D22 ZD30 Throttle cutting out / Intro

[scottm]

Turned out that either Nissan - or a backyard repairer - had used a single solid core wire to provide power to ignition/accessories and lights. The wire from the battery to the ignition/accessories had broken inside its insulator but this break was not visible on the outside. I found it by testing power delivery at various points in the cable then running my fingers over the cable and trying to bend the cable slightly to see if there were any variations (looking for things like the break that I did find). I am not in favour of single-core wiring in mobile structures - motor homes, caravans, campers, cars or motorbikes. Because they're mobile, they move - not just forwards and backwards, but up and down on uneven surfaces. This shakes the wires - and single core becomes brittle and fractures. It's something else you might want to consider.

Ok, that's an interesting story. I understand this might not be my exact problem but out of curiosity that cable was going to the area near the key hole / ignition from the ECU? Do basically all of these potential wires causing problems go into ECU / fuse box at some point ? Just thinking if I could be looking for a needle in a haystack, I should be going through systematically so I know at the end very thing has been checked. Would you recommend starting at ECU or fuse box and tracing from there?

Not sure if this is a silly question but, is there some way to drop the wiring down to work on it? I find myself on the drivers side floor, neck craned upwards and back twisted just to see what I'm doing.

Where the previous owner has just twisted and taped wires he's tapped into for the aftermarket cruise control should I just solder them in to rule them out altogether? (although I have re-taped a few it doesn't fill me with great confidence).

Cheers!

 

[scottm]

Also, how do you practically test power delivery as you described at various points in the cable? All I know about a multimeter is that if I earth it and put the positive on a live wire it will tell me how many volts are going to it. Not sure how you'd do that between two points.

 

[Old.Tony]

The broken cable in this instance ended up being a few cm from the battery. It was intermittent and fooled us a couple of times but we kept moving things around and found it.

Many cables have connectors in them as they are routed around the place. If you expect positive power in a cable, clamp the negative lead of the multimeter to the battery negative then start touching connectors. This one has power, next one forward has power, next one has nothing, so the break is in between the 2nd and 3rd connectors.

Another method between two points on a single cable is to set the multimeter to measure resistance. Touch the two leads together to see what to expect when you have a good connection (turn on the beep function if it has one) then go hunting.

 

[Rumpig]

It has to be the TPS wire where the cruise control connects to it, or the wire from the TPS to the cruise control unit ( i am guessing as i don't have a wiring diagram for the cruise control to know what else it connects to. ) On my car the TPS wire is the middle one on the brown plug
. A sheilded wire is just ordinary wire with a braided wire coating and then another outer layer of insulation, like co-axial. The outer layer of braid is to stop electrical interference reaching the inner core affecting it's signal. If when they installed the C.C they spliced the wire the outer braid may be in contact with the innec core earthing it out.

 

[scottm]

SOLVED once and for all

It has to be the TPS wire where the cruise control connects to it, or the wire from the TPS to the cruise control unit ( i am guessing as i don't have a wiring diagram for the cruise control to know what else it connects to. ) On my car the TPS wire is the middle one on the brown plug
. A sheilded wire is just ordinary wire with a braided wire coating and then another outer layer of insulation, like co-axial. The outer layer of braid is to stop electrical interference reaching the inner core affecting it's signal. If when they installed the C.C they spliced the wire the outer braid may be in contact with the innec core earthing it out.

I just wanted to jump on and share my joy at finally having categorically found the problem and solution.

First off I checked the TPS wire as Rumpig suggested but found the aftermarket cruise control had not tapped into it at all, the cruise control must come with a whole new plug that just "plugs and plays". Picture below (I note the wiring colours are different to Rumpigs too):

So I started rifling around looking for other wires etc that look dodgy / frayed etc and found this:

The connection is the equivalent of the one that comes from the pedal (you can see in next pic where it attached on the accelerator pedal assembly) in my setup with the cruise control it goes: Two pin connector from pedal -> Cruise control -> Two pin connector to ECU.

You can see that the pin is hanging out and even though it only looks like a bit from this picture there was only a tiny amount of the pin actually connecting. I pushed it back in all the way (had to use a very tiny screwdriver but a paperclip would do). Once I did this I couldn't get the car to fault at all.

Just to be sure I took out the red pin (tested both hanging by a thread, and completely out) and got exactly the fault / symptoms I have been experiencing but like absolute clockwork. Unplugged it and plugged it in a few more times with more tests (also got my wife to observe that I was hallucinating and I had indeed nailed the problem). I'm 100% convinced this has been the problem. I can't rule out that maybe bad earthing was exacerbating the problem though...

Here's another pic of the whole assembly with the problem connector on the far right currently disconnected. Does anybody know what it actually is?

Thanks to all who helped with this, I can hardly describe how happy I am to have confidence in driving the Nav again and not having to worry about stalling half way through a round-a-bout.

 

[nuckin futs]

that red wire on the 2 pin plug looks like its been getting pinched by something

 

[scottm]

that red wire on the 2 pin plug looks like its been getting pinched by something

True, forgot to mention that... I just taped it up so it wouldn't short against anything. Considered soldering a short replacement wire in but I only had thicker stuff and it didn't seem to be damaged, the sheath had just split slightly....

Think it's worth worrying about or just see how it goes?

 

[nuckin futs]

doesnt look like the actual wires cut, but could of been shorting out. yeh, id tape it and see how it goes. knowledgable bunch of blokes these guys. lots of people would be stuffed and a lot poorer without them. keep up the good work guys

 

[Rumpig]

The CC should also connect to the brake pedal switch as well as the clutch pedal switch, so if you engage either it cuts out. The plug may be for either of those.
And good that it's finally sorted, intermittent problems are a bitch!

 

[scottm]

The CC should also connect to the brake pedal switch as well as the clutch pedal switch, so if you engage either it cuts out. The plug may be for either of those.
And good that it's finally sorted, intermittent problems are a bitch!

Sorry, I wasn't clear... That plug is connected to the accelerator pedal, I just wasn't sure of it's exact purpose?

Once that pin was pushed in properly and plug reconnected everything worked perfectly.

 

[Old.Tony]

Congratulations on solving it, as pointed out, intermittent problems are the absolute worst, because they're never there when you try looking for the cause.

That wire does look like it's been caught between something and I'd say you're lucky it didn't short out and ruin the CC or something else. My advice is to grab a bag of cable ties and go to town with them under the dash!

 

[Rumpig]

Sorry, I wasn't clear... That plug is connected to the accelerator pedal, I just wasn't sure of it's exact purpose?

Once that pin was pushed in properly and plug reconnected everything worked perfectly.

The pedal has switches for 100% and 0 % but i wouldn't have thought the CC uses those.

 

[scottm]

The pedal has switches for 100% and 0 % but i wouldn't have thought the CC uses those.

Yep, what for I don't know but it definitely goes into and back out of CC