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A Short to ground will have a parasitic effect on Voltage so yes it's possible. I'm not saying that's it but in Bob's case that's a strong possiblity.
The wiring I have found in the early Contours leaves much to be desired, 6 of my 7 recalls I recently had done were due to wiring.
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Originally posted by Bob Blaylock:
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I guess I should mention that the P0402 code only ever occurred when the car was stationary and idling, while the codes related to the O2 sensor and to the mixture being lean have only occurred while the car is in motion.
... . FWIW, this article may shed some light, or further confuse the issue: EGR system may be cause of engine warning light My question: was the car idling at 2000 RPM when P0402 came on? Mine idles at about 650 RPMs. This article suggests that the fault, if it is EGR related, would have occurred at higher engine speed, 2000 RPMs or above?
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DT wrote: For a 96 Zetec, I would guess the car mileage is approaching 70K miles, more or less? 126,539 miles as of its last gas fill two days ago. It should be about 200 more than that now, give or take a dozen miles.
{I do hate spam, but that isn't really part of my email address. Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me. No advertisements. Spammers will be dealt with very harshly!} ------- Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
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DT wrote: My question: was the car idling at 2000 RPM when P0402 came on? Mine idles at about 650 RPMs. No. I do not think I've ever seen my engine idle that high, othe r than immediately after a cold start. When I've been able to correlate the P0402 code with engine activity, it's matched up with a drop in idle speed and a marked amount of roughness in the idle. I believe the test has been discussed in this thread, whereby you apply a vacuum to the EGR valve while the engine is idling. If all is well, doing this will cause the engine to either stall or to idle very, very badly. The effect that I have experienced that matches up with the occurrence of the P0402 code (and which I often get without generating a code) is much like the bad idle you get if this test doesn't quite kill the engine entirely, but not quite that bad.
{I do hate spam, but that isn't really part of my email address. Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me. No advertisements. Spammers will be dealt with very harshly!} ------- Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
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After my last posting last night, I went outside, with a few tools and a can of deoxidant contact cleaner, thinking to clean any O2-sensor-related connectors I could find. I was only able to get at one of them ? the main connector for the primary O2 sensor. On the way to work this morning (about 50 miles), I did not get any trouble codes, and I also didn't notice any sign of the rough idle that I had been blaming on the EGR valve. I wonder if it's possible that this one connector was the entire source of the trouble. This seems unlikely, as I do not see how any fault in this connector could explain the simultaneous drop on both O2 sensors. I guess I'll have to wait and see if any of the troubles recur.
{I do hate spam, but that isn't really part of my email address. Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me. No advertisements. Spammers will be dealt with very harshly!} ------- Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
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Gee the time spent looking at this could have paid for an O2 sensor. I realize the heated ones are a bit more than the $19.95 Bosch sensor for my 87 Buick LeSofa(er I mean LeSabre) but can't be too much more. One other, not so smart @$$ comment. The O2 sensor after the cat IS tied to the upstream sensor, IIRC. I think the folks who make the MIL eliminators for those who've done the "Mystery Mod" use this information to craft the circuitry for that item. Check out this page on how to build your own MIL eliminators. http://www.eaton-design.com/mustang/mil/ Now I've spent enough time here as well. OBTW, another reason for code P0171 is a dirty MAF, I think Lee Cox was having problems with that. Some brake parts cleaner on the body and some electrical contact cleaner on the wire should clean that right up, FWIW. TB
Tony Boner Personal: 98cdw27@charter.net Work: tony.boner@sun.com Saving the computer world from WinBloze as Unix/Solaris/Java Guru http://www.sun.com 1998 Contour SVT Pre-E1 618/6535 Born On Date: 4/30/1997 Now with Aussie Bar induced mild oversteer.
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I've just finished going through the O2 sensor data both from my drive to work this morning, and my drive home this evening. No sign at all of the ?drop-to-zero? glitch that I observed several times during last night's drive home, and no trouble codes at all. The activity on both sensors looks normal, or at least consistent with what I think to be normal behavior for the sensors on this car. Perhaps it really was just a dirty connector, and by cleaning that connector last night, perhaps Ive repaired this problem.
I do still get the rough idle, which I've been attributing to the EGR valve. When I get the money together for a new EGR valve, we'll see if it clears that up.
{I do hate spam, but that isn't really part of my email address. Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me. No advertisements. Spammers will be dealt with very harshly!} ------- Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
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Bob, do you live in a dusty climate? One silly thing that causes P0402 EGR Stuck Open codes is the the little sponge filter on the EGR solenoid gets clogged up. When this happens, solenoid holds a vacuum even when none is called for. So you get EGR flow when none is called for. Carefully (use a pocket knife) pull the cap off the EGR solenoid and clean the sponge filter inside. You may break a couple of the tabs on the solenoid cap, but that's okay. It will still hold.
Rob Weiss
'99 Mystique, 2.5L, MTX,Black/Tan, 37K miles
SVT Air Intake & Throttle Hang Plug
Build Date: December 14, 1998
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Rob Weiss wrote: Bob, do you live in a dusty climate? One silly thing that causes P0402 EGR Stuck Open codes is the the little sponge filter on the EGR solenoid gets clogged up. When this happens, solenoid holds a vacuum even when none is called for. So you get EGR flow when none is called for. Carefully (use a pocket knife) pull the cap off the EGR solenoid and clean the sponge filter inside. You may break a couple of the tabs on the solenoid cap, but that's okay. It will still hold. That seems like good thinking. I do, in fact, live in a dusty area. But if you read my original posting this thread, you'll see that I wrote, ?I then tested the EGR Vacuum Regulator Solenoid, which controls the EGR valve, and determined that it was malfunctioning, so I replaced it.
This seemed to cure that problem, but several weeks later, it returned, and I was again getting the P0402 code. On further testing, I determined that the EGR valve itself was failing to consistently close all the way when it should, and that it was the EGR valve itself, and not some other component, which was failing. By way of verifying that it was the EGR valve itself, and not the solenoid, I disconnected the vacuum hose from the EGR valve, and had the P0402 code occur while the EGR valve was thus disconnected, and while there was no way that the EGR valve could be receiving a vacuum to open it. Without a vacuum, the EGR valve should have remained tightly closed, but the P0402 code would seem to indicate that it was slightly open.
{I do hate spam, but that isn't really part of my email address. Remove the string ?HatesSpam? from the email address ?BobHatesSpam@blaylock.to? to email me. No advertisements. Spammers will be dealt with very harshly!} ------- Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
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