1999 GMC Sierra question

[bensonwe]

Good morning all. I have a 99 sierra that is having starting problems. While cold it will start no problem. Once driven awhile and shut off, I go to start it and it will not start. I let it sit for a minute, retry to start and it starts as if nothing is wrong. It has a 5.3 engine. I started noticing the problem mid September out squirrel hunting. I didnt have much time then to work on it but now work is slowing so i thought now i would. This truck is not driven much so the urgency to fix is not there but i would like to figure it out. Any thoughts on the problem are appreciated. Thanks and merry Christmas.

[Geezer in NH]

When it won't start get out and kick the gas tank. If it then starts right up it is the fuel pump in the tank.
My 94 Silverado had that problem and my 2001 Sierra has had it's replaced also after the same problem.

Your 99 is due for one if it has not been changed as of now.

[Minerat]

Another sign it may be the fuel pump is the gas gage will show no fuel when you first turn on the key. But if you shut the key off and on again it will register fuel and then start. My 2000 Silverado did that when the fuel pump began to die at 90k.

[CastingFool]

May not have anything to do with your problem, but check your distributor cap and rotor for wear. My old 96 silverado normally started like a dream, both instances where I had a difficult time starting it, the cap and rotor were worn. Some times moisture can get inside the cap and causes problems with starting.

[bensonwe]

Thanks for the ideas, i will try them. A thought i had was maybe the fuel pressure regulator? Do these go bad slowly or all at once?

[Petrol & Powder]

When you say that it will not start when warm, does that mean it cranks but doesn't start or it will not even turn over?

[lefty o]

i'd look at the fuel pressure regulator first, they can go bad all at once or slowly, and they cause funky starting at times when they do.

[bensonwe]

Sorry i wasnt very clear. Once warm and shut off, when i try to start it again it will crank but not start. I just got back from the store about 20 miles there and back and in my drive same thing. Will crank but not start. But turn ignition off and then try to start and it fires right up. BTW when i jumped in it this morning it started like a champ.

[dh2]

I would bet on the fuel pump ( in tank) like others have said , but I would feel better with a fuel pressure test

[clum553946]

There are quite a few GMC & Chevy truck forums. You can try surfing those to see if people have had the same problem & what was the cause.

[Minerat]

But turn ignition off and then try to start and it fires right up.

That's exactly what I had, once the fuel pump was replaced it worked fine. I got to the point where I would start it like a diesel only just turn the key on and off. Seemed to charge the system then it would start no problem.

[Jniedbalski]

My 94 Chevy had this problem but it was the pick up in the distributer It’s located under the plate that the ignition module sits on. You have to take the distributer out and take it appart. The 99 Gmc I have dosent have a distributer. So it’s probably a fuel pump problem. It also could be a crank or cam sensor .once the motor starts spinning the ecm computer turns the fuel and spark on. Some times they start acting funny. My fuel guage also acts up a lot showing empty when the tank is full. Going down the road it can go up and down all the time but dosent mess with starting

[brass410]

don't bother cking for dist/rotor ign parts that truck uses cop ign (coil on plug triggered by crank/cam inputs to ecm) 1st ck would be fuel press test followed by cking fuel press regulator (pull vacuum hose off and see if fuel runs out if it does replace it, its *****) you didn't mention if mil lite was on, if it is ck and see what codes have been set, possible failing crank sensor. These trucks have a real reputation for bad grounds on the wirirng harness (show up when warm usually) Two grounds I routinely clean and repair wire ends on, are on the rear of R&L cylinder heads pinched up tight to firewall of engine compartment they are 15 mm heads and about 3/4 inch long you"ll be speaking in tongues when you have to do them. hope this helps

[Geezer in NH]

The fuel gauge going up and down is a constant problem with GM. Even with a full new riser and sender, pump and float the gauge problem came back in under 2 years.

Right now I fill the tank and it goes from empty to 1/2 in about 3 hours then drive 50 miles and reads correct until it lights up out of fuel. I set the millage counter and go by how far I have been. We also keep a 6 gallon can in the back.

[HATCH]

Once warm and shut off, when i try to start it again it will crank but not start.

do your little drive. Come back.
Turn the key on for 20 secs, then turn it off and then back on for 20 secs, then off and then start it up.
See if it starts up
So key on 20 secs, key off 2 sec, key on 20 secs, key off 2 secs, key on - start

the fuel pump runs for a few seconds when you first turn the key on

[bob208]

could be as simple as the fuel filter clogging up. I have seen so many problems with fuel filters I change mine every 2 years. my fuel gauge has not worked since I have had the truck. I zero the trip meter and fill at 250 mi.

[Jniedbalski]

Brass 410 is correct about bad grounds. Don’t remember if it’s on the fire wall or head but it should be on the passenger side fire wall or rear of the head . It could also be behind the tranny fill tube on the rear side of the passenger side head. Also just another problem with the older trucks that could cause them to run funny or rich . They had two brass screw in temp sensors. One for the computer and one just for the temp guage. One was by the thermostat housing and one was in the driver side head up front or in the block below the head. This was on the older throttle body 350 motors. My 94 I replaced the brass sensor and it cured a over rich condition caused by the temp sensor. I always also always run a extra ground on old vehicles to the fire wall and the motor and to battery ground. Keeps from having electrical problems and also always clean the extra grounds up also if I can find them

[jsizemore]

Fuel pressure gauge on the rail tells the story. If the pressure is low then it could be the regulator or pump. Clamp the return line from the regulator and if it's still low then you know it's the pump. The pros drop the tank. Us amateurs tilt the bed. Buy a good pump or you'll be back sooner than you like.

[brass410]

fuel press is critical on these engines anything less than 53 psi you'll have trouble. aftermarket fuel pumps brand new often have only 54-55 psi, just beware buy quality pump. If you have the pump unit out of the tank, very carefully remove the plug on the assembly where the wires pass thru the body down to the sender unit and pump, this is a trouble some spot for bad/poor connection sometimes the plug will even be melted causeing intermittent no/hard starts.

[jsizemore]

My 2003 4.3 ran 23 psi. I figured the gauge was wrong so carried it to a real mechanic with real tools. 23 psi. He said it shouldn't run or be easy starting. It never happened. My problem was running out of fuel under heavy load or high speed and bucking/down shifting.

I'm convinced that changing your fuel filter every year will help the fuel pump live an easier, longer life.