Hey All,

Been trying to solve this mystery for a few days now. Hope you can help me!

Background: for the past year I've noticed petrol use going up in my car. Then 6 months ago, my car wouldn't start for a couple of tries in the morning (could hear cranking, but no start). On the 3rd try, it started and after 20 min ish the check engine light came on. The OBDII scanner showed a P0340 code (camshaft position sensor), with the following freeze frame:

P0340

FUELSYS1 OL

FUELSYS2 N/A

LOAD_PCT(%) 45.1

ETC (C) 90 

SHRTFT1(%) 3.1

LONGFT1(%) -3.9

RPM (/min) 808

VSS (km/h) 0

The car felt fine to drive, so I wasn't in a rush to change the sensor. By the time I got the sensor (original Ford) a week later, the check engine light went away, and again, the car felt fine so I left it (albeit petrol use was still high). Fast forward a 6 months, a couple of weeks ago the P0340 code came on again. The following was the freeze frame I got:

P0340

FUELSYS1 CL

FUELSYS2 N/A

LOAD_PCT(%) 34.1

ETC (C) 90 

SHRTFT1(%) -2.3

LONGFT1(%) -2.3

RPM (/min) 792

VSS (km/h) 0

This time I was ready with the sensor! Changed the sensor, and the car drove perfectly for 2 days. Then, on the morning of the 3rd day, it wouldn't start (cranking but no start). After what felt like the 10th attempt, it finally started. No error code. All seemed fine, until I put it into D (automatic), engine started hunting(?) or misfiring (not sure what the difference is tbh). Tried reverse, same issue. It was clear the car was going nowhere. See all the work I've put into (attempting!) to fix it below.

Symptoms: the car now starts just fine. No codes. But once the car starts:

• On cold engine: 
  • Running at 1200 RPM ish.
  • On Parking/Neutral - all feels fine.
    • Switch AC on - engine starts hunting/misfiring (again, excuse my terminology, I'm not sure what's the difference).
  • On Drive/Reverse - hunting.
    • Switch AC on - makes it worse.
• On hot engine:
  • Engine temperature never goes above normal.
  • RPM goes slowly and nicely to 800 RPM ish.
  • On Parking/Neutral - occasional hunting.
    • Switch AC on - makes it worse.
  • On Drive/Reverse - hunting.
    • Switch AC on - the worst.
  • Typical OBDII reading while hot:

    • FUELSYS2 N/A

    • LOAD_PCT(%) 33

    • ETC (C) 90

    • SHRTFT1(%) -2.3

    • LONGFT1(%) -1.3

    • SHRTFT2(%) -3.1

    • LONGFT2(%) -1.6

    • RPM (/min) 799 (drops temporarily every time I get misfiring while in gear with AC on, or just one or the other)

    • Speed (km/h) 0

    • SPARKADV (angle) 14

    • MAF (g/s) 1.95

    • TP (%) 18.8

    • O2B1S1 (V) fluctuates between 0-1

    • O2B1S1 (V) fluctuates between 0-0.6

 

 

Diagnosis: this is where things get interesting. I should mention that some of the parts I already had as spares... Should also mention that I reset the ECU every time I changed a part and let the car idle for 10-15 min before attempting to increase the load on the car.

Sensors

• Camshaft sensor:
  • Theory: new Original Ford sensor is messed up.
  • Fix: replaced with old sensor (also original).
  • Result: no difference.
• Crankshaft sensor:
  • Theory: if the cam sensor was faulty, maybe the crank sensor was also crap. Alternatively, maybe a cam sensor code for a crank sensor fault?
  • Fix: replaced with new sensor (aftermarket).
  • Result: no difference.

Air issues

• ICV:
  • Theory 1: dirty.
  • Fix 1: wasn't dirty but cleaned with carb cleaner, then also replaced with new aftermarket.
  • Result 1: no difference.
  • Theory 2: ICV not controlled by ECU (due to ECU or wiring).
  • Test 2: disconnected while engine is running.
  • Result 2: engine stops immediately, so seems fine.
  • Theory 3: ICV not regulated properly by ECU.
  • Test 3: turned on AC while watching RPM.
  • Result 3: RPM doesn't drop, so seems ECU compensates well through ICV?
• Throttle:
  • Theory: dirty.
  • Fix: cleaned with carb cleaner.
  • Result: no difference.
• Throttle position sensor:
  • Theory: not reading idle correctly.
  • Fix: replaced with new aftermarket (original was Ford). Also tried to reset its position by switching ignition on for 10 sec, pressing the pedal all the way in and out 5 times, switching ignition off for 10 sec, starting the engine and letting it idle. 
  • Result: TP(%) went down from 18.8 to 17.3, but made no real difference.
• Air filter:
  • Theory: clogged by something, even though I change once a year.
  • Test: opened and checked.
  • Result: seems pretty clean actually (10 months on this filter to date).
• MAF:
  • Theory 1: dirty so messes up air readings by the ECU.
  • Fix 1: cleaned with contact cleaner.
  • Result 1: no difference. Still reading around 2 g/s at idle when engine is hot.
  • Theory 2: dysfunctional.
  • Test 2: disconnected while engine is running.
  • Result 2: engine stops immediately, so seems fine. Again, readings seem normal and increase linearly (as far as I can tell) with throttle opening.
• Air leak:
  • Theory: leads to dysfunctional idle.
  • Fix: sprayed carb cleaner all around air intake areas, throttle, ICV etc. Also visually checked hoses.
  • Result: RPM remained the same and couldn't see any visual issues.

