Terry,

Applying the “one-thing-at-a-time” philosophy, why not drain the fuel and inspect the screen? While I agree that “Dirt in the tank is USUALLY not that predictable.” the symptoms are the same. In any case, you will be better off eliminating that possibility for no cost.

Did you feel the pump? Did you look at it with the IR thermometer? Was it hot? The problem manifested itself both before and after the original pump was replaced with the rebuilt unit and no change in noise leads me to suspect it isn’t the pump, although I certainly won’t rule it out.

I agree that eventually you will want to replace the pump with new. First find the problem without throwing $400 parts at it. I would do the two proposed tests and re-clean the screen before buying a new pump.



Terry, you are right on! There are remarkable benefits to this Pelican Forum. Any DIY guy, shop, or mechanic that doesn’t monitor and record the information here is … well, a fool. I wish this technology had been available when I was in the Porsche business. I still find it hard to believe how hard I had to work to have all the information possible for my mechanics. Today, I would dedicate a substantial part of someone’s day to gather, sort, organize, and disseminate the information available.

I am a firm believer that no one person has “all the answers.” Bruce Anderson, Jerry Woods, Chuck Stoddard and many others and I would spend untold hours on the phone, at Parades and other events discussing this stuff. Now it can be on-line for everyone’s benefit. Interestingly, I don’t think it is any disadvantage to the pros to contribute. “There is no substitute” for those knowledgeable eyeballs, skilled hands, and well organized shops.

Best,
Grady

Jay,

Sorry, I didn’t mean to be coy. I was referring to the screen in the fuel tank.

Now that you said you cleaned the fuel screen I have some other CMA questions. When you cleaned the “horribly clogged” screen, did you clean the fuel tank? Have you tested the fuel flow? Do you have a fuel pressure gauge that you can monitor while driving?

Again, I’m sorry I gave a surely, smart a$$ post.

Best,
Grady

Terry,

I agree with Grady, you need to use a systematic approach to fixing this stuff. I've never heard of a failure mode based on heating of the pump, even though it's down near the heat exchanger.

Now, it's your lucky day. IF you agree to check the filter screen as Grady described, then I will send you one of my two spare electric MFI fuel pumps, as used on my 911E. IF you change out the pump for mine and it works, you agree to send me $100 plus the cost of my shipping to you. If it doesn't work, you agree to send me my pump back plus the cost of my shipping to you.

The pump was working when removed and is a much better alternative for testing than $400 for a new pump. No warranty expressed or implied, your mileage may vary, void where prohibited, etc.

If you are up for it send me a PM with your address, I am going to my hangar this weekend and will get the pump and mail it to you.

No problem Grady, I'm a smart a$$ myself, I wasn't focusing outside of being a hot issue for some other reasons I guess I didn't mention.

The screen was clogged bad by what appeared to be mostly corrosion and such. When I removed the screen, no other dirt really came out. When I looked into the tank during my rebuild, it looked good. Now that I've filled it for the first time in a long time, I should see how this looks. I'll pull the sender, and look for garbage in the tank.

Another reason I see this as a temperature issue is this happened on the exact same route, going to work, only when I was in stop-and-go traffic for a long time (weekdays). I had to go into work twice on the weekend, and I would get on the highway sooner because of less traffic. This could all be coincidence, and if my tank is clean, and replacing the restrictor doesn't help, I'll need to buy a pressure gauge to monitor fuel pressure while driving.

Jay,

This clogging of the screen from rust in the tank is a fairly insidious problem. The corrosion you found on the screen came from the bottom of the tank. If you just cleaned the screen and not the tank, then the same problem will reappear.

Go back and study my recommendations to Terry. Go read the thread I cited. I wouldn’t be surprised if the screen is clogged again.

I won’t dismiss a temperature effect. As I explained above, when the fuel pressure is low and there isn’t much (any) return flow, the mechanical MFI pump pistons can cavitate as the fuel gets warm.

