Fuel pump will not prime, possibly an ecu issue?

[Teck09]

So I am just finishing up the remaining bits of my rebuild and ran into a problem. It is my understanding that the fuel pump should prime every time the ignition is switched on and I am not getting a fuel pump prime signal when doing so. Prior to the rebuild the car was completely stock and ran great. Complicating this matter, I somehow managed to misplace/discard my stock ecu so I purchased a T box to replace it. I trust the seller and he assured me it was a running car when the ecu was pulled. All signs point to my car originally having an M box but I cannot know for sure. If it somehow didn't I think this could be a problem.

It has been a while since I have done any significant flashing/reading of ecu's so I am bit rusty. How can I tell if the ecu is a match for my car/cluster? I am waiting on my VCDS license from Ross-Tech and assume I need it to do anything as far as reading/recoding the cluster. I was able to successfully download the T box .bin file using Nefmoto as well as upload my tuner provided base file so I believe the ecu is fine. I know North American S4's don't have an IMMO but thought maybe the T box came from an out of country car so I tried scanning for the immobilizer but VCDS lite but says there is no controller found. I am assuming that means no immo? Like i said, I am rusty lol.

I'll continue my search on here and Nefmoto but would appreciate any ideas or suggestions. Thanks.

[christianb5s4]

The pump does not necessarily prime every time you turn the key if lets say you turn the key to on, then off then on again soon after since the system already built up pressure the first time the pump primed.

For the immobilizer, if the controller is not found you should be good to go!

[Teck09]

The pump does not necessarily prime every time you turn the key if lets say you turn the key to on, then off then on again soon after since the system already built up pressure the first time the pump primed.

For the immobilizer, if the controller is not found you should be good to go!

Thanks for the reply. It didn't prime the first time or any time after so that is what led me to believe it was an ecu issue. I've heard of cars powering the pump while cranking but I can't try that since I'm not quite there yet. Just trying to eliminate any problems before first statup.

[skree25]

My pump doesn’t prime with key to on. Can you jump the fuse to verify the pump has power jic? Reverse polarity had my wires crossed when I installed my new pump which caused some headache on new engine startup


Sent from my iPhone using Audizine

[slowSfaux]

I tried to narrow down under what circumstances the fuel pump actually primes with the key on, and wasn't able to repeat 100% consistency. 80% of the time it will prime during the first key on cycle after sitting overnight (8+ hours shut off). Outside of that, the pump will prime about 20% of the time on a hot restart. I don't understand why it doesn't just prime every time the ignition is switched on, but nonetheless, your fuel system is probably fine. After having the battery disconnected for awhile, my fuel pump sometimes won't prime at all until cranking.

[julex]

I tried to narrow down under what circumstances the fuel pump actually primes with the key on, and wasn't able to repeat 100% consistency. 80% of the time it will prime during the first key on cycle after sitting overnight (8+ hours shut off). Outside of that, the pump will prime about 20% of the time on a hot restart. I don't understand why it doesn't just prime every time the ignition is switched on, but nonetheless, your fuel system is probably fine. After having the battery disconnected for awhile, my fuel pump sometimes won't prime at all until cranking.

Well, during cranking it must prime/run as otherwise your car would not start at all. And if it doesn't then there is something wrong with the electronics/electrics. Most likely relay or the pump is simply blown. Blown pump is usually running in a capricious manner, one time it does, the other it doesn't

[AvantGuard]

There is also a mechanical possibility. If you recently changed your fuel filter, it is very easy, when pushing it back in place, to kink one of the hard plastic lines and shut off the fuel flow. Ask me how I know.

[slowSfaux]

We aren't talking about cranking here, we're discussing key on, engine off, before cranking.

I guess I should have clarified, my fuel pump always came on during cranking.

[Teck09]

My pump doesn’t prime with key to on. Can you jump the fuse to verify the pump has power jic? Reverse polarity had my wires crossed when I installed my new pump which caused some headache on new engine startup


Sent from my iPhone using Audizine

Thanks for checking, that could be good news. I may not have a problem then. I've bypassed the relay all together and everything operates as it is intended. I have also opened the fuel pump relay to check for corrosion and the like, everything looks brand new. I then reinstalled it with the cover removed, turned the key on then activated the relay manually. It operates as intended. This leads me to believe that the ecu isn't sending the proper signal. It will click (I can hear and feel it) extremely fast when the key is turned to on/engine off but not enough to actually trip the relay and send the power to the pump. When I measure the ground output to the relay from the ecu I am getting a constant signal (not an intermittent as I expect a prime signal to be) but not enough to trip the relay. After reading your post and the ones that follow it looks like cranking the car is the key here.

