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oprj45 · Joined: 19 Jul 2005 Posts: 23 Location: San Francisco, CA

has any one had this problem: recently while driving i'll suddenly lose power on the throttle; i give it gas but the tac drops and the car slows. electrical power is fine because the lights/radio are still on. while still driving i can turn the ignition and she starts right up no problem, and i go about my way. it's becoming more frequent and happened twice on my last trip, and three times the trip before!

any ideas?

i also think i have the classic hot-start problem. she starts fine cold, but if i drive it any good distance, then let it sit (say to run into the store..etc..) and then start it up again, it pretty much always takes 4-6 turns to turn over.. hot-start problem?

i know i need to replace all my hoses and o-rings.. just trying to figure out how much that'll cost. and i'm sure i could use a new distributor cap and probably plugs.. no?

thanks for any insight!
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Porsche 924 - 1982 - Northern Cali

timstar92404 · Joined: 22 Sep 2004 Posts: 2075 Location: richmond BC

yeah that's a hot start problem if you want to fix it properly I've been told by lots of people that it's most likley the fuel pump check valve which results in fuel pressure dropping after shutdown.
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78 924 sold.
85.5 944

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Sounds like the breakerless sensor module inside of the distributor is getting ready to check out on you.

This is a common problem on 81 and later cars with 100K miles or more on them. Other makes of cars use a similar Bosch designed and supplied module inside of the distributor, and they all crap out about the same number of miles.

It may be cheaper to buy a rebuilt distributor, than buying the module, and saving a machine shop disassemble the distributor and replace the module. When the one in my 81 924 died, I removed the distributor and had a local Bosch Authorized Service Center, disassemble it, replace the module, and test the completed distributor. Only the module itself was dead.

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

i'm actually having the same problem with mine (sudden power loss with dropping RPM). it's very very intermittent for me. i'd say it only happens on every 3rd or 4th trip i make, on average, although it's not that regular. it's weird.. sometimes it'll happen once, and other times, it will keep happening. i should look into a rebuilt dizzy myself.
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'81 US 931 "Rochelle"

oprj45 · Joined: 19 Jul 2005 Posts: 23 Location: San Francisco, CA

oprj45 · Joined: 19 Jul 2005 Posts: 23 Location: San Francisco, CA

Smoothie · Posted: Sat Feb 04, 2006 7:27 am Post subject:

"distributor" = the whole thing that bolts into the head, not just the cap. The distributor is press-fit together, so requires some light machine shop work to disassemble, replace the module, and reassemble.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Sat Feb 04, 2006 7:37 am Post subject:

The problem, when you have the hot start problem, is that the lines between fuel pump, fuel distributor, and injectors (incl cold start valve) lose pressure. What keeps pressure in the system are - the fuel pump check valve, the pressure regulator inside the fuel distributor, the injectors, cold start valve and the fuel accumulator - the accumulator keeps approx. 40cc of fuel in a bladder under spring pressure. You could have a leak at any one of these points causing pressure to drop, then heat from the engine, mainly affecting the lines to the injectors, causes vapor lock. The problem wouldn't be with the fuel pump. If it's an intermittant and not too serious problem, the car should start while hot just by holding the throttle to the floor while starting - this helps to clear the vapor lock quicker. The "hot start fix" uses a switch wired to the cold start valve - this has the same affect of clearing the vapor lock by moving more fuel through the lines as well as by spraying more fuel into the intake. -But the real problem is a leak somewhere. You have the options of finding and fixing the leak, holding the pedal down while starting, or doing the hot start fix with the added switch.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Ozzie · Posted: Sat Feb 04, 2006 7:50 am Post subject:

From feedback I have received the most common fault is the check valve on the fuel pump.
The check valve is a replaceable unit and cheap compared to the pump.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

oprj45 · Joined: 19 Jul 2005 Posts: 23 Location: San Francisco, CA

Smoothie · Posted: Fri Feb 10, 2006 9:20 am Post subject:

pc_evans10 · Posted: Mon Feb 13, 2006 4:52 am Post subject:

My UK 924 has just recovered from EXACTLY the same problem you're describing (well fingers crossed - managed a 600mile round trip this weekend with no probs whatsoever).

Having posted my dilema on this forum a month or so ago, the general concensus seemed to be to try replacing the Ignition Control Unit (little grey box bolted inside the the engine bay by the leftr headlight). Loacl porsche garage quoted me hundreds (literally) of pounds for a replacement, so went onto eBay and found one instantly for £24.99!

And all I can say is that since fitting this box she seems to be behaving like a normal car again

oprj45 · Joined: 19 Jul 2005 Posts: 23 Location: San Francisco, CA

Ok, first, so sorry for a late follow-up (for anyone who was following this.)

Here’s what the actual problem turned out to be! The wire to my external fuel pump was loose, essentially cutting power every time it would wiggle free. (side note: this most likely created a spark that, had there been a fuel leak in the area, I probably would have had a nice explosion on my hands.)

Upon further investigation into the fuel pump itself; it was determined (based on the age of the pump and the excessively loud noise it was making), that the pump was ready to fail. So I replaced it (not cheap!) Since then, I’ve actually had a significant increase in performance and reliability. It used to feel like it would “sputter” if I gave it too much gas. Now it flies, and boy does it feel great!

However, I still have the hot-start issue, so the “check valve” fix is not the case here, since I have a new fuel pump and check valve. Since I haven’t replace the hoses/o-rings/etc, I’m not surprised. Holding the pedal down, as suggest by Smoothie, works great and usually starts by
the 3rd turn. In fact when it does start, it starts with a punch! Hence the freeing of the Vapor Lock.

Thanks again for all your insight/suggestions!
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Porsche 924 - 1982 - Northern Cali