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!! |
JeffBowlsby |
Jun 30 2019, 05:22 PM
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#2
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914 Wiring Harnesses Group: Members Posts: 8,663 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None |
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. |
Morrie |
Jun 30 2019, 09:47 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 |
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. QUOTE 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. QUOTE 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. |
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