR valve and connect hose to vacuum gauge.
Start engine and bring to an idle.
While monitoring vacuum gauge, disconnect the EGR Vacuum Regulator solenoid vehicle harness connector.
The EGR valve requires vacuum greater than 5.4 kPa (1.6 in-Hg) to begin to open. If the vacuum reading remains greater than 5.4 kPa (1.6 in-Hg) after the EGR Vacuum Regulator solenoid is electrically disconnected, this would indicate a mechanical fault in the EGR Vacuum Regulator solenoid.
Does the EGR vacuum remain greater than 5.4 kPa (1.6 in-Hg) at idle even after EGR Vacuum Regulator solenoid is electrically disconnected?
Yes No
This indicates a fault in the EGR Vacuum Regulator solenoid. GO to HE25 . GO to HE26 .

HE25 INSPECT EGR VACUUM REGULATOR SOLENOID VENT FOR PLUGGING
Note: A plugged EGR Vacuum Regulator solenoid vent will not allow EGR vacuum to vent to atmosphere.

Key off.
Disconnect EGR Vacuum Regulator solenoid vacuum hoses.
Remove EGR Vacuum Regulator solenoid vent cap (if removable).
Remove filter and inspect for blockage or icing in some cases.
With the EGR vacuum supply port plugged, apply 34-51 kPa (10-15 in-Hg) of vacuum directly to EGR Vacuum Regulator solenoid vacuum source port with a hand vacuum pump. If the vacuum holds or is slow to release to atmosphere, the EGR Vacuum Regulator solenoid vent could be plugged or restricted.




Is the EGR Vacuum Regulator solenoid vent or vent filter plugged or restricted?
Yes No
SERVICE EGR Vacuum Regulator solenoid as necessary. If unable to service, REPLACE EGR Vacuum Regulator solenoid. RECONNECT all components. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test . REPLACE damaged EGR Vacuum Regulator solenoid. RECONNECT all components. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

HE26 MEASURE EGR VACUUM REGULATOR SOLENOID COIL RESISTANCE
Key off.
EGR Vacuum Regulator solenoid disconnected.
Measure resistance across EGR Vacuum Regulator solenoid.
Is resistance between 26 and 40 ohms?
Yes No
GO to HE27 . REPLACE damaged EGR Vacuum Regulator solenoid. RECONNECT all components. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

 

I'll add this. For the miss code, my mom's Silverado popped a 307 on us, cylinder 7 misfire. Well...it drove the mechanic so insane he did the labour for free, over $1500 in work, he just charged us parts, he was so happy to get it done.

Turned out to be a head gasket causing it to misfire. Explain that one to me.

Random sorry, just my two cents on misfires.