1800: P1800ES fuel injection

[VolvoRoyS]

Originally Posted by c1800

Here’s a pic of the TPS, As shown in the wiring diagram and the picture below, the 4 numbered leads on the TPS, from top to bottom are:

17, 14, 20, 9.

Edit, picture somehow loaded turned 90* to the right, the right side of the picture is the top.

Thanks. I think my wiring is correct on that basis, although I can't see any numbers on the switch where the white plug enters; on my car I have 9, 20, 14,17 written top to bottom which made me think something was wrong. On reflection it seems unlikely that a previous owner would have meddled but you never know!

[142 Guy]

Originally Posted by VolvoRoyS

I'm also trying to work what new plugs and boots to order from that D-jet site you suggested as I would like to re-instate the wiring to the cold start valve, replacing the thermo timer with a switch that completes the circuit. I can find 3 white wires that have been messed with that might have originally led to the TTS, one of which is earthed; is this likely to be it?

Unfortunately I cannot advise on the later D jet cold start arrangement. My
D jet was 1971 vintage and the cold start valve was controlled by the ECU rather than by the thermal timer on the later D jet systems.

[Laird Scooby]

Originally Posted by VolvoRoyS

Once again many thanks for a prompt reply. The diagram seems pretty clear, so it is wired correctly. I have yet to check out the operation of the TPS. Although the engine idles quite well now it has poor response to the accelerator making it prone to stalling. I'm hoping I can fix that with attention to the TPS.
I'm also trying to work what new plugs and boots to order from that D-jet site you suggested as I would like to re-instate the wiring to the cold start valve, replacing the thermo timer with a switch that completes the circuit. I can find 3 white wires that have been messed with that might have originally led to the TTS, one of which is earthed; is this likely to be it?

I'm going from memory now and it's a long time since i learned this bit and never really had to use it so don't take it as gospel, more of a guide to what's probably meant to happen.

One of those white wires will become live with ignition on. This is your +12V feed to the TTS. This feeds the switch itself inside and the small heater inside the TTS and the heater earths out through the earth wire.
As the heater warms up, it moves the bi-metallic strip disconnecting the output contact after ~8S usually but depends on ambient temperature and engine temperature as well.

The output wire (the other white one) goes to the cold start valve to energise it so extra fuel is injected for the first 8 seconds or so on a cold engine.

There is something in the back of my mind that says the white feed wire is only powered during cranking, from an extra terminal on the starter that is only fed while the starter is engaged.

With that in mind, use your multimeter to determine when the white feed wire actually has +12V on it (with ignition or only during cranking) and then use your resistance setting on the meter to check which contact the white wires go to that has a continuity of a few Ohms to earth. This is going to be the heater coil to warm the bi-metallic strip.

That's the one to connect the +12V feed from whichever white wire has +12V on either with ignition or during cranking.

The other white wire will go to the other teminal on the TTS so it is switched as described and only feeds the CSV for a few seconds.

Note that because of the position of the TTS on the engine, the engine heat will warm the TTS up so that it effectively disables the TTS and CSV above certain temperatures so you don't get the extra fuel on a hot start.

Hopefully one of the others with a 1972-on car with D-Jet can confirm/correct this, like i said i'm going from memory from about 35 years ago and never really used it since.

Gives you an idea what to look for though!

[c1800]

“ I would like to re-instate the wiring to the cold start valve, replacing the thermo timer with a switch that completes the circuit. I can find 3 white wires that have been messed with that might have originally led to the TTS, one of which is earthed; is this likely to be it?”

The tiny numbers on the FI white wires will provide a clue. Do you have a wiring diagram? I got mine from this place, easy to read.

https://colorwiringdiagrams.com/prod...r-wiper-fitted

Sorry can’t give you a better answer, mine is a ‘71 with no TTS. other than to say the TTS is earthed through the body of the switch to the engine block.

[Laird Scooby]

Have a look at this :

https://www.sw-em.com/bosch_d-jetronic_injection.htm

Scroll down for the P1800ES diagrams, item #34 is the TTS and #76 is the CSV, the back of my mind was right, it's fed from the starter during cranking but the rest is as i described for the circuit.

