S4c stalls at cold

[Last S4]

Hi all,
Thanks for the info from my last post - I have new leads and ign coil arriving Monday and will I am waiting for a reply from Dreadnougt ref tuning.

I started the car yesterday and today with exactly the same problem. Starts up first time no bother but if you touch the accelerator before the engine is warm it stalls. It struggles to start up again and once started will do the same again. I am not talking about hard revving the engine, just a touch on the pedal kills it.
This symptom disappears once warm.
Any ideas?

I am off to grind away some of my drive so the car can get out without grounding out, and then have a go at getting the electric mirrors to work. They do nothing at all.

Thanks, Steve.

[Barkychoc]

I'd see how it is when the leads etc are changed - I do know some of the history of your car as I exchanged a few emails with Martyn the previous owner before he bought it (very nice chap too).

Have you disconnected the battery or had the electrics disconnected at all?
The ECU has to learn a few settings again when the battery has been off - it takes a complete warm up (till the fans come on) and cool down cycle for it to achieve this I think.

TVRGIT is the expert - I'm sure he'll add to this.

There's a few things it could be but haphazardly changing things may not achieve anything and get expensive.
Ignition leads are always worthwhile though if their age is unknown.
If you can find the spec for the ECU temperature sensor (it may be a different sensor to the one for the gauge) I'd check the resistance of that - just incase it isn't working properly and the ECU thinks the engine is warm so delivers too little petrol - but thats an armchair guess.

Sorry if I'm a little vague - mine is a V8

[tvrgit]

Hi Steve

As Barkychoc says, the ECU temperature sensor may be a good place to start. If the engine is being overfuelled on cold idle, then the plugs will start to foul up, and the tiny extra fuel when you press the accelerator may kill it.

Could possibly be the throttle pot, being worn and giving a "spike" reading when the throttle just opens (if it's gonna wear, that's where it will wear most!) and the ecu thinks you've opened the throttle to full steam ahead so it stokes up the boilers with fuel, which the plugs can't burn...

Then I would take off the idle speed control valve and clean it with carb cleaner - if it's choked then the idle is all over the place.

Other thoughts - you could try taking a couple of spark plugs out when the engine's been running cold, and see if they're fouled or too wet with fuel (they will be, just make sure it's not too much!) Might give you a start.

[Last S4]

tvrgit said:

Hi Steve

As Barkychoc says, the ECU temperature sensor may be a good place to start. If the engine is being overfuelled on cold idle, then the plugs will start to foul up, and the tiny extra fuel when you press the accelerator may kill it.

Hi,
The temperature sensor sounds good to me, if that caused over fueling then that would explain why it takes some effort to start it back up. Cannot be that expensive to just replace it either?
I have already taken the idle speed control valve off and it all seems free enough.
I will try and source a temperature sensor and take it from there.
Thanks again,
Steve.

[Barkychoc]

I was actually thinking the other way - that the temp sensor is duff so the ECU thinks the engine is warm so under fuels when cold - but fuels just fine when its warm.

Another armchair guess

[Last S4]

Hi,
The sensor is gubbed!
I removed it and check the resistance at room temp, it should be 2.5k ohms, it was 27k ohms.
I then ran it under a cold tap (as if its a cold morning) and instead of about 5k it was 49k ohms.
Where do I buy one!
I will make some phone calls tomorrow to the local Ford dealer.
Thanks very much guys.
Steve.

[Barkychoc]

Sorry don't want to doubt but are you sure you were reading the scale correctly - both readings are out more or less by a factor of 10 which suggests its could be working OK give or take the odd zero here and there!

[Last S4]

Hi,
I am an electrical engineer and served my time in the manufacturing industry in maintenance depts.
Thanks for pointing out the potentially obvious flaw though.
I felt the readings were too close to a factor 10 and checked them, its correct.
Cheers,
Steve.

[Barkychoc]

Sorry Steve are you saying then that you think the sensor is duff or OK?

