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!!

[StratPlayer]

Check the plenum for leaks, cracks around the the brass stud supports, Cisco to see if the plenum to half is attached to the bottom half of the plenum with no gaps, if you see gaps see if you can blow air into the gaps. I have the engine set up as you and just went through the same issue’s:

[Morrie]

Check the plenum for leaks, cracks around the the brass stud supports, Cisco to see if the plenum to half is attached to the bottom half of the plenum with no gaps, if you see gaps see if you can blow air into the gaps. I have the engine set up as you and just went through the same issue’s:

I should have mentioned this. I have a small smoke machine that I purchased just for this. I discovered that the system is tight with the exception of the cold start injector which was missing the gaskets and puffing smoke. I sealed that up and checked the system again. I still have a small bit of smoke coming from under the intake plenum which I suspect is a crack or leak as you suggest but I did not chase it as I wanted to go through the rest of the components before tearing the system apart.

Also want to mention I have temp sensor 2 unplugged as with the heat here in texas I think it was doing g more harm than good further leaning the mixture. With that installed I get a lower rougher idle that threatens to stall the motor. I’ve also pulled the decel valve for now just to simplify and remove variables from the equation.

If at any point I pull the plug off the vacuum port for the dec valve while running the idle rises to around 1600 RPMs and holds which
Makes me think that the small vacuum leak I noted with the smoke test is not the culprit of my low idle and max idle mixture. (More air makes it idle faster.)

More info. I decided to tinker with one of the ecu inputs by putting a 1k pot in series with the CHT sensor presumably to trick the ecu into making the mixture richer. I can turn it up and stall the motor similar to turning the ecu idle mixture m ow CW. It seemed counter to what I expected.

All strange but I am committed to figuring it out. I bought a D-Jet car with fuel injection intact as part of the hobby and learning experience. I’m all in.

[914_teener]

Check the plenum for leaks, cracks around the the brass stud supports, Cisco to see if the plenum to half is attached to the bottom half of the plenum with no gaps, if you see gaps see if you can blow air into the gaps. I have the engine set up as you and just went through the same issue’s:

I should have mentioned this. I have a small smoke machine that I purchased just for this. I discovered that the system is tight with the exception of the cold start injector which was missing the gaskets and puffing smoke. I sealed that up and checked the system again. I still have a small bit of smoke coming from under the intake plenum which I suspect is a crack or leak as you suggest but I did not chase it as I wanted to go through the rest of the components before tearing the system apart.

Also want to mention I have temp sensor 2 unplugged as with the heat here in texas I think it was doing g more harm than good further leaning the mixture. With that installed I get a lower rougher idle that threatens to stall the motor. I’ve also pulled the decel valve for now just to simplify and remove variables from the equation.

If at any point I pull the plug off the vacuum port for the dec valve while running the idle rises to around 1600 RPMs and holds which
Makes me think that the small vacuum leak I noted with the smoke test is not the culprit of my low idle and max idle mixture. (More air makes it idle faster.)

More info. I decided to tinker with one of the ecu inputs by putting a 1k pot in series with the CHT sensor presumably to trick the ecu into making the mixture richer. I can turn it up and stall the motor similar to turning the ecu idle mixture m ow CW. It seemed counter to what I expected.

All strange but I am committed to figuring it out. I bought a D-Jet car with fuel injection intact as part of the hobby and learning experience. I’m all in.

Wait........you have what you believe might be a crack in the plenum and it is not going to checked and tested.

This needs to be investgated and checked or you will chase your tail.

[Morrie]

Wait........you have what you believe might be a crack in the plenum and it is not going to checked and tested.

This needs to be investgated and checked or you will chase your tail.

I absolutely do plan to investigate and correct this. The smoke machine was a fantastic investment and showed me that small leak I would have had a hard time locating without it!

I wanted to leave the system intact, investigate everything (I think I am doing pretty good for a rookie!) and then go take it down. Right now the only thing I am tearing down to chase is the leak on the plenum. Everything else seems good so far. Also think I should check injector flow before I take it abart to make sure that’s all good.

[914_teener]

Wait........you have what you believe might be a crack in the plenum and it is not going to checked and tested.

This needs to be investgated and checked or you will chase your tail.

I absolutely do plan to investigate and correct this. The smoke machine was a fantastic investment and showed me that small leak I would have had a hard time locating without it!

I wanted to leave the system intact, investigate everything (I think I am doing pretty good for a rookie!) and then go take it down. Right now the only thing I am tearing down to chase is the leak on the plenum. Everything else seems good so far. Also think I should check injector flow before I take it abart to make sure that’s all good.

I would have them flow checked and bench tested while you are repairing the plenum.

Witchhunter is a good source. That way you know the bodies aren't cracked and leaking or not flowing correctly.

Leaking injectors are not a good thing.

[Morrie]

I would have them flow checked and bench tested while you are repairing the plenum.

Witchhunter is a good source. That way you know the bodies aren't cracked and leaking or not flowing correctly.

Leaking injectors are not a good thing.

That is solid advice. Also replacing all fuel lines and clamps while I am at it. My Wife's Dad passed away Friday so I am away from the project a little bit. I will post when I get to the next step. I am going to at least see if it starts and runs with the other computer before I take it apart. I also need to come up with a list of gaskets and seals for the injection system. Its too warm here in Texas for it to be fun to go drive much in July, so a few hours here and there working on the car in front of the fan getting her ready for fall is good times.