D-Jet lean theories |
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D-Jet lean theories |
Morrie |
Jun 30 2019, 01:03 PM
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#1
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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!! |
rjames |
Aug 17 2019, 11:27 PM
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#2
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I'm made of metal Group: Members Posts: 4,111 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest |
Fix any vacuum leaks first.
Then I would adjust the MPS. If you are running lean and all else is good, it likely needs to be adjusted, especially if it wasn’t originally mated with your engine, or your engine isn’t stock. I just went through this myself. |
Morrie |
Sep 30 2019, 04:08 PM
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#3
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Member Group: Members Posts: 181 Joined: 8-October 07 From: Cedar Park, Texas Member No.: 8,198 Region Association: Southwest Region |
I thought I would share an update, and mention the last issue I am seeing. The car is running very well now. I am running a 73 ECU and MPS with a breather box that has the correct (NOS) PCV valve installed and the engine starts and runs well. Timing is set and verified, I am running a 123 Distributor currently.
One ongoing issue throughout all this is the cold idle. The AAR has been tested and opens and closes with temperature. If I plug its intake with a cold engine, the engine stalls so I know it is helping. My cold idle speed, however is still very low, sub 1000 RPMs, in the range of 500-700 RPMs. If I unplug the output side of the AAR that leads to the CSV and allow the hose to go to open air on the line feeding the CSV, the idle comes up as you would expect, around 2000RPMs. The input side of the AAR is plumbed to the air cleaner. When fully warmed, my idle is about 1000RPMs. I sent the MPS off to Chris at Tangerine and he went through it. He verified that the diaphragm was in good condition. He enriched the mixture slightly as is his normal process, and this has made a positive difference. I have not been able to get a bung welded into the header yet for my LM1, though the MPS is now converted by Chris to be externally adjustable. Any thoughts? Is it normal for there to be at least some restriction in the AAR when cold? I have three of them and they all seem to perform the same. |
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