Hard start in warmer weather

[bear8236]

Yet another problem here.
'02 Duramax w/ 6-speed manual, 4x4, 150k miles, all 8 injectors already replaced plus one more this year. Harmonic balancer replaced...
There is the history, now the problem
Living in Texas so right now it's about mid 30's in the morning at the coldest and just recentely went up to mid to high 80's during some days. Starting in the morning is fine, no hesitation, no stuttering, fires up and goes. The problem comes after the truck has warmed up then is turned off and try to restart it. Sounds like it's cranking fast enough but won't start. I have to crank on it for what seems like 5 sec or more, then if finally will fire up. 85 degrees yesterday and it was terriable, as described. Today had a cold front blow through and it started fine this morning, fine at lunch, and for the ride home, but after got home, turned it off, and tried to restart it, and it hesitated a little, but nothing like yesterday. So, seems to be temperature related.
Just replaced fuel filter after this first started happening, but didn't help.
The things I've come up with were possibly air in the fuel system, but wouldn't that cause the problem all the time, not just when it's warm? Same thing for injector problems? Same thing for fuel delivery. Those just seem like they wouldn't be temp sensitive.
Other thing was glow plugs. It starts fine when it's cold so I think the plugs are ok. But what I've noticed today was that after the truck is warm and turned off, then I turn the ignition to on I hear the relays click on then immediately off. Should this happen? Should the glow plugs come on at start up no matter what the engine temp? What tells the ECM to pull in the glow plug relays? What tells the ECM to turn them off? Right now when the engine is cold the glow plugs come on, engine starts fine, then after 15 sec or so (not really sure on the time) they will go off. Should it be the same with a warm engine?
If not glow plugs, then could someone maybe point me in the right direction. Other than the hard starting when warm, the truck runs fine. And even after the hard start, once it fires up, it doens't miss a beat, just as long as I don't turn it off...

Any help would be greately apprecaited. Also, any suggestions for a good affordable scanner, one that will dispaly real time values like temps, injector info?, things besides just diagnostic codes. Was looking at the Predator...

Thanks

[More Power]

There are some types of engine starting problems that become more apparent during the spring and fall when temperature extremes are at their widest. In general, large temperature fluctuations produce more pressure differential inside the fuel tank as the fuel and air expand and then contract throughout the daily cycle. This can exacerbate an air leak in the fuel lines or make it harder for the fuel injection pump to draw fuel.

These diesel fuel tank caps are supposed to limit tank pressure to no more than 2 psi and/or vacuum to no more than 2". A bad cap can cause problems.

Try loosening the fuel tank cap as a test. :)

Jim

[bear8236]

If this helps anyone else...
Fuel Injector Pump was the problem.

[bear8236]

I was just reading through my subscribed threads, and saw this one. My comment of "fuel injector pump" being the problem was WRONG! Dealer #1 misdiagnosis, replaced injector pump. Worked for a while. Dealer #2 misdiagnosis, replaced injector pump again, under warranty. Dealer #2 2nd misdiagnosis, fuel filter element housing needed to be replaced.
Finally Dealer #3 either had a understanding of these engines and/or did the test (pretty extensive test) required to get to the real problem resulting in 8 injectors and fuel lines. The test wasn't just the balance rate test but I believe the high pressure side test?

Anyway, hope this might save someone some money and time.

[More Power]

Thanks for the followup. I spoke to another Duramax owner this morning who said his truck had become hard to start when hot. A new set of injectors solved his problem. Just like yours, the fuel-rail pressure couldn't keep up with one or more injectors that had developed exessive fuel-return flow. This sort of problem becomes more apparent when the engine is at or near operating temperature because the fuel thins as it heats up.

Jim