Fuel delivery problem?, starts hard when cold,

[mike2004tct]

'97 Blazer, 68k miles.
No raw gas smell, or visible leaks.
Starts OK when warm.

Fuel pressure readings;

Cold, sitting for more than 17 hours, key off = 0 psi

Turn key on, no start = 30 psi, then drops to 0 psi within 5 seconds of pump priming finish.

Pressure while cranking = 62 psi
Pressure when enging starts/idling = 54 psi
Pressure while driving between 30-45mph = 47 to 60 psi (60 under load, 47 at steady speeds). Idling at stop = 54 psi.

Turn ignition off, pressure goes to 62 psi for 2 seconds, drops to 0 within 10 seconds.

Turn ignition on within 10 minutes of previous shut-off (no start), pressure = 62 psi.
Turn key off = stays at 60 psi for 2 seconds, drains to 0 in less than 10 seconds.

Opinions?


This is a 17 month old Delphi unit (the 3rd I've had in the truck), Fuel filter was changed with pump, about 10k miles ago.

Within the past 3 months, I've also replaced the VCM, distributor,coil, and ignition module(VCM burnt them all up). It's been a hard starter ever since the electrical problems began, and it getting worse (occassionally takes longer to start; 3 crank sessions at 10 seconds each before firing- Saturday, and Monday for instance, Sunday and today it started fine)

Punmp is bad, see post #4

[MT-2500]

Originally Posted by mike2004tct

'97 Blazer, 68k miles.
No raw gas smell, or visible leaks.
Starts OK when warm.

Fuel pressure readings;

Cold, sitting for more than 17 hours, key off = 0 psi

Turn key on, no start = 30 psi, then drops to 0 psi within 5 seconds of pump priming finish.

Pressure while cranking = 62 psi
Pressure when enging starts/idling = 54 psi
Pressure while driving between 30-45mph = 47 to 60 psi (60 under load, 47 at steady speeds). Idling at stop = 54 psi.

Turn ignition off, pressure goes to 62 psi for 2 seconds, drops to 0 within 10 seconds.

Turn ignition on within 10 minutes of previous shut-off (no start), pressure = 62 psi.
Turn key off = stays at 60 psi for 2 seconds, drains to 0 in less than 10 seconds.

Opinions?


This is a 17 month old Delphi unit (the 3rd I've had in the truck), Fuel filter was changed with pump, about 10k miles ago.

Within the past 3 months, I've also replaced the VCM, distributor,coil, and ignition module(VCM burnt them all up). It's been a hard starter ever since the electrical problems began, and it getting worse (occassionally takes longer to start; 3 crank sessions at 10 seconds each before firing- Saturday, and Monday for instance, Sunday and today it started fine)

Mike.
Pressure is to low.
Could be weak pump or pressure regulator not holding pressure,
Hard to start cold is low fuel pressure.
You need 64 -65 lbs on a cold start.
With good volumn and pump capable of pumping full pressure.
Run a full pressure check.
Make sure pump puts out 95 lbs of pressure or more direct pressure.
Block or plug return line for direct pressure check.
And drive it about a hr and recheck pressure when hot.

Also check the wiring and voltage and grounds to fuel pump.
And recheck the fuek filter.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Good Luck

[Schrade]

Originally Posted by mike2004tct

'97 Blazer, 68k miles.
No raw gas smell, or visible leaks.
Starts OK when warm.

Fuel pressure readings;

Cold, sitting for more than 17 hours, key off = 0 psi

Turn key on, no start = 30 psi, then drops to 0 psi within 5 seconds of pump priming finish.

Pressure while cranking = 62 psi
Pressure when enging starts/idling = 54 psi
Pressure while driving between 30-45mph = 47 to 60 psi (60 under load, 47 at steady speeds). Idling at stop = 54 psi.

Turn ignition off, pressure goes to 62 psi for 2 seconds, drops to 0 within 10 seconds.

Turn ignition on within 10 minutes of previous shut-off (no start), pressure = 62 psi.
Turn key off = stays at 60 psi for 2 seconds, drains to 0 in less than 10 seconds.

Opinions?


This is a 17 month old Delphi unit (the 3rd I've had in the truck), Fuel filter was changed with pump, about 10k miles ago.

Within the past 3 months, I've also replaced the VCM, distributor,coil, and ignition module(VCM burnt them all up). It's been a hard starter ever since the electrical problems began, and it getting worse (occassionally takes longer to start; 3 crank sessions at 10 seconds each before firing- Saturday, and Monday for instance, Sunday and today it started fine)

Excellent job testing fuel pressure!!! Even when driving!

One additional driving-pressure test; pedal down test. This confirms that the vacuum-controlled FPR will respond to engine load. I don't know what the spec pressure is for this test, but I do know it has to be done to confirm proper FPR function.

Also you might have to note the pressure differences between idle with vacuum OFF of FPR, and idle with vacuum ON FPR. Again, I don't know what the spec difference should be - check the Chevy shop book...

[mike2004tct]

Well, fuel pump #3 just crapped out. Delphi FG0072., I installed it June,2006.
So, not much better than the carter crap that lasted 14 months (delphi lasted twice as long, whooopeee).
Bummer.

