Cold starting

[Patrick Dolan]

Just wondering if someone could explain to me what components do what in doing a cold start? Last spring I had some trouble with cold starts and it is of course still a problem now. I assume the heating grid is either not getting current or is an open circuit.

Second question: sometimes I have a high idle (1,100 RPM). No other symptoms, just the high idle. Have not had chance to pull any codes, but I seem to remember something related to this in some long gone threads.

Should have my shop roof spray foamed on Tuesday, and should be able to get truck in by Thursday for some long overdue service.

 

[Ozymandias]

Well, there is a grid heater, that's about it.

But bad news for you, these engines start fine all the way down to minus 30° without the grid heater, at that cold it maybe takes 3 seconds to fire but they do.
So if you have start problems now in fall, you have probably a problem somewhere with your injection system if everything electric wise is fine.

If it goes to high idle by itself you have three possible situations, below 32° outside temp and idle longer then a minute or so transmission in P, an overheat situation of the coolant or your battery is depleted beyond a certain limit and the truck tries to charge it as fast as possible.

Combined with your start problem it might be the batteries or the wiring of them,

 

[Patrick Dolan]

Can I assume the intake air grid is switched by the computer? Assume there is a relay doing the high amperage switching. What generates the command to operate heater?

Batteries are ancient and weak, but no where near bad enough to prevent start. This particular truck in its youth would start down to -40C without being plugged in but not a lot of miles on it yet (260k kms = 160k mi.)

 

[p-Bar]

There's a solenoid for the switching of the grid heater. I would put a volt meter on power connection and see how low the voltage gets during cranking. If it's to low the injectors won't fire.

 

[petersonj]

Batteries are ancient and weak, but no where near bad enough to prevent start

That statement makes me cringe. These trucks need strong batteries - all the time. If I were in your shoes, I would continue to troubleshoot and verify grid heater operation after I replaced the batteries.

Anything slower that fast cranking speed delays fuel pressure build-up and delays reaching compression ignition temperature in the cylinder for the fuel to burn.

- John

 

[BigPapa]

That statement makes me cringe.

…long overdue service.

This one, too.

 

[Killer223]

i'd try leaving it connected to a battery maintainer or charger overnight, see if you have the same starting issues in the morning.

 

[Patrick Dolan]

i'd try leaving it connected to a battery maintainer or charger overnight, see if you have the same starting issues in the morning.

I will meter out the grid and relay first, and if they ARE switching on (which I doubt, as I can usually hear/feel the load of heating grid cycling after a cold start and that didn't seem to be happening last spring). Then I will just try higher voltage cranking, but judging by the way it behaves, that is not likely the problem.

Just for the record: I don't replace ANYTHING until I have diagnosed it's actual condition - even batteries. I have more than a dozen pieces of equipment and vehicles to keep running, and just throwing batteries or money at them willy-nilly would break the bank.

 

[Killer223]

I will meter out the grid and relay first, and if they ARE switching on (which I doubt, as I can usually hear/feel the load of heating grid cycling after a cold start and that didn't seem to be happening last spring). Then I will just try higher voltage cranking, but judging by the way it behaves, that is not likely the problem.

Just for the record: I don't replace ANYTHING until I have diagnosed it's actual condition - even batteries. I have more than a dozen pieces of equipment and vehicles to keep running, and just throwing batteries or money at them willy-nilly would break the bank.

i would agree, i don't throw money at a problem, i diagnose it first. hence what i suggested was a free test. you can check voltage to the grid on colder mornings. to make sure it's running.
are you getting the wait to start light on the dash? waiting for it to turn off? can you hear the click of the relay when doing so?

 

[Ozymandias]

If they don't work the truck throws a code.

 

[BigPapa]

If you have one available, hook another truck to it and see if it starts easier.

 

[p-Bar]

The courtesy will dim when the heater kicks. Ozy is correct too

 

[AH64ID]

Most likely cold starting issues are batteries. I ran without a grid heater and with semi-weak batteries started at -25°F, but she was angry. It could also be the injectors, what’s their status?

Those semi-weak batteries also took out my alternator brushes.

The grid heater starts working at an intake air temps below 66°F. Cummins states they aren’t needed until 10°F, so above that is for emissions. On my 05 I reprogrammed them not to come on until below 32°F and even then it wasn’t for long.

On my ‘22 I have to wait for the WTS light, aside from remote starts. These motors start in the cold fast and easy with good batteries.

 

[Patrick Dolan]

There is enough battery left to easily start ANY diesel at these (-20C now) temperatures. They draw down because it is cranking a very long time before starting, and most times by that time cranking is then too slow. This truck has for the last 19 years started after a few pistons hit TDC, not tens of seconds of grinding the starter.

Before I get it into shop (should happen today, will need to be washed and dried) I am still trying to find out WHAT triggers the "wait to start" light. Yeah, the ECU but from WHAT sensor and where in the manual do I find verification of what sensor and testing procedures? I can find a general description of the heater in 14-90 and the IAT/MAP sensor in 14-93 but nothing to tie them together. Does the light turn on directly from data bus? Is it powered from the output that activates the grid heater relays?

Not sure what my shop laptop has on it that will work with American trucks. What software will let me access the sensor suites directly for testing (as I can do easily with VAGCOM on my German junk)??

 

[sag2]

The grid heater is triggered by the coolant temp sensor and the intake temp sensor. Once it hits the low temp threshold (approx 50°-60°) it will ground the relay and turn on the grid heater for a period of time dependent on temp. If the engine is not cranked the WTS light will turn on for a predetermined time, then go out. After starting if the temps are cool enough the grid heater will cycle on and off for another predetermined time depending on temps. Unfortunately I do not have a chart showing the times vs. temps.
Your hard starting problem is more likely low fuel pressure from leaks or bad injectors.

 

[AH64ID]

The grid heater is triggered by the coolant temp sensor and the intake temp sensor. Once it hits the low temp threshold (approx 50°-60°) it will ground the relay and turn on the grid heater for a period of time dependent on temp. If the engine is not cranked the WTS light will turn on for a predetermined time, then go out. After starting if the temps are cool enough the grid heater will cycle on and off for another predetermined time depending on temps. Unfortunately I do not have a chart showing the times vs. temps.
Your hard starting problem is more likely low fuel pressure from leaks or bad injectors.

The temp is 66°F for the sub-forum of this thread. If the OP posts his truck info I can look up the specific time tables.

 

[Patrick Dolan]

Sorry to be gone, but had to deal with business. Just home a couple of days, but all of the connectors had been cleaned and re-seated in my absence and now everything works as it should....except the truck doesn't start. I is sitting in the shop at about 45degF and some times you can crank several 30 second sessions and it will not go, and sometimes it will start on one of these. The batteries were easily good enough for 2 such sessions, but since they were left parked for 2 years before I started using the truck, I did throw a new set into the racks - all made zero difference.

I assume now that one of the pumps or some injector(s) are failing. Sadly, using my generic OBDII AE reader, this no-start seems to set no codes. Don't want to buy a full Chrysler suite, as this is the only D-C (FCA) vehicle I have and only 2 in our combined fleet ('15 5500). What is best way to capture low pressure feed numbers and high pressure rail in real time?

Thought the truck info was in sig, but do not see that so: it is an '03 xt cab shortbox 3500 with NV5600 and 4wd.