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Geo Metro Code 51 Solution Sequence and Side Benefits

02-08-2012, 12:30 AM
02/09/12 For many months I have both enjoyed and appreciated this forum. It is time I attempted to contribute, by offering a solution to a common Check Engine fault that, hopefully, can benefit others, just as you folks have benefited me. So, here goes: My subject tonight is the most annoying Check Engine light, which, after placing a 10 amp fuse in the diagnostic-switch socket of the fuse box which is located under the instrument panel on the driver's side and turning the ignition switch on, and seeing Code '51" flashing, I, along with so many other Metro owners are chagrined to learn that it represents an 'egr system failure'. Initially, it would seem reasonable to deduce that I had a bad egr-valve. Okay, the system actually has quite a few components, like the egr-valve itself, a vacuum switching valve, a vacuum modulator, the ecm itself, connecting vacuum lines and electrical wires, as well as the exhaust gas passageway, without which nothing useful can happen at all. Folks, let's just see how easily a person can cut to the end-game, solve the problem, and enjoy the benefits. #1. Remove the fuse from the diagnostic-fuse slot and put it away. #2. Completely warm up the engine. If you open the hood and feel that the upper radiator hose is quite warm, then you know that the engine is completely warmed up. #3. Reach along side the throttle body and grab the throttle cable linkage and rev up the engine to over 3000 rpm several times while looking at the egr-valve diaphram. It should move in and out each time you accelerate the engine as I explained. If it doesn't do this, there is a good chance that the egr-valve itself is carboned up. Remove it (2 bolts) and clean it and try this test again. Normally, a good cleaning will do the trick. #4. Let's assume that the egr-valve now works as intended and does, in fact move in and out as you repeatedly rev the engine. The next step is to pull off the vacuum line that attaches to the egr-valve diaphram, again, with the engine at idle. When you pull off this vacuum line, the engine should stall (die). It is my belief that it probably will not die. By the way, the mere fact that the egr-valve is moving in and out when you rev'd the engine has exhonorated the egr-valve itself, the vacuum switching valve, the vacuum modulator and the ecm. At this point you have good reason to smile. #5. Now, remove the egr-valve (2 bolts) and also remove the exhaust manifold. It's not a bad idea to also disconnect the negative cable from the battery, as this will protect your car from any inadvertant short circuits. Also, remove the air cleaner and the pcv valve (positive crankcase ventilation valve), and also, remove the 4 bolts that attach the throttle body to the intake manifold along with the short spring in the throttle linkage. It is not necessary to disconnect the actual linkage itself, as you are not fully removing the throttle body, but merely so you can lift it out of your way. #6. You will need a can of carburator/choke cleaner, a reaming tool such as a coat hanger or any other homemade flexible reaming device to clean out the exhaust-gas passageways that exists in 3 sections.
1st section is within the exhaust manifold itself, alongside of the #3 cylinder exhaust port, the 2nd section mates to it and travels to the inlet port of the egr-valve, and the 3rd section goes from the other egr-valve port, along side, to the exiting port in the intake manifold just underneath the throttle body, and lastly, you will need an air compressor that is capable of providing as much as 120 psi. #7. In the exhaust manifold the exhaust passageway is quite short, but it makes a 90 degree turn. When you clean out the passageway in the 2nd section you will want to be able to see your reaming tool protrude as coming out of the egr-valve entry port each time you push the reaming tool in. Then you'll know that that section is clear. The most difficult section is the 3rd section to the intake manifold plenum. Alternate with choke cleaner used liberally, the reaming tool, and applied compressed air. Remember that you should be able to see the end of the reaming tool appear in the plenum below where the throttle body bolts on. That's why you removed the 4 attachment bolts for the throttle body, which is now out of your way. The reaming tool I used was the one offered in this forum by DoctorBill. When that section finally breaks free, you'll know it because there will no longer be any back pressure sound when you pull back on the compressed air chuck from the egr-valve port. Okay, the problem source is now gone. Reattach the throttle body, the linkage spring, the air cleaner, the exhaust manifold and the egr-valve itself and of course, the vacuum line to the egr-valve diaphram. Reconnect the negative cable to the battery, and voila, you will be pleasantly surprised. Oh, by the way, do clean the pcv valve also. There will be plenty of gunky goo in it. Be careful to NOT install the pcv valve upside down. Blow into it. It is a one-way valve, and the air travel should be top-down, and NOT the other way.

You will find that you can now cruise all day long at 65 or more without the check engine light coming on. Furthermore, you'll discover that whatever oil consumption you have been previously experiencing, it will simply disappear. When I bought my 1994 Metro in August of 2007, it had 86,000 miles on it and right away I discovered that it consumed a quart of oil in 490 miles. Here we are in February of 2012 and the car has 137,400 miles on it and since solving my Code 51 problem as described above, I've gone 1420 miles and used only 1/4 quart of oil. As far as mileage goes, you'll not suffer at all. If your Metro has a 5-speed manual transaxle, then you should expect to receive approx 50 mpg if you run at 55 mph and below in highway driving. If you average about 65 mph then you'll only achieve between 45 and 46.5 mpg. At least, this is what I am experiencing.

As a final note worth sharing, I do substitute a quart of Lucas Heavy Duty Engine Oil Stabilizer for one quart of normal engine oil when I do an oil change, and I do use Acetone as an additive in my fuel. Just wanted to place all of my cards face up. Hopefully, this information will be helpful to someone in this forum.

Happy motoring.

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