Surging and Unsettled Idel after MPS Rebuild, '74 2.0L D-Jet Options

[914four]

Running down a bucking issue and found my MPS to be leaking. After rebuilding the MPS and verifying a good seal, everything went back together okay. When I started the car, the engine surged up and down and would not idle.

The electrical connector socket on the MPS does not appear to be keyed and using the diagram below from Clay's D-Jet troubleshooting guide it seems I may have plugged in the MPS wire incorrectly. I ohmed the wires from the ECU connector to the MPS socket and made sure the wires are in the order shown in the diagram.

The wires look to be looping back from terminal 7 to 15 and 8 to 10 so that the socket could be plugged in either way and work correctly. Could plugging in the MPS wires incorrectly have damaged the ECU? If not, what should I be looking for that would cause the surging and lack of idle?

[DRPHIL914]

I agree with all the above,
you are running lean- this happens after MPS rebuilds - I have done several and have had issues once they were resealed- did you replace the diaphragm too, or just the o-ring seals? if you replaced the copper diaphragm and did not remove the epoxy around the plug, you will need to do that in order to adjust the inner and outer screws and full load stop to get it with in spec.
also I had 2 mps that were set to what was believed to be factory spec, and once on my car( using a wave-tec LCR meter per Anders site and others) yet both were too lean, so I had to adjust them and I did that by following Brad's instructions and having a A/F meter installed so that I know exactly where the mixture is -
Jeff Bowlsby can check your MPS and set it to the factory specs if you send it to him.

- remember, if you start to play with this when you turn the inner screw, you have to hold the outer one still, and it does not take much, say just a quarter turn can make a big difference.
- adjust the idle screw on the mps and see ifthat helps, make sure you have no vac leaks anywere, - if you cant adjust idle with the ECU adjustment then your TPS is not set correctly. -

Phil

[pbanders]

Jeff Bowlsby can check your MPS and set it to the factory specs if you send it to him.

- remember, if you start to play with this when you turn the inner screw, you have to hold the outer one still, and it does not take much, say just a quarter turn can make a big difference.
- adjust the idle screw on the mps and see ifthat helps, make sure you have no vac leaks anywere, - if you cant adjust idle with the ECU adjustment then your TPS is not set correctly. -

Phil is right, setting an MPS to duplicate the factory spec requires careful adjustment. The inner main mixture screw is particularly sensitive. I came up with using an LCR meter to adjust the MPS because such meters are fairly available, but the more accurate method is to duplicate the D-Jet system on the benchtop and adjust the injection pulse width. I have a EFI Associates tester that lets me do just that, with 0.1 ms sensitivity. To vary an MPS by 0.1 ms requires less than 1/8 of a turn of the main mixture screw.

The ECU idle knob is also quite sensitive. Each click corresponds to a change in CO of about 0.5%. Make any changes 1 click at a time, reset the idle bleed screw to the correct idle rpm, and give it a minute or two to settle before deciding to make any further changes.