2.7 to 3.2 Conversion Issue: Fuel Pump

[Fishrule]

Hello all,

Ever since I inherited a former track car from my father, I've been a huge fan of this forum. My dad converted his 2.7 liter '77 911S to a 3.2 liter engine from an '89. The car is fast, fun and surprising reliable so far, given the conversion. Unfortunately, he has few memories of the conversion process, so any problems I encounter send me scurrying to this treasure-trove of information. I would be seriously screwed without you all.

I've searched at length for a solution to my specific issue without much success, so here it is: the fuel pump buzzing was getting progressively louder, especially on hot days, so to avoid the stranded-by-the-side-of-the-road issue I decided to replace it. But with which model? The 1977 version (911-608-102-00-M14) or the 1989 model (944-608-102-04-M14)? Several Pelicanites stated that it doesn't really matter, the 3.2 will chug along happily with the higher pressure of the older pump, allowing the pressure regulator to keep things in check. Others recommend going with the younger, lower pressure model. I chose the latter because it seems like the pump should match the engine and it's management system. Besides, it was cheaper. But therein lies the crux of my problem. The newer pump has a check valve, the diameter of which is larger than both the banjo fitting on the existing fuel line, and the end cap (see photos).





I've tried swapping the ends between the two to no avail, they're different sizes on the pump side as well. I don't have a lot of money, so buying a new fuel line ($88) from our hosts is a last resort, and besides, I don't even know if the other, non-pump end of the line will need to be converted to a different size as well! Can I buy a different banjo fitting (sure hope I'm using the right term here) and attach it to the fuel line, then buy the right end cap from our hosts?

This car is new to me and, if I'm honest, I have no business owning it from a financial standpoint. But I absolutely love it, and I want to keep it on the road. That means doing the work myself and relying on you wonderful people for advice. It is very much appreciated.

[catuck]

I asked the exact question years ago :
http://forums.pelicanparts.com/porsche-911-technical-forum/105606-cis-fuel-pump-3-2-motronic.html
I had no trouble with the CIS pump

[eolson]

I think your best bet (and cheapest) would be to adapt the correct size banjo fitting onto the existing fuel line and use the newer pump. If it's not too hard for you to pull the fuel line you could even have a custom hose shop do it. Otherwise, if I remember right, the line going from the pump to the engine is a hard line, so you could cut the end off, flare the remaining tube, and use good fuel injection hose and clamps to adapt the correct size banjo fitting. The hose and clamps would cost less than $10, the proper tool to cut the hard line is cheap, and the banjo fitting with a barbed adapter is probably less than $20. If you have the tools or could borrow them (most places like Autozone rent for free) then you could be all set for less than $30.

Maybe someone has a better idea?

Edit, this is all assuming you already bought the later style pump...

[boyt911sc]

Fishrule,

Post the thread & pitch of the banjo bolts for these FP's. So you would like to use your old smaller banjo fitting to your new FP and I might be able to help you in your predicament. Measure the spec and I'll look into my stash of assorted metric fittings. That should be an easy fix. Keep us posted.

Tony

[Fishrule]

Chris - You're spot-on, of course, that is a very similar situation. Only, I already have the FP for the 3.2, and, maybe the pressure regulator will last longer if it isn't working so hard to reduce the feed coming from a CIS fuel pump? I'm not a mechanic, obviously. I would like to use the 3.2 FP if I can. It is nice to know that I have an out, admittedly. Thanks.

eolson, I have soft (rubber) lines going from the tank to the FP, and from the FP (on the check valve side) off into the chassis somewhere (really, I don't know!), so no hard line work to do here. But I agree, the best bet seems to be to replace the banjo, sealing rings and cap nut on the existing fuel line. Now I just have to find them...

Tony, I'm embarrassed to say that I don't know how to measure the thread and/or pitch. I can tell you that the check valve on the new FP from the 3.2 is 10mm in diameter where it screws into the FP, and 12mm in diameter where it meets the banjo fitting and the cap nut. Can anyone else answer Tony's question?

