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Another DTC P0300 misery


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Old 03-08-2013, 04:47 PM   #1
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2007 suburban LT, 4WD 136,000 miles--I have a code reader but not a scanner---- I had a DTC p0449 (have had this twice before on this Sub)--I replace the solenoid, then had continued rough idle with codes P0300, P0102, and P0171.

I replaced plugs first with Bosch Platinum, then replaced those with new AC delco iridium (#41-110)---- passenger side rear plug is a real pain to replace!
Put in new plug wires. cleaned the MAF sensor and throttle body. THe P0171 and P0102 codes cleared. still had P0300 code.

Checked next for vacuum leak, but unable to find any leak including spraying carb cleaner with engine running and no change in engine speed.
But the spark plugs now look wet to me --dark brown to black with slght odor of gasoline. I figured a vacuum leak would cause a lean mixture.

Fuel pressure is 55 with key on, engine not running--it drifts down to about 52 after 2 minutes; with engine running fuel pressure is 60

Neighbor recommended replacing camshaft position sensor--I did this but still had P0300 and rough idle.

I checked the air intake assembly for leaks--couldn;t find any--replaced the throttle body gasket--ran great for 20 minutes with no codes and no flashing MIL. Then 2 hours later, restarted engine and MIL flashing with P0300 back after about 3 minutes.


Can a bad O2 sensor cause this? iF so, why no DTC code for the bad sensor?

appreciate any advice on where to go next with this. thanks

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Old 03-08-2013, 05:07 PM   #2
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I seen you did a few items. GM's Like Bosch plugs.

Here is some info I was able to find

A code P0300 may mean that one or more of the following has happened:
Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer

_____________________________________________
1979 Monte Carlo with a 400hp+ 350ci.
1983 T10 w/2.8L getting parked till can restore and put a v8 in
1994 Blazer 4dr with the CPI(FOR SALE)
1995 Blazer 4Dr 4X4(FOR SALE)
2002 Trailblazer LT
2007 Envoy Denali

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Old 03-08-2013, 06:08 PM   #3
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thanks montec--I been referiring to a similar list---I'm just trying to minimize slapping new parts on unnecessarily. In few more paychecks I'll have enogh $ for a mechanic to put it on a scanner.
I forgot to add-- on my code reader, on live data, fuel system 1 1n 2 both indicate fault,----my guess is fuel pressure regulator but I think this is part of the fuelpump assembly.

MAP ranges from about 10.6 --11.5 inches Hg at idle. Is this low? Before I change the intake manifold gasket, I wanted to try to confirm a vacuum leak.

thanks again for any advice

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Old 03-09-2013, 02:25 AM   #4
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After re-reading your original posts, I've come to see with the Evap code you fixed twice could have some meaning.

Have you replaced the gas cap with an OEM one?

Have you cleaned the MAF sensor?

Do you run a K&N filter? those are know for making them dirty. These are delicate items and there is a specific cleaner you can use that's an aerosol cleaner, not bad priced.

Check PCV valve(cheap to replace)?

Bank one lean, could be a faltly O2 sensor.

When did you last replace the fuel filter? And dont get a Fram one.(there has been recalls due to them leaking)

Could be a dirty Fuel injector as well. Run some lucas fuel system cleaner thru it. I would say after you replace fuel filter. I like the lucas one as it does work and isn't harse like many of the other ones.

_____________________________________________
1979 Monte Carlo with a 400hp+ 350ci.
1983 T10 w/2.8L getting parked till can restore and put a v8 in
1994 Blazer 4dr with the CPI(FOR SALE)
1995 Blazer 4Dr 4X4(FOR SALE)
2002 Trailblazer LT
2007 Envoy Denali

Independent AmsOil Dealer

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Old 03-09-2013, 01:57 PM   #5
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thanks for update.
I had cleaned the MAF sensor with MAF cleaner, borrowed by neighbor's MAF sensor from his Tahoe with same engine--no change--that code went off after I cleaned all the electrical connectors to the MAF and also the engine grounds.

Never used a K & N filter--I always have used a Fram air filter.

Not sure if there is an inline fuel filter --I'll be looking today

Plan on changing the gas cap and PCV filter and run some lucas fuel system cleaner.
Next would be the O2 sensor.

thanks again.

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Old 05-28-2013, 02:21 PM   #6
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followup on this P0300 code:

I ended up replacing both upstream O2 sensors, then got P0307 and P0171 codes.

Pulled the driver side valve cover and found excessive play in the intake valve for cylinder #7. The lifter for the intake valve on # 7 was stuck in a compressed position---this is one of the AFM lifters.

Replaced it,and after correcting a small vacuum leak at the the emission purge valve, engine running smoothly now for past 3 days with no codes----only problem now is intermittent stabilitrak warning--looking into this for my next adventure.

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Old 05-28-2013, 03:26 PM   #7
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Glad you got that fixed. As for your next adventure I wish you luck. I hate electronics.

_____________________________________________
1979 Monte Carlo with a 400hp+ 350ci.
1983 T10 w/2.8L getting parked till can restore and put a v8 in
1994 Blazer 4dr with the CPI(FOR SALE)
1995 Blazer 4Dr 4X4(FOR SALE)
2002 Trailblazer LT
2007 Envoy Denali

Independent AmsOil Dealer

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