In-tank Fuel Pump Modification

E28 technical advice asked and given! Troubleshooting, modifications and more.
Ju@n
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Re: In-tank Fuel Pump Modification

Post by Ju@n »

demetk wrote:I put a Walbro pump in my car and it starts within 1 sec of cranking. You will need to get back in there and check it out. Post pics.
+1!
EIP11
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Re: In-tank Fuel Pump Modification

Post by EIP11 »

I have a brand new TRE 255 pump that I am looking to sell. I ended up using an Aeromotive pump instead.

The box is open but everything is still sealed in the original plastic bags. If I return to TRE I have to pay for shipping and a 20% restocking fee. Before going that route I decided to see if anyone here was looking for one, and save them and myself some money.

I am looking to sell it for $70 shipped priority within the US. I originally paid $79.
cek
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Re: In-tank Fuel Pump Modification

Post by cek »

Dake wrote: The owner said they'll be back in stock in about 2 weeks. He suggested I use this one instead, which is in stock, the TRE 343:

https://treperformance.com/i-873-chevy- ... -1998.html

He said the only difference is the location and size of the bottom inlet - same pump with the same flow rate as the 340. Since it would take 2 weeks + shipping to get the 340, I'm going to give the 343 a try. I'll report back.

Customer service-wise TRE is great. They shipped my 343 out today (Friday) for free while I ship the 340 back.
Did you get this 343 version? How'd it work out?
MajorChipHazard
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Re: In-tank Fuel Pump Modification

Post by MajorChipHazard »

What should the flow rate be?Is there a minimum or max rating?I see majority of the members who have done the mod used pumps with 255lph rating.Is this the recommended flow rate?
ElGuappo
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Re: In-tank Fuel Pump Modification

Post by ElGuappo »

Most use a 255lph pump since that is the most commonly available fuel injection type.
The fuel pressure regulator and return line are what does the work here though.
tn535i
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Re: In-tank Fuel Pump Modification

Post by tn535i »

Pumps are generally designed to operate within some range of flow and head pressure. Best to stick with what has already been defined as the right range for the rest of the fuel system so the overall restriction and regulator don't become a problem.

Nothing short of 'extreme' you might do with modifications or alternate injectors would require something different. 1/2 the rated flow of the 255 l pump would probably support 400-500 hP so probably you could get by with a bit lower flow pump if it can make the required head pressure.
MajorChipHazard
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Re: In-tank Fuel Pump Modification

Post by MajorChipHazard »

Thanks for the info guys.And also,thanks to everyone who contributed and showing ways of doing the mod.I done mine a few days ago,but,still had a hard start issue and over fueling.Turns out,the FPR had its days too.
Changed it,and now she's idling strong,starts up on the first turn,no hesitation while driving.Like a new engine has been fitted . :D
smitherz
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Re: In-tank Fuel Pump Modification

Post by smitherz »

Hi all,
New guy here and have read thru this thread over and over.

I had a bunch of rust in my tank and did an Evapo-rust/POR15 tank treatment to it. While I was in there I decided to do the mod to my car. Its actually an E23 1979 733i but from what I have learned in the 2 months I have had it basically the same mechanicals in general. I removed the original in-tank pump, external pump, damping unit and replaced the nasty filter with a new Hengst filter. After getting it to finally get all the air out of the line it started up. Now if I just nurse the acceleration it operates just fine. If I try to accelerate anything moderately hard it will barely hold its own like lack of fuel-vs-air. It seems to be fine sitting still in park and reving the engine up just not under any sort of load. I used the TRE-340 for the mod and used short pieces of hose inside the bigger line to downsize it to the filter and attach the pump to the normal outlet of the pump mount. I would not expect it to be a pressure issue but not sure what I need to look at.

