Hello everyone, I was checking my car over with conzult and came across a fault I am not sure about so hoping someone here may be able to help.

 

The TPS was showing 0.90 volts, spec should be around 0.42 so I tried to adjust but it wont go any lower, my first thought was a faulty TPS so I swapped it for another which was working fine when removed but this also only goes to 0.90 volts as well, have I been unlucky with 2 bad TPS sensors or is there another cause you may know about ?

 

Also I am not sure if this is related but when using conzult with the engine running if I try to open the idle adjustment section it causes the engine to faulter and die, I am sure it did not do this before? am I missing something obvious or is it just down to a faulty TPS ?

The problem with been unable to adjust the tps can be an ecu issue but more likely a wiring issue and NOT always with the tps cables.

 

Tricky issue you have there, the wiring loom has many screened cables and the screening on these cables comes to a common point at one end, a wiring fault on another sensor to its screen will impact on other sensor readings. I have found this a few times and even wiring the tps completely often does not cure the issue, in fact as the tps and temp sensor use a common return it is the most likely cause and rewiring both sesnors can be the only fix.

In common with lots of zed wiring issues there is a chance it is intermittrent and you may well find checking on another day it is ok...flipping maddening that is in the workshop let alone at home on your own zed.

 

The issue with the stalling out when entering the tickover mode on ConZult is caused by too low a base idle, try setting it higher before starting the engine.

 

Good luck.

 

Jeff TT

Base idle adjustment guide... (in case you didn't know how) :)

 

http://www.300zx.co.uk/forums/showthread.php?t=83687&referrerid=16305

Thanks Jeff, where would you suggest I start to try and solve the problem? I took the car for a spin and its gear changes are all over the place now I guess because I have moved the TPS and can no longer find the correct point again. Local garages usually say no when they see the car and it may be if I can get it drivable I have to bring it to you as I have no idea where the wiring goes from the TPS to replace it.

Yes as you mention the tps will effect the gear change on the auto box, the best you can hope for is a compromise at the moment, the lower the figure you get the better for your gear change, so as you look at the tps from the passenger side rotatate it clock wise so it moves upwards to its max and lock it off, still will not be correct but the best you can hope for with the corrupted signal issue.

 

The cables from the tps go directly to the ecu, the temp sensor common return is spliced into it within the loom at a dedicated junction that is burried deep in the loom bundle.

 

It is worth taking a look at the loom from the temp sensor at the front past the tps and to the bulkead just in case your lucky and can see some damage or chaffing, I do doubt it though, it is a real pain in the ass fault and although I have seen several times is not that common in the bigger picture, one customer got so frustrated with it as we tried to help him over the phone he ripped the loom out and fitted a new one which solved the problem but was a very expensive way to do it.

 

 

Jeff TT

This could be an adjustment fault as it's very rare that wiring fault can cause change in voltage signal (even if its can happen) usually wires are causing open or short cicuit.If you want I could have a look for you (diagnosis is free on 300ZX as I love them:tt1:).

This could be an adjustment fault as it's very rare that wiring fault can cause change in voltage signal

 

 

Jeff TT

:lol:

Ok, I have been playing with the car this morning and not getting wound by it at all, staying perfectly calm and not kicking it in frustration !!

 

I can adjust one TPS from 0.9 to 1.12 the other from 0.9 to 1.08, have checked the wiring and there are no visible signs of damage or chaffing, had a quick look at the ECU just to make sure there were no obvious problems there like water getting in and all looks fine.

 

The only thoughts I have now are swapping the TPS for a new one and then perhaps the ECU for a second hand unit, then if that fails a trip to Zedworld.

 

Jeff in your opinion would you say thats a good idea or am I just wasting time and money and I should just get it to you ?

Do a continuity test on the 3 wires, you might have to use a long bit of wire to get the length to connect, but here goes:

 

pin 48 of the ecu is the power supply to the tps (oran/blue)

pin 38 of the ecu is the throttle open circuit (white)

pin 30 of the ecu is the TPS and the temp sensor ground (black)

 

Also worth noting that wires to pin 38 and 48 also go Tee off to the AT control unit, so you might have a problem or short there. HTH

 

If you get no continuity or intermittent reading then its more likely to be the wiring rather than 2 duff TPS sensors.

If all else fails then take it to Jeff, its one of those jobs that is often easier to source and rectify in the flesh rather than on the forum

Do a continuity test on the 3 wires, you might have to use a long bit of wire to get the length to connect, but here goes:

 

pin 48 of the ecu is the power supply to the tps (oran/blue)

pin 38 of the ecu is the throttle open circuit (white)

pin 30 of the ecu is the TPS and the temp sensor ground (black)

 

Also worth noting that wires to pin 38 and 48 also go Tee off to the AT control unit, so you might have a problem or short there. HTH

 

If you get no continuity or intermittent reading then its more likely to be the wiring rather than 2 duff TPS sensors.

If all else fails then take it to Jeff, its one of those jobs that is often easier to source and rectify in the flesh rather than on the forum

 

Thank you for the info groover, I would definately prefer to take it to Jeff only problem I have now is the car is undrivable so would have the added expense of trailering the car to him on top of repairs, having just moved house this is an expense I really did not need :cry:

Hello mate did you find the problem ?

Hello mate did you find the problem ?

 

I believe it to be the ECU, have checked out all the wiring as best as possible using the info Groover gave and also from a couple of other websites, I am just waiting delivery of an ECU and will see what happens, if not then its off to Zedworld as I have exhausted all my own ideas on the subject.

I will be near to you (croydon) at Tuesday evening tomorrow, if you want a second opinion I could have a look for you (free of charge of course as I love difficult cases :) ) Send me a PM(or call me at 07852291335) if you do. ;)

Edited August 23, 201114 yr by slymagic

Ok I have ruled out the TPS and the ECU being the fault so now it seems the only option left is to rewire the TPS, has any got any tips for me, I am reasonablly confident with a pair of wire cutters and soldering iron, I am fed up of the car sat there so hope to get it done this or next weekend depending on the weather.

Update in case anyone searches for this and needs help.

 

As stated I ruled out every other option so as Jeff stated it was a case of rewiring the TPS which I did and cured the problem straight away this alone is a fairly simple task, at first glance the wiring looked to be in ok condition but I found that while the engine was running if I moved the ECU a little the engine began to run very badly, it seemed very likely that somewhere in the harness between ECU and bulkhead there were problems, this became even more apparent while driving, with everything bolted back in driving over a bump would cause running issues, thinking it was possibly a bad connection somewhere I went to clean up / check all connections and this is where I found out how bad the harness condition was and decided to fit a new EFI harness, expensive but very much worth it.