Under normal (proper) operation there are almost two liters per minute of fuel being returned to the fuel tank. With the flow restricted to marginally what the engine is using, the stirring energy of the pump and the heat transfer from the very hot heater waste air to the fuel lines can cause some fuel components to vaporize. MFI absolutely does not like this.

I think this can account for your symptoms although I wouldn’t rule anything out.

Best,
Grady

John,
I have PM'ed you. Thanks for the offer.

I still plan to follow thru on checking the tank screen, installing the meter (even if it says "OIL"), etc.

I don't know if this problem predated the installation of the rebuilt pump. It just plain stopped working while I was installing and adjusting the MFI unit. There were to many other things that were going wrong to tell if I was having this same problem with the original pump.

If I'm lucky it will solve this problem, but I've never been accused of being lucky before, so why start now. Either way, I have learned a lot about my MFI.

Terry

Well I took the wife for a ride down Lake Shore Drive tonite, thinking 'it's' cool out, it will be a nice leasurely drive...I have a hot fuel issue...right??' well the first half was fun. The second half---my car was bucking like a bronco. I managed to stumble home (car & wife), and then it just died.

The nice thing about an external electric pump like our MFIs, you can hear it run. Well, it sounded like it was sucking some serious air!

Your right Grady, my screen is probably clogged...or, I actually might be almost out of gas. My fuel gage doesn't work properly (I think), and while I thought I filled it up, maybe it just cut out early?? I will feel like an extreme idiot, but that would be nice if it's all it is. I'll look at it tomorrow after work. I only have 200 miles on it since the rebuild, so maybe it's sucking down alot of gas during break-in?

Jay,

Having just brought my 72 911T out of a 10 yr storage with gas in the tank for the whole ten years, here are some of the problems that I experienced on an intermittent basis, that cause problems that I blamed on the MFI:

- left rear rubber brake line was bad. Started off down the road just fine and every time you applied the brake and released it, the brake shoe did not return all the way back. After about 10-15 times of applying the brake the rear wheel was locked up, BUT it felt like the car was gradually running out of gas. Stop on the side of the road for a few minutes and everything was fine again, until you started applying the brakes again. I found it only because one time on the road side, as I was discussing my cars birth right, I leaned against the wheel. Smoke coming out from under an early 911 is not always from oil on the heat exchanger.

- All of the fuel lines were clogged. While they allowed flow at idle and the engine ran ok, at speed it ran out of gas. Clean all the metal lines to the injector nozzles and replace all rubber with new. Reusing one old piece is the same as not changing any. Warning, use Grady's revised diagram for the hoses at the filter. It is correct.

-Check and recheck the fuel pump (see this thread) even if you "know" its good, that includes "new" ones. Short term testing with a pressure gauge will lie to you. I had to run it 30-40 minutes at 4000 rpm, sitting outside my garade, while watching the gauge the WHOLE time to spot problems. Mine would drop for only a few seconds at a time. You already know why I telling you this.

-Replace the fuel filter. It is bad if you have not changed it since you got the car

_Is your idle speed (8mm socket thru the fan thing) actually adjusting? Mine was stuck in full rich position. I would push and turn that screw ( If I remember correctly, this is really only a spring-loaded flat blade screwdriver that you push into a slot on the back of a rod. This is why you have to rotate the screw until it falls into the slot, THEN when you turn it , it will click) all day long waiting for the "click" it was suppose to make. Believe me you will hear and feel the click when it happens. If you don't then its time to repair/replace/clean this screw. This is an on-the-car repair. Very easy to remove. Remember, there is oil behind that cover, so be prepared to lose ounce or two.

Assume Grady and Cramer are right UNTIL you prove them wrong.

I know sometimes you feel like looking for a cliff, but hang in there. The '72 Targa looks to good going down the road to kill it.

