Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> Required Voltage to Coil
Ansbacher
post Apr 5 2018, 06:20 PM
Post #1


Senior Member
***

Group: Members
Posts: 689
Joined: 4-July 14
From: Tampa Bay, Florida
Member No.: 17,589
For the last month or so my '74 2.0L (carbureted) has been getting progressively harder to start, especially when sitting after running. Today it finally will not start hot or cold. I ruled out the carbs and fuel supply. I also replaced the battery when this problem arose. I am measuring 12.54 volts on the battery (static) but am only getting 11.54 volts at the +terminal of the coil with ignition on. Should that be enough to start the car? In addition, as this problem got worse, the engine running just got worse and worse, misfiring, and erratic idle. Any ideas?

Ansbacher
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
 
 Reply to this topicStart new topic
Replies(1 - 13)
iankarr
post Apr 5 2018, 06:40 PM
Post #2


The wrencher formerly known as Cuddy_K
****

Group: Members
Posts: 2,473
Joined: 22-May 15
From: Heber City, UT
Member No.: 18,749
Region Association: Intermountain Region
First I’d check the grounds (behind battery, under relay panel, transsmission ground strap). The slow deterioration sounds like a loose ground that’s getting looser or more corroded over time...
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Dave_Darling
post Apr 6 2018, 12:09 AM
Post #3


914 Idiot
**********

Group: Members
Posts: 14,986
Joined: 9-January 03
From: Silicon Valley / Kailua-Kona
Member No.: 121
Region Association: Northern California
The coil needs less than 10V to work. It may even work with much lower voltage than that! You may wind up with lousy high-RPM running if the voltage drops low enough, but I think that would be quite low indeed!

My injected car ran with a non-functioning alternator until the center console voltmeter dropped below 9V. Not sure how much that was at the coil, but I figure that 9V was about when the injection gave up. I think it might have run quite a bit longer with carbs!

--DD
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
falcor75
post Apr 6 2018, 12:17 AM
Post #4


Senior Member
***

Group: Members
Posts: 1,579
Joined: 22-November 12
From: Sweden
Member No.: 15,176
Region Association: Scandinavia
There's no real load on the battery with just the ignition on, monitor the voltage when cranking and see if it goes much lower than the static reading.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Spoke
post Apr 6 2018, 09:29 AM
Post #5


Jerry
*****

Group: Members
Posts: 6,978
Joined: 29-October 04
From: Allentown, PA
Member No.: 3,031
Region Association: None
QUOTE(falcor75 @ Apr 6 2018, 02:17 AM) *

There's no real load on the battery with just the ignition on, monitor the voltage when cranking and see if it goes much lower than the static reading.


(IMG:style_emoticons/default/agree.gif)

Also you may read a low voltage if the coil is being energized when doing a static (engine not cranking or running) test. Coil current may be very high (much higher than when running) for a static test resulting in a larger voltage drop than seen when the engine is running or cranking.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Ansbacher
post Apr 6 2018, 02:07 PM
Post #6


Senior Member
***

Group: Members
Posts: 689
Joined: 4-July 14
From: Tampa Bay, Florida
Member No.: 17,589
OK, I got 9.5 Volts at the coil + terminal when cranking. I tried a different coil and a different condenser- still no start, just cranks. Points had just been cleaned and adjusted to a good dwell (checked when the engine was still limping). Definitely getting fuel. I cleaned the ground strap connection underneath the rear trunk, but I cannot get a wrench to the bolt that holds the other end of the ground strap to the rear of the transmission. Am I going to have to remove the muffler to get to it or is there a trick somebody knows? It does look a bit corroded and I want to clean it up. HEEELLLPP!