[jimed]

My Steve Heath book (1st edn) says 0 deg C 9.2k ohms and 20 deg C 2.5K ohms so that suggests the sender is duff but by a factor of 10 which does seem strange ... BUT ... I've also got a copy of the relevant pages from an ("Autodata") manual which lists various parameters for engines (for the trade) and that says Coolant Temp Sensors - all models (ie incl 2.8 and 2.9 amongst others)
Temp deg c Resistance
0 90-100 K ohms
20 35-40 K ohms
40 15-18 K ohms
60 7-8 K ohms
100 1.9-2.2 K ohms
- which if it is correct does seem to suggest that the Steve Heath book may be wrong and the sensor in question may be OK. Does anyone have a definitive staement on this?? It wouild be a pity to waste some money on a new one until he knows what it should be and hence whether it is OK.
Jim

[Last S4]

Barkychoc said:

Sorry Steve are you saying then that you think the sensor is duff or OK?

Hi,
I agree with "jimed". If Steve Heath is right the sensor is duff, if Autodata is right the sensor is ok.
I tried three Ford dealers today. One parts dept did not answer all day. One said that the part was not listed and I should bring it in (during office hours), the last dealer did not even have a parts dept.

[bridgdav]

Ask Steve directly..?

shpub on here.

http://www.pistonheads.com/gassing/profile.asp?mem...

[Last S4]

I have just emailed Steve Heath, hopefully we will get some info back.

[shpub]

The confusion is simply resolved: you are not looking at the right section. You are quoting my figures for the V8S lucas sensor and not the Ford one.

The S Bible quotes the Ford sensor at about 50kohm at 15C and 3.5kohm at 80C.

Edited by shpub on Monday 27th April 20:33

[tozerman]

Last S4 said:

I started the car yesterday and today with exactly the same problem. Starts up first time no bother but if you touch the accelerator before the engine is warm it stalls. It struggles to start up again and once started will do the same again. I am not talking about hard revving the engine, just a touch on the pedal kills it.
This symptom disappears once warm.
Any ideas?

It sounds to me like it could possibly be an air leak on the inlet side somewhere. When you open the throttle even a tiny bit if there is not enough vacumn in the first place that will cause the engine to cut out. Retrace your steps a bit and think about what you have touched since you bought the car and you might find out that there is a very simple explanation. Good luck.
Cheers.....Tony..

[Last S4]

tozerman said:

It sounds to me like it could possibly be an air leak on the inlet side somewhere. When you open the throttle even a tiny bit if there is not enough vacumn in the first place that will cause the engine to cut out. Retrace your steps a bit and think about what you have touched since you bought the car and you might find out that there is a very simple explanation. Good luck.
Cheers.....Tony..

Hi Tony,
Thanks for that - I looked at the vacuum pipes but not the manifold, I will check it later.
The previous owner told me about this problem before I made the trip down and then when I arrived. He was very upfront which I did appreciate having travelled down from Edinburgh.
Cheers, Steve

[Last S4]

shpub said:

The confusion is simply resolved: you are not looking at the right section. You are quoting my figures for the V8S lucas sensor and not the Ford one.

The S Bible quotes the Ford sensor at about 50kohm at 15C and 3.5kohm at 80C.

Edited by shpub on Monday 27th April 20:33

Thanks for the info, I have looked and you are right I was looking at the V8 page.
Any suggestions you have on the problem would be appreciated. I want to get to the bottom of this before going to a rolling road.

[Barkychoc]

I'm not sure this sounds such a hot idea but one method for finding an air leak is to squirt lighter fuel around various joints - if there's a leak it sucks the lighter fuel in and the revs momentarily increase.
Be careful if you do this

[tozerman]

One good way to find air leaks is to get some screenwash tubing or similar, put one end in your best ear and waft the other end around all the joints and connections etc and if you find a leak the tube will act like a stephoscope so you can pinpoint any leaks if there are some.
cheers.....Tony..

[Last S4]

Just an update.
I bought a new ECU coolant sensor and tested the resistances as below - all in K ohms:
Temp........Old Sensor...New Sensor
8C...........55.4........52.2
12.5C.......52.0........50.1
20C..........38.6........37.8
30C..........26.8........26.6
40C..........17.4........17.2
50C..........12.1........12.1
60C..........8.4.........8.5

I was hoping to see a much bigger difference meaning I had found the fault.
Prior to this test I had fitted new leads and ignition coil. The existing coil lead was an original Ford part and the rest were Lucas so they all had to go. This made a slight difference to the tickover.
I have now fitted the new ECU temp sensor which has improved the running further at cold.
Now the engine does not stall when you give it some throttle at cold, but it still hesitates before revving.

I am going to give the diagnostic tool a try now (as mentioned in recent thread).
Thanks, Steve.