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Ford Mondeo: Mysterious problem, several symptoms

Hello all! I have a 2001 Ford Mondeo (2.0 Duratec HE engine) with 47k miles (yes, that’s low for a 19 yo car!) which I’m trying to fix for the past 4 months. Unfortunately, I’m running out of hairs in my head :frowning:

These are the symptoms:

-At the traffic light, the engine stalls (rough idle) and hesitates when the throttle pedal is pressed, it continues hesitating until ~1500 RPM
-The engine stalls even more if the A/C is turned ON and/or when engine is cold
-High fuel consumption at city
-It gets to the operating temperature too quick
-Fuel trim when stopped is STFT -4% and LTFT +11%
-Fuel trims stabilizes at 0% above 55-60 mph
-When the throttle is briefly pressed and released, the engine takes a couple of seconds to completely reduce the RPMs to idle
-When coasting, if I shift from Drive to Neutral, the RPMs raises to almost 2k and returns to idle only when the car is near to a stop
-The normal RPM for this engine is 720 +/-50, when stopped in Drive, the RPMs stays at ~800 RPM
-Harsh downshift from 3rd to 2nd, unless I brake veeery smoothly
-No error codes

What I did so far:

-Spark plugs changed: little to no difference
-Spark cables: resistance seems OK, all cables below 2k ohms
-Throttle body removed, cleaned and inspected for leaks at the seals and flaps
-Vacuum leak fixed at the injectors (seal changed)
-Injectors tested for leaks
-Vacuum leak fixed at the intake port (intake manifold removed and seals changed)
-PCV hose changed, although it wasn’t broken
-PCV valve inspected, looks fine
-MAF sensor inspected, not dirt or visually damaged
-Thermostat changed, it was physically broken and locked open
-EVAP hoses are not leaking air
-Brake vacuum lines are not leaking air
-Swirl flaps actuator is not leaking air
-Air filter is OK

Where I’m lost:

-I still suspect that there is a vacuum leak somewhere because of the fuel trims and fuel comsumption, but I tried to blow a cigar in the intake manifold and it didn’t leaked anywhere, I put all my lungs on it and nothing. Is there any other way to test for vacuum leaks with efficiency?
-Can it be a fuel pump? It is pretty old despite the low mileage, but at the same time, the car is not hesitating at high RPMs when the pump has to do more effort I suppose.
-I don’t know how to test the coil pack, it can be bad?

Any help/tip is much appreciated!


from how your fuel trims change when driving under load, it indeed looks like a vacuum leak

search YouTube for “DIY smoke machine” instructions, you can make one with a resistance wire, wick and old platic can and few wires/hoses, it will help you to smoke-test your engine bay much better than “cigar method”

Is your speedometer working and showing correct speed?

Thanks thegreendrag0n and CapitalTruck

Yesterday I got my hands on a smoke machine (not DIY machine) and an air compressor, first I pumped smoke through the PCV hose which connects to the intake manifold, (not to the PCV valve) it didn’t leaked anywhere except to a small amount through the throttle body flap. Then I connected the compressor and tried to pump air into the intake, it did not leaked also, in fact when I released the air, I noticed that it had been built quite some pressure inside the intake manifold. I did the same test with the brake hose disconnected and sealed, the results were the same, also, the MAP sensor is measuring 5 PSI at idle. (~10 inHg)

Today I compared the speedometer with the GPS, the car is measuring 1-2 mph more than the GPS.

I checked the spark plugs and cables again. The plugs shows some soot, the cables has 1.8 to 4.7 kohms, depending on the size.

I don’t know, maybe the fuel pump is going bad and the injectors are working more on the open state to compensate the lack of pressure and thus the high fuel trims?

…or maybe the coil pack is failing, however defective coil packs tends to work better at cold and worse at hot temperatures, right? In this case, cold is worse.

Really don’t know…what do you think, guys? Any suggestion?



My friend has a Contour that acted all goofy when speed sensor went out. The fact that speedo works fine ices that idea.