Good luck,

Terry

Yep, most of the above has been done when I rebuilt the engine. I rebuilt the brake calipers, replaced all rubber brake lines, replaced all rubber fuel hose, replaced all ignition tune-up parts, replaced fuel filter, replaced breather hoses, Cleaned my throttle bodies and made sure they moved freely, opened up the MFI pump access covers to make sure everything was free, etc. I basically had every mechanical component on my car disassembled and either cleaned or rebuilt (minues the trans). I haven't made any adjustments to the fuel system yet since I've only put on a bit over 200 miles since I rebuilt the engine, and I don't want to keep adding variables to any problems I may find.

I'm feeling pretty good today since I likely have a clogged tank screen...or no more gas. Both are an easy fix :)

I'll keep you posted on the root cause, and let you know what else I find as I get this engine rebuild and fuel system sorted out.

John Cramer,
I need to return to pump you lent me. I need your address. Email or call me at 410-215-4732
Terry

guys,

The restrictor in my system was found at the approximate location circled in red, in the diagram below ...

It was approximately vitamin-pill shaped ... cylindrical, steel, 8.0 mm in diameter, 11.0 mm long, with gently-rounded ends, and had a ~1.5 mm [1/16"] hole drilled in the center, lengthwise. It was a tight friction fit inside the 7 mm ID OEM hose, and the old hose had to be cut away with large diagonal pliers to remove it.

It was actually a miracle that I found it at all ... that only happened because I decided to cut back from the ends of the hose to find out how far the cracks in the rubber part of the hose extended from the ends ... my hose wasn't leaking, but the hose ends were frayed at the cotton braid, and every end had cracks in the rubber where fitted over a barb fitting, including under the swaged crimp rings! I don't remember now if I found one 'consensus' value or not, because I was pretty amazed at finding the restrictor hiding in that hose!

http://forums.pelicanparts.com/uploa...1093029034.jpg

Warren, thanks for sharing that diagram. I like it, I like it a lot.

???

Anyone know, 1st if it's necessary, 2nd if so, how to bleed the fuel system when you are reassembling the tank, hose, and pump?

As usual, Grady was on the money. I looked into the tank only to find alot of crap plugging my inlet screen. Now if I can only stop working so much to get that tank out, and have it cleaned and sealed.

There's alot of good info in this thread!

Jay:
Grady lives in Colorado, I have met him a couple times and he is a great resource. FWIW I just want to point out that on the first page this thread, I offered up what was probably the situation (IMHO) with your corroded tank from my first hand experience with the very same problem on my '72T. It took me three iterations of cleaning my intake screen before I pulled my tank to fix the problem. Rust never sleeps anywhere on an old 911. HTH and this board is amazing source for all of us Porsche buds.

Warren,

The position you indicate in red is in the pressure relief circuit for the pump that returns to the tank. The spec for that pressure relief valve is 2.0 bar. As I understand the system, that pressure relief valve never opens unless there is some abnormal restriction in the main fuel flow circuit. That restriction is not in the circuit that determines the fuel pressure at the MFI pump.

I do not doubt you found a restrictor there. My question is; why is it there?

Best,
Grady

Grady,

My best SWAG is that it was a cheap, redundant backup to keep pressure high to the filter and plenum 'loop' in case the relief valve in the pump stuck open due to contamination or other problem ... kind of a 'limp' mode, if you will ...

grady,

Looking back at the Parts Catalog diagram ... i just realized that it doesn't accurately depict the layout and connections to the 'Tee' ... and that I circled the wrong leg in your diagram ... it has only been about 17 years, after all!

Below are the revised diagrams relating to where I found the restrictor:

http://forums.pelicanparts.com/uploa...1093156491.jpg


http://forums.pelicanparts.com/uploa...1093156593.jpg

Warren, Grady,
Has it been determined that this in-line restrictor is a factory item and should be there. I did not find one in my original hose that I replaced (why do P-guys keep "old" parts?). If so, is it needed?
Terry Hastings

I fixed my 72T MFI with a new intake (gas cap $10.00 Pelican) filter and new tank yesterday. My college buddy helped me with the new repro tank. Once the return banjo fitting finally sealed I put in 5 gallons and my pump is humming happily today.

