Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

What would cause a 931 fuel pump fuse to fail?
Goto page Previous  1, 2, 3
 
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech.
View previous topic :: View next topic  
Author Message
Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1181
Location: Washington DC area

PostPosted: Wed Oct 21, 2020 3:09 am    Post subject: Reply with quote

Sounds like your issue was the negative terminal on the battery (intermittently not connected). If your radio dropped on and off at the same time as the car running rough, they both share a need for a ground. Clean and clamp it tight, then drive.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
Back to top
View user's profile Send private message
chuck21401  



Joined: 20 Feb 2005
Posts: 375
Location: Annapolis, MD

PostPosted: Thu Oct 22, 2020 1:17 am    Post subject: Reply with quote

Fifty50Plus wrote:
Sounds like your issue was the negative terminal on the battery (intermittently not connected). If your radio dropped on and off at the same time as the car running rough, they both share a need for a ground. Clean and clamp it tight, then drive.


Yeah, it does seem like a grounding issue. It's possible that the negative terminal was loose. It's definitely tight now. And the cable running from battery to the body looks like new including the bolt to the body.

I'm going to double check other grounds. When I was under the dash last time I checked the grounds...everything was tight and looked like the PO had cleaned each ring connector and there was new bolt there as well.

The ground from the alternator to the intake manifold looked old so I bought a replacement for $12. I plan to replace that...but looks like I need to move the alternator to get the bolt out....not a big deal...just a bit more involved.

And will also check to see that other wires are tight......maybe something is coming loose from vibration.


_________________
1981 Porsche 931
Back to top
View user's profile Send private message
chuck21401  



Joined: 20 Feb 2005
Posts: 375
Location: Annapolis, MD

PostPosted: Sun May 02, 2021 2:23 am    Post subject: Reply with quote

I was driving back from Lowe's the other day. Exited the highway on to one of my favorite off ramps and accelerated....suddenly no power as if it ran out of gas. Coasted to the shoulder. Car would not restart. Checked the fuel pump fuse...not blown. I was not in a good spot so not much more I could do on the side of the road.

Luckily I had switched car insurance to Hagerty two weeks ago and my policy included free towing. ($288/year, 5000 mile/year limit, full coverage, $5000 agreed value - seemed like a good deal).

My wife picked me up and the car was back in the garage later that evening.
I had left the flashers on so the battery was run down.

Charged up the battery and then pulled out the multi-meter. No voltage at either side of the fuel pump fuse.

Pulled the fuel pump relay. Noticed that the plastic at the base of pin 87 was discolored and the pin was loose. Opened up the relay. A small chunk of solder fell out. It was hard to see but it appeared that the soldering failed. Re-soldered pin 87 and reinstalled. Car started right up. I'm not confident in my soldering skills so I bought a new relay and will keep another new spare in the glove box (which I have heard suggested many times).








_________________
1981 Porsche 931
Back to top
View user's profile Send private message
MOTANUL  



Joined: 19 Nov 2018
Posts: 163
Location: ROMANIA BUCHAREST

PostPosted: Fri May 07, 2021 7:54 am    Post subject: Reply with quote

I also had the fuse melted and the blackened contact area between the fuse box and the fuse. The best solution was to put a new modern fuse in place. It has a much larger contact surface and no longer heats up. I also changed the relay because it smell burned. I checked and it wasn't good for 924 turbo.
https://www.conexelectronic.ro/7574-thickbox_default/SUPORT-SIGURANTA-PE-FIR-AUTO.jpg

All the problems were caused by a gas pump that was short-circuited only after about 5 minutes. After this period it melted the wires or the fuse ...

It also melted the wires from the device used to measure the amperage during testing ... A rather expensive professional device. I suggest you check a longer period (for short periods the pump works in the parameters). If, for example, the fuse melts after 10 minutes, it may be necessary to test it also 10 minutes for the defect to manifest.
_________________
1980 Porsche 924 Turbo (931) diamond silver metallic/helios blue metallic
sold Porsche 924 NA 1979
Back to top
View user's profile Send private message
chuck21401  



Joined: 20 Feb 2005
Posts: 375
Location: Annapolis, MD

PostPosted: Wed May 12, 2021 3:55 am    Post subject: Reply with quote

MOTANUL wrote:
I also had the fuse melted and the blackened contact area between the fuse box and the fuse. The best solution was to put a new modern fuse in place. It has a much larger contact surface and no longer heats up. I also changed the relay because it smell burned. I checked and it wasn't good for 924 turbo.
https://www.conexelectronic.ro/7574-thickbox_default/SUPORT-SIGURANTA-PE-FIR-AUTO.jpg

All the problems were caused by a gas pump that was short-circuited only after about 5 minutes. After this period it melted the wires or the fuse ...

It also melted the wires from the device used to measure the amperage during testing ... A rather expensive professional device. I suggest you check a longer period (for short periods the pump works in the parameters). If, for example, the fuse melts after 10 minutes, it may be necessary to test it also 10 minutes for the defect to manifest.


Adding a modern fuse makes sense.

On my car I replaced the fuel pump relay with a new one and it seems to be running fine. The fuse does not seem to be heating up but I'll keep an eye on it.
_________________
1981 Porsche 931
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech. All times are GMT + 10 Hours
Goto page Previous  1, 2, 3
Page 3 of 3

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group