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Matt
Matt, Mechanical Engineer
Category: Ford
Satisfied Customers: 20614
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a problem with my mk7 petrol/LPG transit. When cold

Customer Question

I have a problem with my mk7 petrol/LPG transit. When cold it runs really rough, like it's only running on two cylinders, it coughs, splutters and has little to no power. This used to only happen while it started on petrol, once the LPG took over it was fine, but today it did it on LPG too leading me to believe this might be an electrical fault. I've read people talking about a cold start relay? Once warm it runs fine. Any ideas?
Submitted: 2 years ago.
Category: Ford
Expert:  Matt replied 2 years ago.
Hello

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine


Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile
Customer: replied 2 years ago.

Hi Matt,

I've not been able to detect any leaks at all. Have cleaned the butterfly valve MAF (it's an all in one unit). Still have the same problem with the exception that now it does not matter if it's cold or warm. Driving home tonight the engine light came on.

It feels like it's misfiring or only running on two or three cylinders. When sitting still the engine revs without error. The problem only occurs under load, when accelerating etc.

Best.

Ashley

Expert:  Matt replied 2 years ago.
Hello Ashley


Ok if you now have an check engine light then the quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

You can do a very rough and ready check yourself by unplugging sensors one at a time and seeing if any of them change the driving condition which would indicate the most recently unplugged sensor is the faulty one. This method is not foolproof though and reading a fault code off is the better method.

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