D-Jet lean theories Options

[Morrie]

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!!

[JeffBowlsby]

I responded to that above. Where does your beach/red wire originate?

[Morrie]

I responded to that above. Where does your beach/red wire originate?

Hi Jeff,

I had some time to trace wiring. The black wire with red stripe you see in the picture is part of the ignition harness. I printed out your 73-76 D-Jet Ignition Harness Diagram and used it for a reference. On my car, the black wire with red stripe originates at the relay board on pin 12, which maps to the AAR, so in this picture the wire is connected incorectly to the thermotime switch.

The white wire you see with the crack in the insulation originates in the FI harness.

I'm a little confused by the wiring diagram for the FI harness of a 75-76 GC engine code. It appears as if in the diagram the thermotime switch goes to both pins 32 and 33. Does this mean that the 18/33 connection on the 4 pin connector of the relay board, the Thermotime switch, and the cold start injector are all connected? It looks like there is a series connection from 31 on the relay board connector to 31 on the cold start valve, then out of the cold start valve on 32 to the thermotime switch which is connected in parallel with pin 33 on the relay board. Do I have that right?

Thanks again for the help!
Morrie