Thanks,
Scott
1979 733i
davintosh
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Re: In-tank Fuel Pump Modification

Post by davintosh »

Before throwing any more parts at it, I'd put a gauge on the fuel line and measure your fuel pressure. If it's low, that could be caused by a blocked line somewhere, or maybe a bad fuel pressure regulator. If pressure looks good and the FPR is in working order, maybe take a look at the injectors.

You might also want to post your question in its own thread in Tech Talk; that might get more attention and and some more experienced guys chiming in.
--
Dave
Bigreading
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Re: In-tank Fuel Pump Modification

Post by Bigreading »

When the wires from the old inline pump get tied off does it need to be together to close a circuit or the them speretly.

Many thanks
Mike W.
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Re: In-tank Fuel Pump Modification

Post by Mike W. »

Insulate them individually. If you tie them together you'll short the fuel pump circuit and blow the fuse, hopefully. If you don't blow the fuse you'll start a fire, so to avoid all of that, just insulate them with heat shrink tubing, fold one back on itself, then tape the two insulated wires together, then secure somewhere up there so they don't rub out and short to ground.

You can do it simpler, but the above requires multiple things to go wrong before they can short.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

It seems very obvious but I'm still confused so please bear with me: Am I interpreting correctly there's no need for a coupler between the 12X18 hose and fuel filter as originally posted?
cek wrote: Nov 23, 2014 3:35 AM
wkohler wrote:Is the nylon coupling you got rated for fuel?
Probably not.
Image

but simply do as explained and shown below?

Image
cek wrote: Feb 19, 2017 1:45 PM First, take the original rubber connector that goes from the original transfer pump and cut it in half, where the smaller diameter section meets the larger diameter section.You'll use the smaller diameter piece INSIDE your 12x13 tubing to step the size down.

Under the car Use the other piece of tubing you salvaged from the old in-tank pump to size-reduce the 12x18 line coming from your tank to the filter.
So in essence the same rubber connector piece can be utilized for both, the in-tank pump mod AND also the 12X18 hose to fuel filter. Is that the case here? Thanks in advance.
davintosh
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Re: In-tank Fuel Pump Modification

Post by davintosh »

harrypalmer wrote: Jul 07, 2020 1:14 PM It seems very obvious but I'm still confused so please bear with me: Am I interpreting correctly there's no need for a coupler between the 12X18 hose and fuel filter as originally posted?
In looking back on where that conversation came from, I'd recommend disregarding Charlie's (cek) reference to that nylon coupler. Pretty sure he gave up on that idea.

The coupler idea was primarily to deal with the different tubing sizes that go between the original in-tank pump and the primary pump that's under the car. If you use the original outlet on the in-tank assembly, you could do as Charlie did, and use one of the smaller pieces of hose inserted into the bigger hose as an adapter. I can see how that would work really well.

What I did was to swap the inlet and outlet pipes on the in-tank assembly so that the same size hose could be used between the pump and the filter. That way the only place you need to worry about different tubing sizes is on the return side. Here's the comment where I described what I did:
viewtopic.php?f=3&t=101410&p=1312469&#p1312469 (also viewtopic.php?p=1443787#p1443787 )

Image Image

Image Image

The barbed adapter that I used at the top of the assembly could easily be replaced with Charlie's method of stepping down from the larger tubing size to the smaller. Or you could come up with a better idea.

Does that help?
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

Yes it does. Thank you very much!
cek
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Re: In-tank Fuel Pump Modification

Post by cek »

@davintosh did it right (as usual). Do as he said.

(I did it right on Minerva).
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

davintosh wrote: Jul 07, 2020 11:09 PM
harrypalmer wrote: Jul 07, 2020 1:14 PM It seems very obvious but I'm still confused so please bear with me: Am I interpreting correctly there's no need for a coupler between the 12X18 hose and fuel filter as originally posted?
In looking back on where that conversation came from, I'd recommend disregarding Charlie's (cek) reference to that nylon coupler. Pretty sure he gave up on that idea.

