Hi, be gentle with me I'm a newbie!

My car is an '06 1.6 zetec se. The issue is an annoying hesitation that I can't track down, particularly noticeable when sharply opening the throttle. I also have a surging, more noticeable in lower gears. The car was serviced only a few months back. I have checked PCV hose/valve. Swapped coil pack for a known good one. I also tried spraying soapy water around looking for vacuum leaks. I have access to Forscan software that shows no codes or pending codes. I don't really want to fire the parts shotgun, so how do I diagnose a misfire/hesitation with no codes?

12 hours ago, wild_one said:

The issue is an annoying hesitation that I can't track down, particularly noticeable when sharply opening the throttle. I also have a surging, more noticeable in lower gears. The car was serviced only a few months back. I have checked PCV hose/valve. Swapped coil pack for a known good one. I also tried spraying soapy water around looking for vacuum leaks. I have access to Forscan software that shows no codes or pending codes.

Minor faults can be very hard to pin down. Plugs and leads are main suspects for hesitations. Modern Ford engines tend to have a big plug gap, 1mm or more. This increases the voltage needed, and puts a huge strain on leads, coil pack and ECU. It is probably for a small gain in efficiency or emissions, by getting a bigger spark. Check the plug gaps, and narrow down to the min. allowed, say a bit under 1mm. The high voltage can jump from the lead to the cylinder head if the seal between lead and plug is less than perfect, or there is some dirt there. Opening the throttle increases gas pressure in the cylinder prior to spark, which maximises the voltage needed. 1mm gap inside the cylinder is equivalent to well over 12mm outside.

The other suspect area is a sticky throttle body, or bad connections to it.

Bubble tests will not detect vacuum leaks, as air is being drawn in. The best way to check for vacuum leaks is to use the fuel trim values that can be read by Forscan. There are internet articles on this. The extra air has to be compensated for by the ECU, and this can be seen by changes in trim values.

The ECU is fairly good at detecting true misfires, and badly sticking throttles. Keep monitoring with Forscan, or a similar system. Sometimes you just have to wait for a minor but annoying problem to develop a bit until it can be seen more clearly.

I had about 6 months of annoying droning before I was able to track it down to a particular wheel bearing. Also I get annoying P0299 errors (Turbo underboost) if I open the throttle quickly at lowish rpm. It has no real drivability symptoms. I am not dismantling all the stuff at the back of the engine until I get some better idea of the cause!

 

4 minutes ago, Tdci-Peter said:

Minor faults can be very hard to pin down. Plugs and leads are main suspects for hesitations. Modern Ford engines tend to have a big plug gap, 1mm or more. This increases the voltage needed, and puts a huge strain on leads, coil pack and ECU. It is probably for a small gain in efficiency or emissions, by getting a bigger spark. Check the plug gaps, and narrow down to the min. allowed, say a bit under 1mm. The high voltage can jump from the lead to the cylinder head if the seal between lead and plug is less than perfect, or there is some dirt there. Opening the throttle increases gas pressure in the cylinder prior to spark, which maximises the voltage needed. 1mm gap inside the cylinder is equivalent to well over 12mm outside.

The other suspect area is a sticky throttle body, or bad connections to it.

Bubble tests will not detect vacuum leaks, as air is being drawn in. The best way to check for vacuum leaks is to use the fuel trim values that can be read by Forscan. There are internet articles on this. The extra air has to be compensated for by the ECU, and this can be seen by changes in trim values.

The ECU is fairly good at detecting true misfires, and badly sticking throttles. Keep monitoring with Forscan, or a similar system. Sometimes you just have to wait for a minor but annoying problem to develop a bit until it can be seen more clearly.

I had about 6 months of annoying droning before I was able to track it down to a particular wheel bearing. Also I get annoying P0299 errors (Turbo underboost) if I open the throttle quickly at lowish rpm. It has no real drivability symptoms. I am not dismantling all the stuff at the back of the engine until I get some better idea of the cause!

 

Thanks for the replay. I did search around youtube and investigate fuel trims but mine seem fine, very good actually considering there is a fault somewhere. But I think as you say,  I will have to wait for it to develop. Would I be correct in thinking that a misfire would have to be petty bad before a code was logged?

