Hard to start after sitting for a few days -- crank sensor?

lunytnz · January 11, 2015

My 99 with 5.7L is really hard to start when it has been sitting for a few days (usually at least 3 days).

It cranks over, but seems to run into resistance each time around. If I crank and hold it for about 5-10 seconds, it will fire, but what seems like only on a couple of cylinders, then dies. Sometimes, it seems to backfire. If I keep trying, It *does* eventually start (just the other day, I think it took about 20 tries over a few minutes to get it to start. Once it starts, it runs rough for about 10 seconds, then runs fine. I've checked the fuel pressure and it's fine (about 60 PSI), even after sitting for a few days. If I drive it for at least 10 minutes, it will start fine the next day. If I let it idle for 10 minutes, it's not enough to make a difference the next day. One of the weirdest problems I've ever encountered, for sure!

When driving it daily, or maybe letting it sit for one day, it starts right up with the normal crank time.

After talking with another mechanic, we were thinking it could be fuel leaking from the FPR into a cylinder, or two. My gas mileage was down, too, so we replaced the FPR (and the spider injector assembly, as well). We found evidence of leaking fuel, but it didn't fix the hard start problem. The mechanic that replaced the FPR/spider injection was talking with a buddy and suggested it could possibly be the Crankshaft Position Sensor (mentioning that there was a TSB for that sensor; though I haven't been able to find it). The thinking is that if the crank sensor is not working right, it could be throwing the timing way off and trying to fire at the wrong time.

I've been having this problem for the past 3 years. Has anyone else had this kind of problem? Does it make sense that a crank sensor could be the cause? I've tried throwing parts at problems, before, and I can do that again, but I know it's always better to diagnose. However, this one seems pretty hard to diagnose and it sets no codes when it happens.

00Silverado4x4 · January 12, 2015

Sounds like you may need a tune up and double check the timing.

~john · January 12, 2015

My '96 did something similar during a brief cold spell. Cranked, sputtered, knocked, and died. I had my other down as well. Later, when it warmed to the mid 50s, all about 40 degrees warmer, it turned over just fine.

Another thought might be the gas pump. That you might be able to hear actually run for a couple of seconds.

lunytnz · January 13, 2015

Thanks for the replies. I have about 30,000 miles on the cap, rotor and plug wires. 60K on the plugs. So, it's not like they are brand new, but it's surprising that it runs just fine once it gets past this hard start. What makes you think the plugs, wires, cap and rotor are the likely culprit?

I also have plenty of fuel pressure (at about 60 PSI), even after it's been sitting a few days. And it doesn't happen just in cold weather. I typically drive it daily in the winter, except when I'm out of town. I've noticed it most in the summer, when I'm typically driving my other car everyday, and it usually sits for weeks at a time. In fact, the first time I noticed the hard-start problem was on a summer camping trip after it sat at the campsite for 3 days. It's been getting progressively worse (meaning harder and harder to start) over time.