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.   
​
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.   
​
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.

The TVS was replaced with a brand new one. There was no change in the miss after that was done.

Yes, the photo is of the old one, but as I believe I detailed all that has been done within my most recent summary (above).

jim

Hi Jim,

so still problems with new TS and no problems if you omit pin 9 ?

"so still problems with new TS and no problems if you omit pin 9 ?"

That is correct. And I cannot tell any difference in acceleration when #9 IS connected.

Hi Jim,

please remove ECU connector and TS connector and measure resistance of 9 and 20 to ground and all other pins of TS connector.

9 and 20 must act one after the other and then ECU reacts by enriching fuel mixture. I assume that you have an isolation problem or fake impulses on 9 and 20.

Hi Dr. D-jet,

Let me make sure I know what you are suggesting. I am putting your comments in italics.
"please remove ECU connector and TS connector and measure resistance of 9 and 20 to ground and all other pins of TS connector."

Do you mean connect a VOM to the spade connectors of the TS and then to ground to see the resistance?

What should the resistance be?

Or are you asking me to check for continuity between the wires from the TS connector to the ECU connector? I have done that.

"9 and 20 must act one after the other and then ECU reacts by enriching fuel mixture. I assume that you have an isolation problem or fake impulses on 9 and 20."

Removing the ECU connector from the ECU is very difficult because in this particular car I need to remove a good portion of the air conditioning unit because of where everything is located. I can do it but want to make sure I am doing what you are suggesting before I undertake this two-hour process.

jim
P.S. Does the 'notify of reply" work. I check the box but I never get a notification.

 

Hi Jim,

all I want to see is whether there is a break or isolation issue on your engine wiring harness. That could either inhibit or create fake impulses from 9 and 20. You cannot measure that while TS and ECU are connected as ECU has pull up resistors inside. You should also make sure that impulses from 9 / 20 only occur when pressing down gas pedal not while it comes up.

ECU integrates pulses from 9 and 20 only if they come one after the other and then depending of pulse speed enriches fuel mixture. That is why removing 9 or 20 is enough to disable acceleration enrichment. Fake pulses would create false enrichment.

When TS is disconnected you should see less power when accelerating.

Hi Volker,

I have established that there is no break or interruption in the wiring harness between the TS and ECU by disconnecting from both and checking continuity.

It's possible that there is less power when accelerating with the TS or lead #9 disconnected, but it is not all that noticeable. These cars did not have that much torque in the first place!

I am at the end of the fault possibility line. I have now connected and spare, known good ECU and wiring harness to the system and will drive the car this morning. If the miss persists, I am out of things to check or do. Perhaps the owner will want a set of DCOE 45 side drafts.

New addition:  known good ECU and wiring harness makes no difference -- miss persists.

Well, it looks like I have stumped everyone in the worldwide community. I've done every known test (and then some) plus substituted a known good wiring harness and ECU without solving the problem.

On B20E vacuum advance correction is negative. Do you have a vacuum correction on your 123 distributor ? Are you sure C curve is the right one for a B20E ?

 

There is a vacuum connection on the 123, and it's plugged into the induction manifold port where the original Bosch distributor was connected.

I know the system uses vacuum retard, not advance.

Yes, Curve C is the correct one for the B20F (not E).

Hi to All,
I just got knowledge of an OPEL Technical Information from 1974 - maybe regarding the problem.

There are two ground connectors at the D-Jet-engine-harness that have to be connected to the two different screws  of the cold-start-valve.

Once removed the harness or the connectors, they both could be connected to one point.
This could lead to interruptions in normal cruising when the engine is warm.

Sounds quite strange, but Opel would not have published such an information without a reason. We know about other information regarding electrical induction... 

- I would try to connect the ground wires of the injectors to an additive, different ground... -

Regards
Norbert

 

Hi Norbert,

that souns gobbledygook to me. Why shoudl it make a difference if you connect 2 grounding points to both sides of CSV or just one. Contrary: It is always difficult if 2 ground connections are on differen potential. That can create stray currents and bad effects. But a difference between hosuing of CSV left side and right side on purpose is very strange.

Yes,
this sounds absolutely strange.
It is told the TI is from March 13th, 1974.

I have not seen it till now, but this was reported - not by spammers - in 2008.
I contacted the one who is still active today but did not get an answer till now.

Regards
Norbert

Hi,
I now received the Technical Information regarding the engine-bucking


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Regards
Norbert