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> 914 1.7 FI Question, Accel Enrichment injector operation
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post Jun 26 2017, 10:35 AM
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I have a 1.7 with stock injection that fires two injectors when the throttle is opened. (key on, engine not running.)

Are only two triggered or are all four?

If all four, is the TPS likely a problem source?

Where is the best Theory of Operation for this system? The big blue Bosch Book?

FWIW All of the injectors fire (in pairs) when running so the r is not a ECU, harness or injector problem.

The car is pretty lame until it gets up in the
revs.
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914_teener
post Jun 26 2017, 11:27 AM
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The injectors firing in pairs is how it works.

Check out Brad Anders website for information.

You can Goggle his name and 914.
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TheCabinetmaker
post Jun 26 2017, 12:00 PM
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Injectors fire in pairs. All four won't fire with the engine not running. The signal comes from the injector points in the bottom of the distributor.The distributor is turned by a gear the engages with the cam. Cam no turn, points no fire!
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post Jun 29 2017, 09:50 AM
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QUOTE(Retread @ Jun 26 2017, 04:35 PM) *

I have a 1.7 with stock injection that fires two injectors when the throttle is opened. (key on, engine not running.)

Are only two triggered or are all four?

If all four, is the TPS likely a problem source?

Where is the best Theory of Operation for this system? The big blue Bosch Book?

FWIW All of the injectors fire (in pairs) when running so the r is not a ECU, harness or injector problem.

The car is pretty lame until it gets up in the
revs.


I think I was not clear in my original post. While running all four injectors fire in pairs as they should (Tested with Noi light). I was under the impression that a static test of the enrichment function by turning the key on and Actuating the throttle, engine not turning over. I presumed that those trigger signals came from teh TPS to teh ECU and then to the injectors, and it would seem that hitting all lfour might be better balance acceleration.

I have not been able to locate Brad Anders web site.
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TheCabinetmaker
post Jun 29 2017, 10:20 AM
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https://members.rennlist.com/pbanders/DJetParts.htm

Tps stands for throttle position switch. It tells the ecu what position the throttle is in (closed, part load, wide open throttle). Period!

I guess I'm not really understanding just what your question is.
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mgphoto
post Jun 29 2017, 10:31 AM
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With the key on engine stopped there will be 10 pulses from the injectors on depressing the throttle.
Do your injectors fire on different side?
Mike
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post Jun 29 2017, 10:40 AM
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I thought it was like 20 pulses, but I could be wrong. Yes, with ignition on, you could depress the accelerator, or move the throttle by hand in the engine bay, and you should hear a series of "clicks" as you move the throttle. Those are the throttle position sensor blades wiping across the traces on the board.

Brad Anders' site: https://members.rennlist.com/pbanders/
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post Jun 29 2017, 12:11 PM
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QUOTE(Retread @ Jun 29 2017, 08:50 AM) *

QUOTE(Retread @ Jun 26 2017, 04:35 PM) *

I have a 1.7 with stock injection that fires two injectors when the throttle is opened. (key on, engine not running.)

Are only two triggered or are all four?

If all four, is the TPS likely a problem source?

Where is the best Theory of Operation for this system? The big blue Bosch Book?

FWIW All of the injectors fire (in pairs) when running so the r is not a ECU, harness or injector problem.

The car is pretty lame until it gets up in the
revs.


I think I was not clear in my original post. While running all four injectors fire in pairs as they should (Tested with Noi light). I was under the impression that a static test of the enrichment function by turning the key on and Actuating the throttle, engine not turning over. I presumed that those trigger signals came from teh TPS to teh ECU and then to the injectors, and it would seem that hitting all lfour might be better balance acceleration.

I have not been able to locate Brad Anders web site.



You might want to read the article on how the TPS functions. It enriches the mixture not by firing the other two injectors. That is handled by the trigger points. It does mention that if the TPS is worn or misadjusted it will produce symtoms your car is having.

Good luck
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post Jul 3 2017, 07:46 PM
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OK. Test mode: Noid Light. Engine not running. Key on. NOID light triggers on Cyl 2 & 3 when throttle is opened.

Nothing on Cyl 1 & 4.

Read all of Bosch Big Blue and read throgh thru Brad Anders wonderful stuff on Rennlist and his site.

Tried Facebook and Twitter to reach him and got a reply that he would have to go look at the schematics.

I am good on relay logic, JK Flip-flops and low level computer HW stuff like treading through networks of Nand & And gates,
but I never was much at analog stuff.

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post Jul 3 2017, 08:41 PM
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Nothing seems awry from what has been presented so far. The trigger points initiate the pulse cycles to the injectors in pairs, the ECU determines the pulse length (open time) based on signals from the sensors to close the injectors. 1&4, 2&3, opposite cylinders in an X-formation. Your engine (dizzy) position sounds like it is oriented at the 2&3 position currently. So rotate the engine or dizzy (easy to do on the bench) and see if you get pulses for the 1&4 injectors. The center trigger point pole is common, alternating between the outer two poles.
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Spoke
post Jul 3 2017, 09:07 PM
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I didn't think it mattered where the dizzy position is WRT the TPS. I thought that's why there's 2 rows of fingers; one for 1&4 and one for 2&3. Opening the throttle should fire 1-4, then 2-3, then 1-4, then 2-3, etc.
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post Jul 4 2017, 09:00 AM
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Two of the pairs fire behind open valves and two of the pairs fire behind closed valves.
Don't know why, reducing the wiring?
Mike
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post Jul 4 2017, 10:50 AM
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You guys need to do some more reading about the tps. It has nothing to do with the injectors firing. That's controlled by the distributor trigger points! The tps tells the ecu what position the throttle is in. Either closed (for idle mixture), part load (cruise), and wide open throttle (self explanatory). Period! It doesn't matter when the injectors spray. The fuel is setting in the intake waiting for the valve to open.
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post Jul 4 2017, 11:27 AM
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QUOTE(Spoke @ Jul 4 2017, 03:07 AM) *

I didn't think it mattered where the dizzy position is WRT the TPS. I thought that's why there's 2 rows of fingers; one for 1&4 and one for 2&3. Opening the throttle should fire 1-4, then 2-3, then 1-4, then 2-3, etc.


