99 Suburban won't fire (5.7L)

[no_cash_money]

Sat out in the cold for about a week and wouldn't start so I pushed it into the garage to warm up.

After reading as much as I could about fuel pressure problems I changed the fuel filter and then decided to replace the fuel pressure regulator, so I just got done replacing that and still no fire (hope I did it right). Fuel pressure jumps to 60 with the pump running for 2 seconds and drops down to 50 when it stops, and holds pretty steady after that. If I remember correctly the pressure dropped off much faster before I replaced the FPR. I actually got it to start a few days ago with some resistance, but as of now it won't.

At this point I am wondering if it might just be the fuel pump going bad again, or possible fuel injectors leaking but I didn't notice anything when I replaced the FPR.

Is it possible for a pump to have weak pressure if the grounds are bad?

Any help appreciated. Thanks.

[MT-2500]

Originally Posted by no_cash_money

Sat out in the cold for about a week and wouldn't start so I pushed it into the garage to warm up.

After reading as much as I could about fuel pressure problems I changed the fuel filter and then decided to replace the fuel pressure regulator, so I just got done replacing that and still no fire (hope I did it right). Fuel pressure jumps to 60 with the pump running for 2 seconds and drops down to 50 when it stops, and holds pretty steady after that. If I remember correctly the pressure dropped off much faster before I replaced the FPR. I actually got it to start a few days ago with some resistance, but as of now it won't.

At this point I am wondering if it might just be the fuel pump going bad again, or possible fuel injectors leaking but I didn't notice anything when I replaced the FPR.

Is it possible for a pump to have weak pressure if the grounds are bad?

Any help appreciated. Thanks.

Specs are 60/66 lbs.

You need around 65 cold cranking pressure for injectors to squit fuel.

Just key on is not much of a fuel pressure check.

First thing to check is squirt some carb cleaner into intake and see if it will fire up.
If so you have a fuel delivery problem.

When checking fuel pump jumper pump and check pump running pressure.
Then pinch off or block return line and see if pump will go to full pressure 95-105 lbs.
But do not run pump for over a second or 2 at full pressure.
Check engine cranking pressure and full pressure and post back pressure readings and if it will fire on carb cleaner..
Do not use starting fluid unless you want to blow it up.

Also check for good spark to all plugs while cranking.

[no_cash_money]

Started up today with some hesitation---I wonder if starter is going bad with all the cranking lately.

Cold cranking pressure was 60 (I assume this means pressure at rail while cranking when engine is cold) and dropped down to 50 at idle.

What does this mean?..."When checking fuel pump jumper pump and check pump running pressure."

I still need to pinch the return line and measure pressure. Do I do this while engine is idling? What will this tell me?

[MT-2500]

Originally Posted by no_cash_money

Started up today with some hesitation---I wonder if starter is going bad with all the cranking lately.

Cold cranking pressure was 60 (I assume this means pressure at rail while cranking when engine is cold) and dropped down to 50 at idle.

What does this mean?..."When checking fuel pump jumper pump and check pump running pressure."

I still need to pinch the return line and measure pressure. Do I do this while engine is idling? What will this tell me?

If engine still cranks normal starter is good.

On that end first thing is make sure battery does not get run down.

Fuel pressure is to low.
You need 64-65 engine cranking cold.

50 lbs is way to low idle.

Should be around 62 idle.
Engine under load should jump to 64-65.

And as always make sure fuel pressure gage is reading good.
If you are not sure.
Check against a known good gauge.

While you have it running run it on the road and see what pressure does on road.

With return line blocked or pluged and fuel pump running fuel pressure should jump to full pressure 95 to 105 lbs bif pump is good.
But only run pump at full pressure for not over 1 or 2 seconds.
Post back all pressure readings.
Return line blocked and engine on road readings.

[no_cash_money]

had my wife watch the gauge a few times as i pinched the return line---90psi---engine almost stalled out everytime but i held it for less than 2 seconds

went down the road and under normal acceleration it would get up between 56-59 at the most

i bought another gauge (same Actron as before) and i got the same readings, so unless i got two bad gauges my readings are correct

i bet its been operating at these pressures all summer long and its only now acting up because i had it outside sitting below freezing---doesn't seem like its running any differently than before

next step fuel pump?