[c1800]

Good find Dave , I looked all over for that diagram, couldn’t remember where I saw it!

[Laird Scooby]

Originally Posted by c1800

Good find Dave , I looked all over for that diagram, couldn’t remember where I saw it!

Thanks, it came up in the first three results when i searched online but that said, i don't use the same serach engine as most of the planet. Always used the same one for the past however long (15-20 years ish) so perhaps its algorithms have adjusted to what i want to find rather than what it thinks i want to find!

[VolvoRoyS]

Originally Posted by c1800

“ I would like to re-instate the wiring to the cold start valve, replacing the thermo timer with a switch that completes the circuit. I can find 3 white wires that have been messed with that might have originally led to the TTS, one of which is earthed; is this likely to be it?”

The tiny numbers on the FI white wires will provide a clue. Do you have a wiring diagram? I got mine from this place, easy to read.

https://colorwiringdiagrams.com/prod...r-wiper-fitted

Sorry can’t give you a better answer, mine is a ‘71 with no TTS. other than to say the TTS is earthed through the body of the switch to the engine block.

OK. So on closer inspection I can see numbers on these 3 wires: 33, 34 and what could be 18. What's more there is continuity at the chopped off wires at the cold start valve end with 33 and 34, so it would appear that some previous owner did what I am planning to do: fit a switch between the wires that go to the thermo timer. I can't find the wire at the starter end because the brake servo makes it difficult to see.
Then it seems another PO had by-passed all this with new wire; a red wire is fitted to the starter solenoid and wends its way to a switch under the dash and then another red wire goes from the switch to the cold start valve where one connector is then earthed. This does work but I find loose red wire about the engine bay bit a bit ugly. So just need to locate missing wire white wire numered18 at the starter end; any ideas where I might look? Would it be in the wiring harness? I expect it has been chopped off which is making it hard to find.

[VolvoRoyS]

Originally Posted by 142 Guy

Perhaps another owner with a D jet can pull back the wire harness and advise whether the wire numbers match up with the switch numbers and whether 17 is in the top or bottom position. Failing that, about the only way to confirm what is going on would be to do a functional test on the switch. Using a continuity tester connect between what you think are 14 and 17 which are the connections to the idle switch (based upon the wire numbers). With the throttle closed the idle switch should be closed (0 ohms) and once the throttle comes off the stop the switch should go open (infinite ohms). If that is correct then the switch is probably wired up as it should be. You can check the 14 - 9 and 14 - 20 contact operations if you want to - these should go alternately open and closed as you open the throttle.

OK, so have spent some time checking out the TPS. Assuming that the order is 17,14,20,9 with 17 at the top I tested all possible pairs of wires - 6 in all. I connected a meter between pairs of pins and observed what happened when I rotated the throttle to max. Results were:

17-14 open circuit throughout range and on return
17-20 alternate open circuit/closed circuit with closed at max; on return open
17-9 open circuit throughout range and on return
14-20 alternate open circuit/closed circuit with open at max; on return open
14-9 mostly open circuit; brief closed circuit on initial movement
20-9 closed circuit initially, open circuit on opening throttle

This is looking very interesting. The above uses the numbers on the wires on the plug. If I now use the numbers on the switch body the results would be:

9-20 open circuit throughout range and on return
14-9 alternate open circuit/closed circuit with closed at max; on return open
17-9 open circuit throughout range and on return
14-20 alternate open circuit/closed circuit with open at max; on return open
20-17 mostly open circuit; brief closed circuit on initial movement
14-17 closed circuit initially, open circuit on opening throttle

It's looking increasing likely that the wires in the plug have been reversed- maybe the switch has been changed and different switches have reversed connections? Need to get someone to confirm ordering of wires before I reverse them as I wouldn't want to damage the ECU.

Thanks so much for the information.

[Ron Kwas]

LS;

I briefly compared your description with my detailed contact/function drawing here:

Source: https://www.sw-em.com/bosch_d-jetronic_injection.htm
...it does look like the function you have observed is correct, but you might want to double check it against the detailed drawing and note out any inconsistencies or questions.

Good Hunting!