what is the normal behavior for fuel pressure when starting?
#11
11-18-2013, 05:54 PM
Thanks chris015. I compare Rock Auto and Amazon a lot. I have Amazon prime so most of the time Amazon with "free" shipping works out.
I'll do some shopping. Bummed I have to replace the fuel pump.
I'll do some shopping. Bummed I have to replace the fuel pump.
#12
11-18-2013, 05:57 PM
Your pressure is too low and leakdown is excessive. Key on, engine off, fuel pump running, pressure must be 60psi to 66psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. Yes, the check valve is part of the pump, not serviced seperately.
Your results indicate that there is a problem with fuel delivery, but it does NOT tell what, or where, the problem is. The next step in diagnosis requires you to do a little "creative plumbing" with the pressure tester. The tester must be connected to the pump pressure output line. This is done at the fuel filter. All pressure and flow must dead end at the tester, (no fuel allowed to the engine). Key on, engine off, fuel pump running, pressure must be 73psi to 108psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, the pump needs replacement. If it passes both parts of the test, the problem is inside the plenum.
FYI: Delphi and AC Delco pumps are exactly the same, they come off the same assembly line, just a different box.
Your results indicate that there is a problem with fuel delivery, but it does NOT tell what, or where, the problem is. The next step in diagnosis requires you to do a little "creative plumbing" with the pressure tester. The tester must be connected to the pump pressure output line. This is done at the fuel filter. All pressure and flow must dead end at the tester, (no fuel allowed to the engine). Key on, engine off, fuel pump running, pressure must be 73psi to 108psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, the pump needs replacement. If it passes both parts of the test, the problem is inside the plenum.
FYI: Delphi and AC Delco pumps are exactly the same, they come off the same assembly line, just a different box.
#13
11-18-2013, 06:08 PM
Get one of these: Dorman Products - 800-170 it screws into the filter outlet. Make sure the filter is not restricted. There is a barb on the end to attach a rubber line, (must be fuel injection rated line) then connect the other end to the pressure tester: Any auto parts store can get it for you for ~$5
EDIT: This is one that I made for checking 98 and newer with quick disconnect. Your 96 would be similar:
The shut off valve is to isolate the pump for checking maximum output pressure and leakdown. With the valve open, you can check regulated pressure, same as checking at the service port by the distributor.
EDIT: This is one that I made for checking 98 and newer with quick disconnect. Your 96 would be similar:
The shut off valve is to isolate the pump for checking maximum output pressure and leakdown. With the valve open, you can check regulated pressure, same as checking at the service port by the distributor.
Last edited by Captain Hook; 11-18-2013 at 06:18 PM.
#14
01-17-2014, 08:46 PM
Just wanted to follow up and say thanks for the help with this. I finally was able to rig up a fuel pressure gauge on the fuel line on the feed side of the fuel filter. Turning the key started the fuel pump to cycle for a few seconds. Pressure went up to about 75 and then the fuel pump stopped and the pressure dropped quickly to zero, a matter of 5-10 seconds, so I'm going to assume that the fuel pump is bad. I just ordered the AC Delco MU1735 from Amazon for $144 shipped. Bargain!
Now to read up on dropping the tank and replacing it.
Too bad I just filled up the tank.
Thanks again for everyone's help.
Now to read up on dropping the tank and replacing it.
Too bad I just filled up the tank.
Thanks again for everyone's help.
#15
01-17-2014, 09:16 PM
I just cut a trap door under the carpet in the back of my Jimmy. hinged it up and its the best thing I have ever done.
had to do the pump recently again and took 15-20 minutes tops to put the new pump in, pulled up carpet, cut the sealer, opened the door and had instant access to the pump.
had to do the pump recently again and took 15-20 minutes tops to put the new pump in, pulled up carpet, cut the sealer, opened the door and had instant access to the pump.
#16
01-17-2014, 10:35 PM
I just cut a trap door under the carpet in the back of my Jimmy. hinged it up and its the best thing I have ever done.
had to do the pump recently again and took 15-20 minutes tops to put the new pump in, pulled up carpet, cut the sealer, opened the door and had instant access to the pump.
had to do the pump recently again and took 15-20 minutes tops to put the new pump in, pulled up carpet, cut the sealer, opened the door and had instant access to the pump.
#17
02-12-2014, 04:36 PM
I wanted to follow up with everyone. I know a lot of threads just die.
I ended up replacing the fuel pump. I bought an AC Delco from Amazon. Bit strange but it only had 2 support posts instead of 3. A redesign I guess.
The new pump is quiet! The long crank is gone. The car literally starts the second you touch the key. Very cool!
What a pain to get the tank out. I could do it a lot easier second time around. Here are some thoughts in no particular order. Hope this helps someone out some day.
First, I had a full tank of gas... so I had to drain it. I was going to siphon it out but no, there's a check ball in the fuel filler line.