31 minutes ago, wild_one said:

Would I be correct in thinking that a misfire would have to be petty bad before a code was logged?

The ECU is really looking for detonations (knock or pinking), as these can damage the engine. But am pretty sure from other reports that it also detects non-ignition, or missing firings. However it would be easier to detect these in steady driving, rather than the rapidly changing conditions when the throttle opens quickly. So it may have difficulty detecting minor problems in short term dynamic conditions.

On deisel engines, the EGR can also cause power fluctuations and hesitation. The EGR on a petrol engine is smaller, if fitted at all (I don't think the TI-VCT has an EGR, it uses the valve timing to do the same job). But it is another possible suspect, as is the cam timing on the TI-VCT. But I would thoroughly look at spark problems first.

Can anyone confirm how much resistance should be in the standard ignition leads? I have a basic multimeter and set it to 20k ohms range. the leads read 3.5k, 3.5k, 5.0k and 7.5k. I'm concerned about the 7.5k being high?

16 hours ago, wild_one said:

the leads read 3.5k, 3.5k, 5.0k and 7.5k. I'm concerned about the 7.5k being high?

Usually the resistance will be roughly in proportion to the length, and I seem to recall values up to 10k being common.

If the 7.5k one is longer than the others, and produces a consistent reading even when gently flexed and pulled, then I would say it was ok. Any variations or if it is short, then replace. Also carefully check the rubber ends for splits, cracks, or being oily and too soft.

That voltage can jump quite a distance in free air, and much further by tracking along contaminated or damaged insulating surfaces.

Well, changing the plugs has made a huge difference. It no longer hesitates (touch wood), and actually revs up to the red line smoothly. But, the 'surging' is still there and the 'hunting' while on a light throttle. In my gut it feels like an air leak but I guess I'm into removing the inlet manifold at this point?

On 7/23/2018 at 10:33 PM, wild_one said:

Hi, be gentle with me I'm a newbie!

My car is an '06 1.6 zetec se. The issue is an annoying hesitation that I can't track down, particularly noticeable when sharply opening the throttle. I also have a surging, more noticeable in lower gears. The car was serviced only a few months back. I have checked PCV hose/valve. Swapped coil pack for a known good one. I also tried spraying soapy water around looking for vacuum leaks. I have access to Forscan software that shows no codes or pending codes. I don't really want to fire the parts shotgun, so how do I diagnose a misfire/hesitation with no codes?

Have you checked injector seals. They can become hard, then brittle and split due to engine temperatures going from cold to hot then cold again ect. Just a thought.

On 7/26/2018 at 10:36 PM, chongobambino said:

Have you checked injector seals. They can become hard, then brittle and split due to engine temperatures going from cold to hot then cold again ect. Just a thought.

Hi, thanks for the reply. To be honest I do sometimes get a feint smell of fuel in the car and I did the usual checks for leaks around the injectors and fuel lines but I didn't find anything. Is there a more definitive check for leaking seals.

I am just pondering removing the inlet manifold and replacing the seals on that?

On 7/26/2018 at 2:15 PM, wild_one said:

But, the 'surging' is still there and the 'hunting' while on a light throttle. In my gut it feels like an air leak but I guess I'm into removing the inlet manifold at this point?

If the 'surge' is a delayed response to a accelerator pedal opening, then I would be suspecting a sticky throttle body first. This also stacks up with hunting on idle, as very fine control of the throttle valve is needed then.

Air leaks bad enough to affect driving like that should show up in the fuel trims that you have checked already. Though it is always a good idea to re-check, and generally keep an eye on, parameters like that. Fault symptoms can come and go.

17 hours ago, Tdci-Peter said:

If the 'surge' is a delayed response to a accelerator pedal opening, then I would be suspecting a sticky throttle body first. This also stacks up with hunting on idle, as very fine control of the throttle valve is needed then.

Air leaks bad enough to affect driving like that should show up in the fuel trims that you have checked already. Though it is always a good idea to re-check, and generally keep an eye on, parameters like that. Fault symptoms can come and go.

