Throttle Pot sourcing

[Technoholic]

Hi guys

I've been searching the old threads but I'm none the wiser. getting back to try to fix my shunting issue, my next step is the throttle pot. Reading 67% max in Rovergauge so I think it might need to be changed.

Is there a drop in replacement available these days? The Racetech one seems to be but it is a lot of money. Is there any alternative? Or I don't mind having to modify connectors if that's what needs to be done but I don't know which throttle pot I need in the first place to do this.

Thanks

[Belle427]

It is possible to adjust it by elongating the mounting holes so it can be turned slightly.
This is all that may need doing, its better to connect up a multimeter when setting it.
There are some past threads with the expected voltage readings.

[spitfire4v8]

Before you go spending money on a throttle pot check you're actually getting full throttle first.
Either wedge the pedal at full travel, or get someone to press it for you .. remove the hose from the plenum and look where the butterfly is. It should be at right angles to the airflow IE least restriction.
I once had a Tuscan SP6 pick up 50hp on the dyno just by adjusting the throttle so it opened fully. Cheapest 50hp ever.
Check it.

[bobfather]

Throttle pot failure does not normally do this. The normal failure mode is intermittent or open circuit on one of the three wires which results with a zero reading on rovergauge

[Technoholic]

spitfire4v8 said:

Before you go spending money on a throttle pot check you're actually getting full throttle first.
Either wedge the pedal at full travel, or get someone to press it for you .. remove the hose from the plenum and look where the butterfly is. It should be at right angles to the airflow IE least restriction.
I once had a Tuscan SP6 pick up 50hp on the dyno just by adjusting the throttle so it opened fully. Cheapest 50hp ever.
Check it.

well well well. I just tested it. The butterfly is opened about maybe 75-80% i.e. it's not fully horizontal when the pedal hits the stop.

Thanks for that tip, I think I saw that in an earlier thread and forgot to check.

How do I adjust this!?

[ric355]

You should be able to verify whether it's a problem with the cable/pedal range by looking at rover gauge and operating the throttle from the plenum itself i.e. move the lever section that moves when the cable is pulled, without pulling the cable itself (cable will just go loose). This will take the cable and pedal side of things out of the equation.

If you can get it to 100% that way on Rover Gauge then it implies the throttle pedal end needs adjusting (if you have a pedal stop for example) or there is an issue with the cable. On the other hand, if you still can't get it to 100% then it's either the TPS or a mechanical restriction somewhere on the plenum.

[Technoholic]

Just done a test. I can get to 92% by manually operating the lever which I believe might be the maximum expected in RG?

I found the adjuster nut but it seems to be as tight as it will go. Is there any adjustment on the pedal end?

[ric355]

Technoholic said:

Just done a test. I can get to 92% by manually operating the lever which I believe might be the maximum expected in RG?

I found the adjuster nut but it seems to be as tight as it will go. Is there any adjustment on the pedal end?

Given your test result the pedal end is where you need to be. On my car there is a throttle stop at the top of the pedal, mounted on the chassis rather than the pedal itself. It's just a bolt with lock nuts on it. If you get your head into the footwell you should be able to see it opposite the throttle cable mounting point.

[Technoholic]

Ok so I’m effect I need to make the pedal travel further then, by winding that stop back a bit?

[Technoholic]

Right, I’ve found the stopper and adjusted it. I have managed to get it to the point where Rovergauge is reading 91% with foot to the floor. However the bolt is at the end of its travel, I couldn’t move it any more. I presume this is ok?

[Steve_D]

You could also have just adjusted the cable at the throttle body. The pedal has a limit stop when pressed but just hangs on the cable when at rest. Adjusting (shortening) the cable would give you the wider opening but at rest the pedal would sit a little higher.

Steve

[Technoholic]

Steve_D said:

You could also have just adjusted the cable at the throttle body. The pedal has a limit stop when pressed but just hangs on the cable when at rest. Adjusting (shortening) the cable would give you the wider opening but at rest the pedal would sit a little higher.

