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Hard starting...low startup fuel pressure

5K views 12 replies 6 participants last post by  Big_kid 
#1 ·
RE: 94 4.3L W Fuel pump?
Lately this van has been requiring a lot of cranks to get it started when cold. Once started then all is well. Found that spraying starter fluid into the intake will allow it to start up immediately. I checked fuel pressure at the fuel rail when the van was cold and found that when the fuel pump is initially turned on (engine off), I received a reading of 42#. I turned the ignition switch off and then on again just to reenergize the fuel pump and the pressure did increase to 48#. With the engine running, I have 54#. Turning the engine off and testing for leakage, I found that my fuel pressure will gradually decrease to 40# over the period of 2 hours. I changed the fuel filter to see if that would increase my pressure but that did not change the readings. I am thinking that I have to change the fuel pump but want a second opinion before going the time and expense. Any suggestions?
 
#2 ·
That 42 lbs is a little low. Does the fuel pump make a steady hum while its running or does the sound get louder/quieter from time to time? When was the last time the fuel filter was changed?
 
#3 ·
Thanks for responding so quickly.

I replaced the fuel filter right after taking my first pressure testing because I wanted to see a before and after test result but I received the same pressure readings. I also thought that 42# was a little on the weak side for the first prime but wasn't sure especially when I received 54# when the motor was running. I do hear the fuel pump priming for 2 seconds when the ignition key is turned on (motor not running) and again for each other time that I restart the fuel pump (turning the pump off, wait 10 seconds and restart the fuel pump).

The battery is fully charged and has low voltage drop when cranking; replaced distributor cap, rotor, plugs, and wires not too long ago. The van just doesn't like to startup when cold (or what could be just low fuel pressure) but when I spray a little fuel into the intake (CMFI), the engine immediately starts without hesitation. Almost like me and my morning coffee. Once the van has been started, I usually do not have a problem in a four hour window so I am thinking that when the fuel line still has prior pressure and when the fuel pump is activated again, it primes the fuel line back to an acceptable pressure, whereas, when the van has been sitting for a long time and fuel line pressure has returned to 0#, the required pressure cannot be met.

When testing for pressure leakage, I found my fuel pressure dropped approx 14# in 2 hours when all was turned off. Is this pressure drop within the normal specifications?

Shouldn't there be a vacuum sound when releasing the gas cap? When I release the cap, I do not hear anything. Could this be a factor or am I just reaching. I am frustrated with this but don't want to spend $$$ on unnecessary procedures and parts.
 
#4 ·
The only time I get a hissing sound from vacuum when removing the cap is when I'm low on fuel.

Using the starter fluid makes sense with the low fuel pressure. In that instant, you are running lean and using the starter fluid will richen the air/fuel ratio up.

I seem to remember about a part in the gas tank that caused low fuel pressure. Hopefully someone will chime in on that.
 
#5 ·
Check the voltage at the battery and at the pump before you go spending hard earned cash on a new pump. With the pressure coming up once it's running, it almost seems as if the battery might be somewhat low,and once the alternator is turning, you're getting proper voltage , resulting in higher pressure. Just my :2:
 
#6 ·
...and I think that part on the pump that causes the low pressure is the pulse dampener, which can be bypassed with a length of high pressure fuel line. I dunno, neither of mine have it, lol.(already roundfiled)
 
#7 ·
rev_les said:
...and I think that part on the pump that causes the low pressure is the pulse dampener, which can be bypassed with a length of high pressure fuel line. I dunno, neither of mine have it, lol.(already roundfiled)
Thank you, I couldn't remember the name of that thing.
 
#8 ·
There was a person that had a similar problem, and he checked the ground wire just before the fuel tank (underneath the vehicle) and found that to be badly corroded and once he cleaned it up, the pump ran fine after that.

This would be another avenue to check to make sure it isn't your problem as well before you replace the pump. If everything is fine at the ground connection and harness (as already mentioned) then replace the pump. The Pulse Dampener is pressure related, and your well within the fuel pressure bleed down specs from what you posted.

PS: Make sure you're getting 12 volts with the Gray wire that leads to the fuel tank (plug-in connection) as well before replacing the pump.:)
 
#9 ·
After finding I had 12V just before the tank, I decided to replace the fuel pump which was easier than I anticipated. Afterwards, the van now starts up immediately and seems to have that old pep back into the pedal. Just want to thank all of you for your input. Just as a note - I am surprised that the fuel pump's pre-filter is as small as it is considering the effort it takes to clean/replace it. Once that thing starts getting clogged from the acculation of tank crud, you start having problems. I would have thought they would incorporated a prefilter with a larger surface area (and still fit though the mounting hole of the tank). I really shouldn't complain too much as my tank had never been dropped in the 15 years I have owned it.

PROCEDURES:
I put the rear wheels on ramps to give me lots of room; blocked front wheels
Disconnected battery
Put transmittion in neutral to remove the drivetrain torque pressure
Removed driveshaft by removing 4 bolts at axle (easier access to tank)
Removed 4 plastic retainer pins to remove the plastic shield (between the driveshaft and tank)
Disconnected the 2 rubber hoses + 2 metal lines; disconnected the rubber hose at filler
Put a floor jack under tank to assist in lowering tank
Removed the 4 bolts that secured the 2 tank straps
Lowered tank to ground and pulled partway out from under van with wiring loom still attached.
Cut 4 wires (grey, black, purple, and black/white stripped) about 6 inches from tank (easier for my situation)
Used brass punch and hammer to rotate and remove retainer ring
Removed fuel pump assembly from tank
Checked all electrical connectors to determine if dirty connectors were at fault. Not an issue.
Removed and replaced the fuel pump I bought from Kragen for $79 +$10 for a new pump prefilter. Internet sales were cheaper but time was a factor.
Cleaned all electrical connectors on assembly
Cleaned interior of the gas tank. A little more tank crud than I anticipated.
Reinstalled the fuel pump assembly into tank
Used wire nuts and black tape to reattach wiring
Reinstalled tank
 
#11 ·
I would not recommend wire nuts in an automotive application - solder connections and heat shrink are best, but butt connectors and heat shrink are second best.

Wire nuts are designed for house work, ie work that won't vibrate constantly. Even with the electrical tape, they aren't exactly suitable...
 
#12 ·
Thanks for the update snfett. I'm glad you got the problem fixed .:)
 
#13 ·
astro355 said:
... I also think its easy but just happen to be in the minority with you. Good job!
A minority of 3! My Astro was the EASIEST tank I've ever dropped in any vehicle.

Leeann_93 said:
I would not recommend wire nuts in an automotive application - solder connections and heat shrink are best, but butt connectors and heat shrink are second best...
X2. I'd get those things out of there before they leave you stranded somewhere. I know it's too late now, but the tank harness unplugs & the ground wire unbolts from the underside near the driver's seat. (At least it does on mine)

Glad you got it going though- Thanks for the update & writeup!
 
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