HELP! VW Fuel Pump Relay Problem
Many of you know what i drive, but '98 VW golf with the ABA OBD2 and mostly stock harness.
Last weekend we took the rally car to the NWTC car show and found after about 40 minutes of driving the car straingly shut off at 60mph and could not be restarted (popped clutch while rolling and tried the key). Switched the fuel pump relay (167 or 162 whatever that number is) Car fired right up. Then on the way home about 40 minutes into the drive, did it again. Switched the relay back to the "bad" one, fired right up...
Noticed the second time the relay was very hot to the touch. The driving we did was at about 4000rpms for the entire 40 minutes, fancy trans. The wires to the pump were not hot. Nothing smelled like burning. Never happened before this but it has been cold, LSPR and Snodrift are the only places where it would have run this long without being turned off.
1) So heres the thoughts, vw relays suck and we just have to deal with it.
2) We have a short somewhere between the relay and the power. Bad ground?
3) We are running the pump harder then it is used to... is that possible or is it all one speed - on
4) Pump is dying?
5) anyone know of a heavy duty vw relay (different code?)
6) Just put a switch in and call it good? Will this burn up the pump?
Bypass the relay.
My car runs the pump continuously, haven't had an issue yet (I assume after posting this it will fail this weekend).
On my car there is a wire soldered to the relay that makes the pump always run. After that wire fell off at 100AW, I was talking to somebody(Merbach?) who suggested running a secondary power wire with a switch beside the driver so you can switch it on if/when the relay fails.
Holly cow Chad were you waiting for this post? haha that was fast. That is exactly what i wanted to hear. We were thinking of putting a switch that would bypass the relay but make the relay do the work until it dies then flip the switch and continue
I have done that with SAABs in the past. They use the same Bosch relays as VW. Just be sure to fuse the wire at the point it receives power so that if it is the fuel pump going bad, the wire won't melt.
I have had a similar problem with my mk II. The high pressure pump would slow down to the point that the engine would barely run, but only when the weather was cold. I installed a brand new relay and I never had the problem again. I hope this helps.
A pump going into the toilet can pull a lot of extra current and make the relays and all sorts of things unhappy.
Make sure you have good grounds, clean contacts, etc. If you got ambitious, you could measure the current draw of the pump, although with a spec to compare to, it's a bit academic.
A warm relay is something you don't want in your pants.
A hot relay is something you don't want in your car.
Originally Posted by C_Eixen
Beware bypassing the relay to allow the pump to run all the time (or whenever the ignition is on).
The VW relays have a built-in safety feature that prevents the relay from running unless there is input from the coil/tach. No rpm signal = no fuel pump running... this is important when there is an engine fire.
Scenario... fuel line ruptures, spraying fuel all over the engine/exhaust. Fuel ignites, melting various wires, grounding out the ignition system, stalling the engine. Stalled engine = 0 rpm = fuel pump shutoff... no more fuel being sprayed on the engine... no more fuel for the fire (except burning plastic/rubber).
Ask me how I know.
If you're going to 'bypass' the relay with a HD relay... use the existing relay output (the +ve wire going to the fuel pump) to trigger the added HD relay.
"some" people just use an oil pressure switch to turn on the fuel pump relay.
I have mine on a toggle on the dash.
No need for the complex foo foo ignition signal triggered relay at all.
Or use a spring loaded switch and flip it 'on' for 2 seconds before starting to get pressure in the system. Then use the oil pressure switch to keep the relay on and cut it off if the engine stops running.....
And Paul, sounds like the contacts in the realy may heve burned, and aare getting hot due to that. It'as a somewhat vicious cycle: the contact resistance goes up, it heat, which makes the resistance go up more. and so on. If nothing else was hot or odd, seems like new realys are the ticket. Like what Robert ran into....I've had this happen to a fuel pump relay in a Dodge when driven hard; a new relay fixed it fine.
Last edited by starion887; 05-06-2009 at 11:01 AM.
Thanks for the help everyone. I would like to say just replacing the relays would be the easies thing but both the ones that were failing were new, one with only sno*drift on it and the other brand spankin new. Great input and keep it coming.