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914World.com _ 914World Garage _ Cursed Bucking!
Posted by: Gcotton92203 Mar 11 2015, 03:46 PM
Hey, here's a stupid question. Anyone know where I can get a "GOOD" 1973 2.0 throttle positioner. I've developed that cursed bucking just off idle during slow acceleration but the rest of the power band is fine. I've cleaned up the circuit board as best I can and a new board may fix my problem but I'm not sure the contacts are all that great either so I'd just as soon replace the whole relay. Yeah, yeah, I know. put a carb on it. Just trying to stay as original as possible.
Gary
760 702-7251
gary@musicmagic.biz
Posted by: monkeyboy Mar 11 2015, 04:35 PM
Look up the number at Summit Racing. I am pretty sure Bosch still sells these.
Posted by: 914_teener Mar 11 2015, 04:55 PM
Check the alignment of the board "wipers" on the switch.
There is a procedure on the Bird Board and many threads here on it.
Dave Sprinkle is a member vendor and has new boards here.
Also check your fuel pressure and the fuel rail.
Posted by: somd914 Mar 11 2015, 04:56 PM
Take a look here:
http://www.914world.com/bbs2/index.php?showtopic=95583&st=0
I bought one of these kits a few years back - good stuff.
Not sure if he is still around and making them...
Posted by: mepstein Mar 11 2015, 05:25 PM
Take a look here:
http://www.914world.com/bbs2/index.php?showtopic=95583&st=0
I bought one of these kits a few years back - good stuff.
Not sure if he is still around and making them...
I think 914rubber has them
Posted by: warrenoliver Mar 11 2015, 07:44 PM
I got one from BDStone914 - good guy to deal with. 
Changing the board didn't fix my issues completely. Changing out the whole unit helped a lot.
YMMV
Warrenoliver
Posted by: JawjaPorsche Mar 11 2015, 07:51 PM
http://shop.914rubber.com/Porsche-914-Throttle-position-sensor-board-72-73-only-914TPS17.htm
Posted by: davesprinkle Mar 11 2015, 08:18 PM
I've got repair kits for the 2.0liter cars and the late 1.7liter cars. The new boards can help if the problem is caused by worn traces on the board.
However, there are other potential source of trouble -- the wipers can get corroded, there are little directional leaf contacts in the stem of the sensor that can corrode, and let's not forget about aged wiring terminals or broken wires.
So, yeah, a new board can help, but everything else needs to be OK.
A replacement board is only $35. If you need one, send me a PM.
Posted by: Gcotton92203 Mar 11 2015, 08:45 PM
I ordered the board today from 914 rubber. It's the cheapest I found at $48. and I've had good luck with their other products. I would have preferred to change the entire unit just to be sure. I'm sure someone somewhere in the world has a "new old stock" unit but I'm sure I'll never find it. I fully intend to keep this car as it is in great condition, no rust and I have very little money in it. Sooner or later I'm sure I'll switch to carbs but I'll always keep the F.I. parts for the day it's resold.
Posted by: 914_teener Mar 11 2015, 10:13 PM
I ordered the board today from 914 rubber. It's the cheapest I found at $48. and I've had good luck with their other products. I would have preferred to change the entire unit just to be sure. I'm sure someone somewhere in the world has a "new old stock" unit but I'm sure I'll never find it. I fully intend to keep this car as it is in great condition, no rust and I have very little money in it. Sooner or later I'm sure I'll switch to carbs but I'll always keep the F.I. parts for the day it's resold.
Unh hunh.
Posted by: dknechtly Mar 13 2015, 01:50 PM
Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.
Posted by: Gcotton92203 Mar 13 2015, 02:18 PM
Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.
Wow! lots of good info. I just converted to a Pertronix but it still did the same bucking just off idle. I'm pretty sure it's a worn circuit board. I just hoped I could find a new complete replacement but I guess people in Hell want ice water too. I also believe I'll be facing the vapor lock issue as I sometimes hear gurgling in the gas tank when starting warm after several minutes rest. Other than that I have no other issues with the way it runs and intend to keep it injected as long as humanly possible
Posted by: marksteinhilber Mar 13 2015, 02:53 PM
Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.
