Changing Firing Order

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Nov 17, 2011 | 04:17 PM

Hawk180

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Changing Firing Order

Being the tinkerer I am and somewhat of a half-A%$ed engineer, I have been studying the possibilities of changing the firing order of a 7.3 powerstroke to get rid of the oil starvation issues in #8 injector. My line of thinking is this: Since #8 is fired right after #6, the stock HPOP and oil rail leaves the #8 injector somewhat starved for oil if using the AD injector in #8. Navistar patched this problem by installing the lon-lead AE injector which delays the firing a couple of milliseconds to let the oil pressure recover in the rail before the solenoid opens the oil valve in #8. It works pretty good, but is a band-aid fix.

I am currently researching having a custom ground camshaft made for me and then either having a custom tuned ICM or re-pinning the connectors. Another fix I am looking into is drilling out the oil passeges in the rail a little bit and putting in one size larger fittings and HPOP hoses. I think these 7.3s will be around a while and it would be cool to get them running smooth and nice. These mods could be done on a rebuild and maybe if they work out be incorporated into most of the 7.3's eventually.

Nov 17, 2011 | 06:03 PM

BigAlsPSD

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Joined: May 2009

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From: Pea Ridge, AR

Interesting idea, Why not do the easier fix, and add a high pressure crossover line?

Riffraff Diesel Performance Parts: - HPX

Riffraff Diesel Performance Parts: - FRx

Nov 17, 2011 | 06:23 PM

Shake-N-Bake

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From: Mesa AZ

Quote:

Originally Posted by Hawk180

...Navistar patched this problem by installing the lon-lead AE injector which delays the firing a couple of milliseconds to let the oil pressure recover in the rail before the solenoid opens the oil valve in #8. It works pretty good, but is a band-aid fix...

According to Rosewood Diesel, the AE injector has a slightly shorter intensifier piston which causes the prime shot to begin a tiny bit sooner. I have always imagined the "dead head" issue was more a factor of fuel flow vs oil flow since the oil should easily be able to recover after the #6 fires due to the much higher psi...but fuel might not be able to recover as quickly since it is regulated to much lower pressures.

I think the best cure for the dead head issue is single shots and a regulated return. Those engines seem to run pretty well.