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1977 924 fuel dizzy swi... - oh, never mind. Resto Blog!
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Sat Jul 29, 2017 4:47 pm    Post subject: 1977 924 fuel dizzy swi... - oh, never mind. Resto Blog! Reply with quote

Greetings, all. I've been away from wrenching on 924s for a long time and won't bore anyone with the details but I have to say it's wonderful to be back working on water-cooled Porsches. It's also heartening to see many of the same names I knew - partly because you lot will be able to point me in the right direction with the following:

Short version: 1977 924. Fuel pump runs with key in "RUN" position and lifting the sensor plate on the fuel dizzy shuts it off. Yes, I know - that's exactly the opposite of what's supposed to be going on. I'm stumped but I'm thinking the solution is something simple.

The car was a freebie and my son and I are bringing it back to life. I have a shop full of rusting, moldy old car parts and a couple of 924 wrecks in the yard that we've been scavenging bits and pieces from. He's cobbled together most of an interior and changed both fenders.

I've replaced a very dead fuel pump, blown out fuel lines and filters, changed a fuel hose or two and teched out the wiring to the pump. Pump's good. Wiring's good. Switch on dizzy kills the pump. 'Sup with that? One important piece of information: we don't have the original fuel pump relay. Instead I'm using a 4-pin fused relay that tested good - after all, I simply need voltage across 30 and 87 to make the pump run. The relay's switched circuit is open until voltage is applied, then it closes and I get good continuity across 30 and 87 - same effect as plugging in a jumper. I know the pump runs well - our last test revealed an accumulator that leaks like the Titanic.

But why does lifting the airflow sensor plate shut the pump off?

Thanks in advance!
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'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks


Last edited by Slam on Mon Sep 11, 2017 7:19 am; edited 1 time in total
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Harm  



Joined: 02 Apr 2009
Posts: 1341
Location: Holland

PostPosted: Sat Jul 29, 2017 5:49 pm    Post subject: Re: 1977 924 fuel dizzy switch query Reply with quote

No tag signal (coil) kills pump to avoid fireball conversion?
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brian19600  



Joined: 28 Oct 2013
Posts: 375
Location: NJ/CT

PostPosted: Sat Jul 29, 2017 8:39 pm    Post subject: Reply with quote

The 77/78 doesn't require a coil signal. As a side note, the fuel pump relay for the 77/78 is hard to find and not cheap when you do get one.

Not sure why you have the problem you do, but I had the same problem when restoring mine. It would run whenever the ign. was on. (don't know if lifting the plate would have changed that). The problem was in the connector in the harness. I only found that by wiggling the wiring. I didn't quite understand why a bad connection would make it want to run. But I repaired it and everything was fine.

Here is a post on fuel pump relays:http://www.924board.org/viewtopic.php?p=289748

and here:http://www.924board.org/viewtopic.php?t=10331&postdays=0&postorder=asc&start=0
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Eric P  



Joined: 21 Jun 2017
Posts: 175
Location: NY, USA

PostPosted: Sat Jul 29, 2017 9:56 pm    Post subject: Reply with quote

Fuel distributors are fairly simple things. There aren't a heck of a lot of parts to go bad in there. Did you double check the direction of the piston in the bore? There's definitely a top and bottom. I've never put one in going the wrong direction, but I could see some strange issues if you did. Other than that, the tiny holes in it gunk up and the o-rings go bad over time.

I'd probably check the piston first and go from there.
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1980 924 NA, US model
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Sun Jul 30, 2017 5:11 am    Post subject: Reply with quote

Harm: pre-1979 cars don't look for tach signal, they take the signal from the AFM switch. Fireball conversion may be an option but right now this 924 is sitting too close to wifey's 944!

Brian19600 - thanks for the linkys. I did check the wiring harness connector and it seems good. I know the 77/78-specific FPR is unobtainium and I'm trying a workaround. My thought was a 4-pin relay would do the trick, I just need to understand why the AFM switch would cause the relay to open rather than close.

Eric P - Before I open THAT can o'worms I need to get fuel to the dizzy when and how it's needed, so my attention won't turn to the fuel distributor/injectors until the pump runs when it should. I did check plunger action and it was a little sluggish but a good soak is freeing it up.

Today I'll swap out the accumulator and keep trying to outsmart that AFM switch.

Thanks, all.
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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brian19600  



Joined: 28 Oct 2013
Posts: 375
Location: NJ/CT

PostPosted: Sun Jul 30, 2017 8:35 am    Post subject: Reply with quote

Einmalig has the relay used. Yeah the price is high. But it is the right part....

http://www.einmaligparts.com/Relay-Fuel-Pump-924-1976-7817_p_90763.html

Woolies in England sells them for $30 but he's out of stock. Maybe an email to him?
http://www.wooliesworkshop.com/ourshop/prod_6068520-Porsche-924-fuel-pump-Fuse-tester-Relay-477-906-059-197778-Porsche-924-fuel-pump-Fuse-tester-Relay-477906059-197778.html
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Sun Jul 30, 2017 5:27 pm    Post subject: Reply with quote

Thank you, sir. I'll keep an eye on the latter. Price of the former is quite steep. Seems to me the workaround may be a VW or Audi 6-pin equivalent with a fuse on the 87\30 circuit.

Got her running today! Fixed the accumulator leak, which was as easy as tightening the fittings. Pulled and cleaned the injectors, got a decent spray. Jumpered the fuel pump and she started first turn of the key. Ran like crap, so the can of worms that is the fuel dizzy is now officially open. Like every other 924 that's sat neglected for years, this one's fuel plunger is gummed up. I may try to free it or I may replace the dizzy with another I dug up in my shop, languishing at the bottom of a soggy cardboard box. But that's a battle for another day.