Regardless of outcome, I appreciate everyone's help.

Kyle

[boyt911sc]

Kyle,

Please post the numbers on the body of the FP's. The Bosch FP would have something like this:0-580-254-984. Need the last 3 digits only. The -984 has 12 mm x 1.5 (FP side) and 10 mm x 1.24 ( banjo side and could change to anything). Looking at your new pump it might have something like 14 mm x 1.5 and 12 mm x 1.5 (banjo side).

So what size is your current banjo fitting? Knowing the size and pitch of both FP's would be really helpful. If I would guess you have a 10 mm banjo on your fuel line. Getting the new FP to the size of your banjo fitting is the goal. Or simply use a bigger banjo to fit the new FP. Contact Len (BoxsterGT) for your hard to find metric fitting.

Tony

[BoxsterGT]

I will try to help with this. Both pumps will put out similar pressures, as its the regulator that limits the actual fuel pressure. The early pump has a 10mm Banjo and the later pump has a 12mm Banjo. Your lowest cost is to stay with the original pump as long as its working.

When you change up to the 12mm pump you will need a new Banjo & copper crush washers & cap nut. They are not expensive, but then you must fit this Banjo to the old hose that is likely ready for replacement. So you then need to fit a new front hose over to the tunnel. Again, not expensive, but the issue will be with the connections to the tunnel tube.

The original hose is permanently crimped to the Polyamid tunnel tube. Buying a new tunnel tube adds to the cost and its a major pain to replace. Not technically difficult, just time consuming and a pain in the butt to do, so this is not an option unless absolutely necessary.

If you must go with the new pump, I would be happy to help with new hose & fittings. You will have a hose clamp at the tunnel, but it should be OK with periodic inspection.

Happy to answer any questions, but please email me as my PM box is almost always full and I cannot send photos via PM.

Have a great Porsche day.

Len at Autosportengineering dot com

[Fishrule]

Tony, The old Bosch pump is stamped just as you suspected: 0-580-254-984. The new one is a Bosch as well but is completely devoid of identification, unless it's printed on a microdot somewhere. Regardless, I still have the box it came in. The number on the box is 0-580-464-021.

Len, We've already corresponded via email, but your explanation is very illuminating. The new, 3.2 FP is, number one, here in my hot little hands and I have for some reason decided that it has to go in the car. Can't really explain that. That it might be subject to a restocking fee (our Host was noncommittal on this) if I return it, and that the older, CIS version is far more expensive might have something to do with it.

Changing out the original hose sounds like the way forward, although the whole "permanently crimped" concept gives me pause. I have a habit of breaking things permanently affixed to other things. If you can reasonably say that I'll be successful getting it off, I'd like to give it a go.

Thank you both for you time and effort.

Kyle

[Walt Fricke]

Kyle - if I have this right, your old pump uses a 10mm diameter banjo, and the new one is 12mm. However, the one way residual pressure valves (which have the 10 and 12mm outer ends) also are different sizes where they screw into the pump body.

So obtain a reducer which has a male end of the right diameter and pitch to screw into the pump body, and a female end which will receive your old RPV.

That way you won't have to futz around with the hose. Since you have both pumps, it should be easy to pull both RPVs and determine diameters and thread pitch. Don't ask me where to find the piece you need, but its got to be out there somewhere.

If you do futz with the hose, it will involve using a Dremel with cutting wheel to slit the steel clamp which holds the existing hose onto the fuel line which disappears into the tunnel. And to slit, carefully, the hose itself. When you get the hose off there should be a steel hose barbed fitting underneath all that stuff. A replacement hose would slip over this barbed end, and be clamped onto it with, preferably, a crimp fitting (you'd need to find and borrow a tool to do that, as well as obtaining the cylindrical piece which gets crimped). Or with a hose clamp.

[BoxsterGT]

Here are original Porsche Polyamid Tunnel Lines showing the permanent connections to rubber hose up front......................





