Location of throttle potentiometer on TVR S1 2.8?
Discussion
My TVR had been running very rough recently. It runs perfectly for the first 30 minutes or so of the journey, but once the engine has warmed up, that is when it starts to play up (Juddering, cutting out, reluctant to pull away, doesn't accelerate freely).
At first I thought that it was a fuel starvation issue and I had my mechanic replace the fuel pump, fuel pump relay, fuel filter. He also cleaned out the petrol tank filter) which was filthy) and the problem still persists.
I'm getting to the end of my tether with it and after doing a search of the forums I thought I had found the culprit, the throttle potentiometer. I asked my mechanic to replace it and he has been unable to find it. Does my car have one and if so where is it? I'm wondering if they were only fitted to the 2.9 model and that's why he cannot find it. If this is the case, what could be causing my problems and how could it be solved, would a diagnostic check be an idea? I really don't know. but it's is ruining my enjoyment of what has always been a really nice car to own.
At first I thought that it was a fuel starvation issue and I had my mechanic replace the fuel pump, fuel pump relay, fuel filter. He also cleaned out the petrol tank filter) which was filthy) and the problem still persists.
I'm getting to the end of my tether with it and after doing a search of the forums I thought I had found the culprit, the throttle potentiometer. I asked my mechanic to replace it and he has been unable to find it. Does my car have one and if so where is it? I'm wondering if they were only fitted to the 2.9 model and that's why he cannot find it. If this is the case, what could be causing my problems and how could it be solved, would a diagnostic check be an idea? I really don't know. but it's is ruining my enjoyment of what has always been a really nice car to own.
RayS1 said:
I thought I had found the culprit, the throttle potentiometer.
Don't think you've got one, the 2.8 uses a very different fuel injection system to the later 2.9 engined cars. Have no experience of that engine myself but isn'y it a more mechanical and less electronic system?Looking at the wiring diagram there are still however a few electrical bits 'n bobs that could be playing up?
Hopefully someone with knowledge and experience of that engine will be along soon, good luck !
Might be worth checking out some Capri or Sierra Forums, lot of them used that engine? Or try and find an "old school" mechanic who worked on them back when they were a modern engine.
Bottom left area of this wiring diagram
Edited by phillpot on Thursday 29th November 06:55
Hi there, Mike is right, no throttle potentiometer on the S1 Jetronic system. First of all your best bet is to try to find someone in a local garage or tuning firm who understands this Bosch system. It is a good few years now since the Jetronic was last used in Fords so the 'knowledge' is getting thinner on the ground each year. Your average diagnostic service may well not have the expertise. Ask around, if you can find a diagnostic firm who CAN do Jetronic then use them (and let the forum know!).
It isnt particularly complex, and is pretty reliable once set up right, but it is different to any 'modern' electronic system.
Difficult to advise without some tests but there are a couple of possibilities you might try which are specific to the S1. Does the car always run fine from cold then problem arises when it warms up?
Two immediate possibilities:
There is a cold start relay on the offside rear of the plenum chamber (probably a blue connector), this opens a 7th injector to richen the mixture. They are known to become unreliable with age, and yours could be 25 years old by now. Disconnect it once it has started and see if that makes a difference. Plenty of Fords ran with it disconnected although it might need to be on when the weather is very cold. If it is faulty it can give hot starting problems as well.
There is a spark enhancing module, normally on the nearside front of the bulkhead or in that region. An aluminium box with about 6 wires if I remember rightly (cannot check at the moment), again with age these can become unreliable. They tend to work OK when cold then become less effective as they heat up. First, test the spark: if it is very much worse when hot then the module is a likely culprit. It could of course also be a failing coil. Try another coil and if the spark still deteriorates markedly when warm then the module looks favourite. One possible way to test the module is to run the car with the bonnet closed and check the time before it runs rough(jam the throttle at about 200rpm so you do not need to wait too long). Let it cool. Do it again with the bonnet open, and see if it runs considerably longer. With the bonnet open the module stays cooler much longer.