Warren, your revised diagram matches my pump lines perfectly.

Still three more weeks in the short arm cast, but I'm back in the saddle again!

Update time....
In my most recent bout with my 72T MFI having these "events", I found that I had good gas flow at the tank, 1/2 that flow at the fuel pump intake and output and a simular amount at the filter output to the MFI.The pressure went up to 30 psi when the line was clamped shut.

Well I took Grady's advice and one again went thru the cleaning of my gas tank, tank filter and gas lines up to the fuel pump and a new fuel pump. I found "crap" in the metal lines running thru the body, used compressed air and wire to clean it out. Ended up with 14-16 psi and a liter in 40 seconds at the output to the MFI of the fuel filter. This was a 30-40% increase over the pre-cleaning readings. (how do you tell if the tank filter is clogged, the mesh is so fine I could not see thru it, but air and cleaning fluid flowed thru it ok)

Took the car out and it ran great. Fuel pressure remained at 14 psi and no "events". Once again I was a happy P-car owner
THEN........................
On the way to work, about 20 miles into the 30 mile drive, the "events" started again, and this time the fuel pressure stayed below 10 psi for the remainder of the trip. The car continued to run ok except for the 10 or so 20 second long " events" with lost power and popping in the pipes

The only thing that I have not taken apart and cleaned is the fuel filter housing. Is there something inside this that could allow a blockage to form? Does anyone have a good diagram on taking this apart?

So, am I looking in the wrong place? Is there an electrical item that can affect the pump pressure or flow?
Terry Hastings

Here is a diagram of the fuel filter console.
Fitting #9 is the “overflow valve” that is a restriction in the return.
The one in the pipe/hose assembly seems to be in addition.
"
http://forums.pelicanparts.com/uploa...1095690225.jpg "
(C) 1972 Dr. Ing. h.c. F. Porsche A.G.


Best,
Grady

Terry,

To really properly inspect the screen in the tank fitting, you should remove it from the tank. Looking at it through the fuel level sending opening can fool you. The weave of the screen can clearly show even when the screen is almost completely restricted. The screen fitting is easiest to loosen when the tank is bolted in place.

I’m surprised that the pipes were that restricted. Good that you found that. I have always worried about that but never found one so restricted. I think a rifle bore brush for a .22 caliber or close can fit the pipes. That might be a good cleaning tool. Are your pipes in the tunnel factory or other? Plastic or metal? If you feel they need replacing, I would recommend stainless steel with a swage like the factory fittings.

When you disassemble the fuel filter console, investigate all the fittings and passages.


Your question about the electrical connection to the pump is a good one. With the engine running, you should have very close to battery voltage (~14.2V) at the pump. If there is more than a few tenths of a volt difference, I would inspect and clean all the connections. An easy measurement is to put one lead of your voltmeter at the battery + and the other at the electric fuel pump +, you are measuring the drop in the positive wiring. You should also confirm there is very little voltage between the negative pump terminal and the chassis ground.

The MFI electric Bosch fuel pump (Porsche 901.608.105.00, Bosch 058097 0001) is rated at 3.5A @ 12V. It turns approximately 2800 RPM and delivers (free flow) 125 liters per hour. The safety pressure relief valve in the pump opens at 28 PSI but the system pressure is regulated at 14.2 PSI by the restrictions in the return line.

