I have a 99 cummins that wont start when its hot. I changed lift pump to tank type, changed fuel filter & nothing helped. It starts good when it's cold. Anyone know why this is?

 

Mine was doin the exact same thing. And i did the exact same thing you did. It ended up having somethin to do with the fuel shut off solenoid. I havnt figured it out yet but its between the relay, the blue wire(fuseable link) or the solenoid itself. Check that stuff. Idk if theres a diff. But mine is a 96 12 valve

 

OK. I'll check out the soleniod, at least that gives me something else to check out. Everything I'm hearing is that it's the injector pump. I don't know because in the cooler weather (below mid 80's) it's been starting fine.. ???

 

We have learned this past summer that long crank times when warm or hot are not always caused by a worn-out distributor on the injection pump. Before you replace the injection pump for this symptom be sure that the starter cranking speed is adequate. This is important as it is a mechanical pump in the injection pump that makes more pressure and flow the faster it turns, and when the pressure created during cranking is not enough to pop off at least three injectors, the engine will not start. So there may be as many as two causes for this symptom. One, is that it's not cranking fast enough to make enough pressure, the other is the pressure is being lost in a worn-out distributor that is expanded due to heat soak, OR BOTH. Before buying a pump we suggest that you first check electrical parameters for the starting system. A good starter at operating temperature can draw from 450-700 amps, and the battery voltage should never go below 10 volts during cranking. If your starter draws more than these specs, or the battery voltage goes below 10 volts when cranking, you need to fix the starting system, FIRST.

When you have determined that the electrical system is up to snuff, then you can try our clever trick of running cold water from the garden hose over the injection pump when it's hot, for a few minutes, and if that makes it start right away, then you know cranking pressure is the issue, because you shrunk the metal in the distributor and it fits tighter to the rotor and makes more pressure. This indicates a worn out distributor, and a replacement VP44 is needed. If you have just replaced the injection pump and the problem did not go away, then most likely you have a slow crank problem. If you didn't have the problem before the pump swap, then most likely it is a pump issue, BUT,,,,the sad truth here is that a replacement pump may have a worn-out distributor just like the previous pump did. No one wants to put a new distributor on every pump, as it is SO EXPENSIVE. As of this moment in the industry, there is no good test available to the rebuilder to accurately determine if a distributor will perform correctly in hot conditions. The best any rebuilder can do is check pressure and fuel volume from the VP44 at cranking speed on the test stand and if it passes Bosch specs, then it has to be presumed good. This test is performed in a 70° air-conditioned pump room and in the real world pumps are subjected to the latent heat transfer from a 195° engine! The bottom line is you REALLY have to test the starter and batteries first to make an accurate diagnosis for this frustrating symptom.

Another cause of this issue that we have run into recently, is a delay getting 12 volts to the primary side of the fuel system relay. This shows up as a delayed battery voltage on pin seven (red wire with a green tracer on Dodges) in the plug going into the VP44. First test for the delay by removing the big plug on the injection pump and verifying the time it takes to get battery voltage on pin 7 of the plug or on the red wire with a green tracer. To accomplish this, pull the locking slide in the plug toward the fender. There are two half round indents on the slide lock and you will need to pull pretty hard toward the fender while wiggling the main plug with the other hand pulling toward the firewall. When you have the plug in your hand, hold it so it looks like a smiley face, with six pins below the smile and three pins above. Use a test light or voltmeter to verify how soon you see battery voltage on the bottom right pin (Pin 7) after putting the ignition switch in both the “run” and “start” key functions. When you reinstall plug and push in the slide lock, push the plug toward the pump and you will see that when the lock moves in, it pulls the plug in towards the pump. When you think it is on correctly try to remove the plug by pulling on it. If it comes off you didn’t get plug on far enough before you slid the locking slide in. This test tells you when the injection pump is getting electrical power from the fuel system relay in the PDC (Fuse-box under the hood). The ECM not only turns on this relay but this relay also powers another part of the ECM that turns on the lift pump too. The electric lift pump is powered directly from the ECM, not the relay, to control WHEN it comes on. An audible indicator of this delayed voltage or start problem is when you don't hear the electric lift pump come on for 4 seconds when the key is first turned on and for 25 seconds when it is turned to the start function. The relay enable power goes through two connectors, #125 and #130 between the ECM and the relay. The delay problem can be caused by a delayed signal on the brown wire with a white tracer at the ECM connector, indicating a bad ECM, OR a loose connector #125 on the firewall. We have not heard of #130 being a problem yet! Working on these old trucks nowadays is getting pretty interesting, eh?