Adding lift pump, need key-on power source. Help?

Hey guys!

My 1997 Jetta TDI has been having some weird issues that feel an awful lot like fuel starvation under load. I've been down the diagnostics rabbit-hole and have determined that my injection pump is having a hard time pulling fuel from the tank up to the engine bay. My solution is to add an electric lift pump.

I have installed an AirTech lift pump and done some road testing with the pump wired straight to the battery and it seems to resolve my weird fuel supply and power issues.

Now, I obviously need to power this lift pump in such a way that is safe and provides key-on power. The pump is rated to pull 2amps.

I'm a pretty good DIYer, but also know that electrical isn't my strong suit. Can anyone provide fairly idiot-proof suggestions as to where I might draw a key-on power source for my lift pump?

Thanks for reading, I really appreciate any help or input!
Brad

First off, if your TDI is feeling like its fuel starved, change the fuel filter, Ditzel mod or Nictane kit, Healthy TDI would never be fuel starved if it’s got a good filter and if you did, your masking over another issue all together unless your looking at BIG power and your fuel needs are not met. (225+hp is where you start to see fuel delivery issues.
2nd off, you should have considered the Walbro 12V, 8-11 psi, 45 gal/hr fuel pump, it’s the best bang for your buck and takes up little to no room compared to the other systems and is 100% nonrestrictive if it fails.
Now on to your electrical issue, just install a 30/40 amp relay on the ignition and take power off the battery. Make sure to use the right size wire. google "DC volts wire size chart" and select the right gauge wire for the distance you are going with it and install a fuse rated at what the pump says it draws or the rating that it recommends the fuse to be. Put that fuse AT THE BATTERY. Wiring up a relay is simple. Power in and power out is the ignition, relay in and relay out is the battery connection. Done.

To be "safe" an electric fuel pump needs to shut off if if the engine isn't running. It would really suck if you got in an accident and were incapacitated and couldn't reach the key while the pump continues to merrily pump fuel feeding the fire that can accompany an accident.

A vary important safety consideration is that ALL modern cars with an OEM electric fuel pump stop pumping fuel if the engine is not running and/or there is a rollover.

Like Mongler alluded to, find and fix the actual problem. Adding an electric fuel pump is just putting a Band Aid on a lack of proper maintenance problem.

oh yes, i was in a rush, connect the relay not to the ignition, but to the fuel shut off on the IP. thats how i saw the DIY for the walbro

That's a good point to get the run signal since it drops out if the key is left on but the engine isn't started. Picks up again if the starter is engaged.

Never tested it but I'm guessing it also drops out if the engine stalls.

There's probably a way to wire it in with safeguards so that it will discontinue pumping fuel should the engine shut down but since i haven't looked at this I can't say how you would do it although I can tell you that the IP fuel solenoid would be a circuit to look at first for a trigger for the relay to run the lift pump, that at least would be the first place I'd look.

Circuit 15 is run power and that's available in the fuse box but again you want to be safe about it.

I tend to side with the above posts in that the lift pump really just addressing the symptom rather than the real problem. On these cars you don't need the external lift pump and if the one-way valves back at the tank are functioning properly then there's no drain-back problems to worry about.

Good luck though

Steve

the DIY for the walbro is to go to the shutoff solenoid, same with the bulldog kit.

I thought about this a while back, but never did anything with it.

My plan was to buy a switch that supplies either power or ground, based on oil pressure. Mount the switch in one of the empty ports in the oil filter flange.

-Todd

With a TDI MK3 there is no way to defuel the engine with EGTs getting to hot like a bulldog system for the Cummins or other diesels. I tried this once, it worked well but I decided to just go with water injection and xnay this trick.

If you’re driving and you have the foot on the gas and you put your foot on the brake it defuels the engine. I wired up the brake switch with my Auber gauge relay and set the EGT limit to 1550. It worked great. Soon as I hit that limit the engine would defuel until the relay kicked off at the setting of 1300. No it just runs the water meth pump.
I’m sure you could work that into the pumps relay easily. BTW defiantly get an Auber gauge. They have that relay in them so you can have it defuel and turn off the pump at the same time.