Ansbacher
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
falcor75
post Apr 6 2018, 02:21 PM
Post #7


Senior Member
***

Group: Members
Posts: 1,579
Joined: 22-November 12
From: Sweden
Member No.: 15,176
Region Association: Scandinavia
Could be a dead cell in the battery, if you have a pair of jumper leads try connecting them to another battery and try cranking again.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Ansbacher
post Apr 6 2018, 04:24 PM
Post #8


Senior Member
***

Group: Members
Posts: 689
Joined: 4-July 14
From: Tampa Bay, Florida
Member No.: 17,589
OK, tried to jump start the car. Would not start, just cranked. Also cleaned the ground connection above the fuse panel. Cranked a bit better but would not start. Pulled a plug to watch the spark- it is definitely weak, a reddish purple, NOT bluish white like it should be.

Ansbacher
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
jcd914
post Apr 6 2018, 04:29 PM
Post #9


Advanced Member
****

Group: Members
Posts: 2,081
Joined: 7-February 08
From: Sacramento, CA
Member No.: 8,684
Region Association: Northern California
Check your points and the ground wire on the advance plate in the distributor.

Jim
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Dave_Darling
post Apr 6 2018, 05:48 PM
Post #10


914 Idiot
**********

Group: Members
Posts: 14,986
Joined: 9-January 03
From: Silicon Valley / Kailua-Kona
Member No.: 121
Region Association: Northern California
Do you know that you are not getting spark? Tape a spare spark plug to a ground, plug a spark plug wire into it, and have someone crank the starter while you watch the plug. Sparks will be obvious if they are happening.

--DD
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Ansbacher
post Apr 6 2018, 06:15 PM
Post #11


Senior Member
***

Group: Members
Posts: 689
Joined: 4-July 14
From: Tampa Bay, Florida
Member No.: 17,589
QUOTE(Dave_Darling @ Apr 6 2018, 07:48 PM) *

Do you know that you are not getting spark? Tape a spare spark plug to a ground, plug a spark plug wire into it, and have someone crank the starter while you watch the plug. Sparks will be obvious if they are happening.

--DD


Dave, Reference two responses up (the one from me). Yes, I am getting a very weak spark. I also tried some different timing positions of the distributor, advanced and retarded. Still wont fire. Guess it is not enough to ignite the fuel.


Ansbacher
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Ansbacher
post Apr 7 2018, 01:48 PM
Post #12


Senior Member
***

Group: Members
Posts: 689
Joined: 4-July 14
From: Tampa Bay, Florida
Member No.: 17,589
Well, I got it running. Hard to believe, but it was plugs! Pulled out the NGKs (which looked perfectly fine) and replaced them with my used standby set of Bosch. Fired right up. What I noticed is that all of the little nipple adaptors that screw on to the threaded top of the plugs were loose as a goose on the NGKs. They would not tighten up. They went on nice and tight on the Bosch. I have to use them with the plug wires I have in order for them to snap on properly. Not sure how this happened, as things were fine when I first installed the NGKs. Anyone else run into this sort of thing?

Anyway, thanks everyone for their help on this problem.

Ansbacher
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
rudedude
post Apr 7 2018, 02:02 PM
Post #13


Senior Member
***

Group: Members
Posts: 509
Joined: 1-January 05
From: minneapolis, mn
Member No.: 3,387
Region Association: Upper MidWest
My honda v6 outboard motor has a slight intermittent miss and then all of a sudden wouldn't run. Turned out all 6 ngk quit at the same time. Way cheaper than the ecu I thought I was going to need
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
IronHillRestorations
post Apr 7 2018, 09:03 PM
Post #14


I. I. R. C.
*****

Group: Members
Posts: 6,719
Joined: 18-March 03
From: West TN
Member No.: 439
Region Association: None
How old are the points and condenser?
User is online!Profile CardPM
Go to the top of the page
+Quote Post
« Next Oldest · 914World Garage · Next Newest »
 

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 

Display Mode: Switch to: Standard · Linear+ · Switch to: Outline

Track this topic · Email this topic · Print this topic · Subscribe to this forum

- Lo-Fi Version Time is now: 18th May 2024 - 06:01 AM
Invision Power Board v9.1.4 © 2024  IPS, Inc.
All rights reserved 914World.com © since 2002
914World.com is the fastest growing online 914 community!
We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ...