Testing fuel pump draw

[GothingNC]

Per the Bentley it says to hook up a jumper wire at terminal 87a and 86 in the relay socket, then go under the car and disconnect the black (power) wire at the pump and hook up the Ammeter between the pump positive terminal and the black wire , then turn the key on.

Will pulling the fuse pump fuse and hooking up the ammeter between the top and bottom of the fuel pump fuse holder provide the same results instead of going under the car?

Also, can I test the draw while the engine is running this way?

Thanks !

[T77911S]

i did it at the fuse block. removed the fuse and put the meter in line there. i had 7.7 amps. (my fuse was getting hot so i thought i would see what the current was). you can either start the car or remove the connector on the AFM. strating and running it would be easier. i am curious as to what you read.

[billybek]

It should produce the results you are looking for. There could be some extra draw for relays and electronics associated with the fuel system, but the draw to them should be minimal.
The description you gave eliminates all other draw that could be on this circuit.
Make sure you use a meter that is internally fused for inline use...
Hope it goes well!!

[GothingNC]

Would I still need to jump the fuel pump relay or just turn the key?

Just wanted to know if I could check the draw this way so I don't have to jack the car up on a weekly basis to check the amperage draw.

I'm just a little paranoid about having another melt down and a trip back home on a flatbed

This along with checking the CV joint bolts, brakes, tires, oil leaks, belt etc will probably require me to set up a pre-flight check list every time I leave the garage

Thanks

[T77911S]

i would pull the fuse, connect the meter and have someone else start the car while you read the current.

cv joint come off?
i had one come off. i cleaned the cv joints and put in new bolts and washers with locktite.
you can get a bag 50 of bolts and washers from fastenal for the price of 12 anywhere else.

[GothingNC]

Thanks !

The outboard side side of the CV joint let go when I was making a slow right hand turn. I thought it was the tranny but was happy to see the axle sitting in the trailing arm.

I picked up a set of 12 Porsche bolts for about $16 at the local Porsche shop, used blue loctite and indexed them with red paint marks.

[boyt911sc]

Originally Posted by GothingNC

Per the Bentley it says to hook up a jumper wire at terminal 87a and 86 in the relay socket, then go under the car and disconnect the black (power) wire at the pump and hook up the Ammeter between the pump positive terminal and the black wire , then turn the key on.

Will pulling the fuse pump fuse and hooking up the ammeter between the top and bottom of the fuel pump fuse holder provide the same results instead of going under the car?

Also, can I test the draw while the engine is running this way?

Thanks !

John,

When you put a jumper wire between terminals #87a and #86 and turn the ignition switch to ON position, FP (fuel pump) will not run!!!!!. You need to energize terminal #30 to make the fuel pump run or hot wire the FP directly.

You can measure the current (ampere) of the FP if you jumper terminals 87a & 30 and have the ignition ON. Measurement should be done at the FP terminal. Keep us posted.

Tony

[GothingNC]

Originally Posted by boyt911sc

John,

When you put a jumper wire between terminals #87a and #86 and turn the ignition switch to ON position, FP (fuel pump) will not run!!!!!. You need to energize terminal #30 to make the fuel pump run or hot wire the FP directly.

You can measure the current (ampere) of the FP if you jumper terminals 87a & 30 and have the ignition ON. Measurement should be done at the FP terminal. Keep us posted.

Tony

Tony,

Thanks for the correction, 87a and 86 are used to check for voltage.

So you are saying measurement at the FP terminal is at the pump itself per the Bentley,and not rely on checking it via the fuse holder, correct?

[911pcars]

... and when you measure current flow of your fuel pump, what do you compare it with? AFAIK, the factory doesn't list amp. draw specs. Thus, all you end up with is just a base line reference point to compare with similar pumps or your pump further along in it's lifespan.

It's the same with most other electrical components in a vehicle.

IMHO, it's better to measure fuel pressure and volume to determine the health of a FP.

Sherwood

[boyt911sc]

Originally Posted by GothingNC

Tony,

Thanks for the correction, 87a and 86 are used to check for voltage.

So you are saying measurement at the FP terminal is at the pump itself per the Bentley,and not rely on checking it via the fuse holder, correct?

John,

Like what Sherwood mentioned, I don't worry about the current draw of my fuel pumps. As long as I get the correct system and control pressures, I'll be more than satisfied. If you measure the current (amp) thru the fuse, double check the wiring diagram or the actual wiring that there is no other component/s in the circuit. If I remember correctly, the rev limiter is in the same circuit (may or may not affect the total draw).

Suppose you're able to measure the total current flow to the FP, what do you do next? Do you know the recommended amperage for the FP? Please advise. Thanks.

Tony

[GothingNC]

Tony,

The Bentley states that the pump current should be in the range of 4 to 6 amps.

I had a fuse box fire a few months ago that took out my fuel pump and window relays & melted the sockets.

Previous owner had a bayonet style fuse going from the lower connection of the FP fuse terminal and joining to the top of the hazard fuse holder since the FP fuse holder was broken.

I replaced the 10 block fuse holder, FP & hazard relay, installed new fuses and got rid of the bypass fuse holder so it's now back to stock.

Went underneath and checked the pump and it looks like a recent Bosch unit and the connections had zero corrosion. I was thinking maybe the pump seized causing a large power draw that overwhelmed the fuse.

Hooked everything back up just to see if it would start and it did, car runs great and the fuse along with the relay are cool to the touch.

[MURF]

The Atc Fuse Conversion Is Common On Sc[vw Fuse Type Cars]the Connections Get Loose And Dirty And A Fuse Conversion Will Stop The Fuse From Getting Hot.we Update Fuse Size From 25 Amp To 30 Amp..almost All Your Racers Have Done This For Reliability

[T77911S]

i measured mine at the fuse block (7.7A) not to test my pump, but because the fuse was getting hot and i was just curious. i also cleaned the wire ends and the fuse connections to help reduce resistance.

[spuggy]

Originally Posted by GothingNC

Tony,

The Bentley states that the pump current should be in the range of 4 to 6 amps.

But Bosch quote higher figures that that for at least some pumps.