I tried to narrow down under what circumstances the fuel pump actually primes with the key on, and wasn't able to repeat 100% consistency. 80% of the time it will prime during the first key on cycle after sitting overnight (8+ hours shut off). Outside of that, the pump will prime about 20% of the time on a hot restart. I don't understand why it doesn't just prime every time the ignition is switched on, but nonetheless, your fuel system is probably fine. After having the battery disconnected for awhile, my fuel pump sometimes won't prime at all until cranking.

Thanks for trying and it seems to confirm somewhat of what Skree25 is experiencing. It has been so long since I have driven the car I cannot recall if it primed every time or not.

Well, during cranking it must prime/run as otherwise your car would not start at all. And if it doesn't then there is something wrong with the electronics/electrics. Most likely relay or the pump is simply blown. Blown pump is usually running in a capricious manner, one time it does, the other it doesn't

I am beginning to think that I am chasing a non-existent issue. I am not at the point where I can crank the car to see if the signal appears but suspect that may be the case. As stated, the car ran fine when it was torn down, the relay has been checked along with the pump wiring. Barring an ecu problem I may be wasting my time.

Thanks for the replies so far and the effort in checking your cars. I suppose I'll stop worrying about it for the time being and get to the point where I can actually crank it over to see if that solves my problem.

[slowSfaux]

My testing was done over the course of about 6 months. After I installed my 044 fuel pump, I was chasing a hard start issue. It turned out that the 044 check valve was garbage and wouldn't hold any pressure. But the info is still fresh in mind because of all the trouble I had finding a suitable check valve and fittings to make it work. Besides that, the fuel pump sounds like pushing a metal shopping cart on an asphalt surface, so it's not a guessing game whether the pump primes or not. Everyone within about 30ft KNOWS that shit comes on.

[christianb5s4]

My testing was done over the course of about 6 months. After I installed my 044 fuel pump, I was chasing a hard start issue. It turned out that the 044 check valve was garbage and wouldn't hold any pressure. But the info is still fresh in mind because of all the trouble I had finding a suitable check valve and fittings to make it work. Besides that, the fuel pump sounds like pushing a metal shopping cart on an asphalt surface, so it's not a guessing game whether the pump primes or not. Everyone within about 30ft KNOWS that shit comes on.

Because race car! I didn't realize how loud my 044 was until I switch to the high pressure Walbro 450 and it was crazy quiet.

[Teck09]

Same here. I have a Bosch inline on another car and that little bastard is loud. The Walbro 450 in the S4 is nearly silent. So much so that when testing my wiring I jumped the relay and was wondering why it wouldn't run. Got out to make sure the battery was connected and realized it was spraying fuel all over the place out of the open rail feed line.

[Teck09]

Well I finally got to where I am ready to crank the car and see if it will fire. Put the key in, clutch in, turned the key aaaaaaaaand, nothing. No crank, no fire, no nothing. I am not even getting a click from the starter when I turn the key. The dash lights up as usual and doesn't do anything when I turn the key. I have double and triple checked to make sure everything is hooked up and am at a loss. I am not experienced enough to use VCDS to diagnose what may be wrong so if anyone is willing to help I would be grateful. Is there a way to check with VCDS to see what is preventing the no start Like the starter signal or something?

[slowSfaux]

Battery connections clean and tight at the battery as well as the starter? Ground wire at the passenger side engine mount bracket clean and tight? Clutch switch tampered with during your engine removal for any reason (clutch stop)?

[Teck09]

Thanks for the suggestions but I actually figured it out. For some reason after the new clutch and slave, the pedal cannot go far enough to engage the under dash clutch switch. Unplugged it, jumped the connection amd it fired right off. Doing the first oil change now and burnishing the lifters as I type! This has been a long road, fingers crossed it all goes well from here on out. I appreciate all of the help so far guys, wouldn't be this far along without everyone's willingness to share their knowledge with me. I am truly grateful!

[slowSfaux]

Awesome, good catch. FYI you can adjust the clutch switch to engage higher if the pedal no longer travels to the floor.

[Teck09]

Awesome, good catch. FYI you can adjust the clutch switch to engage higher if the pedal no longer travels to the floor.

I can see the nut holding it on and will adjust it tomorrow. Thanks!

[Teck09]

Just to put a bow on this thread and the original problem. It turned out that the fuel pump signal isn't active unless I am cranking the car. Haven't started it more than a few times but have yet to notice the iump priming. Seems odd to me but as long as it starts I am gtg. Thanks again for all the help.