Why won't my truck roll start cold?

[extragoode]

My S-10 did it all the time (cronic strater problems, good thing it was a manua!l). In my parking lot for work, theres a section that is on maybe a 5% grade. I can let it down the slope to almost 10 mph and dump the clutch. I can feel and hear the engine turning. I've tried 1st, 2nd, 3rd, and reverse. Nothing. I know it's enough potential energy to start it though, because I've started with the key and shut it down, then roll started, and it fired right off!

[SVOboy]

Is the fuel pump not priming well when cold?

[diesel_john]

cycle the key a couple times, can you hear the fuel pump load up.

the vw has a safety to prevent hitting the starter when the engine is running, but also won't key start if i cut injector pump power until i cycle the key to off.

totally different reason than cycling for the gas engine, some fuel pump relays have a built in timer which only runs the in tank pump for a few seconds to purge to fuel rail. but it is always a good idea to turn the key to on and wait for a couple seconds before going on to the start positon.

[extragoode]

So the fuel pump should start paying attention when the key is turned to the on position? It doesn't neccessarily have to wait for the engine to turn a couple times? I'll give the key thing a try tomorrow. I assume by cycle the key you mean turn it to on, then off, then on again, right?

[BBsGarage]

when you start it normally cold, does it start right away or does it take a few seconds and revolutions of the starter?

[JohnnyGrey]

GM ECU's operate the fuel pump based on crank position sensor activity. Maybe this is not the case for your new truck.

[extragoode]

Ok, the key cycling thing didn't work. I tried it twice. The first time a couple times, the last time, a whole bunch of times. I can't hear anything from the engine, but that could be because of the extremely loud beeping my truck makes when you turn the key on, yeah the airbag says it's still going to work and by the way, you don't have your seatbelt on yet!

Now that you mention it, it does take a longer crack on a cold start. Not much, maybe 1.5-2 seconds instead of .5-1 second. And I've noticed that it takes more to get the engine started again on glides that are more than .5 miles or so, or if I sit at a long light, 2-3 minutes, with engine off. What does that mean? Obviously, it's taking more energy to start it cold than warm, duh, but is there anything I can do about it?

[diesel_john]

Originally Posted by extragoode

Ok, the key cycling thing didn't work.

I would check fuel pressure and watch what happens when the key is turned to on but not started. And have someone listen back by the tank, should be easy to heard the pump come on. Note pressure without starting the engine. Low fuel pressure could be filter, low volt to pump, etc. Its either fuel or spark obviously, I am just exploring fuel first.

it is always a good idea to turn the key to on and wait for a couple seconds before going on to the start positon.

[rbhollabaugh]

A couple things. Does the car have a cold start injector? If so, these are activated only when the starter is running.
The ECU may only turn the fuel pump on when either the starter is running or the engine RPM is over a certain number.

Rich