Cam belt

• Theory: timing messed up because belt is faulty
• Test: changed belt and tensioner 10k miles / 2 years ago. Seems to be running fine.

Fuel delivery

• Theory: not enough fuel passing through when engine under load at idle (through AC or D/R gears). Wasn't sure if that's it, because all seemed fine when increasing RPM.
• Test: no fix applied as fuel trims seemed fine, reading SHRTFT1 (-2.3 to 0.8), LONGFT1 (-0.8), SHRTFT2 (-3 to 0.8), LONGFT2 (-0.8).
• Result: moved on to another theory.

Electricals

• Theory: battery / alternator messed up, so when under load at idle, car starts misfiring.
• Test: tested battery with battery tester and monitored voltage under load while getting symptoms.
• Fix: cleaned all relevant connectors and earths to chassis with contact cleaner (also cleaner earths to chassis with wire brush).
• Result: battery test comes back ok. Voltage on idle is 14.7v then when increasing load by turning on AC and putting into D goes to 13.4-14.3v. Seemed fine to me.

Ignition issues

• Spark plugs:
  • Theory: changed them about 20k miles ago (motocraft). Probably messed up because I have a rocker gasket leak and they sit in a bit of oil.
  • Fix: replaced with new.
  • Result: no difference.
• Ignition coils:
  • Theory: old or messed up because of the oil.
  • Fix: did not change them as assumed that if they're messed up, I should notice misfiring at high RPM - which I don't.
  • Result: cannot exclude this option, but is my rationale correct at all?
• Live data:
  • Theory: misfiring should reveal itself through the SPARKADV on the scanner.
  • Test: I tested the SPARKADV on idle, which is when I get the symptoms.
  • Result: 10-14 degrees. Seemed normal to me.

 

So this is it. I don't know what to test anymore. No more ideas. It's my first focus and I love it. I don't want to get rid of this car. If anyone has any ideas - do tell! Thank you!

I'm a bit lost TBF.

A 1.6 Mk1 Focus doesn't have VVT so won't have a Cam position sensor

But it will have a Crank Position sensor.

And you can't have an idle issue under load, idling is zero load

Does your speedo work correctly?

A lot of MK1 Focus had trouble with the speed sensor (ignore if you have ABS)

You could be using loads of fuel if you're coked up, especially on an auto because they don't rev

You could be suffering from sticking valves

What fuel are you putting in?

If it's not E5, switch to E5 (Super Unleaded) and take the car for a good long run and try to get it to hold a gear so you can hold the revs above 4,500RPM for a couple of minutes

Tesco is good value Super Unleaded

Also, bearing in mind this is a 20 year old car, has the transmission fluid ever been changed

I would change the HT leads and coil too

I haven't read all that.  Just wanted to say that the Mk1 1.6 does have a cam sensor.  P0340 would suggest a wiring fault between sensor & PCM to me.

It does have a cam sensor??? But no VVT?

I can understand ST170/RS having one

13 minutes ago, DaveT70 said:

It does have a cam sensor??? But no VVT?

I can understand ST170/RS having one

Plenty of engines have a cam sensor without VVT.

Blimey!

Ford normally cost most things out, yet leave a Cam position sensor on a fixed cam engine.

They amaze me

Sorry for going AWOL! Urgent life things came up.

 

On 2/19/2025 at 12:23 PM, DaveT70 said:

Also, bearing in mind this is a 20 year old car, has the transmission fluid ever been changed

I would change the HT leads and coil too

It was indeed the coil pack! Thanks for the suggestion!

For diagnosis, I removed the HT leads, one at a time, while the engine was running. RPM dropped only when I removed lead 2. Virtually ZERO difference when I removed 1, 3 or 4. Changed the coil pack + HT leads + reset the PCM and all turned ok. Not only that, the car - obviously - has so much more power now! Can't believe I drove it for 3+ years with a faulty pack without realising. Live and learn.

Thanks for your help guys!