Fuel Pump

gnmike87

Member
Joined
May 11, 2004
I have a walboro 340 pump that when installed on my 86 GN seems to run slow and after taking it around the block only puts out about 20psi at idle. The pump is getting 11.5 volts and is unhotwired right now. This pump I pulled out of my 87 GN and was in working order. The pump itself is only about 2 years old. What else could cause this lack of pressure? Are there any relays that need to be checked? It seems like every time its done this I can wait about an hour, go outside, turn the key and get 35psi.
P.S. The stock pump that was in this car when I bought it did the same thing, but I figured due to its age it was probably going bad.
 
Well. Hopefull when you installed the pump, you got the clamps tight and installed the new hose....
I cant see 2 pumps being bad.

I would crimp the soft spot of your fuel return hose and turn the key on, if the pressure rises past 50 then you have a bad fuel pressure regulator...

What kind of gauge do you have?
Sure it works fine?
BW
 
i crimped my return line and it shot to 85# are you saying my regulator is bad. as for your fuel pump i think when your car is cold your probably getting more volts and when its hot thats when your getting 11.5 volts. my car get 14.3 volts cold and when its warm it gets 13.6 to 13.2 i think thats why your getting more pressure when its cold. get your battery an alternator checked
 
The reason I haven't hot wired it yet is because I have been cahsing too many other probs. Then to top it off the hot wire kit that came with the car has the wrong connector on it so I will have to make one tommorow. Are there any relay's that regulate votage somehow or that tell the ecm when to run the pump. The reason that I ask is that this pump and regulator are both off my 87 Gn which was running fine before removing them. I am almost sure it is somehow a wiring problem I just don't know what. BTW the car I am working on is an 86 GN with the g75 wiring harness according to Racetronix.
 
Even unhotwired its running 11.5-12 volts at idle and is putting out about 20-40 psi...but if you try to take it around the block it quickly drops back to 20psi and the car chugs along.
 
When's the last time you changed the fuel filter?

Even at 11.5 volts, it shouldn't drop down to 20 psi just driving easy around the block.
 
lpaulabbott said:
i crimped my return line and it shot to 85# are you saying my regulator is bad.

No Brian, his car wont make any pressure at all... sort of the leak in the hose to speak.
Voltage doesnt have much to do with it right now, if he has 11.5 thats fine, he needs to see if its reg or pump.
2 pumps bad is uncommon, bad fuel pressure gauge is very common.
BW
 
lpaulabbott said:
i crimped my return line and it shot to 85# are you saying my regulator is bad.
Seems to be a little confusion on the crimping of fuel lines here.
If you crimp only the return line and energize the pump, you will see a very high psi reading at the fuel rail..there is simply no place for the fuel to go so pressure will rise. When you turn off the pump, leaving the return crimped, you should see that pressure remain unless there is a leak somewhere in the line or a leak inside the tank like the clamps not on good, or the pump check valve is bad...none of which sounds like gnmike87s problem.
To isolate the pump check valve or inside tank leak from being the culprit, energize the pump and only crimp off the supply line...you should see pressure at the fuel rail of around 40psi, if it never gets to 40 psi before crimping the supply line, then the regulator is most likely bad. If once the supply line is crimp and pressure drops quickly, you either have a bad regulator or a leaking injector.
In order to determine if its a leaking injector or bad regulator, energize pump (provided that you did reach 40psi) and crimp off both supply and return...if pressure drops then an injector is leaking.

Using this technique, you should be able to determine where the pressure is not holding...inside tank from either a leak or check valve, at the injectors, or at the regulator. But of course, you have to be able to produce at least 40psi before you can do this....if you can't get 40psi, I'm betting on a split hose or bad hose connection inside the tank on the supply line.....

I had that problem cause when I installed the Walbro I cut off the supply line metal nipple where it necked down, and when I slipped the rubber hose over the part I cut off, the edge was sharp and split the hose, causing a similar problem....had to drop the tank again...
 