Again thanks for the reply. The fuel trims are spot on. The surging is most noticeable when driving in second gear at low speed, for example driving around a roundabout. Where with a fixed throttle position the car drives in a series of jerks, almost like you're stabbing at the throttle. As soon as you push the pedal down to accelerate it stops. Sometimes, at motorway speeds you can feel this too, but it's less noticeable?

On 7/29/2018 at 10:26 PM, Tdci-Peter said:

This also stacks up with hunting on idle, as very fine control of the throttle valve is needed then.

Peter, I stand to be corrected but on a petrol engine I don't think the throttle valve (butterfly) is used for fine control of idle. I think it's mainly done by varying the ignition timing.

6 minutes ago, mjt said:

on a petrol engine I don't think the throttle valve (butterfly) is used for fine control of idle. I think it's mainly done by varying the ignition timing.

I have thought before that by getting rid of the idle air control valve (often an unreliable component), and relying on the much bigger main throttle, rapid, fine control would be difficult. Adjusting the fuel injections would throw the emissions out, which are tested at idle on petrol engines, I think. So ignition timing is an interesting option.

But I was not quite right with my "hunting on idle" term, this car seems to be worst at low throttle openings while driving. It could be where the throttle plate is just opening, and is sticking a bit at that point due to wear. I have heard of wear ridges forming that prevent smooth opening.

19 hours ago, wild_one said:

The fuel trims are spot on.

Where with a fixed throttle position the car drives in a series of jerks, almost like you're stabbing at the throttle. As soon as you push the pedal down to accelerate it stops. Sometimes, at motorway speeds you can feel this too, but it's less noticeable?

One item that might be able to do this would be a sticking PCV. If it was cycling and letting air into the intake manifold in bursts, it could lead to jumpy low power driving without affecting the fuel trims, as the average flow would be normal, maybe?

I see it has been checked, but they are not easy to fully test. It could still be a bit sticky in use.

Most leaky seals and gaskets would give a constant air leak that would gradually drive the fuel trims out as the ECU compensated.

3 hours ago, Tdci-Peter said:

I have thought before that by getting rid of the idle air control valve (often an unreliable component), and relying on the much bigger main throttle, rapid, fine control would be difficult. Adjusting the fuel injections would throw the emissions out, which are tested at idle on petrol engines, I think. So ignition timing is an interesting option.

But I was not quite right with my "hunting on idle" term, this car seems to be worst at low throttle openings while driving. It could be where the throttle plate is just opening, and is sticking a bit at that point due to wear. I have heard of wear ridges forming that prevent smooth opening.

One item that might be able to do this would be a sticking PCV. If it was cycling and letting air into the intake manifold in bursts, it could lead to jumpy low power driving without affecting the fuel trims, as the average flow would be normal, maybe?

I see it has been checked, but they are not easy to fully test. It could still be a bit sticky in use.

Most leaky seals and gaskets would give a constant air leak that would gradually drive the fuel trims out as the ECU compensated.

I've driven 400 miles in the car in the last few days. It definitely has a problem on a light throttle and when opening and closing the throttle slightly for example at motorway cruising speeds. If you lift off the throttle at 60mph and then gently push your foot back on the gas you get a little 'hesitation'. When you are holding a constant speed, and look closely at the rev counter, you can see it wobble a little. This unevenness is more noticeable in the lower gears especially for example when you have to creep in first and second gears in traffic, when it surges up and down and its a struggle to hold a constant speed without having to dip the clutch and try again.

But, good fuel trims, no codes or pending codes, and averaging close to 40mpg?

On 7/28/2018 at 10:13 PM, wild_one said:

Hi, thanks for the reply. To be honest I do sometimes get a feint smell of fuel in the car and I did the usual checks for leaks around the injectors and fuel lines but I didn't find anything. Is there a more definitive check for leaking seals.

I am just pondering removing the inlet manifold and replacing the seals on that?

Its worth checking them as its fairly easy to do. A few weeks ago i worked on a mondeo petrol with gas conversion, it ran sweet on gas but stumbled a bit on petrol. Cleaned everything, replaced as many parts as possible just to find no1 and no4 injector seals had gone hard over the years, and i can only assume a previous keeper may have removed injectors for inspection and when putting them back in the seals were not seated in the original way so was drawing air in rather than weeping fuel out. Costs nothing but time to check but cant remember how much they cost. Hope the above helps.