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dml7953

Vortec 5.7 Timing Brain Teaser

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Vortec Runs nicely with Timing set to TDC and CMP at -17 but like **** when set to TDC + CMP at 0 degrees. (GM Recommended setting)

 

I have a 98 C2500 5.7 which has me in a brain fog. When set to TDC on No1 cylinder with the Distributor set exactly to the #8 position it starts and runs fine but throws a P1345 code.  So to adjust the time to 0 degrees on Cam retard I have to move a tooth advanced. The truck will then start and run (like crap with backfires and high idle). So I am confused as to what could be causing it to run so badly when set perfectly according to all the specs and instructions I have read. 

 

I will be most grateful if someone here may be able to shed some light. I really don't want to start a shotgun approach changing Cam and crank Position sensors, distributor, PCM etc. and would rather isolate the correct problem and fix it.

 

Thanks in advance 

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There is a thread a little down the page with the title something like "So I need a scanner to set timing?".  On down 10 or 12 replies, maybe more, somebody posted a YouTube video of guys adjusting timing to get proper cam retard.  The way I'm reading what you wrote above, you're doing it wrong.

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Thanks for the link - I will use the 1345 trouble shooting diagnosis to try to find the fault. I do have a scan tool and have used it to set the Cam Retard. The problem is that this distributor cannot be "timed" in the old fashioned way and is a drop in which means it is either correct or a tooth off retarded or advanced. When installed correctly (no tooth off) the engine runs fine but throws the 1345 code and when i check the cam retard on my scanner it shows between -17 and - 20 degrees. There is no way to adjust  20 degree cam retard without resetting the distributor one tooth off. I am now starting to think that my distributor top rotor (metal part that runs over the Cam sensor that the rotor is screwed to) may have moved on the shaft (it is pressed on during manufacturing) so that when the plastic rotor is pointing to TDC on No1 cylinder the cam retard is 20 degrees off to the helical gear at the bottom of the distributor (Yes I know that is a mouthful :)   ) - It looks like my next step will be to replace the distributor as the helix gear is pinned and there is no adjustment to metal cam that the rotor screws to (which I think may have moved). The only other issues I can think of is Crank sensor or maybe a timing chain jump, but I am still leaning towards and issue with the distributor/cmp sensor at this time. Will keep on looking and will repost when I make progress. Once again thanks for that link with the troubleshooting guide.

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Well - I followed the diagnostic thread from Enthusiast and "Did exactly the same procedure I have used for the 15th time" but I'll be dammed if the Engine didn't start and sound different -- checked the Cam retard  and it was 0.4 degrees so I locked it down and happy for whatever reason, it is now running well again. I really have NO IDEA what I did differently but will take the Win. Thank you Enthusiast  :):):)

 

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Was it having the idle above 1000 that made it work this time?

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