Cold starting issue

Yardstick · March 5, 2007

I just got a new to me 2001 Silverado with the 4.8L engine. It runs great, drives great and generally works very well. I have noticed that the last couple of mornings it doesn't seem to fire up as easily after sitting overnight as it does when it is warm or has been driven that day. This morning and yesterday I got in and hit the key and the starter spun the engine up, but it didn't fire. I let off the key and try again and it started right up. It can sit at work all day (8hrs) and it will start up like I would expect it to. I searched around, but it seems like the usual problem is warm starting issues due to a bad FPR. What's going on with mine?

vuaccordla · March 6, 2007

I also have the same problem with my 01 yukon xl. With the addition of a small knocking sound until about 20 seconds of the engine running then it goes away, but no knocking sound when warm. Any infomation would help.

cschmidt56 · March 6, 2007

Allen,

Try this:

Next COLD start, turn the key to the "ON" position just before it kicks the starter. Have the door of the truck open and listen and see how long the fuel pump kicks on and shuts off. It could be that the fuel rail has not come up to pressure before you start the engine. This MIGHT indicate that you need a new Fuel Filter.

Chris

Yardstick · March 6, 2007

Thanks! I'll try that. It did it again this morning. What clogs fuel filters? I know they get clogged, but I don't get it. I've pulled fuel tanks out of my 1975 Chevy truck with 180,000 miles and my 1979 Jeep with 134,000 miles and both looked absolutely perfect inside, no chunks, no perceptible dust, only clean fuel. Can there really be that much junk in the fuel getting past the sock filters and such? How hard is it to replace the fuel filter one one of these trucks if that's the problem?

Bish · March 6, 2007

Thanks! I'll try that. It did it again this morning. What clogs fuel filters? I know they get clogged, but I don't get it. I've pulled fuel tanks out of my 1975 Chevy truck with 180,000 miles and my 1979 Jeep with 134,000 miles and both looked absolutely perfect inside, no chunks, no perceptible dust, only clean fuel. Can there really be that much junk in the fuel getting past the sock filters and such? How hard is it to replace the fuel filter one one of these trucks if that's the problem?

It is not really that hard to plug a fuel filter. If you fill up at a station with a tanker and their pump filters are not working correctly, one tank of gas can plug the filter. Changing the filter takes about 5-10 minutes. On my Tahoe, it is located on the inside of the frame under the driver's door. I change mine every 10K-15K miles just to be on the safe side. Also, if you have a plugged filter, the pump can overheat working extra hard to push fuel through and you can kill your fuel pump. Of all the changed fuel filters in 190K, I had only 2 occasions where I could not easily blow through the old filter indicating it was quite plugged.

Yardstick · March 7, 2007

I replaced the fuel filter last night in the hope that it would fix the problem. No such luck. It looked like a stocker though, so it was probably a good idea anyway. The pump comes on for a few seconds with the key in the run position before I start the truck. When I crank the engine over, the starter sounds very healthy, but the engine just doesn't seem to catch. Maybe it would eventually, but I don't like to spin a starter for more than a few seconds. When I return the key to the run position and then try cranking again it fires right up and idles fine. The truck runs strong too. It almost seems like the fuel lines are not staying pressurized overnight. What would cause that? I don't see leaks anywhere.

Edit to add: I also found out the air filter in the truck is a K&N. Is it possible the increased airflow from the K&N could cause the stock choke settings to be slightly too lean for a good cold start?

Shaners · March 7, 2007

The oil in the K&N filter can cause a film on the Mass Air Flow sensor. I don't know if it would create a starting problem, but it can cause other little issues.

It probably wouldn't be a bad idea to remove and clean the MAFs though.

Silverado4x4 · March 7, 2007

Your fuel pump in the tank is on its way out, what is happing when the truck sits fuel pressure drops in the lines and when you start the truck in the morning the fuel pump is not building up the pressure fast enough to start the motor on the first try thus longer crank times once the truck is running and then shut back off there is still pressure in the lines therefore truck will start quick. You can take it to a repair shop or dealer and tell them to do a fuel pressure test on your pump. The pump starts running as soon as you turn the key to the run postion as you can hear it, on a good pump it will only run for about a split second before shutting off and waitting for the motor to start then will come back on cause the motor is running, on a weak pump it will run for about 3-4 maybe more seconds before shutting off and waitting for the motor to start

Yardstick · March 7, 2007

Well that sucks. And it's an in-tank pump too... I hate pulling fuel tanks.

How hard is it to get to the MAF sensor? What do you use to clean it? I may switch back to a stock filter. I've never been convinced K&N's were a good type of filter to have.

rjirvine · March 7, 2007

I had to drop the 34 gal tank on my 1988 truck 4 times in its life so I know what PITA it is. From what I gather here on the forums, it's easier to pull the bed, or better yet, pull the bolts on the driver's side and loosen them on teh passenger side and tilt the bed up and change he pump thru the left rear wheel well. I have100k miles on my truck and want to change my pump preemptively so let me now where the best palce to price one is....hope this helps. You can do a search and find out the exact posts that lists how to.

Yardstick · March 7, 2007

CSK shows one for ~$215. It's the same part number and manufacturer as Vatozone shows for $274. Tipping the bed up sounds like a pretty good idea. This thing is so low I was beginning to wonder how I'd get the tank out of there. I do have a transmission jack that might make things a little more manageable if I do decide to drop the tank.

GaryCoral · March 8, 2007

CSK shows one for ~$215. It's the same part number and manufacturer as Vatozone shows for $274. Tipping the bed up sounds like a pretty good idea. This thing is so low I was beginning to wonder how I'd get the tank out of there. I do have a transmission jack that might make things a little more manageable if I do decide to drop the tank.

Most likely a pressure regulator - Same thing happened to me - I also did the fuel pump but that wasn' a cranking issue it just died altogether.

Yardstick · March 8, 2007

I tried listening for the pump again this morning. It ran for about 2 seconds and shut off. I backed the key off to the on position and then back to run then start and it fired right up. It's definitely something to do with the fuel line not coming up to pressure quick enough or not holding pressure when it sits overnight. The truck runs great otherwise. I'm waiting on a shop manual now. Maybe that will have some definitive troubleshooting procedures. Both the pump and regulator sound like reasonable ideas...

ken1mod · March 8, 2007

my truck runs perfectly except for a slight hesitation when started after cold for 20 seconds. that is the worst. sometimes it is not worth chasing a small problem that only lasts 20 seconds.

Ken

Silverado4x4 · March 8, 2007

Another note, when you change the fuel pump try and stay with a GM/AC delco fuel pump as I have seen and heard that aftermarket pumps dont last long, a little bit more money but worth it in the long run. Plus the worst killer to a intank fuel pump is running the tank below 1/4 as the fuel in the tank helps cool the pump.