Another possibility, but less likely as you have changed much of the fuel system, is a drop in fuel pressure when the system is warm. This should really be tested with a proper fuel pressure tester, but it can WITH GREAT CARE be eliminated without. The fuel feed to the cold start relay should be pressurised at all times. If you slacken off the feed to the relay with the engine running there should be very obvious high fuel pressure! If it isnt quite high pressure you still have a fuel problem. BE VERY CAREFUL,spraying fuel onto a hot engine would be a BAD plan!
It isnt particularly complex, and is pretty reliable once set up right, but it is different to any 'modern' electronic system.
Difficult to advise without some tests but there are a couple of possibilities you might try which are specific to the S1. Does the car always run fine from cold then problem arises when it warms up?
Two immediate possibilities:
There is a cold start relay on the offside rear of the plenum chamber (probably a blue connector), this opens a 7th injector to richen the mixture. They are known to become unreliable with age, and yours could be 25 years old by now. Disconnect it once it has started and see if that makes a difference. Plenty of Fords ran with it disconnected although it might need to be on when the weather is very cold. If it is faulty it can give hot starting problems as well.
There is a spark enhancing module, normally on the nearside front of the bulkhead or in that region. An aluminium box with about 6 wires if I remember rightly (cannot check at the moment), again with age these can become unreliable. They tend to work OK when cold then become less effective as they heat up. First, test the spark: if it is very much worse when hot then the module is a likely culprit. It could of course also be a failing coil. Try another coil and if the spark still deteriorates markedly when warm then the module looks favourite. One possible way to test the module is to run the car with the bonnet closed and check the time before it runs rough(jam the throttle at about 200rpm so you do not need to wait too long). Let it cool. Do it again with the bonnet open, and see if it runs considerably longer. With the bonnet open the module stays cooler much longer.
Another possibility, but less likely as you have changed much of the fuel system, is a drop in fuel pressure when the system is warm. This should really be tested with a proper fuel pressure tester, but it can WITH GREAT CARE be eliminated without. The fuel feed to the cold start relay should be pressurised at all times. If you slacken off the feed to the relay with the engine running there should be very obvious high fuel pressure! If it isnt quite high pressure you still have a fuel problem. BE VERY CAREFUL,spraying fuel onto a hot engine would be a BAD plan!
You don't have either a TPS or a cold start relay. The cold start injector is activated by a thermotime switch which should give power for a few seconds on start up.
The symptoms described can be accounted for by one of the following:
- Air leaks in the hose from the airflow meter to the throttle.
- Sticking flap in the airflow meter.
- Warm up regulator letting fuel pressure go too high or low when warm.
- Leaking cold start injector
There a few other possible suspects but these are the normal ones found.
The symptoms described can be accounted for by one of the following:
- Air leaks in the hose from the airflow meter to the throttle.
- Sticking flap in the airflow meter.
- Warm up regulator letting fuel pressure go too high or low when warm.
- Leaking cold start injector
There a few other possible suspects but these are the normal ones found.
I agree with LeTVR. Also possibly mixture adjustment. ( Long 3mm Allen key & HC / CO meter required ).
Have a look at Loach1's thread ( posted just under a month ago ),
"Jetronic experts - am I on the right track?"
Lots of useful info there.
Sorry, can't do links.
Have a look at Loach1's thread ( posted just under a month ago ),
"Jetronic experts - am I on the right track?"
Lots of useful info there.
Sorry, can't do links.
Edited by glenrobbo on Thursday 29th November 10:43
My apologies, sloppy of me, I should have referred to the cold start VALVE rather than RELAY. Nevertheless, these do give problems if the thermotime switch, or other fault, causes the valve to open to any degree when the engine is warm. It wasnt at all unusual to find one disconnected on the old V6 Granada or Capri. My car was bought as a non runner and brought back to life. Both an intermittent fault in the cold start system, and a heat related fault in the ignition module were present, and foxed us for a bit even using a full diagnostic test rig.