The coupler idea was primarily to deal with the different tubing sizes that go between the original in-tank pump and the primary pump that's under the car. If you use the original outlet on the in-tank assembly, you could do as Charlie did, and use one of the smaller pieces of hose inserted into the bigger hose as an adapter. I can see how that would work really well.

What I did was to swap the inlet and outlet pipes on the in-tank assembly so that the same size hose could be used between the pump and the filter. That way the only place you need to worry about different tubing sizes is on the return side. Here's the comment where I described what I did:
viewtopic.php?f=3&t=101410&p=1312469&#p1312469 (also viewtopic.php?p=1443787#p1443787 )

Image Image

Image Image

The barbed adapter that I used at the top of the assembly could easily be replaced with Charlie's method of stepping down from the larger tubing size to the smaller. Or you could come up with a better idea.

Does that help?
Wow I'm :oops: and totally missed the barbed adapter in your pictures. Guess was distracted by the painted top of the in-tank pump. Will do as you suggest. I appreciate your help and thank you for taking the time in your reply. The same goes for Charlie's posts. All invaluable.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

cek wrote: Jul 08, 2020 12:22 AM @davintosh did it right (as usual). Do as he said.

(I did it right on Minerva).
I will, your work on Minerva's fantastic. Thank you Charlie.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

davintosh wrote: Jul 07, 2020 11:09 PM
harrypalmer wrote: Jul 07, 2020 1:14 PM It seems very obvious but I'm still confused so please bear with me: Am I interpreting correctly there's no need for a coupler between the 12X18 hose and fuel filter as originally posted?
In looking back on where that conversation came from, I'd recommend disregarding Charlie's (cek) reference to that nylon coupler. Pretty sure he gave up on that idea.

The coupler idea was primarily to deal with the different tubing sizes that go between the original in-tank pump and the primary pump that's under the car. If you use the original outlet on the in-tank assembly, you could do as Charlie did, and use one of the smaller pieces of hose inserted into the bigger hose as an adapter. I can see how that would work really well.

What I did was to swap the inlet and outlet pipes on the in-tank assembly so that the same size hose could be used between the pump and the filter. That way the only place you need to worry about different tubing sizes is on the return side. Here's the comment where I described what I did:
viewtopic.php?f=3&t=101410&p=1312469&#p1312469 (also viewtopic.php?p=1443787#p1443787 )

Image Image

Image Image

The barbed adapter that I used at the top of the assembly could easily be replaced with Charlie's method of stepping down from the larger tubing size to the smaller. Or you could come up with a better idea.

Does that help?
Before I proceed I need your opinion on this please.

My goal is to keep a one size hose (8X13mm) for both intake and return the way you accomplished it, but with a twist.

To do this:

1. I'd step down the larger tubing size to the smaller, using Charlie's (rubber insert) method to utilize it as the intake tube.

2. Then, I would proceed with Davintosh barbed step down method but only at the top of the assembly so I can fit the 8X13mm hose. This would mean I would not switch the return for the intake lines. Mainly because I don't understand why the slim (return) tube is epoxy-welded.

However, in doing what I am proposing, I can see that the larger intake tubing would somehow be reduced twice: 1 at the pump intake with the rubber insert. And 2 at the top of the assembly with the barbed fitting.

Would this cause any pressure problem, or do you think it may work?

-Jack
davintosh
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Re: In-tank Fuel Pump Modification

Post by davintosh »

Sorry to be late in responding; it's been a crazy week!
harrypalmer wrote: Aug 19, 2020 2:38 PMBefore I proceed I need your opinion on this please.

My goal is to keep a one size hose (8X13mm) for both intake and return the way you accomplished it, but with a twist.

To do this:

1. I'd step down the larger tubing size to the smaller, using Charlie's (rubber insert) method to utilize it as the intake tube.

