First question. Has anyone used a good gun or pipe cleaner to clean out the EGR plate on the back of the head? Are there any liquid chemicals you can use to clean it out without scrubbing the thing? Anything you can do on the engine while driving?

Second, is there a way to test the EGR tempoerature sensor? I don't have my FSM handy as I'm at work, but this problem is bothing me. I'm getting a code 71 that keeps coming back after resetting the ECU.

I have removed and cleaned the temp sensor on the throttle body. There is another sensor of some sort on the EGR valve. What does that do, and can it be tested or replaced?

 

Dave, I have been contemplating an EGR system overhaul (you know after 280k it can't be working like new) as well and am interested in what you find out. There's a link to an FSM somewhere...

I have a 88 FSM and it shows a gas temp sensor on the california vehicles only but has no info on checking its operation.

 

That's true, but for the valve it should only be opening or closing. That shouldn't really wear out. The sensor, on the other hand, could wear out. I could be wrong about the valve part, though.

 

i used carb cleaner and picks but could not get the valve to break loose to move freely under vacuum. carbon is caked in so bad that it has sealed itself. you might just need a new egr valve if it isn't working properly. mine was stuck open so i have to eventually replace it. it is blocked off for the mean time.

 

Is the valve in the EGR rubber? If so, I may have damaged mine with carb cleaner.

 

No do not believe that the valve is rubber. The transducer does have a rubber diaphram, but if it were torn it would not open. I also have the same 71 code on a Corolla, I know not the same but simular. The code you have I understand is part of the EGR system. I have verified that the EGR is working with a vacuum pump, killing the engine, so I am down to the EGR temp sensor as well. It could be as easy as checking its resistance, but dont have the specs. I was also wondering if perhaps adding some SeaFoam to the gas tank would help remove some of the carbon deposits that have accumulated over the years. Maybe someone here has more info or experience with this.

 

I wasn't thinking of using seafoam in the gas tank, but directly in the egr to loosen some gunk and then i'd scrub it off and burn it out.

Does the code 71 affect engine performance, or is it just a warning to the driver?

 

I used a pistol cleaning kit on my old EGR valve (non-sensor type). The gun cleaning solvent worked pretty good at dissolving the crud inside. I tipped the EGR up on end so I could fill it w/ solvent, then let sit for a few hours before hitting the insides with the small round brush. Drain and repeat as needed and then used a hand vacuum pump to pull open the valve to let the solvent get in there. Seemed to work better after the cleaning.

 

This code indicates that the EGR system is not functioning correctly. If this is the case your combustion chamber will burn hotter also creating a higher percentage of NOx.

 

But does it cause the ECU to act differently? Like cutting back the fuel injectors or anything else?

I'm ordering some gun brushes I found on amazon.com so I can clean the EGR better than I have been able to in the past.

Also, why does the engine stall or sputter when the valve is closed? Does it really make that much of a different for the exhaust gases to flow/not flow?

 

Well could be a couple of cases. One is the ECU is commanding the EGR to open and it is not or it is plugged an exhaust gas is not flowing enough to heat up the sensor fast enough to tell the ECU the valve is open (if open, the hot exhaust gas heats up the sensor and that is what the ECU uses to confirm the valve is open). But it could be the the sensor is cakes in soot and not picking up the heat of the gas, or the sensor itself may be defective. In either of the last two cases, all is normal, EGR-wise, just that the sensor is not reading the right temperature. Some folks fool the ECU by jumpering the sensor connector with a resistor.

 

The engine dies at idle when you apply vacuum the to the EGR which is intruducing Exhaust Gas into the combustion chamber. The Exhaust gas does not have the oxygen needed to ignite the fuel mixture.
As for the ECU reacting to the hotter engine temp, there is not really any feedback to the ECU. Many people have EGR block off plates and just increase the radiator size for cooling the engine block to prevent overheating. Just keep an eye on the temp gauge. Also dont know if you have to get a smog check out there, but NOx is a gas that is measured here in CA.

BTW the EGR is only open at cruise speeds between 40 and 60mph.

 

I just checked by EGR by sucking on the vacuum line. I could feel and hear the valve opening and closing, but there was some grinding (guessing carbon buildup). Because I could feel the valve open and close, does this mean the EGR is okay?

 

I was able to test the EGR by sucking on the vacuum line. I could hear and feel the valve opening and closing, though there was some grinding. I'm guessing because of carbon buildup. Does this mean the EGR is okay?

 

I was able to test the EGR by sucking on the vacuum line. I could hear and feel the valve opening and closing, though there was some grinding. I'm guessing because of carbon buildup. Does this mean the EGR is okay?

 

Well, there are several aspects to "EGR being OK". First is as you tested with manual vacuum application, so the valve diaphram is working. Now you need the automatic stuff to actually apply that vacuum at the right time, so you can have a perfect new EGR valve but if it is never told to open, then the EGR system does not work, even though the valve is 100% perfect. Then if the valve is getting vacuum at the right time and opening as it is supposed to, all may not be OK. Why? EGR passages could be clogged internally such that little or no exhaust gas flows. So you could have a perfect EGR modulator and perfect EGR valve, but if the passages are plugged, then the EGR system will not work as designed.

One test is to pull a vacuum on the EGR with engine at idle and see if the engine stumbles/dies. If so, that is saying that enough exhaust gas to kill the engine is getting through. But even that may not be enough for smog testing.

My '85 would kill the engine with opening the EGR, but it failed the NOx smog test as not enough gas was getting recirculated. I found in my case it was some internal soot buildup at the head to header and gasket area and I spent a few hours with a Dremel opening up those passages to allow maximum gas flow and them that dropped my NOx readings to about 1/3 of the original readings. I also shot solvent through all the internal passages and blew them out w/ compressed air. Basically made sure there were no restrictions anywhere and that let me pass smog.

 

For cleaning the rear cover plate, oven cleaner worked pretty well. Soaked, wrapped in a plastic bag, and left it for a day. Two days would have been better.

I used carburetor cleaner and some brushes for the EGR valve itself, being careful not to get any on the diaphragm up top. Hold the valve open to clean around its seat by either sucking on a vacuum line or using a pump if you're fancy.

 

Did you take off the rear cover plate with the head off? If not, how difficult was it to get to?

 

Yeah, the head was off. There isn't much room to work with it on.

 

Eeeew. I'm going to have to do it with the head on. Maybe I'll just gut it with a coat hanger.