Whilst playing with the fuel pressure, I suddenly noticed that the system wouldn't prime when I turned on the ignition (the 2 seconds when you turn on the ignition but not start).

A while back I was playing with the security control ecu in the back, as I thought I had an issue with that (that one was ok, by pure coincidence 2 keyfobs stopped working...). I probably have caused the fuel pump relay to become a little loose, I pressed it in, and the system would prime again. Luckily no harm done as running at full throttle the mixture can become dangerously lean with just 1 fuel pump...

Conclusion, the ECU will use the fuel pump #2 for priming and #1 from the moment you start your car, and if #2 is not working for one reason or another, you will not really notice it.

Now I was working on someone’s else’s car, and I noticed that the mixture got very lean at full throttle, of course I had already forgotten the above, but I had a strong suspicion that there was something wrong with the fuel pressure. Once I put a pressure meter on, and wanted to start the car, I noticed that the fuel system would NOT prime, which gave me a bingo moment, and the above came back to memory. This was an issue with the fuel pump #2.


Just thought to write it up, as you can drive with just one fuel pump, albeit very lean at full throttle, but not noticeable at normal driving. You could damage your engine obviously pretty easy under this condition.

Think this is a rare condition, so no reason for everyone to check, but if you want to, you can via removing the fuel pump relay #1. If your car still starts and runs, fuel pump #2 is ok.

 

I also have noticed that Pump #2 is used for Priming.

Other than priming, I had thought that both Fuel Pumps were only engaged during high power operation.

But just to clarify, after engine start, you have determined that Both Pumps are always running??

 

Pump #2 is only used for priming and kicks in once you go over 3000 rpm at load.

Once you start only Pump #1 is running. But if Pump #1 is unavailable and detected by the ECU, it will automaticaly use pump #2.

 

A good Design. Even if a owner dosen't use High Power very often, the #2 Pump is, at least, "Exercised" when starting the car.

 

You didn't run your dyno test with only one pump, did you?

 

It must have been a very short time that I had this situation, and already some time ago.

I changed my pumps last year, as they were approaching 200Kmiles, I thought it was better to preventively change them, then to wait until one fails, but both where still fine. As I was preparing my car to move into higher boost levels, I opted to go for higher performance pumps, and with the setup last year 1 pump could already flow just enough, so luckily I wasn't in the danger zone.

The reason why I have mentioned "tuned XKR" in the title, is that anyone that uses different pulley setups then stock with their Eaton’s could have an issue as 1 stock pump isn't capable to keep you in the safe zone. Untuned cars might just be ok, they get leaner, but as the basic mixture is already very rich, the danger is slightly less.

 

Doesn't the ecu limit the revs to about 3k rpm with a bad fuel pump? I know when my primary fuel pump failed, I removed the relay so I could still drive around on the secondary pump but I was limited to 3,xxx rpm. Maybe it only limits with the relay pulled.

 

The ECU can detect a Fuel Pump Relay that has been removed or which has a open coil circuit.

The ECU can not detect a Bad Fuel Pump connected to a Good Relay (at least not directly).

 

@SteveM
Somehow on my car the relay was not fully loose, so that could explain why the ECU was not aware it wasn't working.

@Paul,
This is also what I can confirm with the other car, the relay was ok, but the pump was not functioning, and no RPM limitation.

 

I just discovered today that I am only running on Pump #1.

I have no idea how long this has been the case. I am kind of excited...I might be in for a nice performance boostonce #2 is replaced. Interesting situation...no codes, no restricted performance message. Since I am not 'tuned', I suspect no damage done.

I really wonder how many XKRs are driving around like this.