2000 Silverado won't start

Hi, wondering if anyone can help me. My truck won't start when it gets below -20 Celsius. Here's what I have tried and found out.

-Block heater works and engine turns over good.
-Took computer off and warmed it up then reinstalled but still no start.
-New spark plugs and wires.
-Ignition does spark.
-New fuel filter.
-Bought a fuel pressure gauge and noticed there is no fuel pressure.
-Fuel pressure regulator vacuum line has no fuel in it.
-My mechanic says he has never had to change a regulator.
-Added gasline antifreeze.
-Cleaned idle air control sensor.
-Push truck in the shop and after 30 minutes turn key on and can hear fuel pump working and now have fuel pressure and truck starts.
-Took it to the mechanic when it wouldn't start and he banged on the gas tank and then it started.
-Mechanic changed fuel pump.
-Next day was -18 C and it barely started with the exact same symptoms as before and I'm sure it won't start if it gets any colder.
-I have since replaced the fuel pump relay but it hasn't been cold enough to not start since so I don't know if that was it.

Does anyone have any other ideas? Thanks for the help...Jack

this could be water in the fuel....when the fuel pump was replaced this should have been checked...

the fuel filter should be removed and cut open to inspect...for debris and water...

when running what is the fuel pressure? was the NEW pump a delphi?...


the other test would be voltage at the fuel pump and making sure the fuel pump ground at the frame rail is very clean and secure..

replacing the relay at this age is a good idea...the ECT can cause starting problems but you will get fuel pressure,,,also the regulators do fail and if fuel was in the vacuum line this would indicate this..

look for fuel pressure testing here on these forums for the testing proceedure...

this could be water in the fuel....when the fuel pump was replaced this should have been checked...

I wondered about that and it is why I added gasline antifreeze. I have probably been through 20 tanks since the problem started so I figured that probably wasn't it.

the fuel filter should be removed and cut open to inspect...for debris and water...

I haven't done that but have replaced it twice in the last month.


when running what is the fuel pressure? was the NEW pump a delphi?...

When running fuel pressure is 52 psi. It was a Delphi and I assumed it was new at $550.


the other test would be voltage at the fuel pump and making sure the fuel pump ground at the frame rail is very clean and secure..

I will check this next time it doesn't start. Won't be fun at -25.



replacing the relay at this age is a good idea...the ECT can cause starting problems but you will get fuel pressure,,,also the regulators do fail and if fuel was in the vacuum line this would indicate this..

When it wasn't starting it had good spark. When the computer was removed I checked to see if the fuel pump would work without it and it doesn't. Because of this I assumed the computer could fail and not turn on the pump. After I warmed the truck up and got it started I removed the computer and put it outside to get good and cold so I could try a warm truck and cold computer combo and the truck started so I have ruled out the computer for now. There was no fuel in the regulator vacuum line so I have ruled out that also but suppose gas in the line isn't the only indication that it isn't working right. My way of thinking is that when the truck gets shut off the regulator should close to hold pressure so the next morning if it is stuck it should be stuck in the closed position so I should have fuel pressure when I turn the key on. It usually leaks down to about 35 psi overnight so when I first try and start it it fires for a second but once that fuel pressure is gone it just turns over.

This is a frustrating problem because I have to wait for cold weather to see if the problem is fixed. Then if it's not fixed I'm stuck with a truck that won't start and need it for work. I don't think taking it back to the mechanic when it's warm and working fine will do any good. Thanks for the ideas j cAt. I will check the fuel pump ground while it's warm out and figure out the best place to check voltage to the pump so when it gets cold out I'll know what I'm doing.

since it is a delphi pump, and new the pressure should be 60psi approx...since it is low this could be bad ground, positive feed connectors, or even a weak battery/poor connections...

when the temps drop to 10deg f you loose 50% of your battery power...get the battery load tested....to be sure its got plenty of capacity left in it..as well...

when cold you need a lot of fuel pressure,to get it to start...

when cranking check for voltage across the battery...should be 9.5volts or higher...

another test is to put key to ignition on ,,,wait 2sec. then engage starter..

since it is a delphi pump, and new the pressure should be 60psi approx...since it is low this could be bad ground, positive feed connectors, or even a weak battery/poor connections...

when the temps drop to 10deg f you loose 50% of your battery power...get the battery load tested....to be sure its got plenty of capacity left in it..as well...

when cold you need a lot of fuel pressure,to get it to start...

when cranking check for voltage across the battery...should be 9.5volts or higher...

another test is to put key to ignition on ,,,wait 2sec. then engage starter..

j cAT; when I turn the key on fuel pressure goes to 60 psi while the pump is running and the drops to 55 when it turns off. When my truck won't start it is because there is 0 pressure in the fuel rail. I push it in a warm shop and wait 15-30 minutes until the fuel pump works again and I have 55 psi and it starts. My problem seems to be no fuel pressure not low pressure. I think you were on to something with checking for power at the pump when it won't start. I think something isn't letting the power get to the pump when it's cold. What else could it be besides the computer or fuel pump relay? What is and where are the positive feed connectors? Are you just talking about the wiring to the pump?

The battery is only a year old with clean, tight connections and it turns over the engine real good. Couldn't hurt to check the cranking voltage though. It's gonna be nice here for the next weak so I'll have to wait and see if it was the relay. I appreciate the help, thankyou.

with your explaination I would say you are loosing the feed or ground when cold...but you must confirm this at the pump when it is in fail mode...start at relay is the relay energized,is there a feed to contacts of relay to fuel pump motor,work toward the pump,until voltage loss is found...

what throws auto techs off is they ignore grounds...power and a ground return must be solid or problems will occur..

many with weird pump problems have found the filler neck/fuel pump ground point the problem,or even not connected or broken because they forgot to disconnect when dropping the tank...

Ok, I will look into it and let you know. Thanks.

I have noticed also that alot of these trucks had factory undercoating on frame before ground wires where connected and after time will lose contact with frame since its only ground is through the bolt which is tightening tab onto undercoating usually under drivers door near body mount. I aint sure if yours is undercoated but its worth a look! If so just scrape off undercoat and reconnect, its the moisture that is prob. getting in between the ground and frame in cold temp. thats messing up your circuit. Good Luck

I have noticed also that alot of these trucks had factory undercoating on frame before ground wires where connected and after time will lose contact with frame since its only ground is through the bolt which is tightening tab onto undercoating usually under drivers door near body mount. I aint sure if yours is undercoated but its worth a look! If so just scrape off undercoat and reconnect, its the moisture that is prob. getting in between the ground and frame in cold temp. thats messing up your circuit. Good Luck

It appears that this undercoating was applied prior to vehicle assembly as you say and when assembled at factory it was not cleaned and sealed as stated in the repair of such ground connections...that is why I always mention the grounds when wierd problems occur...

just above this frame mount you mentioned is where the brake lines rust out...

It was -22 C yesterday morning and it started good so it seems the relay was the problem. Thanks for all the help...Jack