[MT-2500]

Originally Posted by no_cash_money

had my wife watch the gauge a few times as i pinched the return line---90psi---engine almost stalled out everytime but i held it for less than 2 seconds

went down the road and under normal acceleration it would get up between 56-59 at the most

i bought another gauge (same Ac tron as before) and i got the same readings, so unless i got two bad gauges my readings are correct

i bet its been operating at these pressures all summer long and its only now acting up because i had it outside sitting below freezing---doesn't seem like its running any differently than before

next step fuel pump?

If you are getting 90 lbs full pressure out of fuel pump.
It is good to go.
The pressure regulator is what should hold pressure 60/66 depending on engine vacuum/load.
And should hold/regulate around 65 lbs pressure on cold start.

[no_cash_money]

what are the chances I installed the new FPR wrong? all I did was pull the old one out and put the new one in---didn’t seem too complicated

could my engine vacuum be the problem?


not sure what else I should check if FPR is new and the fuel pump is good

[MT-2500]

Originally Posted by no_cash_money

what are the chances I installed the new FPR wrong? all I did was pull the old one out and put the new one in---didn’t seem too complicated

could my engine vacuum be the problem?


not sure what else I should check if FPR is new and the fuel pump is good

New does not always mean good.

Did you use a GM oem regulator or aftermarket?
Best to use Gm oem from dealer.
As long as no leaks where regulator plugs in you should not have a problem.
If no vacuum or low engine vacuum the pressure should jump up on higher pressure.
Always test it out before you put cover back on.
Fuel pump running engine off it should jump to 65-66 lbs.
Again check your gage with a know good one.
or even try your gage on a tanother truck like yours.

If your gage is good better get a GM OEM pressure regulator.
And test it out befor putting cover back on.

[no_cash_money]

the FPR is a Delphi----i thought that was a decent brand----on a side note the one i received from Rock Auto was missing the barb that the original had---its for the vacuum hose, correct? i figured that since the whole thing was under vacuum that it didnt need one anyways, which is why there was no hose hooked up to the old one

i am gonna buy a different brand of fuel pressure gauge just to be sure

could my fuel injectors be leaking?---how would i be able to tell? or could there be a subtle leak somewhere in the fuel lines that i haven't caught?

what about the check valve on the fuel pump? i have read that those go bad

[MT-2500]

Originally Posted by no_cash_money

the FPR is a Delphi----i thought that was a decent brand----on a side note the one i received from Rock Auto was missing the barb that the original had---its for the vacuum hose, correct? i figured that since the whole thing was under vacuum that it didnt need one anyways, which is why there was no hose hooked up to the old one

i am gonna buy a different brand of fuel pressure gauge just to be sure

could my fuel injectors be leaking?---how would i be able to tell? or could there be a subtle leak somewhere in the fuel lines that i haven't caught?

what about the check valve on the fuel pump? i have read that those go bad

If pump pushes 90 lbs with return line pinched off.
Than the fuel pressure regulator should be able regulate pressure at 60/66 lbls.

Your gage is off or the fuel pressure regulator is bad.

Strange the nipple that is not used is gone.

[MT-2500]

Auto zone and some parts places have fuel pressure testing gauges that they rent/loan.
Good Luck

[no_cash_money]

i used 3 different testers, 2 Actron and 1 Equus, all giving me the same reading so at this point i have to rule out bad readings

it has been starting fine lately, so i think the low fuel pressure has been around for a while and the cold weather made it worse

i wonder if my vacuum isnt as good as it should be----might check the EGR valve

other than that, not sure what else i could do, but cant say i didnt try

thanks for you help MT-2500

[j cAT]

Originally Posted by no_cash_money

i used 3 different testers, 2 Actron and 1 Equus, all giving me the same reading so at this point i have to rule out bad readings

it has been starting fine lately, so i think the low fuel pressure has been around for a while and the cold weather made it worse

i wonder if my vacuum isnt as good as it should be----might check the EGR valve

other than that, not sure what else i could do, but cant say i didnt try

thanks for you help MT-2500

since the pressure of fuel is good at higher rpm, check that at idle you have a good solid alternator output voltage at 14.25volts DC. when reving engine should be a steady 14.25volts. if the voltage varies 12volts to 14 volts this is most likely an alternator issue. the vehicle also may have bad connections/grounds/loose fuse sockets. make sure voltage at pump is 14volts engine running. make sure the pump ground strap/wires are good and clean and secure to the frame.