D-jet miss in '73 Volvo B20

I am officially stumped. Dr. D-jet, I can think of no where else to turn.1973 Volvo 1800 ES, 4 cyl B20.. Significant miss (characterized by owner as “bucking”) that occurs between 1800 and 2200 rpm, most notable under even slight load, but does not take place when the TCV (TPS) is disconnected.Background:  ~100,000 miles on original engine. Relatively new 123 4 R-V-IE distributor set to Curve C. Coil of unknown lineage. There was a ceramic ballast in the circuit that I removed. Previous service included removing and cleaning injectors. Bosch 034 ECU that has obviously been out of the car (plastic cover missing, handwritten note from 2011 on case). This is a very long-standing problem. I have done everything to diagnose the problem. Here’s all of it:·        Cleaned TVS (later style) with electronic cleaner and cotton Q tip. Checked electrical connections as per diagnosis scheme. All checked out OK.·        Replaced TVS (later style) with a new, unused TVS purchased from Fuel Injection. Adjusted new TVS to spec, as described in many locations, including throttle stop, settings on graduated scale by using VOM, and idle speed·        Checked TVS adjustment by counting 20 clicks though throttle rotation·        Checked and set fuel pressure regulator to 30 psi (2 bars)·        Adjusted valves to spec. (0.016” = 0.4mm)·        Checked and reset timing to spec.·        Checked for vacuum leaks with sprayed carb/choke cleaner. None found.·        Checked compression: not outstanding but all within a couple psi of each other·        Cleaned all grounds·        Inspected plugs (NGK BP6HS). Sooty inside, but electrodes are clean and tan. See photo.·        Checked all D-jet sensors and connectors. Data:o   MAP – holds vacuum, Pin 7-15: 122.8 ohms (spec = 90), Pin 8-10: 341 ohms (spec  = 350§  Swapped MAP for another unit within specs. No change.o   Coolant temperature sensor - @20oC = 2857 ohms (spec = 2100-8100)o   Air induction sensor = 380 ohms (spec = 260-340 ohms)·        Checked wiring from TPS to ECU connector. All have continuity as they should.·        Swapped out ECU with another unit. No change.There are no other tests that I know of. And yet the problem persists until I disconnect the TVS. If I had not tried a new TVS I sure would believe that was the problem.

Hi Jim and Welcome to the forum,
we like to undersign our postings here with our first name.

Reading your posting I think you really have almost everything done...

The sparkplugs look like they have different adjustment? ... and the third from the left seems to run a little bit leaner. One injector with problems could be the reason for the 'bucking',
I couldn't find they have been checked and cleaned.

Another point is the TVS. The rotor-arm has to turn with some hindering and the contacts at its end are the 'switches' both for the idle as for the acceleration and deceleration.

All contacts have to be clean and should not be treated with fat, oil or contact-spray.

Regards
Norbert

 

All contacts have been cleaned.

Injectors have been cleaned within last 2000 miles. The plugs are so slightly different that I cannot imagine a major injector problem.

TVS function has been replaced with a new one. Yes, new, not used. All electrical tests of the TVS, both old and new, check out.

jim

Hi,

sorry I have just returned from a long day and will answer tomorrow.

Well, I now know more. Given that disconnecting the TVS eliminated the miss, I decided to remove one wire at a time from the TVS. The first one I removed was #9. That appears to go to the acceleration portion of the TVS.

See picture.   
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My friend David Farrington sent me the image of the 034 ECU circuitry. Within the ECU, #9 appears to connect to #17 and go up to the idle mixture compensation circuitry. Of course it goes elsewhere as well and I am not sufficiently adept to know what all of this does. It all looks interconnected to me.

See attached image.   

I drove the car. NO MISS. And I cannot tell that it runs/drives any differently than I would expect.

A USA based fellow who has long experimented with D-jet  suggested that a stronger throttle spring might eliminate any resonance that could cause a loss of connectivity in the TVS circuitry. To me that seems like quite a long shot, but ... I have no clue where I would find a spring that would have more tension than the existing one. I cannot imagine finding a spring like that at the local hardware store, and am supposing that these were made specially for Bosch. Do you know of a source?

I also should note that the injector harness is taped up as shown here. Who knows what is under that tape, but do you believe what I have discovered in disconnecting #9 could be associated with any issue below that tape?

See photo.   
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At this point I am ready to send the car home pending any suggestions that might allow proper running with #9 connected.

jim

Hi Jim,

with such a dirty Throttle switch I would start polishing it incl. dragging contacts on top. Dicing into electronics will not help. That works.