Bypassing the knock box . . .

[S2_ITBVW]

Hi folks . . .

As many of you know we run a MkII 86ish Jetta GLI. We are currently trying to figure out how to bypass the knock box. So, in theory we believe that we are trying to take the wire that sends the signal from the hall sender to the knock box control and jumper that to the wire (green/white) that runs from the knock box control to the ignition control unit. We thought this should be the red/black wire running into pin position 15, but that did not work. In fact, none of the wires from the hall sender work!!

Also, what voltage do we want running to the ignition control unit after we bypass the knock sensor?

What the heck are we going wrong?

As always, thanks!

DE

[Flyinglizard]

Do you have my Book? the non box wiring is in there.
MM

[shwah]

Do you have the Bentley service manual? The no knock box wiring is in there. Look at the engine wiring diagrams for the 1985 CIS-E cars with no knock sensor, duplicate that.

[S2_ITBVW]

Still not there . . .

We used the Bentley diagram on page 79 for 1985-1987 Jetta (except GLI) to bypass the knock sensor control unit by wiring directly from the hall sender to the ignition control unit. The knock sensor is completely disconnected. In addition, we have unplugged the oxygen sensor to put fuel enrichment entirely under our control.

We have good spark, and the car starts immediately. However, as soon as the car burns off the fuel provided by the cold start injector it dies. We have a constant 8V current running to the differential pressure regulator. That current does not seem to change. We have 5 bars of fuel pressure going into the fuel distributor. The fuel system is fine and was not an issue before we started this process. The car is simply not delivering any fuel. We feel like we have messed up the control of the fuel distributor somehow. Any ideas on how to diagnose/solve this problem?

As always, thanks!

Dave

[shwah]

The timing will be wayyyy off initially. The knock box retards the timing a lot all the time. Get it running, get a light on it and dial it in.

[GTIspirit]

In addition, we have unplugged the oxygen sensor to put fuel enrichment entirely under our control.

We have good spark, and the car starts immediately. However, as soon as the car burns off the fuel provided by the cold start injector it dies. We have a constant 8V current running to the differential pressure regulator. That current does not seem to change. We have 5 bars of fuel pressure going into the fuel distributor. The fuel system is fine and was not an issue before we started this process. The car is simply not delivering any fuel. We feel like we have messed up the control of the fuel distributor somehow. Any ideas on how to diagnose/solve this problem?

The O2 sensor is only used for closed loop control, which occurs at less than full throttle, as determined by the full throttle switch. I'm assuming you're not pressing the gas pedal after start, so the idle switch will be engaged and fueling is determined by the closed loop control. Without the O2 sensor plugged in it goes into a kind of default mode. I forget the exact number, it should be about 10mA or so.

I hope you don't have 8V going across the DPR! Max on the DPR current is around 150mA, and since it's about an 18Ohm actuator that translates to 2.7V differential. Under normal circumstances the KE-Jetronic should be running around 8 to 15mA under WOT, depending on RPM. (At least this is what my stock 1.8L KE-Jetronic box does.) Remember that the DPR is only a fuel trim, the flapper valve to distributor plunger is the main fueling control. But the flapper valve doesn't know RPM, only airflow, hence needing some RPM dependent control from the KE-Jetronic box.

Maybe you disturbed another connector, such as the coolant temperature sensor, which has a huge effect on DPR current for warmup enrichment.

Oh, there is one other possibility. Pin 25 on the KE-Jetronic is the RPM signal from the knock box. It is absolutely necessary to have this RPM signal input to the KE-Jetronic. If for example you had negative current at the DPR valve that would be because the KE-Jetronic thinks the RPM is too high and the fuel cut rev limiter is invoked. Or it does the same thing in case of overrun fuel cutoff, meaning idle switch is tripped and RPM is above a certain range. For reference, pin 12 from the KE-Jetronic is DPR high side, pin 10 is DPR low side. You should definitely check to make sure you don't have negative DPR current (it would be around -66mA), that would cause exactly the problem you describe.

[Flyinglizard]

Unplug the knock box the vac line. The vac line makes way too much advance.
This car will run best with a vac advance distibuter, with no vac connected. If the knock boxvac line is unplugged, you hould have no advance. If you use a standard older vac adavnce dist, you should set the idle reading at about 12* and this should come out to about 31 or 32 at 4000.

What is the test fuel pressure? Should be 70or more running, 40 or so at rest for 20min.
Balance the injectors per my book( Thank you). Set the basic mixture setting at just a drip, minus 1/8 turn, with the pump running .
You should have a stand alone fuel pump switch.
You can get it running with the control pressure box unplugged also, it will take about 1 turn lean but run very well once set . You may need to trim it evey day at the track tho. I have run ours both ways.
Lower control pressure makes a touch more power, if you get the fuel mixture close.

It is very possible that you have disconnected the RPm signel to the fuel pump relay, if you still have one.
It is also possible that you have only one fuel pump running. Both are on the same wire BTW. Unplug the upper pump and listen for the in tank pump.
If the fuel output is low, look inside the tank and dont be afraid to pull it out and wash it with hot soapy water. Clean the strainer and all of the crud, etc. .
MM

[GTIspirit]

Unplug the knock box the vac line. The vac line makes way too much advance......

