D-Jet lean theories |
|
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. |
|
D-Jet lean theories |
Morrie |
Jun 30 2019, 01:03 PM
Post
#1
|
Member Group: Members Posts: 181 Joined: 8-October 07 From: Cedar Park, Texas Member No.: 8,198 Region Association: Southwest Region |
Hi Guys,
When I did a recent tune up on my car's EFI I noticed a few interesting things. Most importantly, the car is running strong, but lean. Here are my observations and findings. Engine is a 1976 2056 running D-Jet and a 123 Distributor. Spark plugs were clean, but a little more white than the golden brown I would like to see. Not severely burnt, no signs of oil consumption. Idle mixture knob on ECU is full CCW to idle. Still surges a little like it is running slightly lean still. AAR tests good. Correct PN. Closes securely within 5 minutes. All new vacuum lines, all lines have clamps. CHT sensor checked. Passes resistance mesurement checks both warm and cold. MPS holds vacuum for 15minutes (Decided that was good enough and terminated test). Checked and adjusted FPR. Now set at 29psi and holds steady. Holds pressure well after shutdown. (check valve) No drop or change in pressure when engine is revved, or during starting. Vacuum line routing checked and re-checked against 1976 requirements. Note that this means that the crankcase is vented to the air cleaner without a PCV valve, unlike the 73 and earlier models. These are the basics of what I have checked. I have not gone aheaad and checked flow on injectors, though it is on my list of open items. Today I pulled the MPS to check the part number. It is the correct part number for a 2.0, but not for a 74-75. Its the proper part for a 73 2.0. Since the 73 2.0 has a different vacuum system, more of a closed circuit with the crankcase, I am theorizing that this sensor is expecting to see higher pressure numbers than the later system, and could be causing it to instruct the computer to operate at more of a lean condition. Any thoughts from those with more experience than I would be great. I am climbing the learning curve here, and am way past clueless and now at the stage where I know enough to be dangerous. Thanks in advance!! |
sholman5 |
Aug 17 2019, 12:24 PM
Post
#2
|
Kraut burner Group: Members Posts: 189 Joined: 11-September 16 From: Ormond beach, Fl. Member No.: 20,391 Region Association: South East States |
|
Morrie |
Aug 17 2019, 12:58 PM
Post
#3
|
Member Group: Members Posts: 181 Joined: 8-October 07 From: Cedar Park, Texas Member No.: 8,198 Region Association: Southwest Region |
Throttle position switch? adjusted and re-checked. Since my original post- Adjusted throttle position sensor after disassembly, inspection, cleaning and testing. Identified the MPS as being for a 1973. Sourced a 1973 ECU to match. Set fuel pressure to spec (was about 3 pounds high) Smoked and corrected air leaks in manifold. New Spark plugs and spark plug wires All new engine compartment fuel lines. cleaned and tightened the EFI harness ground bundle. Cleaned and tested the AAR. I was able to get a few notes from two owners ago about what was done when the engine was built. These are some notes provided to the owner ahead of me when he bought the car, and unfortunately I do not have anything more. Take it for what its worth.... "**** did a special engine rebuild. It's balanced and blue printed motor. Makes a honest 120 h.p. I was going to autocross that car, so I wanted everything that a stock class motor could have. I even had $**** throttle body mods done. It breaths better than stock 2.0, some minor head work, just port matching only. That's all the rules would allow. I traded out $***** worth of work to have ** build that motor. That was back in 1993 or so." 1993 sounds like a long time ago. This car sat and sat and sat. Everything was sticky from sitting, connections, etc... since then I have put about 2000 miles on it and aside from what looks like lean plugs, the car runs fantastic when going down the road is is very quick for a 2.0l car supposedly with stock displacement. |
Lo-Fi Version | Time is now: 17th June 2024 - 12:56 AM |
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 ... |