Not exactly my bowl of soup, but let me throw some ideas against the wall…

Check fuel pressure in injectors rail at idle and under load?

Trims are controlled based on the upstream air/fuel ratio sensor (AKA “upstream oxygen sensor”), any chance it went bad?

What about MAF sensor cleaning?

I’m guessing either there’s still un-metered air leaking into the engine or the exhaust system is clogged. What does the warm-idle intake manifold vacuum measure? Use your own vacuum gauge, don’t rely on the car’s MAP. It should be in the 17-22 inches range. If its’ really only 10 inches, figuring out why is where you should focus. Other tests I’d be considering if I had that problem

  • fuel pressure
  • engine compression
  • throttle position sensor

Hi all,

I don’t have a vacuum gauge or fuel pressure gauge, I might be able to get it, but it’s gonna take some time. Meanwhile, I found your comments interesting and will surely test it.

-Will test the TPS sensor

-MAF sensor is not present on these earliers Duratec HE

-Never thought on leaks on the exhaust manifold, I will check that and remove the cat converter to see if it is clogged.

-Upstream O2 sensor is fluctuating in a strange manner, but at sometimes it manages to swing as it should. It is difficult to say that the sensor is giving wrong information or is fluctuating because the mixture is really wrong.

-Downstream O2 sensor is even more interesting, it’s locked at 1.275 V, no matter what, like if was rich all the time. I will investigate this one first.

Thank you!


There’s different technologies used in O2 sensors these days. Some of them , especially the downstream types, don’t oscillate between 0.1 volt and 0.8 volts. Instead they hold to a fairly narrow voltage range.

As I recall the technology that oscillates rapidly are called lambda sensors and the type the hold to a more steady voltage range are called wide-band sensors.

Looks like it’s a heated, finger-type sensor:

Ok, updates:

-TPS sensor is fine, ranging from 2 kohms to 4.8 kohms, smoothly
-Downstream O2 is not present, it seems that it is not required by law in our market, that’s why it shows a fixed voltage
-EGR valve is also not present, instead, there is an EGR delete, OEM from Ford believe it or not:

-Cat. converter is clean and undamaged
-Exhaust manifold is not leaking
-Intake manifold retested, and not leaking

I removed the Upstream O2 sensor and I may have releaved the issue, the fuel trims went to zero, the transmission hard downshift has gone and the engine misfires badly when load is applied to any RPM and the AC is turned on. I alse hear a ‘pop’ from the throttle body indicating a backfire.

Being that, I’m going for the coil pack, already ordered it should arrive tomorrow. I post the results after change. I will also take the opportunity to change the leads despite they are in good shape.

If that doesn’t work, then I’ll go for the fuel pump.



The new coil pack made a lot of difference. The car is not hesitating or misfiring anymore and it runs smoothly at any RPM. After that I also changed the spark plug leads because despite the resistance of old ones are OK, one of them had a crack, so I took the opportunity. Also, with A/C or not, it is not backfiring anymore.

However, the fuel trims went down just a little bit, and my O2 sensor appears to be a little lazy, sometimes it stays at rich or lean for several seconds, and from what I heard, these old sensors may fail at this mileage/age, so I already ordered a new one.

My learnings so far: Sometimes the O2 sensor can mask a problem, like with the coil pack, so disconnecting it can help you to find or get closer to the root cause.

Congrats on getting it fixed!
I was afraid you were going to write it off at some point, due to the age, but you persisted :slight_smile:

Thanks thegreendrag0n yes I’m glad that at least the car is running well, but it’s just half of the journey, my fuel trims are still high and the O2 sensor seems to be bad, I’m hoping to get the new one delivered today so I can change on Sunday and post the results here.

Have a nice weekend!

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Sorry for not updating here these days, I’m still waiting for the new O2 sensor, unfortunately the last seller sent the wrong one, so I had to order it from China, it will still going to take a couple of weeks.

Meanwhile, I removed the entire intake manifold again, this time I put a gasket from a good brand, and double checked all the connections, hoses, sensors, swirl flaps (deleted) holes, because I want to be absolutely sure that there is no vacuum leaks.

