Hard Starting (common problem)

Hey everyone. I'm new to the Silverado forum and need some help. I have a 2003 Silverado 4.8L 4x4 and I've been having some issues with hard starts. In the morning, when the engine is cold, the truck starts right up without any issues. If I go to shut it off and then start it up again, it starts right back up again with no issues. However, if I let it sit for more than a half and hour, the truck struggles to start. It cranks, tries to fire two or three times, then finally fires up and runs perfectly smooth. This usually takes about 4 to 5 seconds before it starts up. I've cleaned the throttle body real good (which was really dirty), replaced the fuel pressure regulator, purge valve canister, fuel filter, and fuel pump. I've also dumped two cans of fuel injector cleaner in the tank as well (I have a 34 gallon tank). I can't figure out for the life of me why my truck is doing this, and it's not throwing any codes! But, I have begin to notice that this happens more often when the tank is full. The more fuel I burn, the better the truck starts all the time.

Hopefully someone could help me out. I know hard starting is a common problem with the Silverado's, but I can seem to find any posts that have similar symptoms that I'm having. Thanks in advance!

Hey everyone. I'm new to the Silverado forum and need some help. I have a 2003 Silverado 4.8L 4x4 and I've been having some issues with hard starts. In the morning, when the engine is cold, the truck starts right up without any issues. If I go to shut it off and then start it up again, it starts right back up again with no issues. However, if I let it sit for more than a half and hour, the truck struggles to start. It cranks, tries to fire two or three times, then finally fires up and runs perfectly smooth. This usually takes about 4 to 5 seconds before it starts up. I've cleaned the throttle body real good (which was really dirty), replaced the fuel pressure regulator, purge valve canister, fuel filter, and fuel pump. I've also dumped two cans of fuel injector cleaner in the tank as well (I have a 34 gallon tank). I can't figure out for the life of me why my truck is doing this, and it's not throwing any codes! But, I have begin to notice that this happens more often when the tank is full. The more fuel I burn, the better the truck starts all the time.

Hopefully someone could help me out. I know hard starting is a common problem with the Silverado's, but I can seem to find any posts that have similar symptoms that I'm having. Thanks in advance!

with this no DTC found the usual component is the ECT. when this reports the wrong engine temp it will cause the fuel mixture to be incorrect . 10 years of use they get out of proper cal.

what was the fuel pressure results before and after the part replacements. also check for pressure drop on key on engine off test. should hold for a few minutes or drop very little.

with this no DTC found the usual component is the ECT. when this reports the wrong engine temp it will cause the fuel mixture to be incorrect . 10 years of use they get out of proper cal.

what was the fuel pressure results before and after the part replacements. also check for pressure drop on key on engine off test. should hold for a few minutes or drop very little.

Well, I never checked fuel pressure before I made the replacement because I knew the regulator was bad because I had fuel in the vacuum line. Also, I knew the fuel pump was going out because I had to whack the tank sometimes to get the fuel pump to kick on!

After I replaced everything, fuel pressure with the key on, engine off would be around 65 psi. When I started it up, the pressure was hovering just under 55 psi. I checked the fuel pressure again this morning and the readings were similar (right around 65 psi with key on, engine off and right at 55 psi with the engine running). And it started right up no problem.

I will probably go ahead and replace the ECT sensor. The truck does have almost 200,000 miles on it so I would say that it is probably the issue. Plus, it seems to be a relatively inexpensive part.

I'll keep you updated. Thanks a lot!

Ok now I have an update. I did not use the truck at all yesterday, but used it today. Started it up, and it started quicker than ever, literally less than a second. Worked for 11 hours, went to start it again to head home, and started up just fine, may be took a second. Now it was sitting for just about an hour and I went to start it again, and it took almost 7 second to finally start, and you could smell the fuel like the engine had flooded.

Now I did notice something different this time. Once I got the truck started, I popped the hood to check if I could smell gas (which I did). With the truck running, I got back in and the security light was on. I turned the truck off and started it right back up again, and the light was off. What could this mean?????

Another update. I replaced the coolant temp sensor and still no luck. Symptoms are still the same. Checked fuel pressure and everything is perfect. I'm at a lost cause here. Any help would be greatly appreciated!

Another update. I replaced the coolant temp sensor and still no luck. Symptoms are still the same. Checked fuel pressure and everything is perfect. I'm at a lost cause here. Any help would be greatly appreciated!

when the vehicle refuses to start disconnect the MAF then see if it starts.

Ok thanks. I'm away for the weekend with my Buick and will be home Monday. I'll give it a try and let you know what happens. Thanks!

Ok so I unplugged the MAF sensor and nothing changed. I spoke with someone who worked for GM and said that it sounds like the engine may be getting too much back pressure. So the catalytic converters may be beginning to clog up. So this weekend I'm going to cut the cats off and clamp on test pipes and see what happens.

Ok so I unplugged the MAF sensor and nothing changed. I spoke with someone who worked for GM and said that it sounds like the engine may be getting too much back pressure. So the catalytic converters may be beginning to clog up. So this weekend I'm going to cut the cats off and clamp on test pipes and see what happens.

