Focus ST170 Misfiring/Hesitant 2k to 3k rpm

Focus ST170 Misfiring/Hesitant 2k to 3k rpm

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5RedLights

Original Poster:

155 posts

126 months

Wednesday 29th October 2014
quotequote all
Hi

My Focus ST170 (52 reg) has started misfiring/is hesitant when on full throttle between 2k and 3k rpm. It's only usually when on full throttle, and is fine at any other revs. No problems in reaching higher revs or any loss of speed. The problem is intermittent too, but has started happening more often.

I've cleaned the MAF, throttle body and changed the spark plugs. I'm doing the fuel filter this weekend. I've done a self Diagnostic check, and there are no fault codes. The car can also occasionally have a little 'hiccup' while at idle when it is doing the hesitant thing at 2k to 3k. The throttle cable had melted a bit while touching the lift eye on the engine, which is also an earthing point. I've shortened the cable up and put electrical tape over where it had melted, and now isn't touching the eye. This hasn't solved anything.

I've read a few things about what it could be, but just wondered if anyone had had similar experiences. There's a few things it could be, so just wanted to ask some queries regarding these.

Coil pack/HT leads - it's been happening for around 1 month now. If it was these, wouldn't they have gone by now and stopped working completely? Wouldn't these effect the running at all revs, not just 2k to 3k? Would something with these show up on a Diag check?

Fuel pump/fuel pump driver module - I've taken the car around roundabouts on low fuel at speed, and there hasn't been any drop in fuel supply. Wouldn't the issue with fuel supply effect higher revs, rather than just one band of revs? Again, wouldn't problems with fuel show up on a diag check?

PCM firmware/ECU reset - The ST170 has a flatspot around 2k to 3k, and I've read that a fair few earlier models needed a PCM update to sort out this sort of problem. Could this be it?

Appreciate it's an old car, but I could really do with keeping it running for a while and want to solve this issue, but don't want to end up replacing every last part to try and find out what's going on.

Thanks!

lemonslap

960 posts

154 months

Wednesday 29th October 2014
quotequote all
What's your service history like? What are your current miles? The 2500rpm stutter is very common, mine does it.

5RedLights

Original Poster:

155 posts

126 months

Wednesday 29th October 2014
quotequote all
No Service history. Miles are 113k, when I got it, it had done around 98k. Just to add, I've done the DMF, clutch and gearbox since I've had it. It's probably a total coincidence, but I think the stuttering started just after I gave someone a jump start. I've had the car around 5 months and the issue has only been around for about 1 month.

Sometimes, when I put the throttle down full while just under 3k, there's more of a lag than a stutter, and it feels like it's 'stuck' until it gets over 3k, then it's fine. This is why I'd cleaned the TB out, just to make sure it wasn't getting stuck.

The spark plugs I took out looked like standard NGK ones, not the correct Ford ones the ST170 needs, which is what I put in.

I've read about the stutter, but this has been much worse in the last month, and can be very pronounced at patches throughout the 2-3k rev band. As I've said, at other times it feels like the throttle is stuck/lagging, and at idle it can feel occasionally lumpy.

I saw that you'd given some advice on another thread a couple of years back about PCM software based on the self-test dash readout. Would it help if I wrote this out?

Thanks

Edited by 5RedLights on Wednesday 29th October 10:32

lemonslap

960 posts

154 months

Wednesday 29th October 2014
quotequote all
Just to check the spark plugs you fitted were black with white insulators? I have had a ford parts department try to give me the wrong plugs before.

5RedLights

Original Poster:

155 posts

126 months

Wednesday 29th October 2014
quotequote all
Yep, I checked the FINIS code for them to make sure I got the right ones. It actually ran ok for a few days after changing them, then back to the same problem.

lemonslap

960 posts

154 months

Wednesday 29th October 2014
quotequote all
5RedLights said:
Yep, I checked the FINIS code for them to make sure I got the right ones. It actually ran ok for a few days after changing them, then back to the same problem.
Have you tried disconnecting the battery for 1 hour? This will reset the ECU memory back to factory. Just make sure you have any radio codes needed.

I would also change the fuel filter.

Edited by lemonslap on Wednesday 29th October 10:47

Zad

12,695 posts

235 months

Wednesday 29th October 2014
quotequote all
I'm a bit worried that the throttle cable melted where it touched the lifting eye. Normally both would be at ground (zero volts) potential and no current would flow. The fact that current flowed through the throttle cable tells me that maybe the engine isn't properly earthed to chassis, so check any grounding straps are intact and well connected.