I also did the math wrong the last time, accordingly to the MAP, the intake manifold pressure at idle when hot is 18 inHg @ 720 RPM, which is the exactly the RPM mentioned in the owner’s manual. Also, the hissing sound when the A/C is turned on seems to be normal, it is coming from the IACV, the valve is not leaking but the way it was designed, seems to natural that some hissing is produced when the engine is revved. In addition to that, these cars doesn’t have a MAF sensor, and from what I read, when a vaccum leak is produced, the RPM must simply raise. (let me know if I’m saying something wrong here)

The last time I used a smoke machine to the exhaust manifold to find if there was some leakings, this time I used a vac blowing air to the exhaust manifold while spraying soap water. No bubbles appeared, and the pipes didn’t had any rust other than expected.

Now, what can be the reason behind all this, it’s a fuel leak. I decided to inspect the fuel pump and found that the feed pipe was leaking a tiny amount of gas due to bad o-rings. I have already ordered new ones. That could lower the fuel perssure and cause the high fuel trims and bad mileage?

Thank you!



Ok, I finished the job, and to help anyone who face the same issues, here is the symptoms and solutions:

Ford Mondeo MK3 2001, Duratec HE 2.0l, AT transmission, version without MAF sensor and with accelerator cable. (drive-by-wire came a couple of years later)

High fuel trims, poor idle specially with A/C on, hesitating at low revs, higher than normal (720 rpm) at idle, harsh downshifts, hard to start when cold, increased fuel consumption specially at city, engine getting hotter than normal

Before starting:
-Check your air filter
-Clean the injectors if you never did it
-Check the wiring going to the injectors

-Regarding poor idle and low revs hesitation: Check spark plugs and cables. New cables have a resistance of < 2k ohms. Replace the coil pack if the plugs and cables are OK.

-High fuel trims, higher than normal revs at idle and hard to start at cold: Check for vacuum leaks at EVAP hose, brake vacuum line and connection, o-ring seals around fuel injectors, swirl flaps valve & hoses, PCV hose and finally, intake manifold gaskets. In my case was the fuel injector o-rings and the intake manifold gaskets which I had to replace - this guy helped a lot: - and if you are doing this job, consider replacing the swirl flaps or even remove them completely which I did in my case, just don’t forget to seal all the gaps later. Also, if you have a bad thermostat, it’s a good time to replace it as it is hard as hell with the intake manifold blocking the way.

-High fuel trims but with normal idle and hard to start when cold: Check the fuel pressure, it must be at least 3.5 bar. If it is too low, replace the fuel filter. If it persists then your fuel pump is probably faulty.

Side note regarding fuel pump:
This car uses a 3.8 bar fuel pump, which is hard to find depending where you live, in my case they replaced the pump with a 3.0 bar model, so the pump was not bad, it was just wrong and I had to spend a lot of time trying to find this.
If you can’t find a replacement, a 4.0/4.2 bar is also a replacement with the following codes: (don’t forget to look for the fuel flow, it should provide at least 70 l/h)

Fiat - 0.580.453.481
BOSCH - 0 580 453 481
DPL - 18.0481
EURO - 10106
GAUSS - GI3481

Before buying the repair kit, ensure that the old hoses and assembly are in good condition. If you’re buying the entire assembly, ensure that it comes with the pressure regulator.

Side note regarding transmission hard downshifts:
Despite the transmission CD4E have a bad reputation, the version on this car was upgraded so it’s not that bad, and if you have one or more symptoms listed above, it’s very likely that the issues on your transmission are related. DO NOT trash the transmission before ruling out ALL the other issues with the engine. Of course, don’t forget to check the fluid condition/level and if you have to replace it, use Mercon V (latest revisions ONLY) or Dexron III. DO NOT use Mercon LV, Mercon SP, or any other fluid, including the first version of Mercon V, which I think, it doesn’t even exists anymore.

Good luck!

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