| If anyone is interested in what's in the original TT fuel pump, I've put up some pictures of one I've dismantled and I show my findings in this original 1993 TT Z fuel pump. To start,,,,,I had a fuel issue.
I got stuck after a really nice drive. Went to a coffee shop after a nice run, shut the car off, drank some coffee and had a snack, and when I came out to start the car (nice day out and about 60 degrees F), the car would not start. No codes on my car computer (ECUtalk module in the car). I of course was like, 'WTF!!!' Then I thought about it and said 'Hey, I don't here the pump prime when I turn the key.' I hear relays click and have a good battery, but NO prime. I got towed home and got to diagnosing.
First thing I did was go through all (or what I thought was all), the diagnostic steps. Fuse, check! Relay, check! Battery, check!
I would up pulling the pump out of the tank and applying 12vdc from an old car battery I had in the garage. Well, I was shocked to find the pump worked. So it must be the FPCU..... or so I thought.... I would up replacing the power transistor in my FPCU. Those 'can be' notorious for burning out if an old pump draws too much current.
I replaced the main NEC K591 with a newer style MOSFET. I put in a IRLZ44N). Sealed it all up and then all looked good. I thought the old one burned up and my meter was giving me some confirming readings..... again, or so I thought. So now with my rebuild, trusty FPCU.........
I had some really nice runs lately in the Z. Then I put er' away one Saturday after a nice run and when I went to start it up a few days later, the car again would not prime. NO prime. NO start.
WTF!!!!!!????????? I went through the electronics again, but this time before doing anything with the pump, I put my meter on the pump connector and saw that when the key is first turned to 'On' I did get 12vdc at the connector for about 2 seconds. So relays are ok. Fuses are ok. FPCU (apparently), is OK. Power to pump connector seems OK.
But I plug the connector in again, and still NO PRIME.
So it must be the pump??? Right???
I again took that 12 volt old car battery and put it directly on the pump connector, and low and behold, the damn pump ran. Sooooooooooo, what I found was that the cars initial prime signal to the connector will read 12vdc when NOTHING is hooked to it. BUT, when the pump is plugged in, the actual voltage is only 5.95vdc.
And that's when 'under a load with a working fuel pump.' So I found that when the prime signal is transfered to the pump during initial 'prime' it's supposed to be a lower voltage. NOT a full 12 volt high amperage kick to the pump. The pump prime is only about 6vdc when you first turn the key. So I assumed there was not enough voltage/current to get the pump running. But, putting a full 12vdc to the pump from my external car battery kicked it to full speed and made it run.
It's like there's a 'dead-spot' in the pump at a certain position that cannot be overcome with only the initial 5.95vdc from the FPCU. Hence the pump now being 'unreliable' and me not wanting to keep running with this pump. I pulled the pump from the tank once more and put in a new Nissan TT pump and all is well for now. I dismantled the old pump to further diagnose (I'm an electrical engineer by trade and just friggin' inquisitive), and I took lots of pics. Findings;
1) Original TT pump was manufactured by JECS and it has 123,000 miles on it. 2) Brushes still have LOTS of meat on them. The picture where you see the brushes looking like they're at the end of their travel,is not the case though. When the armature is in, the brushes are pushed back in their guides and show lots of material left. Spring that pushes brushed against commutator seem really stout. Pretty shocked about all that for a pump with 123,000 miles on it. 3) The ENTIRE pump, armature, brushes, and all electrical components of the pump, are fully submersed in fuel during running. I'm talking about everything in the pump gets fully wet with fuel.
Kind of scary, but gas is not conductive and with no oxygen under the liquid fuel, a fire cannot start even if the brushes were sparking during running. I found this incredibly interesting. NOTHING is sealed in the pump, and again, it's fully wet on all insides of the pump during its life in the fuel tank. 4) The actual pump mechanism is friggin' cool. Rotary assembly is built with rollers to pump and compress the gasoline.
The check valve ensures the fuel pressure does not go above 100 psi (if the outlet on the pump was blocked from a pinched hose or a totally clogged fuel filter). Then the over-pressure valve would pop open and reduce limit the fuel pressure to about 80-100psi. The rotary assembly is especially interesting and has a special coating on the outer ring. Looks to be some sort of nitride or chromate or something. And it looked in GREAT condition. Again, this is a pump with 123,000 miles on it and the rotating assembly looked new. 5) Near the outfeed of the pump is the pulse damper mechanism and the check valve to keep the fuel lines pressurized after the pump turns off. 6) The thing that showed the most wear (and why I think this pump ultimately became unreliable) was at the commutator. That showed wear. I think that's where I was getting the pump stuck and it would not run on the FPCU's initial 5.95vdc output. I needed a full 12vdc to get the pump to run if it landed on a dead spot. (and YES, I know, I know, that the FPCU controls the 'ground' and does not feed the 12vdc to the pump. But it does 'control' what the pump connector is fed, that ultimately feeds the pump. And again, the initial prime is NOT a full 12 volts and full speed to the pump. It wants the pump to prime the fuel system at lower speed.
The fuel cools the pump and all the moving parts.
It also lubricates everything in the pump assembly. And is the reason, you DON'T want to run these dry and should always avoid running the tank too low if you want maximum longevity from these original pumps.
The fuel in the tank is really the entire cooling system and lubrication system for this stock TT pump. Anway, I put up some pics. The commutator showing 'silver' is after I cleaned it. When I first pulled it, it was dark and does in fact show pretty much the only wear I can see in the pump assembly. Some deep grooves although the brushes look pretty damn good. I also see why you'd need the fuel sock on the inlet tube. ANY debris will be sent right into the pump rotating assembly and also right to the pump brushes and commutator assembly and can ruin the pump in short time. These pumps look stout for sure and are seemingly really build well from what I can tell. Feel free to ask questions if I didn't explain everything or didn't make something clear. Or if I made wrong assumptions or whatever. I'm learning here myself and I'm always willing to learn more.
Vinnie Link to picture gallery;
https://photos.app.goo.gl/MaFti6QBGCoeL3yAA
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