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:

[Bleyseng]

What ECU do you have? What cam is installed? A 037 mps with a later 74-76 ECU should be running rich...

[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.

[Morrie]

What ECU do you have? What cam is installed? A 037 mps with a later 74-76 ECU should be running rich...

I don’t have information on the details of the build unfortunately. The engine was built 15or more years ago by Ed Mayo for a guy who wanted an autoX can them abandoned this car for a wide body 6. I agree I need to pull the ECU and see what’s in there. I have some family stuff to tend to but will get to it as soon as I can carve out some time again.

Thanks guys for the help. I appreciate it.

[JeffBowlsby]

Don't do anything more until you get the correct 043 MPS that your ECU is expecting. And it needs to be recalibrated for the 2056 demand, not a stock 2.0L. The ECU knob only effects idle at...idle. It has no effect off idle because the switch in the TPS deactivates the knob off idle.

Biasing the TS1 only plays with the mixture until it engine is warm, after that, no effect. Unplugging TS1 causes A/F to go full rich. Will car start with TS1 unplugged? It should not.

[Dave_Darling]

Jeff, I think you have switched TS1 and TS2. TS1 is the intake air temp sensor; its effect on mixture is relatively small. TS2 is the head temp sensor and it will kill the engine if you unplug it.

If the FI is set up for the stock 1971cc and you're running 2056cc, you might want to see if a little more fuel pressure helps or hurts. The stock pressure regulator is adjustable, so you can try 1-2 PSI higher to check if that helps or not.

--DD

[JeffBowlsby]

You are right Dave...I had them mixed up. I forget more than I ever knew...

[Morrie]

Don't do anything more until you get the correct 043 MPS that your ECU is expecting.

I agree but first I need to figure out what ECU I have. The PN label is long gone from the top of the unit. When I pull the connector there is a sticker inside that says "XXC 326" Any advice here? I have another ECU here, an 0 280 000 037 for a 72-73 1.7L that has the label still, so at least I know what I am looking for.

And it needs to be recalibrated for the 2056 demand, not a stock 2.0L. The ECU knob only effects idle at...idle. It has no effect off idle because the switch in the TPS deactivates the knob off idle.

This I understand fully. I had read in a comment on one of these BBS that the internals of the MPS are essentially the same and you could send one off and get it rebuilt and set up for whatever engine you like. Some differences in setup (a spacer IIRC) and of course tuning. I have a MPS for a 1.7 here (and most of the rest of the EFI for a 1.7 also) and was thinking of sending that one off and getting it set up for my engine.

Biasing the TS1 only plays with the mixture until it engine is warm, after that, no effect. Unplugging TS1 causes A/F to go full rich. Will car start with TS1 unplugged? It should not.

To avoid confusion here, lets just refer to them as the CHT sensor and ambient air sensor. The ambient air sensor is the one I have unplugged. It definitely does have an impact when I plug it in; the idle drops and the car stumbles on overrun. What I was experimenting with was the CHT sensor. My understanding is that since it is a NTC sensor, the higher cold resistance equates to a richer mixture for cold starts. As the head warms up, the sensor resistance drops, and the ECU then leans out the mixture. I installed a 1k rheostat in series with the CHT sensor and found that the car does seem to run marginally better at idle with a slight increase in resistance, maybe 200 ohms additional. This also seemed to allow me to back off on the idle mixture screw slightly. Since the CHT sensor remains active at all times, I had thought that adding a small amount of additional resistance here would cause the car to run less lean and possible help offset my problem. You are correct though, if you open up the CHT sensor, that is unplug it, the car should not and does not start.

[Morrie]

If the FI is set up for the stock 1971cc and you're running 2056cc, you might want to see if a little more fuel pressure helps or hurts. The stock pressure regulator is adjustable, so you can try 1-2 PSI higher to check if that helps or not.

--DD

Hi Dave, I checked the fuel pressure, and it was just a shade over 30psi. I did drop it slightly to 29psi, and yes, you are correct, the bypass regulator is pretty easy to access and change. I am afraid of overpowering the system with too much fuel pressure, but the thought of experimenting up to a maximum of 35psi just to see if that made a difference did cross my mind. Anyway, for now it is set and stable just a needle width under 30psi.

[Bleyseng]

The 037 ECU is for both the 1.7 and 2.0l in 1973. I would install to go with that 037 MPs. You will need to install 270 resistor on the cht for the idle to run right

[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.

[ChrisFoley]

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

(IMG:style_emoticons/default/agree.gif)

Cracked plenums can have a big effect on idle performance, when manifold vacuum is high and total air load is small.

[Morrie]

The 037 ECU is for both the 1.7 and 2.0l in 1973. I would install to go with that 037 MPs. You will need to install 270 resistor on the cht for the idle to run right

That’s an interesting angle! I wonder if I would need to close the system with a Pav valve on the crankcase vent with a PCV valve? Definitely worth a try! Thank you!!

[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.

[Highland]

Just FYI when Mr. Injector refurbished my injectors they came back with new seals; so now I have a spare set of seals.

If I had known this I would not have bought a set of injector seals.

[Morrie]

Hi Guys,

I had to go out of town for a week but while I am away I wanted to give a bit of an update.

Airbox Leak/ Smoke Test Failure: I disassembled the system and pulled the air box. after sealing it up and testing it independent of the system I now believe that the leak was not in the box itself but rather at the connection to the intake runner boots. The boots are soft and pliable and appeared to be snug. I decided to try using hose clamps for now as an experiment and smoke it again. If this solves the problem then I will install a new set of intake boots.

I do have a question on wiring I am hoping you guys can help me with. I want to mention that I did thoroughly inspect and clean all the EFI grounds and made sure they are properly attached. Chassis grounds are next. On the wiring that goes to the AAR and Thermotime switch. I see a small gauge white wire coming off the EFI harness and a larger gauge black wire with a red stripe coming off what I will call the engine harness. I don't trust anything from the previous owner so I am asking if someone can help me out with some direction. In looking at Jeff's diagrams it appears as if the TTS is the small white wire coming off of the D-Jet Harness and the AAR is the larger black wire that comes off the engine harness. Does that sound right?

Thanks guys....

[JeffBowlsby]

the TTS is the small white wire coming off of the D-Jet Harness YES

the AAR is the larger black wire that comes off the engine harness. Does that sound right? NO

Thanks guys....

Black/Red on the IGNITION harness goes to the coil. As does the Black/Purple.

White wire with a box connector goes to the AAR. Wire on the AAR is red.