I am working on an injected 72 914 1.7.

Tested with key on, engine not running and only one pair (2 injectors) trigger for acceleration enrichment when the throttle is opened. Is one pair all there is or is it supposed to be all four (BOTH PAIRS) ?

The car is pretty gutless coming off of the line and is doing a bit of lean backfire, even at idle. The injectors are new, all the usual checks (Fuel pressure, timing, etc have been done. Vacuum leak check (Assistant nearby with Halon Botttle ) with WD-40 and starting fluid. No leaks found.

All four injectors trigger(in pairs) in the running mode so it is not a harness issue.

I have replaced a defective leaking decel valve, and I am now considering the TPS, but it is very hard to get to on a 1.7; the Throttle body is horizontal and the TPS is under it. (Yuck!)

And where is the best Theory of Operations that described the acceleration enrichment? I have read all the wonderful PB Anders stuff. And the big blue Bosch book.

The trigger points do not play in this scenario, just the TPS and the ECU.

Anyone know how to reach PB Anders?

I have read through all his wonderful stuff and cannot find the answer in all his work or in the big blue Bosch book. General descriptions are all I find.

This car is driving me crazy!

I believe that the trigger points do in fact interact with the TPS enrichment circuit. I'm not sure which way, if they allow the enrichment pulses or if they disallow it, but I remember reading somewhere that when the engine is stopped you can see only one pair of injectors getting the enrichment pulses.

Brad Anders posts on here occasionally. Hopefully he will see your post and respond.

--DD

Brad would know more than I...from what I have read the TPS sends a signal to the ecu. The ecu through the board .....I think the daughter card modulates the signal to the injector to lengthen the duration or the enrichment. Without an occiliscope it wold be hard to check. I.d try swapping thee ECU....assuming you have the right one and that you have checked your AFM with a wideband meter. Have you?

So, I think you may be over thinking this a bit. If you're not getting a good idle, my thought would be that there's something more fundamental going on, like an ignition problem - which may also explain your performance issue. The TPS isn't going to play into idle with the exception of setting the idle circuit (I can't remember if all TPS/ECU's have that).

Having said that, go ahead and pull the TPS. It's not THAT hard to get to. The best way to understand the theory of operation in this case is to pull it and see how it works. Here's a picture of a 2.0 TPS. The block in red is the circuit that tells the ECU if the car is accelerating or decelerating, which impacts enrichment. Make sure those contacts are working based on which direction the TPS is moving. You can figure out when / how those traces and contacts are supposed to have continuity - and when they are not.

Click to view attachment

Brad was active here a couple of months ago but he's gone "dark" again. Here's another resource that may help:

https://oldtimer.tips/en/d-jetronic

Also, I agree with Dave: my understanding, and I could be wrong, is that you're only going to see one pair of injectors firing with ignition on but engine not turning. The trigger points move off of the distributor cam.

One more thing: you can always just disconnect the TPS connector and see if you notice any performance difference. The car will run, and accelerate, even if not optimally, without the TPS connected.

TPS controls idle circuit, when it's adjusted correctly the "pot" on the ECU will vary enrichment. Misadjusted TPS causes the ECU to determine idle, not optimal.
Idle is a separate circuit within the ECU. Trigger points time injection only.
When the TPS comes off the idle circuit pad MPS takes over.
The tracks within the TPS wear out, replacing the circuit board fixes the problem but the new ones wear even faster. Late model TPS circuit boards are designed without a lip on contacting surface which helps prevent wear.
Really easy to remove the throttle body and check the board.
Mike
ps: there are adjustment procedures for the TPS on the web but some leave out a step, which I don't remember just now. The TPS must track on the idle circuit pad when all is said and done.