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Mk1.5 2.0 Zetec E Hesitating During Warmup

Ian T

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Hello everybody, this is my first post, probably like half of all people who sign up to a forum, I'm here to ask for some expert advice from those better in the know about these cars. I'd really appreciate someone setting me right and helping me to solve this. :-)

I've got a 2002 '52 plate mk1 Ghia with the 2.0 Black top Zetec E engine (EDDB).

I've been trying to diagnose a silly fault with it over the last year or so (without lots of commitment I suppose) but am determined to work out what is wrong and fix it, as it's otherwise still a great, tight, well specced and tidy car with only about 104k miles and no rust.

The symptoms are as follows:

From cold, start is fine, idle is smooth and it drives out our driveway just fine, up a gentle incline for about 1/3 of a mile to the traffic lights at the end of the street, then after that, running in 5th gear at 40mph, there's a pronounced hesitation / stutter / miss that develops and persists for about 2 minutes until it gets close to operating temperature. It drives pretty well once warm, but there is a hint of a miss or lack of power sometimes at that (for me) typical 'tickling along' driving style, i.e 1.5k to 2.5k rpm with light throttle. Open the throttle fully and it always clears and accelerates cleanly, the problem only seems to be at light throttle. mpg is good, doing a bit over 40mpg (occasionally 45mpg) on a motorway run.

Last year, I replaced the coil pack, leads (Motorcraft) and plugs (Champion) but that made no difference and I've since been looking at the various sensors to understand whether they are faulty or something else is causing it. I also replaced the thermostat, which was passing and resulted in a 'cold' indication on the gauge.

There is no EGR on my engine (not needed for emissions apparently, so not fitted from new), so I can rule out EGPD sensor / valve faults.

I've been logging via OBD and can't see *much* wrong apart from the adapted Long Term Fuel Trim values at idle, which sits at around -8% at idle (and while decelerating).

So, I've been checking for physical faults:

Fuel pressure: 3.2 bar at idle and 3.8 bar during acceleration.

Idle vacuum: 19-20 inches at 800rpm (gauge pointer 'rattles' a bit)

Vacuum away from idle: Increases to around 21 - 22 inches as revs are increased to around 2,000 rpm, with the car static (no load). Decreases significantly as throttle is 'blipped' open, all as expected I'd say?).

Vacuum leaks: No leak from intake to fuel pressure regulator. No leak in pipework from intake to Evap module on bulkhead, but some vacuum is lost at the small port (i.e. a small amount of air passes through that module somewhere). I disconnected the large pipe to the Evap module and plugged the port at the inlet manifold. If anything, the Long Term Fuel Trim (LTFT) got worse at around -12% (demanding a leaner mixture) at idle. I've not driven it like that (noting loss of servo assistance in brakes). I've looked at (and sprayed carb cleaner over) the PCV valve and its pipe running under the thermostat to the rear of the engine, and while the rubber pipe is hard, with no change in revs or O2 sensor readings from squirting carb cleaner over it, I'd say it's probably OK. At least until I try removing it!

MAF: Hard to know what is 'normal' for this engine. It passes the dynamic test in the Ford IDS software and sits at about 1.9g/s at idle revs. I've cleaned it with carb cleaner and can't *see* any contamination, nor was it any different before or after.

O2 sensors: Sensor 1 (upstream) switches between rich and lean. Looks a bit slow at idle (approx 6 seconds for a weak-rich-weak cycle) but speeds up to perhaps 0.5 seconds when on the move at (say) 3,000rpm. Downstream O2 sensor sits at 0.8V (quite rich) after a prolonged period idling with a hot engine. While on the move, it tends to sit close to the 'wanted' 0.45V that would indicate 'good' mixture.

Throttle Position Sensor: Seems to give a clean, smooth response from closed to open, no glitches or holes in its signal.

Cylinder Head Temperature and Intake Air Temperature sensors both read sensible values and start out within 2 degrees C of each other after 24 hours of the car sitting unused.

Spark plugs: All the same - porcelain is white (pretty clean) and the arm has the heat mark on the elbow, which would suggest that the heat range might be right. They came from Halfords and were looked up from their reference guide, looked identical to the NGKs that came out and if there are doubts I'll just roll down to the local Ford parts counter and buy a set of theirs.

So I'm a bit stumped. I've left the fuel pressure gauge plumbed in and will drive it from cold in the morning with it taped to the windscreen so I can monitor it while it hesitates to rule out a fuel supply problem.

I've read up on the engine a bit (not that I'm an expert!) and understand that the cams are not indexed to the sprockets, so I'm wondering if there could be some setting error from the last cambelt change, or even perhaps a stretched belt that only gives problems really when it's cold. Could something be wrong here and cause what I'm describing?

Thanks for reading this - if it had been a Vauxhall, I'd probably have managed to fix it by now. ;-)



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LOL, we all have our faults. ;-)

I should perhaps admit that I have a Mk2 Astra GTE that I fitted a Vectra GSI (V6) engine into several years ago, partly, I admit, because everyone said it couldn't be done... Vauxhalls have their 'issues' but I've not come across a fault like the one I have on the Focus. My other project car is a little Lotus Elan, also 26 years old this year and also at the affordable end of mototing fun, being both on classic insurance and limited mileage policies.

I should perhaps add to my story above - the hesitation becomes MUCH less at the exact point the ECU goes into closed loop and this can be seen in the OBD data as well (noting time of improvement and comparing against the closed loop flag. What I can't find anywhere on the net is any description of how the Ford ECU/ECM/PCM works during warmup to operating temperature - i.e. how it decides to go into closed loop and which sensors it reads up to that point and which it uses after then.

Grateful for any insights. :)

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