A Couple Different Problems

HDdave · April 26, 2007

2001 2500HD 6.0l, 4l80e, 101k miles

Hi guys, I am having a few problems with my truck. 1. when driving at speeds around 63 and up, my service engine light will randomly come on and flash. The code reads random multiple cylinder misfire, but it runs smooth as always. Someone else had this problem and it was their crankshaft position sensor that was bad.

2. I have to fight with my transmission to get it to shift into overdrive. Any faster than 55 and it just usually wont do it at all. When I'm around 55 I can get it to shift, but then sometimes it will just randomly downshift even when im just cruising on a perfectly flat road (sometimes even a downhill...). I have an appointment tomorrow to get a tranny flush (stock fluid has 101K on it), so I'm hoping that will fix it.

3. This one is not a very big deal but I'm curious about it. My truck has recently gotten a little harder to start. I just haveto crank on it a little longer before it fires than I ever used to. The only change I have made is from 5w-30 dino oil, to 10w-30 synthetic.

Thanks in advance!

ChevyTech007 · April 27, 2007

For the starting problem, possible fuel filter or fuel pump going out. It needs to be scanned to see which cylinder is missing. Trans flush is a good place to start.

Chestah · May 7, 2007

The starting is most likely the weight of the synthetic fluid taking a little longer to move.

496 XL · May 7, 2007

The starting is most likely the weight of the synthetic fluid taking a little longer to move.

HELLO....oil is oil comparing to a starting prob.......did we miss something here on your reply?

you are at the right place for troubleshooting,

496xl

gmc4life · May 8, 2007

2001 2500HD 6.0l, 4l80e, 101k miles
Hi guys, I am having a few problems with my truck. 1. when driving at speeds around 63 and up, my service engine light will randomly come on and flash. The code reads random multiple cylinder misfire, but it runs smooth as always. Someone else had this problem and it was their crankshaft position sensor that was bad.

2. I have to fight with my transmission to get it to shift into overdrive. Any faster than 55 and it just usually wont do it at all. When I'm around 55 I can get it to shift, but then sometimes it will just randomly downshift even when im just cruising on a perfectly flat road (sometimes even a downhill...). I have an appointment tomorrow to get a tranny flush (stock fluid has 101K on it), so I'm hoping that will fix it.

3. This one is not a very big deal but I'm curious about it. My truck has recently gotten a little harder to start. I just haveto crank on it a little longer before it fires than I ever used to. The only change I have made is from 5w-30 dino oil, to 10w-30 synthetic.

Thanks in advance!

I don't think it's your crank...if it was, the engine would not run as smooth as you're saying. If it's the only code you're getting, it could be foul plugs or injectors. Take my word...I had a bad crank sensor and I ended up changing the engine. What happened was that the thrust bearing on the crank let go causing the crank to move back and forth just enough to screw up the sensor.