Author Topic: Lift pump opinions (Read 15033 times)

MikkiJayne · « **Reply #15 on:** November 14, 2007, 01:52:45 am »

Sorry but you are wrong on this one. The ECU has everything to do with controlling the pump!

The fuel pump relay + supply is on the switched ignition, but the - goes straight to the ECU. When the ignition is switched on the ECU gives a brief pulse to the relay to prime the pump, and then switches it off again. Only when it receives a signal that the engine is turning (from the hall sender in the dizzy) does it turn the pump back on. It will remain on while the engine is spinning. If the engine stalls for any reason it will turn the pump off, likewise if you shut it off with the key. Every car with electronic fuel injection does this.

A variation on this is found in A1 and A2 cars with CIS (K-Jet) which don't have an ECU. They have a special relay which gives the pump prime pulse when the ignition is switched on, then they wait for an rpm signal from the coil. When an rpm signal is received a timer circuit will switch on the pump, and will continue to do so while it receives ignition pulses while the engine is running. Again, if the engine stops no more rpm signal so it shuts down, and ditto if you turn it off.

For now I'm going to switch the pump on the ignition, since I don't tend to sit in the car with the ignition on anyway, but in the end I will use the CIS relay triggered from either the ECU rpm output, or the Alternator W wire. That way if there is an accident and the engine stops but the ignition is still on, the pump will turn off and not (potentially) spray fuel everywhere.

RabbitGTDguy · « **Reply #16 on:** November 14, 2007, 04:27:21 am »

interesting...never have seen/heard that before and I've done a few gas-diesel conversions on late mk2 as well (digifant) and a b3 AAZ conversion for friends and never had any issues with the fuel pump there either "running after". We removed the entire ECU harness... and leaving the entire fuel pump circuit intact and it was fine "independent" of the ECU as long as you make sure what you are removing remains a switch circuit and is grounded correctly.

In this case...the wire leading from the ignition to the ECU (in fuel pump circuit) was to initially "prime" the pump and accumulate pressure for starting...turn the engine over, and VROOM.

The pump that is primed is the primary pump for fuel injection w/ the accumulator to of course build pressure in the lines. This was of course removed from the car (as its far to high a pressure to use as a lift pump), however...the transfer pump had no issues.

I know what you mean as well, as I have a b3 variant right now with CIS-E motronic and know about the "primary" (secondary in row with the transfer pump if you want to get technical) does start initially when the key is "on contact" making a connection with the ECU, etc. but never runs after...

Early mk1 and mk2 still do have a control box for CIS...I have one sitting downstairs, its an ECM as plain as day.

Relays are not complex devices, and receive electrical voltage (in a variety of voltages) to essentially turn on/off switches...they don't receive complex square wave signals, etc. and feedback from the ECU. Again...unless we are dealing with the latest in technology that may hand alot of that over to the ECU.

Interesting none the less...maybe we're thinking along the same lines but our talk isn't aligning somewhere...

Are you talking about this whole relationship in regards to getting it setup with the TDI electronics? Maybe thats the issue.

Joe

MikkiJayne · « **Reply #17 on:** November 14, 2007, 04:46:03 am »

I'm beginning to wonder whether US electrics are slightly different to Europe?

On the Corrado the lift pump and pressure pump are wired in parallel, so they both come on together. They run on the same relay, and the same wire in the fusebox, and are triggered by the ECU.

On US CIS cars you did have an ECU of sorts, because I think you had knock sensors and cats way before we did. In that case I would expect that to run the fuel pumps. UK CIS cars didn't have an ECU at all (except the 16V), and they have this special relay I'm talking about which has a circuit board in it.

The circuit is a 555 timer chip. When it powers up (ignition on) it runs the pump for a second or so - the prime pulse - then it turns off. An ignition event will trigger it again, for another second. Since ignition events happen more often than every second, the timer never gets a change to turn off, therefore keeps the pumps running. As soon as the engine stops the timer expires and switches off too.

One very important point to note - on CE2 cars the diesel glow plug relay is in the same location as the gas fuel pump relay. If you leave the fuel pump(s) connected then they will run for a second or so when you turn on the ignition, as the ECU / etc will turn on the glow plugs! That's what your B3 variant is doing :wink:

RabbitGTDguy · « **Reply #18 on:** November 14, 2007, 07:29:39 am »

Interesting...
I don't think the electronics are all that different (with exception to emissions, etc). but I can see what you are saying.

In the end... the "loop" that you are talking about itself (the ECU in this situation) acts like a switch as well. The ECU is still triggered by the ignition and allows the turning on/off of this circuit.
I think we are on the same page now.

In relationship with my b3. I'm doing my second TDI here this winter...currently...rebuilding the motor (or rather prepping for that...) at the moment. It'll be another "mTDI" but I plan on installing a complete AAZ b3 wiring harness. I love the ease of CE2 and its "expandability" if you want to call it that. Makes swaps SOOO much easier. However, when I do the swap, like on the MK2's of previous swaps (non electronic...most were CE2 though) I want to be able to pull the entire ECU loom/engine harness from the motor and install the diesel wiring harness...just cleans things up and makes it much easier.

We I believe were on the same page...just looking from different angles...I was looking starting at the ignition (which does have to "turn on" the ECU to allow this "loop" to occur (i.e. turning on the pump briefly, priming, etc) whereas you were speaking in terms of the ECU itself. I see the potential problem that you are facing and the "way" you were looking at it from the standpoint of adding the TDI electronics into the mix; in which in most cases with exception to PD's had no "lift pumps" there fore...no real way for the signal to occur without creating your own relayed circuit or a switched circuit.

In the b3...I'll have to account for the loss of the ECU triggering the fuel pump circuit which should be some fairly simple wiring to the fuel pump relay to allow this to occur.

Makes sense

Joe