A normal cat/exhaust restriction will cause miss fires and low power.

should get p0300 code.

Rather than cuttingn cats off why not remove the pre cat 02 sensors and see what happens. That should show if it has restrictions.

A normal cat/exhaust restriction will cause miss fires and low power.

should get p0300 code.


That is what I thought. But according to a GM mechanic, this is a classic issue with these trucks. I too find it hard to believe.


Rather than cuttingn cats off why not remove the pre cat 02 sensors and see what happens. That should show if it has restrictions.

That is a good idea. I will try that and see what happens.

My mechanic is stopping by today with one of those very expensive computers to plug into my truck and take readings from all the sensors and what not. Hopefully I can find the issue at hand because it is becoming really annoying! I just wish the CEL would just light up so I can finally figure out what's going on.

That is what I thought. But according to a GM mechanic, this is a classic issue with these trucks. I too find it hard to believe.




That is a good idea. I will try that and see what happens.

My mechanic is stopping by today with one of those very expensive computers to plug into my truck and take readings from all the sensors and what not. Hopefully I can find the issue at hand because it is becoming really annoying! I just wish the CEL would just light up so I can finally figure out what's going on.

Good scanners help.
But a fuel pressure gauge and a vacum gauage may be neded and will also help.

Also codes should be checked and then cleared and drove to see what comes back.

Why not take it to the mechanics shop where he has all of his equipment and more time and let him check it out there?

Good scanners help.
But a fuel pressure gauge and a vacum gauage may be neded and will also help.

Also codes should be checked and then cleared and drove to see what comes back.

Why not take it to the mechanics shop where he has all of his equipment and more time and let him check it out there?

I ran my code scanner on the truck and there are no codes. Fuel pressure is good. Probably will go ahead and have my mechanic check the vacuum.

I haven't had time to get the truck to the shop because I have been so busy with work. That's why I have been doing the work myself. When it finally starts, it runs great. That is why I am just nursing its wounds for now.

However, the truck is getting harder to start in the morning, and has been blowing more black smoke once it finally starts to run. I'm going to pull the plugs today and check them at my mechanics shop while he checks several other things. Thanks for all your help everyone.

I ran my code scanner on the truck and there are no codes. Fuel pressure is good. Probably will go ahead and have my mechanic check the vacuum.

I haven't had time to get the truck to the shop because I have been so busy with work. That's why I have been doing the work myself. When it finally starts, it runs great. That is why I am just nursing its wounds for now.

However, the truck is getting harder to start in the morning, and has been blowing more black smoke once it finally starts to run. I'm going to pull the plugs today and check them at my mechanics shop while he checks several other things. Thanks for all your help everyone.

How good is fuel pressure?
What is cold start pressure?

Confirm all fuel pressures are up to specs.
What is egine running pressure?
How fast is leak down pressure?
Black smoke at start up is to rich fuel.

CHECK VACUMN HOSE TO FUEL PRESSURE REGULATOR for gas in it.
Lot of problems with that type fuel pressure.

How good is fuel pressure?
What is cold start pressure?

Confirm all fuel pressures are up to specs.
What is egine running pressure?
How fast is leak down pressure?
Black smoke at start up is to rich fuel.

CHECK VACUMN HOSE TO FUEL PRESSURE REGULATOR for gas in it.
Lot of problems with that type fuel pressure.

Well I FINALLY fixed my starting issue. At first, I changed the plugs and wires and the truck started great for a day. Then I started having an issue again. So I decided to take off the bed of the truck and inspect the pump. The return line was kinked between the bed and cab of the truck. I fixed that a put the bed on slowly with the help of two buddies, and I haven't had a problem since. I did this on Saturday. Thanks again for the help everyone!

Well I FINALLY fixed my starting issue. At first, I changed the plugs and wires and the truck started great for a day. Then I started having an issue again. So I decided to take off the bed of the truck and inspect the pump. The return line was kinked between the bed and cab of the truck. I fixed that a put the bed on slowly with the help of two buddies, and I haven't had a problem since. I did this on Saturday. Thanks again for the help everyone!

should have seen high pressures with that return line kinked ! that would mess up the starting.

should have seen high pressures with that return line kinked ! that would mess up the starting.

The pressure wasn't bleeding off when shutting off the engine. The pressure wouldn't drop below like 46-48psi. I haven't checked it again since I fixed it, but today is Wednesday and I haven't had any problems at all! So I don't want to check it :iceslolan

The pressure wasn't bleeding off when shutting off the engine. The pressure wouldn't drop below like 46-48psi. I haven't checked it again since I fixed it, but today is Wednesday and I haven't had any problems at all! So I don't want to check it :iceslolan

the fuel pressure should hold on engine shut down. the pressure drop of 5 psi is normal and expected.

however if the return line is restricted this would cause excess fuel pressure. this would dump too much fuel into the cylinders especially on starting. on a hot/heated engine this may not reveal itself.