At least she runs! Woohoo!
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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brian19600  



Joined: 28 Oct 2013
Posts: 375
Location: NJ/CT

PostPosted: Sun Jul 30, 2017 8:37 pm    Post subject: Reply with quote

Excellent! If you come up with a alternative for the relay, let us know. The later relay (433906059) is about $15 and the vw one (321906059) is also cheap, but I thought that that the pins were different along with it's operation.


The VW forums seems to have a discussion on the bus fuel pump relay and wiring it up safely here:
https://www.thesamba.com/vw//forum/viewtopic.php?p=8076149
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Mon Jul 31, 2017 3:35 am    Post subject: Reply with quote

Thanks for the link - good read and timely, as I was discussing the oil-pressure switch cutoff with a friend of mine just yesterday. An elegant solution, because if I disable the AFM switch I'll need some way to kill the fuel pump in the event of a mishap.

Given the wiring diagram on the stock relay, it should be easy to find a replacement. I'm pretty sure the 433 would work, with a fuse on line 30. All it needs to do is close all the circuits when it activates. I'll dig into this further when it's time to wire up the dash properly (as in, get the tach online). I'll be turning my attention to the fuel dizzy next.

In the meantime, wifey's 944 needs some upfixin'.
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Mon Sep 11, 2017 7:17 am    Post subject: Reply with quote

Figured I'd pop by with an update. No, I haven't solved the fuel pump relay issue, largely because I've been sidetracked.

Previously I'd changed out the dead and rusty pump, the barely-recognizable accumulators, and a couple of fuel lines at the back of the car. I blew everything out and managed to piece together a means of fuel delivery that didn't look rickety and leak fuel all over the floor. Sometimes it pays to be a hoarder...

I'd taken the fuel dizzy/AFM off the car for a bit of a refurb. Took plenty of PB Blaster, some heat and some compressed air to get the plunger out of the dizzy but I got it freed up and working smoothly. I also freed up the pressure valve on the dizzy. Turns out the sensor plate was binding so I swapped in an AFM from one of the moldy old cardboard boxes full of various bits I've got lying around. I cobbled together a functional AFM/fuel dizzy assembly and put that lot in the car.

Then it was injector time. I pulled all four and did the "Let's spray raw fuel into glass jars for fun" trick. Spray looked pretty good, and while they were dribbling onto the head and the fuel pump ground and snarled away in the background I adjusted the fuel flow from nothing with the sensor plate at rest to a lovely mist when I moved it. So far so good.

Son and I had verified spark and I did a quick and dirty clean-up on the distributor and changed a plug wire. The car lit on the first turn of the key and I got it to warm up enough for me to adjust distributor timing and tweak the mixture to get it to run smoothly. It even responded to throttle! I toddled off to have coffee and a smoke and feel smug.

A couple of days later I was right back where I started! Start, idle, but throttle killed it. So I yanked the fuel dizzy off the car and checked that plunger. Again. Sure enough, rusty fuel. Oh, brother. So methinks it's back to the ass-end of the car to suss this one. In the meantime I found a better fuel pump - but I don't want to kill it with crap fuel so it can sit on the bench and sulk until it's its turn to come and play.

Stay tuned! (Pun intended.)
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1062
Location: Washington DC area

PostPosted: Mon Sep 11, 2017 3:39 pm    Post subject: Reply with quote

Rusty fuel shouldn't get through a new fuel filter.
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1979 924 NA race car
1982 924 NA race car - Sold
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Tue Sep 12, 2017 3:39 pm    Post subject: Reply with quote

New fuel filters are for the rich.

Our rules of engagement do not include new parts. Yet. We're using up bits and pieces already on hand. Partly to see what's possible. Partly for the fun in the challenge.

Yes, yes. I know!
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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Eric P  



Joined: 21 Jun 2017
Posts: 175
Location: NY, USA

PostPosted: Wed Sep 13, 2017 7:09 am    Post subject: Reply with quote

To be fair, filters are not parts meant to be reused. They're disposable maintenance items meant to keep junk out of your engine. That's pretty important for the correct operation of your vehicle.

Do yourself a favor. Replace all the filters (fuel, air, oil), oil, and spark plugs with new then fiddle with all of the other stuff you're going to re-use. An old fuel filter has old gas, rust, and other undesirables in it. You don't want that getting into your fuel distributor or injectors. That'll open a whole new can of worms and heartbreak. A new set of injectors alone will cost you at least $100. A fuel filter is $10. If anything works its way past your old filter (old varnished gas or rust ), you're going to end up having to get a new filter AND new injectors. Not to mention a rebuild for the distributor.

You have a Porsche. Why cut corners?
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1980 924 NA, US model
1987 924S, US model
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Wed Sep 13, 2017 12:07 pm    Post subject: Reply with quote

Absolutely right on all counts.

Some things are project-dependent. Wifey's 944 got all new filters, static clutch mod, engine build, FOES, some paint, new head, new radiator, new alternator, and on and on.

Eventually I'm sure this little 924 will benefit from the same. But for now, it's all about fun. No need to take myself seriously this time round.
_________________
'84 944 - all-weather workhorse.
'83 944 - still looks like ass.
'87 944 - wifey's DD, alive and well.
'80 924 - tuned by son #1.
'78 924 - blown up by Scottie.
'77 924 - gift from friend. Future project...
Some wrecks
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scm924s  



Joined: 22 Oct 2010
Posts: 226
Location: Gloucester UK

PostPosted: Thu Sep 14, 2017 2:56 am    Post subject: Reply with quote

The 1977 should have an inline filter between tank and pump as standard, otherwise any rubbish from the tank ends up killing the pump. Later cars with in tank and external pumps had a filter on the in tank pump. All in addition to the main fuel filter.
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1988 924S Guards red- sold
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