2. Then, I would proceed with Davintosh barbed step down method but only at the top of the assembly so I can fit the 8X13mm hose. This would mean I would not switch the return for the intake lines. Mainly because I don't understand why the slim (return) tube is epoxy-welded.

However, in doing what I am proposing, I can see that the larger intake tubing would somehow be reduced twice: 1 at the pump intake with the rubber insert. And 2 at the top of the assembly with the barbed fitting.

Would this cause any pressure problem, or do you think it may work?

-Jack
I'm not quite following you here. Are you keeping the original pump setup or converting to a single high-pressure pump in the tank? It's not clear to me where you'd be using the larger fuel hose.

When I made this conversion the larger tubing was eliminated entirely, and I used only the smaller 8mm hose throughout. On the original setup, the larger 12mm hose was only used from the lift pump assembly to the high pressure fuel pump intake; 8mm attached to the output of that pump. By switching the output of the pump to the smaller tube, that meant I could use 8mm to the inlet on the fuel filter. The step-down fitting on the larger pipe on the assembly allowed 8mm to be used for the return line as well.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

Davintosh, no worries.

Bottom line, will attempt a partial combination of both Charlie's method, and your method as well, by installing one TRE pump. Eliminate the external pump, and only utilize 13X8mm hoses everywhere.

Allow me to re-visit:

I'd replicate Charlie's how-to-cut and measure the rubber connector reducer inside the assembly. This would allow me to keep the intake's larger tube as originally intended.

Now, to utilize 8mm hoses everywhere, I'd reduce the same larger assembly tubing (but only) at the top, or exterior of the assembly, using your method; of barbed metal coupler and epoxy/weld it in the same fashion as you described.

Since I have not removed the original assembly from my car yet, I need to figure out unsure how you measured the rubber connector in the smaller tube, and also how you epoxy/welded the larger tube in the inside of the assembly, so I thought I'd better keep the original functionality of both intake and return lines and not switch them just yet, the way you did.

Really hope I'd made sense this time around. English as a second language can be challenging some times. Either way, I'd still appreciate your opinion whenever you have a moment please. Thank you once more. It will give me a valid reason to ship a six pack of your fav brew your way!

-Jack
cek
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Re: In-tank Fuel Pump Modification

Post by cek »

harrypalmer wrote: Aug 26, 2020 4:56 PM Davintosh, no worries.

Bottom line, will attempt a partial combination of both Charlie's method, and your method as well, by installing one TRE pump. Eliminate the external pump, and only utilize 13X8mm hoses everywhere.

Allow me to re-visit:

I'd replicate Charlie's how-to-cut and measure the rubber connector reducer inside the assembly. This would allow me to keep the intake's larger tube as originally intended.

Now, to utilize 8mm hoses everywhere, I'd reduce the same larger assembly tubing (but only) at the top, or exterior of the assembly, using your method; of barbed metal coupler and epoxy/weld it in the same fashion as you described.

Since I have not removed the original assembly from my car yet, I need to figure out unsure how you measured the rubber connector in the smaller tube, and also how you epoxy/welded the larger tube in the inside of the assembly, so I thought I'd better keep the original functionality of both intake and return lines and not switch them just yet, the way you did.

Really hope I'd made sense this time around. English as a second language can be challenging some times. Either way, I'd still appreciate your opinion whenever you have a moment please. Thank you once more. It will give me a valid reason to ship a six pack of your fav brew your way!

-Jack
My suggestion is to get your hands on a hanger so you can "just do it". Either source a used one, or just pull the sucker from your car.

BTW, "English as a FIRST language can be challenging some times." ;-)
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

cek wrote: Aug 26, 2020 5:12 PM
harrypalmer wrote: Aug 26, 2020 4:56 PM Davintosh, no worries.

Bottom line, will attempt a partial combination of both Charlie's method, and your method as well, by installing one TRE pump. Eliminate the external pump, and only utilize 13X8mm hoses everywhere.

