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Old 12-06-2017, 06:39 PM   #1
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96 Wagon Code P0300, running rich

Guys,

My '96 wagon with the LT1 has been running a little rough lately, and stinks (like gas) from the driver's side exhaust. Throwing code P0300 and flashing the SES light now and then.

This started about 4 months ago and so I did what any reasonable person would do and replaced the expensive optispark...go figure, the problem persists. Like I mentioned, only the driver's side exhaust stinks. I took a look at the plugs and sure enough, the drivers side all have some level of oily deposits on them while the pass. side plugs are all clean and dry. Having trouble understanding what would cause this - bad driver's side O2 sensor?

I checked fuel pressure key-on and it was good (44 psi), only lost about 5 psi after 15 minutes. Checked the coil and IAC-valve resistances, all good. Couldn't find any vacuum leaks (even so, doubt that would only affect one bank of cylinders).

Appreciate your insights.

V/R

Alex
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Old 12-06-2017, 07:38 PM   #2
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Re: 96 Wagon Code P0300, running rich

Can you read live data? If so, what is the CTS reporting? How about the MAT? O voltages?
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Old 12-06-2017, 09:09 PM   #3
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Re: 96 Wagon Code P0300, running rich

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Originally Posted by Blue Bowtie View Post
Can you read live data? If so, what is the CTS reporting? How about the MAT? O voltages?
Argh, dont have live data capability right now....understand that could be critical to solving this and am working on it. Wouldnt CTS/ECT and MAT (is that IAT, MAF, or neither?) affect both cylinder banks though? Thats why I was kinda leaning towards o2.


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Old 12-07-2017, 06:45 PM   #4
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Re: 96 Wagon Code P0300, running rich

It could be a front oxygen sensor. It is possible to directly read the sensor output with an analog voltmeter. You would have to back-probe a connector, either right at the sensor or nearer the PCM. A 1 or 2 VDC scale would be appropriate.

Did you also replace the plug wires when the Opti was changed? If so, were the stock aluminum heat shields re-installed at the plugs? It made a difference on my B-body Impala. The wires/boots need that protection. It takes about a half-hour per side to replace the wires into the original clips and looms, but it is worth the effort.
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Old 12-07-2017, 09:08 PM   #5
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Re: 96 Wagon Code P0300, running rich

Pulled out my old ELM327. Tonight I replace the front O2 sensor on the driver side, however it is unclear at this point if that helped or not as the service engine soon light is still blinking and giving code P0 300.

Here is the sensor data:
Timing advance -16
Intake manifold vacuum: 10 inHg
MAF sensor air flow rate: 0.9 lb/min
Short term fuel trim bank one +0.8%
Long term fuel trim bank one +11.7%
Short term fuel trim bank 2. -0.8%
Long term fuel trim bank 2. +3.9%
Intake air temperature 107
Coolant temperature 206

02 sensor one bank 1. .26 V
02 sensor one bank 2. 0.26 V


Should IAT temperature be that high on a 35 night? ( edit: the intake manifold plumbing was pretty warm when I shut off the engine and inspected)

Is 10 inches low for an idle vacuum reading?
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Old 12-08-2017, 06:35 AM   #6
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Re: 96 Wagon Code P0300, running rich

The CTS looks right, and with a warm inlet duct the IAT may not be too far out either.

Did the O sensors vary (cross-count) at all or just remain at the 0.25 bias voltage? If not, the sensors may be dead. The higher LT fuel trims are a sign of that as well.

Yes, 10" Hg is really low. Can you verify that with a gauge? 16-21 is more like it at idle. If the vacuum is that low you may have found a big reason. Brake booster and EGR are suspicious, along with the list of other common potential candidates.
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Old 12-08-2017, 12:07 PM   #7
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Re: 96 Wagon Code P0300, running rich

Best way to check CTS is a cold engine before startup....IAT should equal CTS....

You have a flashing CE light....that means a bad misfire.....doesn't your scan tool count misfires per cylinder? Scan tool should be able to narrow it down to a cylinder....

You replaced the Optispark....whole unit? Cap, rotor, optispark, etc? New or used?

Wires should have been replaced, as well as plugs(using OEM)......also check the wire out of the coil for carboning/rust/arcing......also do a coil output test.....

If it's not secondary ignition, check compression......if ok, possible injector....

I remember when someone would bring in their Firebird with an LT1 engine, at around 100K....would ask them if they ever had a complete tuneup?

Usual answer was no.......they would ask how much it would cost, thinking under $150-200......when you told them it was around $500, minimum, they wanted to pass out......or they would think, I can do a tuneup at home.......

Doing a complete tuneup on these LT1's was a nightmare, because it involved removing the water pump to get to the cap/rotor, and if the w/p had never been replaced, you were putting a new one on, because that weep hole was right on top of the optispark......removing/replacing wires was a nightmare......getting at the plugs was not easy.....and you never did it on a hot engine....customer would have to leave it overnight...
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Old 12-08-2017, 08:08 PM   #8
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Re: 96 Wagon Code P0300, running rich

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Originally Posted by Tech II View Post
Doing a complete tuneup on these LT1's was a nightmare, because it involved removing the water pump to get to the cap/rotor, and if the w/p had never been replaced, you were putting a new one on, because that weep hole was right on top of the optispark ...... removing/replacing wires was a nightmare......getting at the plugs was not easy.....and you never did it on a hot engine....customer would have to leave it overnight...
Preahin' to the choir, brother, but doing it CORRECTLY is essential. Lucky that the B/D bodies all had vented Optis in every year. Not all F/Y bodies did.
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Old 12-08-2017, 09:43 PM   #9
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Re: 96 Wagon Code P0300, running rich

Haha yes, certainly a pain to work on and I have the scars on my hands from the exhaust manifolds. I replaced with brand new Opti from ACDelco.

Im using a very rudimentary scan tool (ELM327) doubt it has that capability. The wires were supposedly replaced during the last tuneup with the plugs 25k miles ago...the EGR was also replaced then and still looks shiny new.

Ill check for vacuum leaks and verify vacuum reading with gauge. I think the O2 sensor voltages varies, but I will verify. Btw this car has 235k miles on it

Thanks for all your advice and insights!
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