Best,
Grady

Grady,
I had the screen out of the tank and in a parts cleaner and could not see thru it. The mesh was almost impossible to see. As a matter of fact, at first i thought it was a piece of brass tubing. Not having seen a new one, I was not certain as to what was "clean". I wanted to replace it, but I could not find a listing for a replacement anywhere, so I was left with giving it a good scrubbing in the cleaner. I had to re-install it since I did not want to tie up a lift while searching for a new one. I could not find it in the factory parts manual. I need to know thia parts name/part number or something just to order one (I just got a part number of 901-201-023-02 form Doug on another thread). I was hoping our host had it listed, but it appears that I will have to give them a call. With a lift, it's not a hard job pulling it out, after you drain the gas. And now that I cleaned out the sending unit, my gas gauge works, I won't have to drain 8 gallons next time.

I was surprised to find crap in the factory tubes. Just a couple of months ago I cleaned them by pulling a wire attached to a small nylon parts brush (the 20+ .22 cal brushes I own were all at the house, not the garage). Maybe the fresh gas, and all the cleaners that I've put into the gas finally started cleaning the walls.

What really surprised me was the amount of sediment that was in the tank. I have had only 50 gal of gas since I had the tank steamed cleaned. I wonder if it came out of the sending unit for the tank, which I just cleaned and it was "full" of crap.

Terry

Terry,

I agree it is a very fine screen. If you have it out again, try some soaking in carb cleaner and a fine wire or tooth brush. Lacquer thinner works well for a final clean.

I looked on PET6 (’73 MFI) and there are two screen fittings listed.
With a 6 mm outlet is 901.201.023.01.
With an 8 mm outlet is 901.201.023.02.
Yes, they are called “gas caps.” The translation hasn’t gotten any better in 40 years or they outsourced to India.
These are the same part numbers listed in my original paper ’72-’73 parts manual only they are called “Tankverschraubung – screwing.”

I have a bunch of rifle cleaning brushes that have a ring on each end so you can pass them back and forth in the bore with a string. Some date to WWII and earlier with my dad. I think these are currently available and are great for all sorts of cleaning applications.

Looking at this prompts me to ask; what is the return fitting in your tank? Have you had that out for cleaning also? I think Porsche occasionally just used a normal supply screen fitting on the return side. That could be restricted also, just from the inside of the screen. Or, is your return to the bottom drain fitting with a banjo? That keeps the debris stirred up while the engine is running.

You might consider a new screen fitting for the fuel pump supply and use the old one (with screen removed) in the other port with just a plug in the drain position. This will give any debris a place to settle without being stirred up by the return flow.

There is a 914 screen fitting that is plastic and I wouldn’t recommend using that part.

The junk in your fuel tank can only come from two places: In with the fuel or from corrosion of the tank. I would recommend you get a funnel with a screen filter in it for fueling the 911. These are readily available at the roundy-round parts suppliers. That will eliminate a potential source. You might consider periodically draining your fuel tank through a coffee filter and see what you find. You may need to seal or replace your tank.

I will be really interested as to what you find in the fuel filter console.


Best,
Grady

Grady,
Thanks for the part numbers. I was wondering what a "screwing" was in the parts book.
It appears our host no longer carrys these parts in stock. They are special order at $40 each???????????? Are they available anywhere else?

I have the banjo fitting on the return line.

I "think" I know where the sediment in the tank came from. The tank, after the original steam cleaning, was filled with new gas from old plastic gas cans that we used in our race car days. When I went to drain the tank this time I noticed that there was a lot of junk in the bottom of these same cans. There is something to be said about doing it yourself.

Terry

Strange that, I just ordered 2 of these in July 2004 for $9.50 each, from our host via phone. Perhaps I got the last two stocked?

They say that they have not had them for a long time. Of course the sales rep was reading from the online catalog which says this.
I will try them again.
Terry

Doug,
I just called again and this time the price was $9.????????????
Terry

Terry,

What is the progress?

What have you found with the fuel filter console?

Have you found a new brass screen fitting? I’ll bet a $9 screen fitting is the 914 plastic version. Stay away from that one to supply screened fuel to the electric pump. It might work as a diffuser in the return circuit.

