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> D jetronic problems
Edchina
post Mar 25 2013, 01:30 PM
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Hi,
I have been troubleshooting the D jetronic on my 914-4 1975, 2 liter engine.
Bought a fine car, but the previous owners messed the D jetronic system up.
Vacuum hoses were missing, throttle switch was new but not adjusted, fuel lines clogged up and temperature sensors not connected.
Here is what I have done so far:

-Overhauled fuel tank.
-Installed new fuel pump and filter.
-Checked fuel pressure at the regulator (2 bar)
-Changed all vacuum hoses (no leaks)
-Adjusted valves
-Checked trigger contacts (looked like new)
-Checked dwell angle (46 deg.) and breaker points
-Adjusted timing
-Adjusted throttle switch
-Compression test showed 121 Psi on all cylinders
-Installed new pressure sensor after the old one failed during vacuum test (membrane cracked)
-checked electric system with Bosch tester
-checked electric system manually

Problem:

Engine is running rich and the idle is high (around 1200 RPM).
By installing a vacuum gage between pressure Manifold and pressure sensor the vacuum changes (-0.65 ~ -0.5 Bar) rather than being constant. Adjusting the bypass screw at the trottle does not change the idle much. The CO value is around 4% and does not change much when adjusting the potentiometer at the control unit.

My question is what is causing the vacuum to rise and fall causing the RPM's to increase and decrease by 400 RPM.

Thanks
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76-914
post Mar 25 2013, 02:47 PM
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What Curt said (IMG:style_emoticons/default/agree.gif) Also, you bought a new MAP or used MAP sensor? If used or rebuilt check it out. Do you know about this site....... http://members.rennlist.com/pbanders/ One other thing......Didn't see a condenser on your list. That's not the problem, though. Two of the most overlooked vac leaks I see are the AAR and Decel valve. Did you change the rubber hoses on intake runners and the injector seals. Be sure the injectors are seated by hand before tightening that 10mm nut down. Just because that gasket is new doesn't mean it sealed. Hang in there, you'll find it. Lean conditions are quite often the result of a vacuum leak.
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Edchina   D jetronic problems   Mar 25 2013, 01:30 PM
The Cabinetmaker   A hunting idle is caused a lean condition. You mus...   Mar 25 2013, 01:46 PM
Edchina   Yes, the vacuum hose was disconnected from the vac...   Mar 25 2013, 02:42 PM
76-914   What Curt said :agree: Also, you bought a new MAP ...   Mar 25 2013, 02:47 PM
Edchina   -Changed the seals for all injectors -Pressure sen...   Mar 25 2013, 02:55 PM
falconfp2001   -Changed the seals for all injectors -Pressure se...   Mar 25 2013, 05:17 PM
mepstein   -Changed the seals for all injectors -Pressure s...   Mar 25 2013, 05:29 PM
JawjaPorsche   If the intake hoses are 40 years old, they probabl...   Mar 25 2013, 03:20 PM
r_towle   Have you cleaned and tested the Throttle Control S...   Mar 25 2013, 06:04 PM
Edchina   The throttle switch was brand new. Just wasn't...   Mar 25 2013, 06:45 PM
Dave_Darling   High idle == vacuum leak or advanced timing. Most...   Mar 25 2013, 09:27 PM
The Cabinetmaker   Where did you get this new tps? Was it a new unit?...   Mar 26 2013, 04:34 AM
Edchina   Where did you get this new tps? Was it a new unit...   Mar 26 2013, 12:12 PM
76-914   You have a NEW MPS? If so, nice find. If it's ...   Mar 26 2013, 08:49 AM
Edchina   I bought it in Germany at a Volkswagen dealer for ...   Mar 26 2013, 12:07 PM
The Cabinetmaker   Pardon me if I missed it, but has it been adjusted...   Mar 26 2013, 04:16 PM
Edchina   Pardon me if I missed it, but has it been adjuste...   Mar 26 2013, 05:27 PM
The Cabinetmaker   Ok, have you tried unpluggingthe tps? It will actu...   Mar 26 2013, 06:31 PM


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