5RedLights

Original Poster:

155 posts

126 months

Wednesday 29th October 2014
quotequote all
I think the melting had more to do with heat to be honest, as the lift eye/surrounding area gets a bit warm.

Thanks anyway.

5RedLights

Original Poster:

155 posts

126 months

Thursday 30th October 2014
quotequote all
lemonslap said:
Have you tried disconnecting the battery for 1 hour? This will reset the ECU memory back to factory. Just make sure you have any radio codes needed.

I would also change the fuel filter.

Edited by lemonslap on Wednesday 29th October 10:47
Hi

ECU re-set. Drove it this morning into work (30 miles) and had the same problem, still at 2-3k rpm. At first, it was also doing an odd thing at idle, where it would drop as usual to around 1k, then on it's own rise up to around 1600rpm, then drop again. It usually stays high when it's warming up, but this is after I'd been doing 20 miles on motorway. Towards the end of the drive, say around 28 miles, this stopped, and although I couldn't fully check it out, the 2k-3k rev issues seemed to stop. Will have to see how it is on drive home later. Would the ECU need a bit of time to re-calibrate everything and to get rid of any problems? Also, towards the end, it didn't seem to have the problem if you dropped from 3k down into in the 2-3k band, then used full throttle.

I've also got the self-test read out dash figures if these would be any help?






lemonslap

960 posts

154 months

Thursday 30th October 2014
quotequote all
5RedLights said:
lemonslap said:
Have you tried disconnecting the battery for 1 hour? This will reset the ECU memory back to factory. Just make sure you have any radio codes needed.

I would also change the fuel filter.

Edited by lemonslap on Wednesday 29th October 10:47
Hi

ECU re-set. Drove it this morning into work (30 miles) and had the same problem, still at 2-3k rpm. At first, it was also doing an odd thing at idle, where it would drop as usual to around 1k, then on it's own rise up to around 1600rpm, then drop again. It usually stays high when it's warming up, but this is after I'd been doing 20 miles on motorway. Towards the end of the drive, say around 28 miles, this stopped, and although I couldn't fully check it out, the 2k-3k rev issues seemed to stop. Will have to see how it is on drive home later. Would the ECU need a bit of time to re-calibrate everything and to get rid of any problems? Also, towards the end, it didn't seem to have the problem if you dropped from 3k down into in the 2-3k band, then used full throttle.

I've also got the self-test read out dash figures if these would be any help?
Yes it will take a bit of time to re calibrate typically about 50 miles, how old is the fuel filter? I would also have a wiggle of the HT leads (best wear gloves for this) and see if the idle changes. The other issue with these engine if neglected on oil changes the inlet valve timing gear can become gummed up (works on oil pressure).

Edited by lemonslap on Thursday 30th October 09:44

5RedLights

Original Poster:

155 posts

126 months

Thursday 30th October 2014
quotequote all
Fuel filter - no idea, but the spark plugs looked fairly old so I'm guessing quite old and overdue. I'll change it tomorrow.

I've ordered some used-but-newer HT leads and coil pack just incase these need changing now or at a later date, but I'll give the current ones a wiggle when I do the fuel filter tomorrow.

Doing another 30 miles tonight so should give ECU time to re-calibrate.

Thanks

lemonslap

960 posts

154 months

Thursday 30th October 2014
quotequote all
5RedLights said:
Fuel filter - no idea, but the spark plugs looked fairly old so I'm guessing quite old and overdue. I'll change it tomorrow.

I've ordered some used-but-newer HT leads and coil pack just incase these need changing now or at a later date, but I'll give the current ones a wiggle when I do the fuel filter tomorrow.

Doing another 30 miles tonight so should give ECU time to re-calibrate.

Thanks
I thought you had already replaced the spark plugs?

When was was the following work last carried out:

Oil change and which oil was used?

Oil filter?

Air filter?

IMRC function checked?

Also I take it the engine management light is working (lights up when the ignition is switched on).

5RedLights

Original Poster:

155 posts

126 months

Thursday 30th October 2014
quotequote all
lemonslap said:
I thought you had already replaced the spark plugs?

When was was the following work last carried out:

Oil change and which oil was used?

Oil filter?

Air filter?

IMRC function checked?

Also I take it the engine management light is working (lights up when the ignition is switched on).
Sorry, spark plugs have been done. I meant the spark plugs looked old, so fair to assume the fuel filter might not have been done for a while too.