Wow! lots of good info. I just converted to a Pertronix but it still did the same bucking just off idle. I'm pretty sure it's a worn circuit board. I just hoped I could find a new complete replacement but I guess people in Hell want ice water too. I also believe I'll be facing the vapor lock issue as I sometimes hear gurgling in the gas tank when starting warm after several minutes rest. Other than that I have no other issues with the way it runs and intend to keep it injected as long as humanly possible
Try the suggested repair where you clean the contacts and /or move the finger to run on a new groove!
Posted by: Amphicar770 Mar 13 2015, 05:48 PM
Circuit board from 914 rubber had my 914 purring like a kitten.
Posted by: The Cabinetmaker Mar 13 2015, 05:56 PM
Gently clean up the board with some 2000 grit wet/dry sandpaper then some lacquer thinner or alcohol.
Posted by: Philip W. Mar 13 2015, 10:41 PM
I got one from BDStone914 - good guy to deal with.
Changing the board didn't fix my issues completely. Changing out the whole unit helped a lot.
YMMV
Warrenoliver
This is exactly what I saw too. The very slightly used one i got from bruce
Has worked flawlessly. Absolutely no bucking! Drove it 250 miles this week and didn't happen once.
Posted by: Gcotton92203 Mar 27 2015, 10:50 AM
Replaced the circuit board. Seems better but still bucks. Improved greatly when fully warm. I have a sneaky suspicion there's a loose ground somewhere.
Posted by: PancakePorsche Mar 28 2015, 12:17 AM
Identical to my car a year ago. A NOS TPS did not help.
I went through the distributor by removing breaker plate and precisely setting trigger point opening, set timing, set ECU, and fuel pressure to 34 PSI.
Now has power everywhere, milage 30+ MPG highway, no bucking. Remember modern fuels are at least 10% methanol so you need to increase volume accordingly. Bucking=lean.
Posted by: The Cabinetmaker Mar 28 2015, 08:30 AM
Tps does not typically cause bucking at off idle, but at cruise. 3200-3600rpm. I would look at dwell and timing.
Posted by: Bleyseng Mar 28 2015, 08:59 AM
Identical to my car a year ago. A NOS TPS did not help.
I went through the distributor by removing breaker plate and precisely setting trigger point opening, set timing, set ECU, and fuel pressure to 34 PSI.
Now has power everywhere, milage 30+ MPG highway, no bucking. Remember modern fuels are at least 10% methanol so you need to increase volume accordingly. Bucking=lean.
yes, off idle is usually caused by sticking advance plates in the dizzy. TPS bucking occurs at 3000 rpm.
Posted by: larss Mar 28 2015, 09:06 AM
The wiper contact points also wear out:
http://www.914world.com/bbs2/index.php?act=ST&f=2&t=243291
Lars S
Posted by: Gcotton92203 Mar 28 2015, 09:35 AM
A stroke of luck last night. I was fortunate enough to meet a group of 914 owners who had come to Palm Springs for a cruise event. Within minutes of arriving a couple of F.I. gurus produced a vacuum gauge and determined the source of my problem was a failing diaphragm in the MPS. Not the best news but fixable. I'm pretty sure the diagnosis was correct since the car ran considerably worse after the vacuum stress test. So I'll be on the phone Monday morning in search of a replacement part. Just want to say thanks to all in the group. A real blessing to have all this knowledge in one spot.
Posted by: boxsterfan Mar 28 2015, 02:38 PM
A stroke of luck last night. I was fortunate enough to meet a group of 914 owners who had come to Palm Springs for a cruise event. Within minutes of arriving a couple of F.I. gurus produced a vacuum gauge and determined the source of my problem was a failing diaphragm in the MPS. Not the best news but fixable. I'm pretty sure the diagnosis was correct since the car ran considerably worse after the vacuum stress test. So I'll be on the phone Monday morning in search of a replacement part. Just want to say thanks to all in the group. A real blessing to have all this knowledge in one spot.
I think Tangerine sells MPS rebuild kits.
Posted by: BeatNavy Mar 28 2015, 02:42 PM
I think Tangerine sells MPS rebuild kits.
They do indeed. It's a pretty easy, and gratifying, repair.
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