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Posted by: Porsche Rescue Sep 22 2008, 09:35 AM

I'm trying to follow the suggestion of Brad Anders and others on this board. They recommend trying a 270 ohm ballast resistor in the the head temp sensor line as a way to richen the mixture as a fix for a poor cold running engine.

I asked for such a resistor and this is all the Radio Shack guy could provide. I had a choice between 220 ohms and 330 so I took 220. What concerns me is that the word "ballast" is nowhere on the item. Are these what I want or do I need keep looking?

Posted by: dr914@autoatlanta.com Sep 22 2008, 09:57 AM

the 270 ohm is available in factory form, but a 12 v radio shack 270 ohm would suffice placed in line with the head temp sensor. It was used to solve the hot running problems not cold running as the temp sensor at a full 2750 did fine to make the car run well cold. The residual 50 or so ohms the sensor provided hot was not quite enough on some of the high compression 2.0 models to give them the fatness of air to fuel ratio when hot so the factory then suggested and produced the resistor to cure this problem make the idle and whole range better (richer)
I would suggest that if you have a cold running problem the resistor is not the solution

Posted by: Spoke Sep 22 2008, 09:58 AM

If you need a 270 ohm resistor and can only find 220 ohm, you can use 2 resistors in series to achieve 270 like 220 + 47 = 267 ohms.

Posted by: So.Cal.914 Sep 22 2008, 10:12 AM

Posted by: jasons Sep 22 2008, 10:28 AM

FWIW My car had a lean idle hunt when fully warm with the 270. I ended up using a variable resistor to dial out the hunt. 270 wasn't enough, I think I ended up in the mid 300's. Now it idles rock steady when warm.

Posted by: Porsche Rescue Sep 22 2008, 10:40 AM

I have another thread on the board asking advice. My problem is: Car starts hard and requires lots of throttle action to keep it going. It coughs and sputters until it is fully warm (5 minutes or more on the road) and then runs perfectly, good idle, good acceleration, good power.
I replaced head temp sensor (not necessary, but did it anyway). It is correct for ECU according to Anders chart. ECU is correct for '70 1.7. AAR is open cold, closed hot. I did complete resistance check on all circuits from the ECU plug as per Anders and all were on spec. That led me to the resistor as a last resort.
Other ideas welcome and appreciated.

Posted by: So.Cal.914 Sep 22 2008, 10:47 AM

QUOTE(jasons @ Sep 22 2008, 09:28 AM)

Posted by: jasons Sep 22 2008, 10:52 AM

QUOTE(So.Cal.914 @ Sep 22 2008, 09:47 AM)

Useing a potentiometer was a cleaver out of the box solution. Good thinking.

Posted by: r_towle Sep 22 2008, 12:04 PM

go back to radio shack.
Buy a variable rate potentiometer (a trun style volume knob)
0-1k ohms rated.

Drive and turn, gently each time.
Use an ohm meter to test the setting each time you turn it.
Once you are happy, go back to radio shack and buy one or several resistors (like you show above) put them inline to add up to the same value the potentiometer was reading when you were happy.

remove the potentiometer and replace it with the resistors.

Rich

Posted by: davep Sep 22 2008, 12:54 PM

http://www.914world.com/bbs2/index.php?showtopic=84088

Posted by: tod914 Sep 22 2008, 01:03 PM

Please let me know what your low idle solution is. I'm very curious myself.

Posted by: orange914 Sep 23 2008, 01:04 AM

i've got the real deal (fact. 2.0/039 ecu resister) from a 73 2.0.
$20 +whatever shipping is to ya

mike

Posted by: Bleyseng Sep 23 2008, 09:29 AM

QUOTE(Porsche Rescue @ Sep 22 2008, 09:40 AM)

Posted by: mike_the_man Sep 23 2008, 05:35 PM

What about the Cold Start Injector? I can't remember how cold it has to be for the injector to fire, but could that contribute? The more I think about it, the less likely that is. The cold start injector only fires when the starting is cranking, correct? I guess that's not likely it. Sorry for the pointless post!

Posted by: Porsche Rescue Sep 23 2008, 06:04 PM

Hi Mike. You're right, only when cranking and less than 50 degrees I think. Thanks for the help anyway. I will muddle on. I have a back-up ECU which I may try just for kicks.

Posted by: orange914 Sep 23 2008, 10:35 PM

i always thought the resister richened up the full rpm range. from there you could set idle as long as off idle up is good... no???

Posted by: Porsche Rescue Sep 24 2008, 10:14 AM

D-jet guru Brad Anders suggests the resistor as a last resort solution to my type of problem. He agrees with you that it richens the mixture over the entire range. He suggests a switch in the cockpit to delete the resistor from the circuit when the car is warm.

Posted by: Porsche Rescue Sep 30 2008, 10:08 AM

changing the cold mix is a bandaid fix until you find the root cause. Look for a vacuum leak too. Poor manifold gaskets act like this as they seal when the get warmed up.
[/quote]

Thanks Geoff. I have been too busy lately to work on the car, but I am anxious to check the torque on the intake manifolds. This engine has less than 5K on a DIY rebuild by the PO (pretty competent guy I think). I can't find any vacuum leaks in the ususal places.
Is it also possible that the heads could be "loose" as well, self-sealing with expansion when hot?

Posted by: davep Sep 30 2008, 01:27 PM

To answer your original question of "ballast resistor" it is more of an application thing. It is the use of a resistor in a ballast situation. That really does not mean much in this instance. What this resistor does is shift the operation range.
The resistors you have are fine, but I don't think they are suited to the wattage very well. See the photo in the link I provided above of an original resistor. To use what you have, put two in parallel, in series with two more in parallel; thus using four resistors and quadrupling the wattage while keeping the resistance the same. Do the same with some 47 ohm resistors, and add them in series to get very close to the 270 ohm original.