Need professional mechanic advice re:EGR Valve

[donozark]

Vehicle:
Late model Pontiac Grand Am GT. Excellant condition. 70K miles. Always maintained,etc.

Problem: "Service engine soon" light came on. Took to dealership. Diagnosed as "in need of new EGR valve." $400!

I first tried to disconnect battery/replace fuse in order to re-set on-board computer. Worked fine for a couple days. Then light came back on.

I then replaced (myself-not dealer) EGR valve with GM/Delco part. Worked good for 2 days, then back on. Exchanged EGR valve for new one. Worked ok for a couple days, then, you guessed it, light came back on!

I pulled it, brass plunger/valves work ok,etc. car runs fine, so apparently problem is non-existant,other than the warning light.

Problem:What next? Can't sell/trade car if "service engine" light comes on during test drive! Guess I should eat crow and go back to dealer? Any PROFESSIONAL suggestions?

[Redbeard]

The EGR passage in the intake may be plugged with Carbon. The EGR Valve is operating properly, but there is no Exhaust Gas Recirculation due to Carbn Buildup.

Please get me the:
Year (Tenth Digit of the VIN Code)
Engine (Eighth Digit of VIN)
Trouble Code it set (Code Number, i.e. 42 or P0042)

It may take a few hours to get back here, but I'll see what I can do.

Redbeard

[Twisted Cross]

It could be the Oxygen sensor in your exhaust system. It monitors the amount of oxygen coming out of the motor and the mixture the computer puts out is controlled by it. It is one of the most important senors when it comes to modern day fuel injection emmision contolled vehicles. When it goes bad it can throw a code that might seem like it would be an EGR valve and it is one of the easiest ways a dishonest dealer can get you into a $400 EGR valve.

The gases in the exhaust cause a reaction with the special metal coating on the sensor that causes a voltage to be sent to the computer. If the voltage is in the corect range which is very small that the Compter monitors then the mixture will be adjusted correctly. If the voltage is non-existant or too high the computer will send the wrong signal to the system. This can look like a failing EGR valve becuse the computer can be sending the wrong signal to the EGR for when and how much to open. When the EGR is opening too much or at the wrong time it will send too much or too little reburned exhaust gas into the engine. Too much from the EGR will cause a rich mixture and too little can cause detonation when the car is hot.

It's a catch-22 that is easily mistaken by an inexperienced mechanic for the EGR or a dishonest shop to sell more parts. At 70,000 miles your Oxygen sensor could very well be ready for replacement. They can last longer, but it is dependent on the quality of gas you use or the oil in your engine. If the products you use have more inpurities in them the metal coating on the sensor can breakdown quicker and the sensor will fail quicker. Could be that it only lasts 60k to 70k also.

Their fairly cheap compared to the the EGR valve so you might want to try it before taking it to the shop. You could tell the tech at the shop that you already replaced the EGR and that will give an idea what is going on then they might not try to rip you off once they know you have some knowledge and make sure you mention the Oxygen sensor to them.

[bars full auto]

My 89 S10 with a 2.5 has done the same thing for 3 years. I also need help.

[donozark]

It's 1995. GT. V-6. 3.1 engine.
Car is out of town at present. Don't have engine code from dealer.
Sorry. Not much help.
I may try the oxygen sensor route but I think we checked that? I cleaned out intake(as well as I could-without removing manifold). That is, if a defective oxygen sensor shows up on diagnostic machine.

[Derf]

The O2 Sensor would show up as a seperate code. My advice would be to take it to a local shop that has an OBDII scanner. And have them scan it and tell you every code that comes up. Some places will do it for free, others charge $20 or so... Just shop around till you find the cheapest place that will scan it for you. Then fix what the codes tell you too. If it comes up as an egr related problem you should check all your vacuum lines that connect to the egr, because a vacuum loss would throw the same code as a blockage... Hope all of this helps...

[Redbeard]

Your Year/Make/Model should have a standard ALDL connector for code retrieval (non-OBD II).
EGR codes are 75, 76, 77. Since it takes several days to reset the code it is Probably the code 77. Allow me to explain:

The EGR Valve has Three Electric Solenoids that are operated by the PCM. It opens each in succession (leaving the previous valves open) depending on several factors including load, vehicle speed, O2 sensor reading, et cetera.
The MAP (Manifold Absolute Pressure) Sensor looks for a Specific Change in Manifold Vacuum when the PCM engauges one or more of the EGR Solenoids.
The Third Solenoid (Code 77) is usually needed during continous highway driving.

Check for Chaffed Wires/Bad Connection/Pushed Out Connectors at the EGR Plug.

Make sure all the holes in the Intake where the EGR mounts are clean.

Have someone with a Scan Tool run the "EGR Function Test" and monitor the MAP Sensor Reading.

There is a test procedure and flowchart, but with my limited typing skills it would take DAYS to post!

Redbeard