How would that work, in case of an accident? Unless the brake is pressed, the pump would always be energized. What am I missing?

-Todd

ToddA1 said:

How would that work, in case of an accident? Unless the brake is pressed, the pump would always be energized. What am I missing?

-Todd

Click to expand...

Power from shutoff solenoid on ip to brake switch and or relay on auber gauge to pump. You dont need the pump when your trying to slow down or when the EGT's are too high.
You need to wire up the switch so that the relay on the auber gauge controlled the switch. your not wiring up the switch to switch the power but rather send the signal to defuel. you do not press the brake to defuel. the switch provides the ECU with a defuel signal and that is what you are connecting to.

I’m not following. If wired the way you mention, will the lift pump shut off if the engine stops?

-Todd

The shutoff solenoid is the definition of "off and on" for fuel. 12v to it and it opens; this allows fuel into the IP. It is wired into the ECU and controlled by a relay with the ignition. So yes. If the airbags deploy, the shutoff solenoid is switched off same with the key tuned off on the ignition. Unfortunate there are not many cars with large amounts of fail safes for turning off the fuel. This is as good as it gets on AHU, ALH, and some other engines. The great part about a diesel is that if you have a fuel spill, its relatively harmless as it takes lots of heat and or compression. Technically if the pump ran full blast with the engine off, it would DO NOTHING but build pressure. The Walbor can handle this. The injectors can’t let fuel in unless they get a signal to open on most cars. But on a TDI the cam on the IP must be in operation for fuel to produce enough PSI to activate the injector’s plunger. It would not be that good though as maybe a tiny bit of fuel would make it past and that could add up but what I do know for sure is that NO fuel is making it past the shutoff solenoid and into the IP if it’s not getting 12v. SO regardless you’re not going to be pumping fuel into the engine, just running the battery down.
I don’t like what I read about lift pumps, they don’t last very long and they are an issue when they fail and don’t produce that much fuel for big power.

OK ill make it a bit clearer
12V comes from the shutoff solenoid and goes into the Auber gauge set closed at 1500 and open at 1300 then the 12v goes to the brake witch wire output to ECU. you are splicing in this wire into the existing (yellow) I think Not sure, then that 12v signal from the relay also goes to the walbro pump other lift pump system into a relay that takes power from the battery to the pump.
When you turn on the car the shutoff solenoid gets 12v and so will the relay for your pump. When the relay on the Auber is closed 12v goes to the (yellow wire) on the brake switch, this sends 12v to the signal wire and signals the ECU to defuel the IP by reducing the voltage on the plunger on the head for the IQ or something (not so sure how that part works). I also night is wrong about the yellow colour of the wire on the brake switch and if I recall I might have had to put a resistor for the signal wire. You have to take a multi meter to that wire and press the pedal down to see what you’re getting to the ECU. It’s either 12v or 5v

I got this to work for a bit but I only had one EGT probe and gauge so I swapped this system into the water Meth pump I have to solve the EGT's for now.

When you go driving again, while the gas pedal is pressed down, step on the brake, within 0.25 of a second the car losses power like it was in a limp mode, its actually the same as a limp mode but just when the brake and the gas is applied. Limp mode and this brake switch both activate a base map of little to now power by defueling the IP, not sure how that works again but I thought it was the position of the QA cam on the head.

Reguarldes of line fuel pressure this will work as its the same fuel regulation regardless. All it does for you is help not kill your turbo. After all you dont need this step just for a lift pump but you still get the pressure and everything works just fine. I am looking at going fast, this means water meth over defuel. I just go though about 1 gallon or distilled water in about 1-1.5 days of WOT raceing

Shutoff solenid on the HP fuel pump for the positive trigger to a new relay. shutoff solenoid is round, looks like an oil pressure sensor, and has one wire coming off of the top. Run power from the battery to a fuse then to the relay, from the relay to the pump.