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

FPR "problem" - circuit experts to the rescue!

 
Post new topic   Reply to topic    924Board.org Forum Index -> General Discussions
View previous topic :: View next topic  
Author Message
Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Fri Apr 12, 2019 3:48 am    Post subject: FPR "problem" - circuit experts to the rescue! Reply with quote

Good evening all!

I know, curiosity will be the death of me, one day. I also know, many of you have WAYYY more pressing questions than this. But I can't help it, I'm curious, so here goes.

I bought 2 KAE 3.300.300 fuel pump relays (they were too cheap to just buy one ) a couple of months ago, for spares. My old one was working fine after re-soldering but we all carry spares, don't we.

So. Out of curiosity ( you guessed it ) I decided to try one of the new ones instead of my old, and guess what? For the first time, I heard my fuel pump prime for a second at ignition on. Who-HOOO! Car started at the first turn of the key. Not that it starts hard otherwise, but that was an eye opener.

Strange thing is though, it doesn't always do the priming. Maybe half the time, my guess. I then tried the second new one. It primes, maybe every 10th time. Hmmmm.

Now is there anybody who can explain how triggering the internal NE555 via switched 12V can sometimes work but not always? I spent a few hours at my kitchen table with a multimeter and a 9v power supply and can't get either to prime from the relay contacts although applying power to specific solder points on the circuit board does work. I'm starting getting a headache from staring at the circuit diagram and pissed at these things not doing what I want.

For reference and the diagram, see http://www.924board.org/viewtopic.php?t=10360&highlight=

Anyone here who can help me make these relays prime all the time? And help me get a break from my inquisitive mind ( until the next challenge that is )?

Thanks in advance,

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW
Back to top
View user's profile Send private message
Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Fri Apr 12, 2019 9:15 am    Post subject: Reply with quote

I think it is common for their to be strange electronic symptoms related to the fuel pump pre-priming often having to do with the power mirror switches..

I don't think it is supposed to prime at all, but strange things can make it..
_________________
80 Turbo - Slightly Modified
Back to top
View user's profile Send private message Yahoo Messenger
Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Fri Apr 12, 2019 1:59 pm    Post subject: Reply with quote

I never knew the relay did prime, and had no problem with that. But now I know it CAN I want it to do it . Always.

I simply can't imagine that this circuit works any different from any other - once in good shape, it should operate securely. Just need to know what to do to get it in good shape. I will and I shall not rest until I have an answer.

I just hope someone can help me get there faster with some background info.

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW
Back to top
View user's profile Send private message
Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Fri Apr 12, 2019 7:14 pm    Post subject: The plot thickens... Reply with quote

So. After some more headscratching and copious caffeine and nicotine intake, I have a slightly unsightly modified KAE relay that ( on the bench ) does exactly what I want.

Connect 15 and 31 to a 9v battery, and the relay closes once for the pre-set time of around a second. Apply a pulse to 1, relay closes. Keep applying the pulse at the frequency the ignition coil would ( if connected to the car ), the relay stays closed. Stop pulsing ( mimicking a stopped engine ), relay opens and cuts power from 30 to 87.

Now all I need to do is test it in the car, then go and do some shopping to retrofit all other relays with this mod.

I soldered a capacitor between the 18k resistor and ground to supply the low the trigger input of my NE555 needs to switch the output to high, thereby closing the relay. I used a 4,7 microF one I found in my parts box, seemingly it does the trick

I'm carefully optimistic - and just a bit finicky

I'll let you all know how this proceeds, just in case some of you are also interested in a car that starts at the first turn of the key EVERY TIME. Imagine...

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> General Discussions All times are GMT + 10 Hours
Page 1 of 1

 
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