Have A 1991 Cummins ,in the morning are when cold Starts fine but when hot are warmed up it want start, any answers to my problem?

 

I'm assuming that when it's hot, it will crank but not start or is it that it won't crank when it's hot?

Hopefully one of the mods will move this to the 1st gen forum where you'll get more feedback on it.

 

Could you maybe explain more about the problem with more details and description?

 

yes in the morning it will start as soon as you hit the key but arter running for 20 or 30 minutes or so and you shut it off it want start engine spins over fine but it just want fire up , after you let it cool off it will fire right up as soon as you hit the key. acts as if it is a fuel problem,dont know.Have replaced filter and manual fuel pump

 

That sounds like the makings of a bad injection pump, but it could be a shut down selinoid problem also.

First I would eliminate that. I would check the power at the selinoid and maybe take it out and remove the plunger and spring and put it back together and use the manual shut down on the side of the pump. This will at least eliminate that part of the pump and if it still does it then the pump might be worn out.

You could also have air getting into the fuel system somewhere, but I think it unlikely if its starting up in the morning like it is.

 

That is a bit odd. First thing that I'd try is to check for 12V at the pump solenoid when the motor is hot and won't start. If it has a full 12V, then proceed to removing the plunger. If you don’t have a voltmeter handy, just try jumpering from the solenoid terminal to the hot lead on the battery to test it. If it starts when jumpered but won’t start w/o the jumper, it’s a wiring problem. It’s possible that there is an electrical connection that’s opening only under hot conditions.

 

have pulled plunger out of solonoid, replaced lift pump, checked for leaks, none ovious still does not start when hot i guess next step is injector pump???

 

Before you jump in and replace the pump. Try pouring water on the pump head to cool it down alittle bit and see if it starts, if it does then there is no doubt that the pump is worn out. I've known a few guys that had 7.3L IDI's that had to do this all the time to get them to start when hot.

Just beware DON'T do this to a known good pump, it could damage the plunger and the hydraulic head.

BTW, how many miles on the truck?

 

68883 farm miles with routine maintenance

 

With that kind of miles you would thing that there was penty of life left in it!............then again,water is an inj pumps worst enimy! Espesuly if the water got in or past the filter, and then the truck wasn't run for several days, and this happed a fue times the pump could be way history!

thay say that the water in the pump is not the problem, it's the water siting in the pump,lines and inj pump that turns to flaky rust that is wors then any dirt getting into the system!
Evan with good maintenance, all it take is one bad tank full and the not used for a fue weeks!

With that said,....i thing that it's the inj pump allso!

letting a truck sit is as hard or harder on it.

 

Farm miles = lots of hours. Do what Mike said and I bet you'll find the pump is worn out.