Thanks to write-up Old_master e-mailed me, I made a gauge to check the pump pressure.

The gauge was made with parts readily avfailable from Napa and Ace Hardware.
Napa 730-5013 steel fuel line repair fitting, 3/8"
1 ft 3/8" hose, 2 clamps.
Ace - 3/8" ball valve
3/8" male to barb fitting (for the hose attachment)
3/8+ male/female adaptor (because the steel tube hot the ball of the valve)

Old Master's parts were somewhat different, but close to the valve (lower unit in the picture above). I clamped the open end of the hose onto the output of the fuel filter, and steel tube into the pipe to the injectors.
Once the fuel pump primed, I shut the valve as soon as the pump stopped.
Pressure gauge registered 52 psi steadily. As soon as the valve was opened, the gas went back thru the pump, and pressure went to 0 immediately.

[MT-2500]

What is going bad on the pump?
Have you checked the voltage and grounds and wiring real good?
VCM and AC-Delco/Delphi puel pump do not go bad often.
If so something is causing them to go.
Mike did you ever figure out what caused the vcm burn up problem you had?

[mike2004tct]

Originally Posted by MT-2500

What is going bad on the pump?
Have you checked the voltage and grounds and wiring real good?
VCM and AC-Delco/Delphi puel pump do not go bad often.
If so something is causing them to go.
Mike did you ever figure out what caused the vcm burn up problem you had?

Took the pump out this morning. Blew into the feed line, and a small stream of gas shot out from underneath the top of the housing.

Did it again, and noticed the gas coming out of a very small hole in the plastic flex tube that runs from the pump to the top cover of the assembly.

Put a new pump in (Another FG0072), and noticed that the plastic hose is much shorter on the new pump. The power connector was also changed (A new one was included, had to splice it on).
Pressure is good (62 psi) before start, and pressure remains at 58 psi for 5 minutes plus, after key is turned off.

[MT-2500]

Originally Posted by mike2004tct

Took the pump out this morning. Blew into the feed line, and a small stream of gas shot out from underneath the top of the housing.

Did it again, and noticed the gas coming out of a very small hole in the plastic flex tube that runs from the pump to the top cover of the assembly.

Put a new pump in (Another FG0072), and noticed that the plastic hose is much shorter on the new pump. The power connector was also changed (A new one was included, had to splice it on).
Pressure is good (62 psi) before start, and pressure remains at 58 psi for 5 minutes plus, after key is turned off.

Thanks for letting us know how it went.
Sounds like you found the problem with bad pump bleed off.
On the plugin wiring you should use solder on the wire splices and seal wires with heat shrink and wire sealer.
Hope they have got the hose problem fixed on newer pump.
Good luck with this one.

[Big J Olds]

Originally Posted by mike2004tct

Well, fuel pump #3 just crapped out. Delphi FG0072., I installed it June,2006.
So, not much better than the carter crap that lasted 14 months (delphi lasted twice as long, whooopeee).
Bummer.

Thanks to write-up Old_master e-mailed me, I made a gauge to check the pump pressure.

The gauge was made with parts readily avfailable from Napa and Ace Hardware.
Napa 730-5013 steel fuel line repair fitting, 3/8"
1 ft 3/8" hose, 2 clamps.
Ace - 3/8" ball valve
3/8" male to barb fitting (for the hose attachment)
3/8+ male/female adaptor (because the steel tube hot the ball of the valve)

Old Master's parts were somewhat different, but close to the valve (lower unit in the picture above). I clamped the open end of the hose onto the output of the fuel filter, and steel tube into the pipe to the injectors.
Once the fuel pump primed, I shut the valve as soon as the pump stopped.
Pressure gauge registered 52 psi steadily. As soon as the valve was opened, the gas went back thru the pump, and pressure went to 0 immediately.

Hey i noticed the "tool" you used to test full pump pressure and was wondering how you were able to get the reading you needed if you hooked it up to the filter side? Isnt that the inlet? Dont you need to block the return line? I would really like to know how that worked because I have to do the same thing on mine before it gets freezing. Thanks

[mike2004tct]

Originally Posted by Big J Olds

Hey i noticed the "tool" you used to test full pump pressure and was wondering how you were able to get the reading you needed if you hooked it up to the filter side? Isnt that the inlet? Dont you need to block the return line? I would really like to know how that worked because I have to do the same thing on mine before it gets freezing. Thanks

The Schrader valve is on the input line side. I removed the fuel line (quick connect side) from the output of the filter, and inserted the tool between the filter and the schrader valve line. The pressure regulator in the intake manifold stops the fuel from returning to the tank via the return line until ~70PSI, at which the reg. would open. So in essance what I did was test the pressure regulator by stopping the fuel flow after the filter. If pressure stays maintained with the tool valve closed, press. reg. is OK. If pressure goes to 0 rather fast with tool valve open, pump is leaking- as was my case, a hole in the fuel pump hose.

[crankyfranky]

location of fuel pressure regulator on 2000 jimmy ?

[mike2004tct]

Originally Posted by crankyfranky

location of fuel pressure regulator on 2000 jimmy ?

Should be the same as my '97, if it's a 4.3 W-vin,MFI V6.

Under the intake manifold. Part of the injector assembly.