Truck Starts Consistently But Not Like It Should

[downplay]

This truck starts every time but I either have to turn it over once, stop, and then turn it over again to start, or on the first time, it will spudder weakly a little, then fire up. Once in a while
it will just turn over strong on the first try but not often.

It now has a brand new alternator, new spark plugs, a new fuel filter, and a new air filter at 144,000 miles. The plugs and filters were overdue. It starts just the same before these updates and after.

The battery only has about 7 months left on it but it shows good on 2 different testers.

Any ideas or suggestions?

As another symptom, it also seems to have slight power loss beginning at about 50 mph+ but it will go up to any speed, not too big of a deal.

Although, this may have changed with the spark plug replacement. I drove it today up to
55 mph and it did not have the loss/shudder feel at 50 and the check engine light did not
come on. Before the new plugs, the light came on almost every time I drove it at any speed. I'll have to drive it some more to see if this has really changed permanently.

[j cAT]

this maybe the fuel pressure or lack of flow. using a pressure gauge measure pressure. see if it is the proper amount. if you have fuel filter replace. cut filter open see if its dirty and rusty if so use another fuel supply station.

after these tests and the filter replacing if you have one then add the injector cleaner techron 2 bottles and fill tank......

[Blue Bowtie]

Can you measure and report the fuel pressure, both KOEO and while running?

It will also help to know what model year and engine is involved.

[downplay]

Originally Posted by Blue Bowtie

Can you measure and report the fuel pressure, both KOEO and while running?

It will also help to know what model year and engine is involved.

Oops, it is a 2002 Chevy Silverado heavy half with the 6.0 liter Vortec. When I replaced the fuel filter, the old one seemed fine. Nothing but clean, clear looking fuel came out.

I'll have to look into checking the fuel pressure. I've only recently become my own mechanic so I'm learning as I go.

Do you think it could be the spark plug wires? There did seem to be a small amount of corrosion on the wire side, on one side of the engine.

Could it be the ignition coil?

I'll test the fuel pressure when I can figure out how, thanks!

[rhandwor]

Auto Zone or Advanced Auto should have loaner fuel pump pressure gauges.

[downplay]

Originally Posted by j cAT

this maybe the fuel pressure or lack of flow. using a pressure gauge measure pressure.

Now I think you guys are right on the money about it being a fuel pressure issue. I got on Youtube and watched some good videos on how to perform the tests.

When I turn the key on (but not the engine) the pressure quickly jumps up to over 50 PSI. But then it very rapidly falls back down to below 10 within just a few seconds.

The same thing happens after the engine is running and I turn the key off. Is this supposed to happen?

It seemed to have the proper pressure while idling, at a constant rev, at quick revs, with the fuel pressure regulator on, and with the fuel pressure regulator off (where it just jumped up slightly). It never went super high or super low during the running tests but stayed in a pretty narrow range around 43 PSI. There was also no fuel in the pressure regulator, in the vacuum tube, and it seemed to have a strong, steady vacuum.

Since it is only losing pressure with the engine off, but pump on, and it happens rapidly, this has to be the check valve in the fuel pump, correct?

Thanks!

[j cAT]

Originally Posted by downplay

Now I think you guys are right on the money about it being a fuel pressure issue. I got on Youtube and watched some good videos on how to perform the tests.

When I turn the key on (but not the engine) the pressure quickly jumps up to over 50 PSI. But then it very rapidly falls back down to below 10 within just a few seconds.

The same thing happens after the engine is running and I turn the key off. Is this supposed to happen?

It seemed to have the proper pressure while idling, at a constant rev, at quick revs, with the fuel pressure regulator on, and with the fuel pressure regulator off (where it just jumped up slightly). It never went super high or super low during the running tests but stayed in a pretty narrow range around 43 PSI. There was also no fuel in the pressure regulator, in the vacuum tube, and it seemed to have a strong, steady vacuum.

Since it is only losing pressure with the engine off, but pump on, and it happens rapidly, this has to be the check valve in the fuel pump, correct?

Thanks!

50 psi is low so KOEO should be 60-62 psi and hold for a few min then very slowly drop , not rapidly.

this means a bad pump check valve if NO fuel line leaks.
only use ac delco or Delphi pumps... even if the auto store gives you an airtex for free do NOT take it.

engine running should be 57 psi about ..

when installing make sure the ground is solid and clean. solder the connector WIRE connections and seal with some rubber heat shrink available at a radio shack store.