This is where you must remove the crimp sleeve & front hose & replace w new using a proper "Norma type" hose clamp.

Len

[BoxsterGT]

This is what I can provide to replace the originals in the tunnel...........



They are available with M14 or M16 Male fittings at each end. Lots of work to install but gives you ease of hose replacement for the future.

Len

[SCrescue]

Kyle,
Have you tried swapping the check valve from the old pump to the new pump?

[Chuck.H]

A question for Len or others (sorry to hijack the thread) -

In the 84-89 cars, what are the trans tunnel fuel lines made out of?

I replaced my front lines by taking a small hobby die grinder and cutting off the crimps shown in the photos above, then using hi-pressure fuel injection rubber lines plus clamps on the exposed barbs.

When I did this, I felt like the tunnel lines were 'bendable', that is they seemed to react like they were aluminum when I was doing the above grinding and positioning of rubber lines. Yet they were plastic coated, again like in the photo above.

My round-about-question is should I have replaced the tunnel lines as well, or, being aluminum or steel would they last way longer than rubber or plastic?

TIA,
Chuck.H
'89 TurboLookTarga, 339k miles

[BoxsterGT]

Some time in the mid to late 70's Porsche changed to the black Polyamid lines shown above. This or a similar product is now being used worldwide by most auto manufacturers.

This is a very durable material that is semi-rigid but it takes a special barbed fitting that is one-way and considered permanent. The only way to re-use this type of fitting is to melt the Poly tube off the fitting. If you try to cut it you run the risk of damaging the barbs.

Some folks say the fittings can be installed on new replacement tube with common hand tools, but that has not been my experience. I had to have special tools made at a machine shop in order to do the assembly correctly.

Up to present, I have heard of no failures of any kind with the black Polyamid line, only failures at the hose connections which are permanent in the factory configuration.

I have recently been advised that this Polyamid line is even suitable for E85 fuels now being preferred by the turbo models.

That is why I started making my new ones with threaded fittings as in photo above.

Len

[Fishrule]

Walt, A reducer would be ideal, but I have no idea if such a thing is available, or where I would obtain it. It would be a very specialized piece of hardware, I suspect. Wouldn't a Dremel create lots of sparks? I've drained the tank but can still smell fuel. Are there precautions I can take? I'll just have to be careful, I guess.

Len, Those new tunnel hoses sure look appealing but I'm going to have to stick with the front hose and clamp, for both ease of installation and financial reasons. I'm guessing that the second line shown in the pictures is the return line - will I need to replace that as well? On the picture below, I assume that I should make shallow cuts along the lines I've drawn, without cutting the barb, of course. Is that correct?



SCrescue, If only. I tried the swap with the greatest of hopes but alas, they're different sizes as well. Thanks anyway.

[Chuck.H]

Kyle -- You only need to cut your line with the arrow. The crimp is slipped onto the barb, and once you cut along the crimp you can put a screwdriver in the slot and break the crimp easily. Then the hose plus broken crimp will slide off.

Chuck.H
'89 TurboLookTarga, 339k miles

[Fishrule]

Chuck, Good information, and a bit of a relief if I'm honest. Sounds quite doable. Thanks.

Kyle

[Fishrule]

Mike (SCrescue), If only. I tried the swap with the greatest of hopes but alas, they're different sizes as well. 10mm on the '89, 12mm on the '77. Thanks anyway.

[Fishrule]

Len, What is the inside diameter of the front fuel line? I might be able to find a banjo fitting with a 12mm eye, but I don't know what size barb to specify.

[SCrescue]

Originally Posted by Fishrule

Mike (SCrescue), If only. I tried the swap with the greatest of hopes but alas, they're different sizes as well. 10mm on the '89, 12mm on the '77. Thanks anyway.

Then I agree with Walt, look for an adapter fitting to mate the old check valve to the new pump. Shouldn't be that hard to find.

Good luck, Mike...

Btw, great looking car, I love the color!