The more I think about this I would use a complete screen fitting in the return line to the tank. The fuel is filtered by the big MFI filter and the screen diffuses the return flow for less disturbance of debris sediment. You can install a drain petcock in the bottom port since you seem to be draining the tank regularly.

Only the Porsche translators would offer a 901.201.023.01 “Screwing” in their parts system. I thought that was only available from another department.

Best,
Grady

Here we go again. I've been sort of buying and selling these cars and this is problem is very typical. For some reason the old Porsches seem to be prone to rust in the tanks and the lines more than any other car. I think they are more prone to rust in general. I've been through the process of trying to isolate the problem, only to find it will eventually reoccur at some other time and place. I've cleaned the lines with solvent, blown compressed air through them and even would push some stiff wire through. For some mysterious reason these measures were not always enough. I have concluded that the only sure and final way to deal with this, and I know it sounds extreme, but just change out all the lines and the tank. It is the only sure way of not being haunted by this problem and wanting to drive your car over a cliff. This includes all the metal lines particularly the ones through the tunnel, that is the suction and return. If you repair or replace sections it will solve the problem temporarily only to have it return at some future date. The alternative in my opinion would be to just sell the car -that's what the previous owner did.

Thats why they put guard rails at all cliffs.
Ed, it runs soooo...good when its right, and since I've had this car for 20 yrs, theres only one way we are going to part company.
So, now it is clean up to the gas filter unit, so I take that apart and clean it out next. I also found that one hose was not replaced, the one from the filter to the MFI. That will come off too.
If this does not clear up the problem, once again it is time to go back to looking at the replacement MFI unit I got from UncleZak as being the cause. One thing is for sure, over the last year, I've learned a lot more about the MFI system then I ever wanted to know.
Terry

Terry any new updates ? Did you fix it ?

Kurt Williams

Kurt,
I no longer have the "every 3 miles no fuel pressure for 10 seconds" problem. After cleaning the fuses and blocks, and replacing the fuel pump fuse with a "new and improved" one, it improved immediately. This increased the flow out of the inline filter from under 900 ml to 1200 ml.

There is still the occasional burp, that that I have a hard time feeling. If I did not have a pressure gauge in the car, I would not even feel or know about most of them. No more stopping along the road shoulder waiting for the pump to fill the MFI back up.

Of course, I did that AFTER cleaning the tank again, replacing the tank filter and replacing that one hose.

The more I drive the better it seem to get.

It is running richer since the fuse change and I have not had a chance to adjust it.

I'm still going to look for a good rebuilt, fresh, MFI pump or get one of those EMI setups for the regulator end of the pump. I think there may be a problem in the regulator end of the pump. If you hear of one let me know.

Terry Hastings

Hey, great news!

You could still have some junk in there, you might splice in a cheapo plastic filter and let the fuel circulate for a few hours (you can do that with the engine off, just have the key on so the fuel circulates in the loop between tank and pump) although you might want to have a battery charger hooked up to keep the batteries strong.

I would very much doubt that your MFI pump is in need of a rebuild in the absence of some major symptoms-- give 'er the old Check, Measure Adjust and see if that richness can be corrected. See my thread in the archives on installing an LM-1 to monitor mixture. . .

Great news.

John,
I have already installed, run and removed a second little inline filter. It was clean after a month.
I had been adjusting the mixture trying to solve my problem, but now that I improved the flow after installing a NEW pump (your old one is still sitting on top of the 'frig as my wife just reminded me) it's time to un-adjust back to where it was.
I have a CO2 gauge installed in the car now. Its in the red only on startup and NOW when I let it idle for several minutes. That should change with the adjustment.
terry Hastings

Sounds great . I currently have a problem with my mfi setup . I found this thread in a search and read the whole thing . I am going to start a new post which will be specific to my problem . If you have any idea`s feel free to add any input .

Kurt Williams