Let us know how you get on.
Let us know how you get on.
Thank you to all who have offered help and advice, it is very much appreciated.
I thought that I would let you know how I am getting on; I have informed my mechanic that my car doesn't have a throttle potentiometer, and I think he was very relieved that this is the case, as he had spent a good deal of time looking for it.
I’m happy to report that my mechanic now thinks that he has gotten to the bottom of the problem, the fuel tank filter that he cleaned out less than 200 miles ago, is now clogged up with rust, rather that a build up of dirt and grime when it was last cleaned, and on further inspection he has discovered that my fuel tank is in fact full of rust! It would appear that this is what is causing my fuel starvation problems as it looks like the rust from the fuel tank, is blocking the fuel filter and then starving the engine of fuel.
It would now appear that I need a replacement fuel tank.
I've done a quick forum search and I need to follow up these four leads:
DC Developments Engineering.
Steve Reid.
David Gerald.
ML Performance Parts.
Does anyone have any other ideas where I can get one, and is it worth considering a stainless steel alternative? Also how much should I expect to pay? Thanks!
I thought that I would let you know how I am getting on; I have informed my mechanic that my car doesn't have a throttle potentiometer, and I think he was very relieved that this is the case, as he had spent a good deal of time looking for it.
I’m happy to report that my mechanic now thinks that he has gotten to the bottom of the problem, the fuel tank filter that he cleaned out less than 200 miles ago, is now clogged up with rust, rather that a build up of dirt and grime when it was last cleaned, and on further inspection he has discovered that my fuel tank is in fact full of rust! It would appear that this is what is causing my fuel starvation problems as it looks like the rust from the fuel tank, is blocking the fuel filter and then starving the engine of fuel.
It would now appear that I need a replacement fuel tank.
I've done a quick forum search and I need to follow up these four leads:
DC Developments Engineering.
Steve Reid.
David Gerald.
ML Performance Parts.
Does anyone have any other ideas where I can get one, and is it worth considering a stainless steel alternative? Also how much should I expect to pay? Thanks!
I recognise the fuel tank problem! Same here. I should have mentioned you need to check for more rust getting into the new pump as well! The best solution is clearly a new tank, let me know how you get on as I may have to do the same! The filter doesnt come out of my tank (there has already been a thread on this. Not all tanks are the same). I took the tank off, removed the fuel gauge sender and power washed it out. I also power washed back through the outlet. The rust and crud was amazing. I then washed it out in clean petrol. The tank was then left to dry (in the sun!!!!). No smokers in our family! I cleaned and checked the outside of the tank and it appeared sound so it was repainted and replaced. I dried out the pump and gently tapped it down on the input side and got it clean again. I knew the problem wouldnt be 100% cured so I bought a special fuel filter from Demon Tweeks which is 'full flow', takes the large bore fuel pipe and has pretty cheap removable elements. 3 elements later it is still getting some rust out but it is reducing! I now leave it with the tank full whenever possible. I suspect however that this is only putting off the inevitable, although perhaps for a couple of years.
greymrj said:
I then washed it out in clean petrol.
White spirit, paraffin or even diesel might be a cheaper (and safer) option ? Ok, the diesel's not cheaper (unless you have some "red") If you are thinking of trying to clean out your exiting tank I've read, but never had need to try, that putting a handful of small stones inside then shaking it like mad helps clean it up ?
(count 'em in and count 'em out)
I'd clean the tank out as well as I could then maybe use something from frost.
http://www.frost.co.uk/catalogsearch/result/?order...
Once you have sorted it it is best to store the car with a full tank then there is less opportunity for condensation to form on the tank walls.
http://www.frost.co.uk/catalogsearch/result/?order...
Once you have sorted it it is best to store the car with a full tank then there is less opportunity for condensation to form on the tank walls.
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