'89 Olds - working on the stumble...

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Old 03-13-03, 07:23 PM
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'89 Olds - working on the stumble...

On the advice of this forum, I checked, cleaned and tested the EGR valve on my 3.8l v-6-equipped '89 Ols 88 to help with a stumble on accelleration with 3 codes indicating EGR flow check. The EGR valve appears to be working fine, so I began looking at the exhaust gas O2 sensor. Since I don't have a multi-meter that will read to .100 vdc, and the price of the sensor was reasonable enough, I replaced the sensor and the spark plugs at the same time. I used Bosch Super spark plugs and a Bosch O2 sensor. Now, at other times in this forum, I have read that GM vehicles PREFER AC/Delco spark plugs. Is this also true of the O2 sensor? And, after disconnecting the battery to clear stored codes, will the ECU need time to "learn" the new sensor? The reason I ask is that the car stumbled a couple of times for my wife on a short trip to the grocery store. I was able to make the car stumble when I drove it after she returned home, but continuing to try to make it do it again under different rates of acceleration, the problem seemed to get less severe. What's up with that? I would appreciate any ideas from anyone who's got one. Thanks in advance - Chris
 
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Old 03-13-03, 08:10 PM
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if this car has a mass airflow sensor held on with 3 screws on the throttle body you may want to remove the 3 screws and clean any buildup off the 2 wire elements with carb cleaner this is a common problem and will cause a stumble. bosch products are usually of good quality so i dont think you will have any problems there. on this old of car there is not much relearning the computer needs to do, mostly idle speed if the o2 sensor had fixed the problem it would not of stumbled again.
 
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Old 03-13-03, 08:21 PM
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I agree with BeJay.
 
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Old 03-14-03, 01:07 AM
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Check the MAF as suggested above, also check for vacuume leaks especially the PCV. Also the crank angle sensor can cause stumble problems. But if you are getting EGR codes I would start with the EGR even if it appears to be working fine.
 
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Old 03-14-03, 05:40 PM
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Okay, here's the latest. After having changed the spark plugs and O2 sensor and cleaning the MAF sensor, I decided to clean the throttle body. When I FINALLY got the TB off, I noticed the inside of it and the adapter between it and the intake manifold were coated with carbon, with a knot of carbon emanating from what looked to be a passage from, of all things, the EGR valve! Removing the EGR valve and this adapter revealed that this was the case - the passage that was supposed to allow exhaust gas from the valve into the intake manifold was closed off with carbon.
Cleaning this passage out proved to be quite an adventure, but I think I finally got it done with drill bits, screwdrivers and oven cleaner. By the way, here's a red hot tip - DO NOT use oven cleaner to clean bare aluminum parts(such as throttle bodies) if you value that bright bare aluminum look. I hope I haven't altered/destroyed the ability of the throttle body to do its job, and just learned that oven cleaner seems to hate aluminum! If anyone else has had this experience, let me know what the outcome was, if anything changed other than the appearance.
The moral is that looking under the EGR valve won't necessarily tell the whole story. Make sure the passage is unplugged before reinstalling the valve. From the school of hard knocks - Chris
 
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Old 03-15-03, 11:25 AM
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GM's of this vintage are known for clogging the EGR ports. In fact, there is a gasket with a built in screen to "correct" this problem.
 
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Old 03-15-03, 03:20 PM
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A gasket with a built-in screen, huh? How some more restriction is supposed to help, I don't understand. Anyway, the car is all back together and the stumble is all but gone. I may chase it some more, but for a 350,000-mile car, it's running really well. I just cleaned the MAF sensor (again) with throttle body spray cleaner, so it's test-drive time. Last time, acceleration from zero through 75mph was WAY smoother than it had been in a long time. Thanks to all for the help. More later - Chris
 
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Old 03-15-03, 03:37 PM
Joe_F
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Ummm, the screen doesn't stop the flow, it traps the carbon particles .

Again, it is slowing down the carbonization process. Generally, the problem is elsewhere that is causing it.

350k on that engine is borrowed time and the thing doesn't owe you a wooden nickel .
 
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