Oil filter and change - apparently done before I got it, oil looked fairly clean around 5 months ago. This is another thing to do soon though. Is it just standard focus 2.0 parts for this, or anything more special for the st170? I can always do this tomorrow too, but didn't think this would be causing the acceleration problems so wanted to check this out first.

air filter - originally had a rubbish cone fitted, now has a new K&N panel filter on it.

I'll have a look, although no DTC fault codes have ever come up on the self-test diag test.

Do you want me to post the readout, to check if there's anything in it that suggests a problem?

Edited by 5RedLights on Thursday 30th October 12:34

lemonslap

960 posts

154 months

Thursday 30th October 2014
quotequote all
5RedLights said:
lemonslap said:
I thought you had already replaced the spark plugs?

When was was the following work last carried out:

Oil change and which oil was used?

Oil filter?

Air filter?

IMRC function checked?

Also I take it the engine management light is working (lights up when the ignition is switched on).
Sorry, spark plugs have been done. I meant the spark plugs looked old, so fair to assume the fuel filter might not have been done for a while too.

Oil filter and change - apparently done before I got it, oil looked fairly clean around 5 months ago. This is another thing to do soon though. Is it just standard focus 2.0 parts for this, or anything more special for the st170? I can always do this tomorrow too, but didn't think this would be causing the acceleration problems so wanted to check this out first.

air filter - originally had a rubbish cone fitted, now has a new K&N panel filter on it.

I'll have a look, although no DTC fault codes have ever come up on the self-test diag test.

Do you want me to post the readout, to check if there's anything in it that suggests a problem?

Edited by 5RedLights on Thursday 30th October 12:34
Oil filter is standard 2.0 zetec (although it's harder to change due to the oil cooler), spark plugs are special as you know. I would do a full service on it, all the filters, spark plugs and oil (fully synth 5w-30). Cambelt (special kit for the ST170) and aux belt is due at 100k or 10 years ( I changed mine at 58k and 8 years and it was all fine), also you need to check the valve clearances at this mileage. Make sure all the above is done then see how it's running.

5RedLights

Original Poster:

155 posts

126 months

Thursday 30th October 2014
quotequote all
On drive home it was much smoother. No stuttering for first 30 minutes, then once I'd been on motorway for a bit, started doing it again. Not sure what this means. Shall I reset again?

I'll get the oil changed as well tomorrow. Cambelt was done before I got it.

Once I've done the fuel filter, will a fuel pressure test show if there are any problems with the fuel pump, fuel rail or fuel pump driver module? Just trying to exclude each possible area as much as I can without spending loads of money.

5RedLights

Original Poster:

155 posts

126 months

Thursday 30th October 2014
quotequote all
Also, how do I check valve clearances?

Thanks

5RedLights

Original Poster:

155 posts

126 months

Monday 3rd November 2014
quotequote all
Did fuel filter, oil and oil filter over weekend, so it now as a new panel filter, new spark plugs, new fuel filter, new oil and oil filter, and had TB and MAF sensor cleaned.

It's still occasionally lumpy at idle, and still stuttering in the 2-3k rev range, only when on full throttle from 2k upwards. It seems that if you floor it at around 2600rpm, it doesn't hesitate.

If it was just the hestitation, I'd assume this was just part of the trademark stutter, but the occasionally rough idle makes me think otherwise.

I'm fitting used-but-newer HT leads and coil pack to see fi that does anything, but after that I'm at a loss as to what it could be. I'll get a fuel pressure test if it's still there, but I think the fuel pressure is fine.

Any suggestions welcome.

Thanks

Zad

12,695 posts

235 months

Monday 3rd November 2014
quotequote all
For faults that take some time to occur, I would tend to think that it is a poor connection, either in the loom somewhere or (more likely) inside a sensor. The engine heat causing the component to expand and make poor connection somewhere. An absolute swine to diagnose, as you ideally need an oscilloscope plugged onto each sensor and then take the car for a ride to see which ECU input is getting the faulty data from the faulty sensor.

Its a pain in the posterior when no fault is logged for something like that!



5RedLights

Original Poster:

155 posts

126 months

Monday 3rd November 2014
quotequote all
Really hope it's not something like that, as I'll never find it! It can happen from start up too, so not sure about something expanding with the heat.

Could a loose engine mount cause the symptoms? At 70mph during the weekend, off throttle, heard a vibration coming from the engine bay, sounding like a loose/old mount.



Edited by 5RedLights on Monday 3rd November 14:36

lemonslap

960 posts

154 months

Monday 3rd November 2014
quotequote all
What Zad said^^ But change the leads and coil pack first as these could cause this.