OK! That is what I was seeking!

I must have a dirty TPS. I will try cleaning it (Pain on 1.7), and if that brings no joy, I will replace it!

Can you tell me which fingers are which by connector pins???

And thanks for the answer!
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post Jul 4 2017, 11:37 AM
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QUOTE(mgphoto @ Jun 29 2017, 04:31 PM) *

With the key on engine stopped there will be 10 pulses from the injectors on depressing the throttle.
Do your injectors fire on different side?
Mike


2 & 3. Front L Rear R. One standard pair.

I thought the Enrichment was independent of the trigger points, sent by the ECU sensing some number of throttle opening signals from the TPS.

Nothing Bosch Blue book or Brad Anders stuff seems to describe the cause, just the effect. Reminds me of the old project flow chart step; "and Then A Miracle Occurs".
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post Jul 4 2017, 12:08 PM
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TPS doesn't really measure position, Wide Open Throttle is controled by the MPS.
It will send 10 injector pulses only on opening, switch within the TPS prevents 10 pulses on the close.
Car will run with the TPS unplugged, a bit sluggish.
Idle is most important function TPS turns on the ECU idle circuit.
Later version of D-Jet had WOT switch built in to the TPS, no 914 was ever equipped that way.
Mike
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post Jul 4 2017, 12:33 PM
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QUOTE(Retread @ Jul 4 2017, 10:37 AM) *

QUOTE(mgphoto @ Jun 29 2017, 04:31 PM) *

With the key on engine stopped there will be 10 pulses from the injectors on depressing the throttle.
Do your injectors fire on different side?
Mike


2 & 3. Front L Rear R. One standard pair.

I thought the Enrichment was independent of the trigger points, sent by the ECU sensing some number of throttle opening signals from the TPS.

Nothing Bosch Blue book or Brad Anders stuff seems to describe the cause, just the effect. Reminds me of the old project flow chart step; "and Then A Miracle Occurs".



As has already mentioned and Jeff mentioned again. It is working as designed.

From the site:

TPS
Function: Senses throttle opening (not closing), sending pulse signals to the ECU to richen the mixture for acceleration. Also senses when the throttle is closed at idling, sending a signal to the ECU to provide idle mixture compensation. Also sends a signal at wide-open-throttle, but this signal is not used by the ECU for full-load enrichment, which is handled by the Manifold Pressure Sensor.

What is the mystery? The analogue circuit that makes this happen? I'm not an EE but there is an article on how this is achieved on that site.
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post Jul 4 2017, 12:42 PM
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QUOTE(Retread @ Jul 4 2017, 10:37 AM) *

QUOTE(mgphoto @ Jun 29 2017, 04:31 PM) *

With the key on engine stopped there will be 10 pulses from the injectors on depressing the throttle.
Do your injectors fire on different side?
Mike


2 & 3. Front L Rear R. One standard pair.

I thought the Enrichment was independent of the trigger points, sent by the ECU sensing some number of throttle opening signals from the TPS.

Nothing Bosch Blue book or Brad Anders stuff seems to describe the cause, just the effect. Reminds me of the old project flow chart step; "and Then A Miracle Occurs".



As described from Brad Anders site:

Acceleration: Due to the finite response time of the pressure sensor and the ECU, and the inertia of the air mass in the intake manifold, there is a delay between the opening of the throttle and the response of the system to the need for added fuel. To reduce this response time, a separate acceleration system is required for good engine response. D-Jetronic uses a set of contacts in the throttle position switch to provide both immediate injection pulses and a temporary acceleration enrichment effect when the throttle is opened.
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post Jul 4 2017, 01:32 PM
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A couple of things to keep in mind:

1. From a separate thread you posted I'm not inclined to believe it's TPS. My hunch is more on ignition or timing. You mentioned idle was erratic. Assuming your TPS is calibrated correctly and the throttle body is working correctly, that would suggest a different problem. Admittedly, that may be a big assumption, but TPS wouldn't give you a bad idle if that assumption is correct.

2. You can just try unplugging the TPS and see that specific symptom goes away.

3. D-Jet was not designed specifically for the 914 - it was used on multiple platforms of the timeframe. That means there may be slight differences in how the TPS works on different cars.

4. Brad's site is a fantastic resource, and he's done an amazing job documenting what he's learned. I've relied on his site tremendously. Having said that, it's not gospel. There are other resources to consult, and he's still discovering new things he didn't know about D-Jet. That's not a specific criticism about anything specifically cited here, just an encouragement to find and use multiple resources where possible.
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post Jul 4 2017, 02:00 PM
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QUOTE(mgphoto @ Jul 4 2017, 01:08 PM) *

TPS doesn't really measure position, Wide Open Throttle is controled by the MPS.
It will send 10 injector pulses only on opening, switch within the TPS prevents 10 pulses on the close.
Car will run with the TPS unplugged, a bit sluggish.
Idle is most important function TPS turns on the ECU idle circuit.
Later version of D-Jet had WOT switch built in to the TPS, no 914 was ever equipped that way.
Mike



From brads djet site,
Also sends a signal at wide-open-throttle, but this signal is not used by the ECU for full-load enrichment, which is handled by the Manifold Pressure Sensor.
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