IP advance with RPM - Diesel Bombers



Ford 83-94 6.9 and 7.3L General Discussion of 83-94 6.9 and 7.3 Liter Ford Diesels

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Old 02-19-2018, 08:33 PM
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Default IP advance with RPM

At what point should the injector fire at idle and at 2K RPM?
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Old 02-20-2018, 02:22 PM
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Fresh 7.3 IDI and a fresh IP.

How is the injection timing supposed to change with RPM? I have asked this question many ways and the only answer I get is "9 degrees at 2K RPM". But the engine doesn't always run at 2K RPM. What should it be between idle and 2K RPM?

I have a Kent Moore J33300 Tach-N-Time with both mag pick up and timing light.

This is the first one I have needed to time.
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Old 03-27-2018, 02:22 AM
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If this helps, I just had the timing adjusted on my 85 6.9L. On the report from the shop it showed .03 degrees [email protected] Rpm when it came in and was set to 4 degrees BTDC @1400 Rpm when they were done. Completely changed the way the truck runs now, bought it in 2010 and it was probably off then. There is a procedure on how to do it properly (goes into detail in the engine manual)... if you can find it David Graham makes a CD ROM complete Ford shop manual set. Mine was $19.99 well worth the money spent.
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Old 03-27-2018, 09:31 AM
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I finally determined that I had it backwards. The system is generally referred to as an advance system, so I thought it was like the mechanical advance in a distributor. But it is actually like the vacuum advance in a distributor. That is, it retards with increasing load, which is implied by accelerator position. So, the timing will be advanced more at idle than at 2K. 2K is chosen because by that point it is expected to be at full retard.

I have talked to people who rebuild those pumps and have all the proper equipment and they think it is an advance system rather than a retard system. They just set them like the equipment indicates. But none of them ever put one on an engine.

I have a Kent Moore J33300 Tach-N-Time with both mag pick up and timing light. I have had the timing set all over the map. From what I have observed, a good setting is take it to the edge of no rattle after warm up. And that will probably be around 8 degrees at 2K and 13 degrees at idle. When you have a way to read timing you need to watch it as RPM changes to see that the retard system works smoothly.
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