I have 2 7.3's and the motor that has high mileage 240,000 runs really rough when cold and shakes and dances and the other which seems to be newly rebuilt runs like perfect even when cold like it just rolled off the show room floor.


The one with higher miles also does not seem to have the cold start throttle mechanism working either but it seems like there is more to it than that.


Could it be because it is more worn or is there more than likely something going on somewhere else...., Thanks.

 

I hate going over this same thing again and again, but:
1. Check the glow plug system. A single dead glow plug will let the engine start, but will produce a miss in one cylinder for a minute or so until it warms up enough.

2. Once the glow plugs are fixed right, timing is next. If it's smoking white, you are retarded. Same with blue smoke, but to a lesser degree.

Seriously - *anything* starting related or smoke related? These two should be your go-to checks. They are the most common source of *any* issues I've seen with all the various IDIs I've owned.

BTW, every single motor I've gotten my hands on has been able to be fixed and start right up without issues. I've had multiple "ether baby" motors that *would not* start without it... fixed the glow plugs and timing? Fires right up on all cylinders at 20F.

 

OK sorry and thank you..... I already ordered the glow plugs and they will be here shortly.


Does letting it do the dance hurt other things like mounting and so forth ? My mechanic said go ahead and run it with this injector pump that I did not change but everybody on this site say's if you put in new injectors then change the pump. Am I taking a chance on messing something else up or destroying this pump ?


Again thanks....

 

If nothing else, pumps and injectors wear, and timing is the first to go.
Generally, with a given set of injectors and pump, the timing will very slowly retard over time by a couple of degrees.

However, lets take a worn pump. It's worn so that it's a couple of degrees retarded, when matched with a worn set of injectors that now pops at, say, 1400PSI.

You replace the injectors with a new set, which pops at 1850PSI. What happens?
The pump has to build more pressure to pop the injector. This takes more time, which makes the pump *more* retarded.

You can either A, replace the pump, or B, compensate by advancing the timing. You have perhaps +-8 degrees of timing available by rotating the pump. More than that can be obtained by skipping the IP gear one tooth compared to the cam gear. You rotate the IP gear clockwise to advance it.
Just be aware of skipping multiple teeth when doing so. Make marks where you are at so you can keep track.

 

Thanks but what I am wondering is if you run a pump to long does it destroy it to where you can't rebuild it ?