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!!

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:

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

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.

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.

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.

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

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

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.



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.



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.

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.

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

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.

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

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!!

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.

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.

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....

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.

Thank you Jeff for the advice, and for your patience while I try and sort this all out. I am out of town but I did find a picture I took before starting to sort all the wiring. You can see the black/red wire that is connected to what I believe is the thermotime switch. On the right side of the picture you see a tattered white wire (I will address that) attached to the AAR wire. Advice appreciated as I sort this all out.

Click to view attachment

I keep hearing about cracked plenums. It is rarely the answer. Be honest, has repairing a cracked plenum really solved your problems? It's almost always something else. Throw some tape over your supposed cracks and report back. It's always something else.

I am afraid my question about the wiring got covered up by the semi-useful comment about the plenum. I will say that there was a small leak around the welded on fitting for one of the runners on mine. I cleaned it up while it was off and ran a bead of JB Weld around it for security and confidence.

Anyhow... any help for the wiring question above would be appreciated now. Appreciate comments on the connections... primarily the wire I show going to the thermotime switch. If not that wire, then which one? thanks!!

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

Throttle position switch?
Click to view attachment

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.

Hey Morrie:

I have seen only one other 73-76 Ignition harness with that black/red AAR valve wire, most typically they are white. So I think you solved that mystery.

Cnfimring, the relay board, the thermotime switch, and the cold start injector are all connected for the 75-76 cars only. It is as you say.

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.

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.

What rpms does it idle at when warm?
Timing set correctly?
Did you calibrate your mps yet?

Sounds like the AAR isn’t opening enough or... is it connected correctly l? The opening facing the passenger side should be connected to the air cleaner box.

I think the last two posts are discussing the aux air regulator (air), not the cold start valve (fuel)

Dbl post, sorry.

That's what I get for writing rapidly at the end of the day. Apologies for the brain fog and lack of clarity. I edited my post, but you are right Jeff, I meant AAR, not CSV.

I updated my post above with corrections and some more info. I have verified the CSV is hooked up correctly, timing is correct, but I have not calibrated the MPS yet. I know that is a key part of the puzzle but still seems odd that the additional air from the CSV isnt sufficient where just opening the line is. I've verified the CSV (not AAR) isn't leaking fuel, but have not verified if it is injecting fuel or not. I should pull the plug on it right after starting and see if there is a negative effect.....

I meant the AAR too. I corrected my previous post (which still applies - you may have an AAR that isn’t opening, or it’s hooked up backwards (unlikely).

As I read it you are now running the 73 2.0L Djet setup with 037 ECU and 037MPS? What about the CHT as it needs to be the 017 73 2.0L only one with 280 ohm resistor for it to idle right.

My suggestion is to make an additional smaller adjustment in the same direction I made the first one. I backed the center screw out one full turn. Go another quarter turn and see if the engine seems to like it.

Hey Chris,

Thanks again for checking out the MPS and making it externally adjustable for me. There was an immediate improvement in how the engine runs, as you suspected. I'll give it another quarter turn and report back. Thanks again!

Shine a light through it in a darkened room. They also develop pinhole rust through.

Smoke tested and no leaks. I think I am good there. (after replacement of all vacuum hoses and sealing a couple small leaks at fittings.)

The further adjustment made the engine come to life. My idle bypass screw now works as it should, my idle mixture screw on the ECU is now close to center. Next is to do some fine tuning with the LM1 and see where I end up.