Steve

Do you mean by adjusting the cable adjuster on the throttle mechanism? Because that’s at its maximum adjustment too

[Classic Chim]

Thats a bit weird, my throttle sits about half way along the adjuster, pictures are always useful when trying to get help on here as it’s just guess work otherwise.
I’m guessing the wrong cable or something.
The TPS wears just off idle as it’s where the throttle often sits on the move and this can cause a poor signal, using RG just make sure it’s progression is smooth to be sure it’s working ok.
I know on aftermarket Ecu you can adjust the TPS so idle is just above this point so you avoid the worm bit, I’m not sure if you can do this with the CUX, hopefully someone more clued up can advise on that one.

[Technoholic]

it could be a stretched cable I guess.


I have done a quick log with RG with the throttle being pressed so I need to import to excel to examine the throttle readings to see if there are any dead spots before changing it.

[bobfather]

Technoholic said:

it could be a stretched cable I guess.

This was my thought too, Very strong return springs and a torturous cable route could do this.

[blitzracing]

Dont get too hung up on this- The TPS has two basic functions 1) to say the car is in idle mode (ie TPS as a low voltage) and 2) add extra fuel when the throttle is floored- fuel enrichment. This is done by looking at the rate of change of TPS voltage I believe, not its peak voltage. Problem is the 5 volt supply rail to the TPS may only be 4.5 volts, so even wide open the ECU wont see 100% at 5 volts. Id save your money on the TPS and look else where. Problem is shunting can be caused by a multitude of issues, so its important to make sure the ignition system is in good order, you dont have wrong temp readings, or very high fuel trims showing something is out of tolerance.

[Steve_D]

Technoholic said:

Steve_D said:

You could also have just adjusted the cable at the throttle body. The pedal has a limit stop when pressed but just hangs on the cable when at rest. Adjusting (shortening) the cable would give you the wider opening but at rest the pedal would sit a little higher.

Steve

Do you mean by adjusting the cable adjuster on the throttle mechanism? Because that’s at its maximum adjustment too

Yes that is what I meant. Very strange you are maxed out on the adjustment. Others have said stretched cable but this could also be a cable in the course of breaking up.

Steve

[Technoholic]

True, it’s fixed for now so will monitor it and put it on the list of things to replace.

[Technoholic]

blitzracing said:

Dont get too hung up on this- The TPS has two basic functions 1) to say the car is in idle mode (ie TPS as a low voltage) and 2) add extra fuel when the throttle is floored- fuel enrichment. This is done by looking at the rate of change of TPS voltage I believe, not its peak voltage. Problem is the 5 volt supply rail to the TPS may only be 4.5 volts, so even wide open the ECU wont see 100% at 5 volts. Id save your money on the TPS and look else where. Problem is shunting can be caused by a multitude of issues, so its important to make sure the ignition system is in good order, you dont have wrong temp readings, or very high fuel trims showing something is out of tolerance.

Yeah I think I’ve ruled the TPS out now as being a problem. Getting the full range as best it can now I think. Just took it for a drive. Nice little extra bit of power with the throttle fully open.

But the shunting is still a right pain in the neck. I’ve noticed my vacuum advance is faulty, let’s air through it so I guess that needs changing but not sure that could create shunting this bad?

If I send you a log file once I get it out for a drive with the laptop connected, would you mind taking a look?

[KevtheRev]

Regarding shunting, I listed everything I could find on the subject then started working through cheapest/easiest first. I got as far as renewing the HT ignition side & pretty much sorted it, but this is my full list.............

1. Check using RG that I/O giving expected readings
2. Check/replace Distributor Cap & rotor arm – cracks or tracking
3. Clean Stepper Motor (idle control valve)
4. New plugs Iridium plugs - NGK BPR6EIX
5. Junk the Spark Plug Extenders. I fitted Accel 9002C Ceramic Leads
6. Check for vacuum leaks, particularly on breather system
7. Check under bonnet electrical connectors & go through plugs & clean/spray
8. Check timing - set to 28 Deg BTDC @<3500rpm
9. Ported v full vacuum advance system see “chimpongas” threads on this subject
10. Ignition Coil
11. Ignition Amplifier
12. Some forum quotes on Plenum spacer having an improvement
13. Remove & get injectors cleaned
14. Modify crankcase ventilation system, fit PCV - would need further understanding of benefits
15. Aftermarket ECU for better control of fuelling & timing