First of all the car is a Rover 200 1.4 16v V-Reg.
This has been an on-going problem since before last christmas and I am totally stumped.
The problem is as follows:
- Car starts fine and idles ok for about 10-20 secs
- After this time engine goes 'chuggy' and unsmooth idle, also feels like it could cut out sometimes.
- If I go to drive off when this is happening the engine is reluctant to rev and have to give it a bit to drive off, and when I do drive off it's like the thing is running on kangaroo petrol.
- Problem still there when engine warm but to lesser extent.
- Car will run ok has no problem accelerating, although initial acceleration in any gear can be a bit jumpy.
I have changed the following:
- Fuel Filter
- HT Leads
- Distributor Cap
- Rotor Arm
- Ignition Coil
- Spark Plugs (correctly gapped)
- Engine Flush
- Oil and Filter change (Wynn?s Valve/Hydraulic Tappet Cleaner added)
- Air Filter change
- T4 Diagnostic carried out, no fault found
- Forte fuel treatment used
- Coolant Temperature Sensor
As you can see where do I go next?
Any help would be greatly appreciated,
Andy
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I wonder whether there is an air inlet temperature sensor as well? Is it correctly connected and giving the right resistance values for air temperature? It sounds as if the engine is running very rich. Is there any black smoke out of the exhaust? After it has been running badly, take out one or more of the spark plugs. Is the insulator and electrode covered in black soot? What colour are they if not sooty? I'm not sure what a T4 diagnostic does, but as the sensor is external to the ECU, it may not show up in such a test. The car may be running OK when cold, as it needs the extra-rich mixture. After a few minutes, it wants a leaner one, but still gets too much fuel, so runs badly.
Hope this helps.
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It may be the opposite to Pete M's suggestion, i.e., that the car has a tendancy towards runnning weak.
During starting, and for a short while thereafter, the engine management unit will be in cold start mode, supplying a richer mixture. This is seperate from the normal fuelling corrections which rely on signals from the coolant temperature sensor.
Perhaps it is when it switches out of cold start mode that the rough running begins.
Checking the plugs for soot will be a good, quick way to rule out my suggestion. The best means of checking this is, however, to interrogate the engine management unit, and check the state of the oxygen sensor integrator (If this value can be obtained by Rover checking tools). In normal running, the integrator should be in the middle of its range.
If it turns out that the engine is prone to running weak, then checks should be made on the components which would allow this
Possibilities include;
Fuel Pressure low
Coolant temperature circuit
Air Temperature Sensor Circuit
Load sensor circuit (MAP or AMFM - I'm not sure which is fitted)
I'm sure there are more, but this should get you going!
Number_Cruncher
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I don't think the cold start unit is disengaging itself, resulting in rich running. What's the MPG like?
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Mike Farrow
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Well I changed the plugs again last week just to double check them and the plugs I took out were spot on, the gap had closed to 0.70mm from 0.85mm but other than that there were perfect. I can't detect any leaks from the inlet manifold or throttle body. Low fuel pressure has crossed my mind as with my ZR when I take the fuel cap off to fill up I always release the cap slowly to let the pressure out gradually as there is quite a hiss where as there is never any pressure there with the 200, yet if there was low fuel pressure why would it run ok for that first 10-20 seconds?
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What colour were the tips, where the combustion deposits would form, of the spark plugs when you took them out?
Black and sooty?
Black and oily?
Biscuit Brown?
White crusty deposits?
Absolutely clean?
Or some other colour?
Number_Cruncher
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Unlikely that spark plug gaps would close up without some mechanical intervention. I trust that they are of the correct reach and have not been nudged by a piston?
Unlikely scenario I know ; plug electodes always erode in my experience!
I agree that it sounds like the mixture is staying too rich.
--
I wasna fu but just had plenty.
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I have just gone and had another look at the plugs I took out and I would say they are quite clean with a touch of light brown deposit.
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What kind of electrical system does it have for detecting engine rotation? Flywheel sensor, or something on the distributor? Does it have a throttle position sensor?
It sounds to me like a faulty sensor somewhere, or just a poor connection, bad wire or poor earth.
Fuel pump relay, poor connections, corroded fuses?
Fuel pressure regulator?
I don't know the car, but those are the kind of things I'd look at on the Volvo.
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If your engine was running so rich as to cause poor running, you would see that on the plugs. Unlike most other contributors to this thread, I don't think your car is running rich.
The pressure or vacuum that is behind the cap when you fill up is nothing at all to do with the pressure at the injector. The tank is usually held at a slight vacuum, while an electrical pump supplies the fuel to the engine at 40 psi or so.
You asked about the fuel pressure. During, and just after starting, the engine management unit supplies a richer than usual mixture by holding opening the injector for longer. This will offset any fault which tends to weaken the mixture. So, the car runs OK for a very short while.
Then, the management unit switches to open loop mode, it reads the data from engine sensors (but not the lambda sensor yet, it isn't hot enought to work yet - hence open loop mode). Based on the data the engine management unit guessses how much fuel is needed. If everything is OK with the engine, this guess is usually good enough to allow you to drive. (After all, pre cat + lambda sensor equipped cars ran in this mode all the time!)
Then, when the lambda sensor gets hot enough, perhaps after a few minutes into your journey, it switches state. The engine management unit picks this up, and switches into closed loop mode, where the exhaust gas composition is measured by the lambda sensor and corrected.
Faults which leave an engine prone to running weak mean that the lambda sensor spends most of its time reading weak, rather than 50 - 50. So, the engine management unit provides correction by richening the mixture by holding the injector open for longer. When you make a demand, like putting your foot down, this normally would require a temporary richening of the mixture, which the engine management unit can't give because it is already providing a more rich than standard miuxture. So, you get a hesitation as you put your foot down.
Practically, another obvious point to check is for air leaks on any vacuum pipes - this will allow air to be sucked in, potentially weakening the mixture.
Number_Cruncher
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Would agree with NC week mixture.Not uncommon for vacuum pipes to split on these
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Steve
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