Hunter with jerky running

[gouldsborough7]

Guys
I am experiencing increasing bother with my Hunter regarding the engine running. Problem: when coasting along at lowish revs (say 1500rpm) in any gear, needing only the
slightest pressure on the accelerator pedal, there is a tendency for the engine to hunt, causing the transmission to jerk backwards & forwards. Pressing the accelerator
slightly to increase speed/revs a bit will overcome this problem, and the engine then runs as good as gold up through the rev range. This problem does not occur when accelerating from a standstill through the gears.

Regular readers of the Forum will have seen a thread I started a year or more ago saying that my engine had a giant flat-spot between 1500-2000 rpm. I virtually cured this by fitting a fuel pressure regulator in the fuel return pipe running at 40 psi.

The engine is a Sierra DOHC 2 litre fuel injection, 2 solid state coils each feeding 2 platinum spark-plugs, ECU and no distributor. It always starts first time and settles down
quickly to around an 1100 rpm tickover. Although the build is 14 years old, it has only done 12,300 miles from new. Built in the factory, originally Marlin installed a brand new engine & gearbox for which the original owner paid handsomely!

If the engine was fitted with a carburettor, I would have suspected slightly gunged up jets or accelerator pump, or more likely a worn throttle spindle allowing extra air into
the manifold. But it is equipped with fuel injection, with the butterfly spindle looking in good order, and nothing else suspicious.

Would welcome any ideas.

Cheers
Mike

[CosworthCabrioLee]

Re: Hunter with jerky running

Hi mike if it was my car and knowing all the various sensors etc on your engine I would get the engine diagnostic checked first to see if any fault codes appear

[gouldsborough7]

Re: Hunter with jerky running

Wow Lee, that was a quick response! I had thought vaguely in those terms, but hoped to avoid spending big bucks at this stage. I don't know where a diagnostic outfit might be in Hertfordshire - I am around 10 miles south of Stevenage. I might search in Yellow Pages.

Cheers
Mike

[copperleaves11]

Re: Hunter with jerky running

Hi Mike. Sounds like your engine is fitted with the ford edis ignition. If so, a possible avenue to check is the vr sensor which picks up pulses from the toothed wheel on the crankshaft.Any movement in the sensor mounting or the toothed wheel will result in an erratic signal. An easy check to verify. Best of luck . Regards David.

[CosworthCabrioLee]

Re: Hunter with jerky running

Hi mike it's only a 5 min job to put on a machine to see what if any codes appear at the most the garage should only charge you 1 hours work.

[cabrioman]

Re: Hunter with jerky running

Mike

I would sugest you have a look on the Sierra Owners club forum http://forum.fordsierraclub.co.uk/viewforum.php?f=82 and maybe post an enquiry on there, there are some very knowledgable guys on the Ford EDIS and management systems that post on there.

I remember talking to a Hunter owner (Bev from Lincolnshire) a couple of years ago who had a similar problem with his Hunter running the same setup. From memory I am pretty sure it was a known fault which had a work around that involved drilling a small hole in the throttle body butterfly, gleaned from the guys on the Sierra forum.

May be worth a try.

John

[gouldsborough7]

Re: Hunter with jerky running

Thanks guys
That's given me a few ideas to work on. Hopefully the Ford Sierra club will provide a solution. The small hole-drilling would be a nice simple remedy. I post a reply once I have resolved this or at least reached a conclusion.
Cheers
Mike

[ggrum]

Re: Hunter with jerky running

Hi Mike,

Did you ever resolve your problem with the flat spot and jerkiness at low revs. I have recently acquired a Cabrio with the same 2 litre DOHC 8V engine and it exhibits exactly the same problem. Other than that the engine performs beautifully and pulls very well considering the modest power output and weight of the car. Thought I would check with you first before hunting on other forums and pulling bits off the car.
Cheers
Geoff

[stewartdjones]

Re: Hunter with jerky running

Hi Mike,
I had a very similar problem with my Cabrio fitted with thr DOHC, this is what a mate suggest who is in the motor trade and it worked for me.

1. Remove the throttle body and inspect the bore and butterfly, clean both with wire wool and wash out with petrol or similar.
2. On the offside of the body and facing the radiator there is the idle speed screw, remove and clean both screw and bore, refit screw.
3. Refit the throttle body.
4. Remove the electrical plug on the idle speed control valve (valve next to the air filter).
5. Start the engine and allow to warm up.
6. Now adjust the idle screw on the throttle in until the idle speed is 850rpm ish.
7. Reconnect the electrical plug on the idle speed control valve, the engine will speed up but will quickly return to idle.
8. Now adjust the mixture to suit the engine , mine is 1.0 co2.

That it I hope.

Ring if you have any questions

Cheers

Stewart
07745407664

[Dane_Rescueman]

Re: Hunter with jerky running

All good stuff above. It could also be worthwhile checking the TPS. I have found these of poor quality and tend to wear at the commonly used areas which are idle, cruise and full throttle. A diagnostic check will show up a worn track in this item.

[ggrum]

Re: Hunter with jerky running

Thanks for all the suggestions. Haven't had the chance to try anything yet and the problem is more of an occasional irritation and doesn't stop me driving the car. I have a feeling that the problem is mainly to do with the idle control valve as, when the engine is revved up and allowed to drop down to idle it briefly drops below the idle speed of about 850 rpm, sometimes almost to the point of stalling, and then recovers. After that it hunts slightly, probably changing by about 50 rpm. I'll probably have a look at it sometime over the next few weeks when the decorating is finished.

[kahawi]

Re: Hunter with jerky running

Hi guys, mention was made here of downloading diagnostics, can anyone advise where/what the diagnostics port looks like and how to find it?
I have this socket, close by the engine management box, but it doesn’t look like OBD(XX)?

IMG_0043.JPG

How do we get diag info out of a DOHC-16v 2,300 Ford unit, is it of any use? What software cables apps etc can be used and is it worth it?
Discuss…..!

[stewartdjones]

Re: Hunter with jerky running

What’s a TPS?

[jon_cox]

Re: Hunter with jerky running

Throttle Position Sensor

[philcoyle]

Re: Hunter with jerky running

Throttle Position Sensor, it sits on the end of the butterfly/throttle flap and it notifies the ECU/engine control unit how much fuel the engine needs at any given throttle position or what size boots you are wearing. A little black plastic device with 3 wires coming out of it.
If you have a dodgy tick over, you can relearn your TPS (now you know what it is) to reset itself, after all the pedal has been up and down like a fiddlers elbow or a few million times, and wear tolerances will vary.

Turn on ignition ONLY and press the throttle pedal fairly quickly FULLY UP AND DOWN at least 10 times, the number of times you need to press the pedal up and down varies from car to car but 10 will cover everything, switch off, now wait a few minutes. Important.
Now start the engine, because the ECU is already programmed it will go to its default setting for the TPS, tickover now restored.

If you check the signal wire voltage from the TPS (check wiring diagram for your model) there's 3 wires ,at rest/tickover look for 0.3-0.5 volts . Depending on model/make the live wire/ecu to TPS feed will be either 5v or 9v, BUT your full throttle voltage should read about 0.5v below your ecu voltage.

This will work on any car with efi .