Hard to start when warm

[Herman_Bolger]

I have a '93 3500 6.5td. I find this a little odd but maybe someone has run across this problem.

In the morning the temp is about 30f out side,and the truck has been sitting overnight, turn the key, push the accelerator down to set the fast idle, wait for the glow plug light to go off, turn the key, and the truck fires up in 2 or 3 revs. It runs great no problems.

The problem starts after the truck has run, and warmed up. If the truck is warm and you shut the truck off and let it sit, and try to start it after about 15 min to maybe an hour, it is hard to start, meaning it turns over for what seems to be a long time then starts.

If I leave the truck sit all day in the cold and repeat the morning procedure, it fires right up?

The truck has a stock jobber rebuild ( bought it this way) with new injectors, new glow plugs, retimed pump,new alt and other stuff. It is a '93 so it has a mech pump.

The truck ran great for the last 6 weeks or so since i put it back on the road after extensive repaint, suspension and exhaust work. It did not have any hot or cold starting problems until this past week.It is not even consistant with the hard starting problem, but it is fairly common right now.

Any suggestions. Oh ya I don't know jack about diesels, i'm a recent convert, from big block chev gas.

Any help would be great, Thanks

[bobt]

Herman, My money is on the glow plug controller. I had the same problem years ago with my '93. Took me about three years of it getting progressively worse before figuring out the problem. The controller goes bad from excess engine heat(in my opinion). Vehicle starts fine when cold. After running awhile then shut off, for the period between about 30 minutes and an hour, it is very hard to start. Truck cools off enough that momentary glow plug time is needed, but controller doesn't recognize that it is needed. I replaced my controller and haven't had the problem since. Sounds like you have the same problem. Hope this helps you.
Bob

[JohnC]

Could be that the injection pump is getting worn and can't make enough pressure to reliably fire the injectors at cranking RPMs when hot. Try matting the throttle or adding a quart of 2 stroke oil to the fuel and see if it starts better.

[Kennedy]

Classic symptoms of pump head/rotor issues. MP had some info about this a few years back, but in a nutshell, adding 10% (30wt non detergent?) motor oil to your fuel is a simple way to test if it is a "viscosity bypass" issue with the pump head. Not siomething I'd want to mess around with in colder climates though for cold start.

[Herman_Bolger]

Thanks for the suggestions.
Lets start with the easiest, I think. Were is the glow plug controller located?
The truck will be coming off the road for the winter to sort out some of these and other issues, but I would like to know that I have a dependable truck if I need it.
Right now I leave the truck running if I am doing a lot off running around, for fear it will not start when I need it to.
So I think that I will change the controller, and if that does not help then I may do the oil mix thing.

Thanks

[charliepeterson]

The GP controller is on top in the back of the engine, driver's side. Gray or black with two big posts and a multi wire plug in the middle.

My guess is the Injector Pump is worn out. The next time it won't start, pour tap water on top of it. This will cool down the head enough so it can build enough pressure to open the injectors.

[bobt]

Herman, How many miles on the truck/injection pump? If in excess of 100K, then I agree that the pump could be the problem. If somewhat less than 100K, then I would try the controller. The advice to try cooling the injection pump with water when it acts up to see if this corrects the problem is good advice, and a cheap way to see if the pump is acting up. If you can rule out the injection pump as the problem, then a bad controller is the next thing that acts exactly like you describe.
Bob

[Herman_Bolger]

OK, I will try the water trick, if water is available. Pardon my ignorance, but why does it matter if the pump is cold. Is it so the inside clearences become tighter? And then create more presure, or somthing else?

[William Fullington]

i was having this exact problem. i added an FSD cooler, replaced fuel filter, injectors are new, checked everything recomended in the troubleshooting guide and nothing helped. It wasnt until i changed the oil pressure switch and electric filter harness that the problem stoped. I cant tell which solved the problem because i replaced both at the same time, but the point is it stopped.

good luck with it. heath diesel offers the electric filter harness cheaper then the dealers here coudl get it for me. and the oil pressure switch is AC delco so your local napa will have it.

[ 11-23-2005, 10:26 AM: Message edited by: William Fullington ]

[Hubert]

Yeah Herman you got it. A cold truck the diesel is cold too ("thick") and the IP can build pressure but if engine and IP are warm. The diesel in the IP is warm too and a little "thinner" so fits have to be better to build as much pressure. Also, after a few minutes the filter housing with heater element will warm the fuel so shortly after start up it may not crank as easily.

The water on the IP will cool the IP to shrink fit some on internals and tighten things up a bit so it can make more pressure.