jwillman

So I have researched the parts manual and the WSM as well as searched posts here and am as confused (actually more confused) as when I started.

Seems that a 1979 may have 1 or two fuel pumps. The second might be in the fuel tank. The car might still run even if the in tank pump (assuming it exists) did not work.

My questions are:

1. how do i determine if I have a second pump and where if I have one it would be located (only in the tank)?
2. is there a test tio determine if the in tank pump is working?
3. If I had an in tank pump would it have to work to get fuel to the external pump below the tank or is the external pump strong enough to suck fuel through it?
4. If I have a second in tank pump can it be deleted or left in inop without affecting the operation of the car?

Thanks

curt_928

Jim, there should be two. If you check on the back of the fuel tank under the rear bumper there is a steel plate that is fixed with 4 or so 10mm nut/bolts. Take that off and the main pump is stapped onto the tank below it. The intank pump is screwed into the tank below it. It can be unscrewed with a pair of pliers pretty easily. Some have deleted it and put a higher flow main pump in (strapped to tank).. if I recall correctly. Big issue with the feed pump (pump in tank) that I've encountered is what called cavitation.. a tendency for the fuel to form bubbles on hot days. The in tank pump feeds the fuel into the main to avoid this cavitation.. and bucking.. Had it happen on my 924.. I think I might have an extra in-tank pump that works lying around somehwere if you need it...

Good luck,

Curt
________________
79 928 5sp silver/blk
02 boxster 5sp blk/blk/blk

ROG100

Jim,
Normally there should be two pumps - one external and one internal.
During 79 there was a VIN split change to the strainer in the tank and all 80 cars had the strainer.

As already explained above it is pretty easy to tell if you have one or not. If not it could have also been removed at some time.
Whether your car was fitted with one originally or not I can tell you from the VIN number.

There are plenty of early cars running succesfully without the internal pump.

jwillman

Curt,

Thanks for the information. The PO already had the cover removed but I had not crawled underneath the back end yet and could not find a diagram / picture of the second in tank pump to know where to start to look.

I will check it out tonight!

Roger vin # is 9289201405

ROG100

Jim,
Yours was fitted with an internal pump.
Roger

jwillman

Thanks Roger.

I will try and take a look at it tonight.

jpitman2

The 2 problems with the in tank pump are that (1) the hose connecting its output to the tank outlet to the externa lpump breaks up (pump weight flopping around), and the pieces go into the external and jam it, or restrict its flow, and (2) it fails to pump, and the external gets overloaded and dies - signal is pump getting noisy.
You can tell if you have an intank pump if there are two wires going to pins on the screw in piece in the tank bottom. My 83 doesnt have an in tank, and the leads for it are taped up down there.
Many believe the in tank pumps are more trouble than they are worth, unless you do heavy fast driving in hot/high conditions. My car ran for several years in 120F conditions with a single external pump, on CIS/K-jet, same injection as yours, no problems.
Be VERY careful trying to unscrew the tank fitting - if the unit has seized on the thread of the insert moulded into the tank, you can spin the insert and the tank is pretty much scrap. I did it once, but managed to seal it up with PC11 gas proof epoxy. There is a pick up filter screw in unit to replace the intank pump......depending on the thread - there was a change here and one of the threaded filters is NLA.
hth
jp 83 Euro S AT 52k

jwillman

So I took a look and there is a cover over the bottom of the tank. Is the in tank filter under that cover? I don't see a way to access without dropping that cover which also looks to be the tank harness.

Seems I have some rust on that anyway. Any source for replacement tank cover / suspension units?

jpitman2

The rusty part in bottom pic is the 'tank cradle' holds the tank in place, 4 long bolts at the ends of metal straps, into the body. In your top pic , follow the hose on the left to the tank, thats the supply line. If there are two wires connected to tags on that hex nut, you have an intank pump; if not, you dont - I cant see any, bit its not too clear in there. It does look a bit different from mine, which is not a big surprise. If your tank doesnt have much fuel in it , you could drop the cradle, and support the tank with something as soon as cradle is clear. Then you would have better access to the outlet fitting. To drain the tank,get a suitable size container, clamp the hose going into the pump, undo the clip, run hose into container,relax the clamp - but be ready to clamp it again if your container gets near full. Keep a fire extinguisher close by!
Do you have a symptom you are trying to fix ?
jp 83 Euro S AT 52k

jwillman

Well as a matter of fact I have an issue with the car starting and then immediately dying. I just jumpered 30 and 87 on the fuel pump relay and the main pump spins up and then immediately begins to cycle. Thoughts?

I don't know how much fuel is in the tank. Guage does not register but much is disconnected in the dash area. I am guessing it is very low from the sound of the tank. Could the surging be low/no fuel?

I am tempted to follw your suggestion to see if I have gas in the tank.

I alos confirmed the wires running to leads at the fitting coming out of the tank.

Thanks

jwillman

So I found a in-tank pump in a box of spare parts that came with the car. Still drainging fuel from the tank, seems to be about empty after 5 gals.

Since I have a replacement pump should I replace or just loose it and go with the strainer? Does the strainer unit listed in the 79 parts manual just thread in to the fitting where the in-tank filter is now? That seems too easy!!!!!

ROG100

The strainer screws in like the pump - same thread.

jpitman2

If the intank pump you found is NEW, maybe- do a search here for people who have replaced the intank with new, and its died much too young - short hose fails. If its used, I would not put it in - its out for a reason, and as remarked elsewhere, its not vital unless operating high, hot and hard.
See this thread....https://rennlist.com/forums/928-foru...fuel-pump.html
Roger, I seem to recall seeing a thread pitch change in the tank insert in the first couple of years, and the very early one listed as NLA?
jp 83 Euro S AT 52k

ROG100

John,
You are right but this car had the later size according to PET.
Early cars had 36M x 1.5 and later cars 37M x 1.5.
IIRC the later would fit the earlier tank insert with some filing down of the thread peaks.
Tank would need a flush afterwards of course.
Roger

jpitman2

Roger,
So Jim should be good to go with the filter and a new external pump....I forgot you had the VIN on hand.
jp 83 S