Since my pump was still pumping fuel, I researched a way to use the pump to drain the tank. I had made a pressure gauge gizmo that hooked to the outlet on the fuel filter. I used those fittings and a length of fuel line to pump the gas into two 5 gallon gas cans.
I found the "test wire" under the hood. Its near the firewall on the drivers side. There's a red wire by itself with a little electrical fitting on the end. Run a wire from the + on the battery to this wire and voila, the pump will run if it still works. It took about 1/2 hour but I pumped all the gas out into the gas cans.
The three fuel lines on the top of the pump are tough. The two outside ones are the type where you squeeze a little flexible bit where the pipe goes into the fitting and then the fitting comes off. These ones leave behind part of the fitting. If you're very careful, you can move these to the new pump. I went ahead and got new bits from Napa. Word of warning, the two fittings are different sizes, so make sure you get both from Napa so you don't have to make two trips. Don't ask.
The middle fitting is a different kind. You just squeeze it and comes off. This one goes to a vent on the top of the tank. More on that in a minute.
Now, on the tank itself, at the end nearest the front of the car, there's a "vent" on the top. Its a little plastic thing that twists into the tank. This fitting has a rubber fuel line hose on it that connects to a metal fuel line and runs to the middle fitting on the fuel pump. Be very careful to remove that fuel line before you drop the tank.
Someone before me was nice enough to break off the pipe fitting on this vent. I always wondered why I smelled fuel now and then. Now I know, it was venting to the atmosphere. I had to buy a new vent from the dealer for $27 and buy a foot of fuel line too, to connect the vent to the metal fuel line, since that was totally gone.
Do yourself a favor and take out the spare tire. Makes it so much easier to sit up under the car and carefully attack the fuel fittings.
There are two electrical connectors on the fuel pump. Make sure you get both before you drop the tank.
One of the hose clamps on the fuel filler hose broke while I was trying to pull the hose off the tank. Be ready to buy new clamps.
Once the tank is out, the swap of the fuel pumps is pretty easy.
When putting the tank back up under the car, raise is up with two jacks if you can. Its easier to stabilize it. Before you get the tank all the way up, hook up the vent in the front and the fittings and connectors on the pump, don't forget the filler lines, then put the tank all the way up in place.
That's it. Thanks for everyone's help.
I ended up replacing the fuel pump. I bought an AC Delco from Amazon. Bit strange but it only had 2 support posts instead of 3. A redesign I guess.
The new pump is quiet! The long crank is gone. The car literally starts the second you touch the key. Very cool!
What a pain to get the tank out. I could do it a lot easier second time around. Here are some thoughts in no particular order. Hope this helps someone out some day.
First, I had a full tank of gas... so I had to drain it. I was going to siphon it out but no, there's a check ball in the fuel filler line.
Since my pump was still pumping fuel, I researched a way to use the pump to drain the tank. I had made a pressure gauge gizmo that hooked to the outlet on the fuel filter. I used those fittings and a length of fuel line to pump the gas into two 5 gallon gas cans.
I found the "test wire" under the hood. Its near the firewall on the drivers side. There's a red wire by itself with a little electrical fitting on the end. Run a wire from the + on the battery to this wire and voila, the pump will run if it still works. It took about 1/2 hour but I pumped all the gas out into the gas cans.
The three fuel lines on the top of the pump are tough. The two outside ones are the type where you squeeze a little flexible bit where the pipe goes into the fitting and then the fitting comes off. These ones leave behind part of the fitting. If you're very careful, you can move these to the new pump. I went ahead and got new bits from Napa. Word of warning, the two fittings are different sizes, so make sure you get both from Napa so you don't have to make two trips. Don't ask.
The middle fitting is a different kind. You just squeeze it and comes off. This one goes to a vent on the top of the tank. More on that in a minute.
Now, on the tank itself, at the end nearest the front of the car, there's a "vent" on the top. Its a little plastic thing that twists into the tank. This fitting has a rubber fuel line hose on it that connects to a metal fuel line and runs to the middle fitting on the fuel pump. Be very careful to remove that fuel line before you drop the tank.
Someone before me was nice enough to break off the pipe fitting on this vent. I always wondered why I smelled fuel now and then. Now I know, it was venting to the atmosphere. I had to buy a new vent from the dealer for $27 and buy a foot of fuel line too, to connect the vent to the metal fuel line, since that was totally gone.
Do yourself a favor and take out the spare tire. Makes it so much easier to sit up under the car and carefully attack the fuel fittings.
There are two electrical connectors on the fuel pump. Make sure you get both before you drop the tank.
One of the hose clamps on the fuel filler hose broke while I was trying to pull the hose off the tank. Be ready to buy new clamps.
Once the tank is out, the swap of the fuel pumps is pretty easy.
When putting the tank back up under the car, raise is up with two jacks if you can. Its easier to stabilize it. Before you get the tank all the way up, hook up the vent in the front and the fittings and connectors on the pump, don't forget the filler lines, then put the tank all the way up in place.
That's it. Thanks for everyone's help.
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