Allow me to re-visit:

I'd replicate Charlie's how-to-cut and measure the rubber connector reducer inside the assembly. This would allow me to keep the intake's larger tube as originally intended.

Now, to utilize 8mm hoses everywhere, I'd reduce the same larger assembly tubing (but only) at the top, or exterior of the assembly, using your method; of barbed metal coupler and epoxy/weld it in the same fashion as you described.

Since I have not removed the original assembly from my car yet, I need to figure out unsure how you measured the rubber connector in the smaller tube, and also how you epoxy/welded the larger tube in the inside of the assembly, so I thought I'd better keep the original functionality of both intake and return lines and not switch them just yet, the way you did.

Really hope I'd made sense this time around. English as a second language can be challenging some times. Either way, I'd still appreciate your opinion whenever you have a moment please. Thank you once more. It will give me a valid reason to ship a six pack of your fav brew your way!

-Jack
My suggestion is to get your hands on a hanger so you can "just do it". Either source a used one, or just pull the sucker from your car.
True! Correct 8mm hoses arrived just now, thus ending my procrastinating.
cek wrote: Aug 26, 2020 5:12 PMBTW, "English as a FIRST language can be challenging some times." ;-)
LOL. Double that ^ ^ ^
So when you said, "(I did it right on Minerva)." how did you do it then? Just curious. Thanks.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

Oops! I did it too ;)

Inspired and encouraged by Davintosh and Charlie, (thank you boys) made the pump modification this weekend by copying Charlie's rubber reducer step method from the OEM in-tank to the new TRE pump pickup. And then sort of adopting Davintosh method of reducing the large tubing with a barbed connector at the top (exterior of the assembly) to hook up with a 8mm hose and here's were I diverted from Davintosh, is that I kept the original intake and return lines to and from the in-tank pump assembly as BMW intended. I was very hesitant of doing it (my way) until I read that Davisntosh also had some doubts too when reversing the lines. So I'm happy to report my car's engine starts right away with no hesitation and have driven her in multiple occasions and scenarios and she feels steady with no pressure loss that I can perceive.

There are many step by step photos of the whole process here: https://www.flickr.com/photos/109547372@N04/? for anyone interested.

I decided to put to use a brand new Airtex assembly that I had stored for years but never used because the rubber reducer was and is unadulterated merd and garbage. Had to rip off some pieces and trim (cut) to fit the larger tube, the retaining electrical side screw, and slightly and gently bend it all enough to fit inside the tank even with the rubber condom thingy, and nothing broke or ripped of.

Much thanks to Charlie because he really made me look more than once at what I needed to pay attention to. Getting the right correct length, measuring multiple times, and also reminding me (through his post) to have the filter pointing to the correct opposite direction of the pickup. Maybe conventional stuff for some here but essential to me, for which I'm grateful.
Lastly, much thanks to Davintosh too, because without his "simple" yet "brilliant" (for me) epoxy weld reducing method I would have not done this. Now, as Charlie suggested, I will be selling both my deleted but still working external and in-tank pumps next. This forum is a great place and I owe my gratitude to many of you. Thanks.
glowell222
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Re: In-tank Fuel Pump Modification

Post by glowell222 »

I have just completed this mod as well while I replaced my fuel tank. I no longer have the small hesitations during acceleration that I never really noticed until they were missing. A very large thank you to those who have contributed to this post.
harrypalmer
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Re: In-tank Fuel Pump Modification

Post by harrypalmer »

glowell222 wrote: Apr 06, 2021 9:13 AM I have just completed this mod as well while I replaced my fuel tank. I no longer have the small hesitations during acceleration that I never really noticed until they were missing. A very large thank you to those who have contributed to this post.
Glad for you. My car now is exactly suffering from some small hesitations during hard acceleration when A/C is not engaged. Oh well.

Prior to this mod I tested two Fuel Pressure Regulators and both were fine. Does anyone have any insight on this please?
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