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2.0L engine runs extremely rich - temperature sensor defect?

Hi there,

I have a 914 with 2.0 D-jetronic engine type GB.
the engine runs, though the exhaust smells like much too rich on CO.
I'm not aible to mesure the exact amount, but could it be that the temperature sensor on the cylinder head gaves wrong information to the EFI?
What happens if I connect the wire to the ground directly, cause I read somewhere that how hotter the engine becomes, the less resistence the sensor should give to the EFI, to reduice the mixture fuel/air.
Any comments on this item?
Thanx

Marc
Zele Belgium.

Old 07-10-2020, 03:23 AM
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That is a possible cause. More resistance on the sender will cause the FI to inject more fuel. Less resistance will cause it to inject less fuel.

You could also have one or more leaky injectors. If the cold start valve sticks open, it will spray fuel into the manifold and you'll get more fuel than you want.

The diaphragm in the manifold pressure sensor could be torn or leaking. That will cause the FI to "see" more air going into the motor than is actually going in, so it will add too much fuel.

The fuel pressure could be too high. Should be 2 bar (2 atmospheres, 29 PSI). If it is higher than that, more fuel will be going into the engine than the FI is trying to send in.

There are a number of possible causes--if the issue is actually your fuel system. Remember that ignition system problems can look like fuel system problems, and even base engine problems can in some cases!

I suggest starting with the basics. Double-check the ignition timing and dwell. Do a compression test. (An intake valve that does not seal will push air back into the intake, raising the pressure there, making it look to the FI like more air is going into the motor! Don't ask how I know this.)

Then move on to testing the parts of the system. Pull a vacuum on the hose to the MPS and make sure it holds. Check that the cold-start valve is not spraying or leaking fuel when the system is pressurized. Check the fuel pressure in the high-pressure loop on top of the engine. Check the resistance of the cylinder head temp sensor.

Just throwing parts at the problem, while good for the parts sellers, is a poor way to fix the problem. It can also cause other issues, like pulling the CHT sensor threads out of the cylinder head. (Again, don't ask how I know that one.) Test and understand what is wrong before you replaced stuff.

--DD
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Old 07-10-2020, 11:05 AM
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Dear Dave,

Thanks for Your advice on this matter.

Marc
Zele
Belgium

Old 07-11-2020, 09:10 PM
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