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Old 05-28-2010, 10:29 AM   #1
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Default 96 SSE stumbling, erratic idle

So I've had this 96 SSE for about 5 years. Before I got it, it was a 'company car', garage kept and maintained by the dealer. I've put about 80,000 miles on it (it'* at 194k). I normally do all of my own maintenance, but this is the 'newest' car I've ever owned and it has more sensors than all my of other cars combined!

There is some history that may be pertinent - so bear with me. Last summer it started hesitating, jerking (sometimes pretty hard), especially on acceleration or under load (going up hill, etc). I thought it was a coil, since I had already replaced two of the three, but it wasn't quite the same as when the others failed. Replacing the last coil didn't help much - I guess it could still be one of the 'new' coils.

At any rate, it had been (since shortly after I got it) occasionally throwing a code P1406, which until recently I couldn't identify. I purchased PCM Scan and and an interface to check the code and it simply told me 'Unknown Diagnostic Code'. I now know it has to do with the EGR circuit. But it'* only occasional maybe once a week and will clear on it'* own if I let it.

At any rate, one day I went out to leave for work and as soon as I started the car it shut-off, like I had turned the key back. Over and over again it did this. No check engine light, it would start fine, engine would respond to the accelerator, but after 2-3 seconds, just shut-off.

After several days of beating my head against the hood (and the battery charger), it finally threw a code - Mass Air Flow sensor - just my luck, the most expensive one! I replaced it, same thing. PCM Scan is showing 2.11 g/* coming from the mass airflow sensor. So I started checking the wiring and found where the +12v lead to the sensor was was cracked and possibly shorting to the +5v where it was cracked as well - more like dry-rotted. I peeled back the covering on the harness and taped up the bare/broken spots and now I get good readings from the sensor. Car starts, and runs, again. But it is still spitting and choking while driving. MAF will drop to 2.11 on occasion still, so I may have other bad spots in the wiring yet to find.

Now that I know more about the obdii params, I've noticed some interesting things: fuel rail pressure sits at 749.29 psi, eq_rat is 0.005 - all the time. I know what these parameters are - and these numbers are not only wrong, but they should change. Are there any other sensors that I should be paying attention to that may tell me why these two parameters aren't changing the way they should?

Was that too long?

Thanks for any help/advice -
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Old 05-28-2010, 10:33 AM   #2
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What is your fuel pressure in lbs? The info you gave on that is confusing. I'm off to go look up the P1406 to find out what it is because you only said EGR and I think that'* a flow code.

Edit: Pintle position circuit.

I would remove the valve and clean it. Likely it'* causing a vacuum leak and that'* the studdering issue. If you need parts, especially the expensive ones it might be wise to post in the wanted section. Something like an EGR, many of us have a lot of spares laying around that we'd sell cheap. As in......super cheap.
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Old 05-28-2010, 10:54 AM   #3
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Thanks for the quick response!

Yeah, I guess didn't elaborate on the EGR code much because I assumed it was unrelated; mostly because it doesn't come up that often. I took the EGR pintle off and cleaned it, but it didn't seem to be that dirty. The tubes going to the intake and exhaust also seemed to be clear.

Your comment about a vacuum leak is curious, what I took off doesn't have any vacuum hoses - am I looking at the wrong part?!

I don't know the fuel rail pressure in lbs, PCM scan is only reporting psi, which I mis-remembered in my post - it'* actually stuck at 742.59. When I attach a mechanical fuel pressure tester, it sits steadily at ~40lbs - no leak down, even after 15 minutes with car shut-off.

Edit: DUH! psi is lbs-per-sq inch, sorry, I wasn't thinking!

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Old 05-28-2010, 11:03 AM   #4
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Our pcm'* can't scan fuel pressure. There'* no sensor for it. Not sure what that reading is, but it is false unless you have a special case car which we've never heard of happening.

My reference of vacuum leak is kinda a general statement about a leak of air that the engine would have to process. If your EGR is stuck open then exhaust gasses are pushing their way through it and into the intake manifold. This would be unmetered air (aka vacuum leak). Sorry for not being clearer.
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Old 05-28-2010, 11:12 AM   #5
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That makes sense. I wondered when I couldn't find any reference to a 'fuel pressure sensor'. PCM scan reveals it as a 'supported pid' but obviously it is just showing a default value.

How can I best check/test the EGR valve? While I did take it off, I did not attempt to dis-assemble. Should I? My 'cleaning' process was limited to holding it, valve side down and spraying throttle body cleaner into the valve chamber. I had read stories of hours spent chipping and scraping away debris, but I saw none of that.
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Old 05-28-2010, 11:23 AM   #6
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For your type of EGR valve there is nothing more to do other than what you have done. To my knowledge there is no way to take it apart like the old school ones.
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Old 05-28-2010, 11:49 AM   #7
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Are there any resources I can go to where I can see a list of pids actually supported by my car? With PCM Scan showing pids as supported - but not really, I don't know if I've got a 'problem' or a default value. Such as the fuel rail pressure, fuel level input, eq_rat (lamda).
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Old 05-28-2010, 11:51 AM   #8
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I believe they are in the FSM, I'm not sure where else you'd see them. Most scan tools I've used say the correct value or nothing if they have a pid that isn't in the pcm.
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Old 05-31-2010, 10:46 PM   #9
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Okay, I got another EGR Valve from junk yard and it hasn't thrown anymore codes (~100 miles). Still getting some chugging though...at an idle and while cruising - especially under load.

Not sure if I should start a new thread for this or not, but I've noticed that I appear to missing a vacuum line. There is the vacuum stack on the intake, one of the lines goes to a electronic device mounted about the fuel rail on the drivers side, one leg goes to the supercharger bypass valve, there is another port that has no line on it. I don't have any vacuum lines hanging, and I can't find another 'open' connection. Any idea where this is supposed to go?
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Old 05-31-2010, 10:49 PM   #10
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That'* not a vacuum line, nothing to worry about.
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