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Fluctuating oil pressure. Hard start.


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2009 gmc sierra 5.3. 5w30 and frame filter. Plugs done in spring. Been having oil pressure ranging from 15 to 50. During all rpm range. Also having a hard start. (6 to 8 secs if holding key before ignition) and can smell gas after starting. Just changed oil and filter last week. Problem started two days ago. What causes all problems at once?

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I would get a manual gauge an confirm pressure. This range of truck has an issue with the oil pressure sensor failing and giving wrong readings. Once you confirm oil pressure you can continue diagnosis. 

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Well, I had read my codes and had a bad upstream 02 sensor. Changed that, found fouling on number 1 plug, I changed them as I do yearly as with wires. That helped and oil pressure stabilized. Still low at idle going off what my truck has always read. Still a bit of a hard start but as bad. I will do that and see what see really reads. Still smelling rich fuel mixture? Shouldnt need to clear that code or do I?

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The code will be logged and should turn off if the issue is resolved. If it is an active code it wont clear do to the issue still being active.

Best thing to have is one of them cheap code readers for clearing codes, unless you want to spent some cash on a more expensive one.

I keep a cheap one on stand by just for clearing codes. If a person looks at the codes every time they come on, you wont have a lot of them stored and will know if its an issue.

Some people let them back log for years.

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The oil pump's pick up tube o-ring typically fails around 160K miles.  You can add two or three more quarts of oil to the engine to submerge the o-ring and if the pressure stabilizes you'll know what to do.  As for the fuel smell and hard starting, try replacing the purge valve with GM OE or ACDelco.  You really need a bi-directional scan tool to test your injectors and coils and such.  

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  • 4 months later...
On 12/12/2019 at 11:43 PM, swathdiver said:

The oil pump's pick up tube o-ring typically fails around 160K miles.  You can add two or three more quarts of oil to the engine to submerge the o-ring and if the pressure stabilizes you'll know what to do.  As for the fuel smell and hard starting, try replacing the purge valve with GM OE or ACDelco.  You really need a bi-directional scan tool to test your injectors and coils and such.  

I think it happens because of dirty oil( sludge sticking to the tube) and the oring is a path of least resistance     it's like a straw  that has a tiny hole  instead of picking up soda you get a lot of air  mixed with soda

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