P0251-shop thinks its timing chain stretch?
1999 Suburban 205,000.
I purchased and installed a rebuilt IP in December from local Stanadyne shop, as pump was shot. I then had same shop set timing after i installed it. Shop had some problems getting it timed but then replaced the cam sensor and all was good.
In February/March I started getting p0251 code, would clear and truck would run fine. Two weeks ago code appears again, I found leak in FFM lower small seal so I replaced it, fuel filter and all rubber fuel lines, cleared code and it ran great.
Tuesday wife back out of garage and it stalls, I have her run scan and its p0251. As I was out of town for work I had it towed to Stanadyne shop. Mechanic called me yesterday and stays he has been running it and the engine will "miss" randomly, doesn't matter if hot or cold. he also tells me the timing has moved half a degree sense he set it back in December so he believes the timing chain has stretched as it has 205,000 although he has not dug into the engine as it was add to labor costs. I asked about the optical sensor and he just stated it was built into the pump so.....I mentioned I changed the one on the old pump at 125k and he just repeated its part of the pump. I had to leave it at shop until Monday as I was not near the shop and it was closing time.
I am not dismissing the chain could be stretched but I would like to try other options before tearing the engine down. From reading forums I am going to do the follow:
1) replace PMD with my spare
2) test lift pump (original)by turning water drain valve on near thermo housing while running
3) hook clear line at water drain and see if air in fuel
4) replace optical sensor.
Mechanic seemed convinced it was mechanical as timing has moved, my question is would any of the above cause timing to move when it "misses" ? Wife stated it would jerk randomly before this happened... I rarely drive this vehicle so I never knew about this.
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