[downplay]

Originally Posted by j cAT

50 psi is low so KOEO
this means a bad pump check valve if NO fuel line leaks.

Wouldn't a fuel line leak be obvious? I am certain there is no fuel dripping anywhere. Could it not be dripping yet still require further inspection?

What are the repercussions of running it like it is? It does start for me every time. With low pressure, it should be running "lean?" Will this damage the engine or other components?

Thanks for all the awesome detailed advice!

[rhandwor]

http://www.ebay.com/itm/331555771517/www.ebay.com/
A check valve won't correct low pressure. Some pressure regulators can be adjusted.
Some people pull the bed and change a pump. Some loosen bolts on pass. side remove on drivers side and lift up enough to remove the pump. Some use a lift and transmission jack under fuel tank.

[j cAT]

Originally Posted by downplay

Wouldn't a fuel line leak be obvious? I am certain there is no fuel dripping anywhere. Could it not be dripping yet still require further inspection?

What are the repercussions of running it like it is? It does start for me every time. With low pressure, it should be running "lean?" Will this damage the engine or other components?

Thanks for all the awesome detailed advice!

the smell of fuel should be about the vehicle if a leak . the fuel pump check valve has a big effect on the fuel pressure where it will be lower. the fuel regulator appears good. the fuel regulator with no vacuum line should read 60psi plus. operating with 50 PSI or less may cause miss fires so that is not good. it can cause damage but not for a short period of time.

fuel pump replacing on truck is best on the truck bed un bolted and lifted..

the fuel filler pipe requires the fasteners removed so the bed is lifted/tilted up. the filler hose is not removed. then with that up you wash/blow off all debris at the fuel pump access and then lube the locker ring then open the tank to remove pump.. make sure all connections are not corroded etc..

dropping the tank can be tough to put back more fuel lines and canister interference etc..

[downplay]

There is no smell or other evidence of leaking fuel that I can detect so I think my fuel lines must be good.

Originally Posted by j cAT

solder the connector WIRE connections and seal with some rubber heat shrink available at a radio shack store.

Soldering? This is something done away from the tank? It sounds scary around a gas tank!

Wow, it is gonna take a little time for me to get my head around all this great advice. Thanks!

[j cAT]

Originally Posted by downplay

There is no smell or other evidence of leaking fuel that I can detect so I think my fuel lines must be good.



Soldering? This is something done away from the tank? It sounds scary around a gas tank!

Wow, it is gonna take a little time for me to get my head around all this great advice. Thanks!

no flame/torch you use a soldering iron about 40 watts with rosin core solder. you also use some rubber heat shrink over these soldered wires.

radio shack has this type stuff. using the crimp on wiring splices will corrode also will cause the pump to get lower volts to it.

this is done with the pump installed .. then you test fuel pressures and make sure its all good then drop the bed down and secure everything.

[downplay]

Originally Posted by j cAT

fuel pump replacing on truck is best on the truck bed un bolted and lifted..

This sounds really smart. I don't think I'll be able to use an overhead winch or anything to lift the bed. It has a plastic liner that is probably best not removed. How many dudes would I need to lift it? Can 2 average guys do it? 4? I just need to plan well. I don't normally have anyone around to help.

[downplay]

What do you think about the "tilt bed" method of accessing the fuel pump? It looks like I can pull this off by myself with enough care and patience. I am fairly handy but certainly a newb mechanic. Will there be enough space for me to work?

Oh, and just to make sure, a fuel pump relay couldn't cause underpressure could it?

[j cAT]

Originally Posted by downplay

This sounds really smart. I don't think I'll be able to use an overhead winch or anything to lift the bed. It has a plastic liner that is probably best not removed. How many dudes would I need to lift it? Can 2 average guys do it? 4? I just need to plan well. I don't normally have anyone around to help.

2 people can do it remove the tail gate. get some 2X4 lumber wood blocks to hold in place/ hold lift . you will be surprised its not all that heavy. but its big so 2 is best. I did it myself but was a much harder job..


check the rear brake line for rust if rusted replace it now.