How would he get pressure at the fuel rail if he crimps the supply line :confused:
If he crimps the return line, then the pressure will shoot up past 50psi, thats what he is needing, higher fuel pressure.

Then isolate the problem either being bad regulator or bad fuel pump rubber hose or clogged new fuel pump.

Since the car has low fuel pressure, then its NOT the fuel pump return check valve, the car will make plenty of fuel pressure if that check valve was bad.
BW
 
Quick6'n'-K.C. said:
How would he get pressure at the fuel rail if he crimps the supply line :confused:
You crimp the supply line after the pump energized and built up pressure in the fuel rail, I usually do it the moment the pump cuts off after energizing for a few seconds when the key is first turned on. Its easier to do with 2 people, especially if the pressure drops quickly....this isolates it from being a leak in the supply line rubber hose in the tank or the check valve. A very bad check valve can keep the pump from building enough pressure because its working against its self..every time the pump diaphram is decompressing, the pressure flows backwards, but it does take a very bad leak in the valve to cause this and is usually not the problem.
 
2QUIK6 said:
You crimp the supply line after the pump energized and built up pressure in the fuel rail, I usually do it the moment the pump cuts off after energizing for a few seconds when the key is first turned on. Its easier to do with 2 people, especially if the pressure drops quickly....this isolates it from being a leak in the supply line rubber hose in the tank or the check valve. A very bad check valve can keep the pump from building enough pressure because its working against its self..every time the pump diaphram is decompressing, the pressure flows backwards, but it does take a very bad leak in the valve to cause this and is usually not the problem.

I thought the check valve was built into the pump, and the isolator was after the pump between the pump and hanger. :confused: Usually delete the isolator once you install the high pressure fuel hose.

If you crimp the return line and turn the key on,fuel pressure rises past 50 and stays, then the fuel pump and fuel pump hose is fine. Next assumption would be bad regulator becuase its not holding the correct psi if you let off the crimp.

If the fuel pressure drops off immediately when you turn the key off,if you have the return crimped, its fuel pump hose, checkvalve, NOT injector because the car runs fine and would take at least 10-20 seconds or more for 80psi to spray through one bad injector. Then it would have a bad start up.

Its either the fuel pump hose is split or the reg is bad, where is the diapragm in our pumps, thought they were gyrator style....
BW
 
Ok today I stole the Hot wire kit from my 87 and the pump won't push any pressure at all now even when I use the jumper wire and connect it to the alternator it gives a weak spark and the pump does nothing. I am going to check the alternator tommorow although any other time I have had alternator falures the battery drains down and the lights dim. None of this has happened on this car yet so who knows. The car cranks fine and would run if it had fuel. Thanks for all the replys, hopefully it is as simple as a bad alternator. I will post my findings tommorow

Also the Fuel filter is brand new :smile:
 
gnmike87 said:
Ok today I stole the Hot wire kit from my 87 and the pump won't push any pressure at all now even when I use the jumper wire and connect it to the alternator it gives a weak spark and the pump does nothing. I am going to check the alternator tommorow although any other time I have had alternator falures the battery drains down and the lights dim. None of this has happened on this car yet so who knows. The car cranks fine and would run if it had fuel. Thanks for all the replys, hopefully it is as simple as a bad alternator. I will post my findings tommorow

Also the Fuel filter is brand new :smile:

Sounds like your new pump may be bad, if it sparks then there is power to it and its grounded.
Did you run it low on fuel quite a few times?
BW
 
Racetronix said:
A leaky checkvalve in a Walbro gerotor pump will not impede the pump's capability to develop pressure. It will only prevent the line from holding pressure when the pump shuts off. There is no diaphragm in a Walbro gerotor fuel pump such as the GSS340M.
Sorry guys, I didn't know they had a different design from the old pumps and the past Bosch pumps..
 
Finally found the problem or so I think. The relay on the Passenger side fenderwell was loosing contact under vibration. Replaced it and the car runs fine in the back yard. The real test will be if it can get me to work and back tommorow.
 
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