Interesting comment about too much spark advance from the knock box.

I expect the stock spark advance table would look something like this:

The source for this table is page 41 of the Volkswagen SSP068 describing the spark map for the 16V knock box, aka, Vollelektronische Zuendung (VEZ).

What's the consensus, too much spark advance under full load?

[S2_ITBVW]

Thanks a bunch for the help and the fantastic information.

We are backing-up and starting the process again. I'll let you know . . .

[Flyinglizard]

The vac line/knock box is designed around the street requirements. You can see 45 * of advance is a lift throttle stiuation. Not good. IMHo
Running a straight curve that does not waver seems like the best way. The knock box can work if the sensor is good, but I have never liked the vac curve overlaid into it. ( for racing)
I try for a steady timing light, and that so far has been with no vac, no knock, set at 29-31* total(8V), (measured at 4000 or over with out any more advance/movement.) YMMV.
PS the car may not run if the water temp snsor is faulty.
MM

[S2_ITBVW]

We have successfully bypassed the knock box and the O2 sensor. I can get particulars if any of you want it, but "in general" we are wired directly from the hall sender to the ignition control module. The mistake we made was in not powering the knock box control at all. It still needs power because it, in turn, sends power to an idle control. We missed this in the 1985 CIS-E schematic.

Also, the timing was indeed WAAAAY off.

So, for the moment we "almost" feel like we know what we are doing.

Thanks very much for the excellent information. We feel like we could write a book on this stu . . . wait, Mike already did that!!

DE

[S2_ITBVW]

Took the car out on the road (I live in the country and the neighbors think it's fun when I drive by) and it is a different machine. The air/fuel is under our control for the first time. It's easy to adjust and it is amazingly stable as compared to before. Now, hopefully, we'll see some horsepower gains . . .

We head to the dyno on Monday to see if we are making progress.

Thanks again for the help.

DE

[Flyinglizard]

Try the AFR @ 12.5 and up to 12.8 to one and see how much it changes. We have found 12.5/1, to keep the valves in a lot longer while giving up very Little.
Also try the timing @ 28, 30, 31-32 and report back here if you would. Ihave found hardly any power change from 28 to 30. A little drop at 32 or over. But please tell us what you find. TIA,MM

[shwah]

Great to hear the progress Dave. Good luck at the dyno. Mike's recommendations above are what we found to be good too.

Mike - I had a motor that liked 29, and another that liked 32. I have not been able to unravel why.

[S2_ITBVW]

Hit the dyno last night and we are very pleased with the results. We were not able to do any "fine tuning" as our dyno time last night was actually free and done in front of an auto tech class at the local community college. We had the differential pressure regulator adjusted 1/2 turn clockwise (just left it there, will test the adjustment on that later). We started out by setting the A/F and got it stable at 12.5 to 1. Didn't get to check HP with the A/F at different levels because we wanted to see, in general, what the fuel enrichment module would do. When we turned it on the A/F went to 11.5 to 1 and did not seem to want to respond to adjustment. So, we feel like any HP improvement with the enrichment module might have been offset by the fact that the A/F mix was too rich. We started out with timing at 29 and got 2 more HP when when went to 30. But that's all the adjustment we did on that. So, lot's more testing to do. We feel confident that we know where to get another 10-15 HP. If we can get that, with the new locked tranny, with the new 13" wheels, we just might have some fun . . .

Does anyone have any experience with Autotech fuel enrichment module?

What a relief to be heading in the right direction!

[pfcs]

Interesting comment about too much spark advance from the knock box.

I expect the stock spark advance table would look something like this:

The source for this table is page 41 of the Volkswagen SSP068 describing the spark map for the 16V knock box, aka, Vollelektronische Zuendung (VEZ).

What's the consensus, too much spark advance under full load?

.......Not if the right column represents full load, although the numbers are weird-absolute pressure in the manifold @WOT will be near atmospheric, i.e: 1,000mBar, not 101. Were there more columns with higher pressures? The data suggests that the right side info is from more & more throttle.


In order to control ~45* timing advance, the unit needs to look at ~60* and retard it's control signal appropriately to generate the needed range of timings. (Digi II also). So if you bypass the knock box or the ignition function in
digifant, your static timing is becomes 60* + whatever your basic timing had been.
I would recommend using one of the later distributors w/no mechanical or vacuum advance. (they have skinny shafts w/o a felt to a screw head in the top) This will take away a good deal of scatter. Just set it straight up, 30-33*

[shwah]

I do not use the vacuum advance distributor. I like the simplicity of no adjustments other than the ones I make. Of course now I am using a new ECU to make those adjustments, but they will be more predictable than what the stock knock box was doing.

[Flyinglizard]

I cant get my cars started with a fixed 31*
I need about 8* of dist twist to get them fired back up, hot.

[shwah]

I cant get my cars started with a fixed 31*
I need about 8* of dist twist to get them fired back up, hot.

Strange. I have never once had a startup issue - hot or cold.