34 replies to this topic

[FlyingScot]

Check MAP reading on ignition without running.
Lambda reading screwy, try disconnecting the plug and check running.
Try the old WD40 trick to search for air leaks especially hoses for servo and emissions control
Is the throttle cable freely moving?
Check throttle body for damage/ distortion.

FS

[Steve220]

Also try resetting the stepper motor to see if it brings the idle down. Turn the car to ignition 2 (don't start the car) and full depress the accelerator 5 times. You'll hear the motor reset itself to base standard. Worth a try!

[FlyingScot]

Also try resetting the stepper motor to see if it brings the idle down. Turn the car to ignition 2 (don't start the car) and full depress the accelerator 5 times. You'll hear the motor reset itself to base standard. Worth a try!

It's an MPi it doesn't have a stepper motor. It's a valve on an MPI

FS

[Steve220]

Typical!

[LukeH]

Check MAP reading on ignition without running.
Lambda reading screwy, try disconnecting the plug and check running.

The readings whilst engine off was;

Tps 0.68v
Map 100.97
02 1.977

I started the engine and revs were 1156rpm, map: 39.44 and o2: 1.943

I killed the engine and dissconected the o2 sensor. Started the engine and revs were much lower around 850-900 and map: 39. Ik killed the engine then reconnected the o2 sensor and started the engine again. After a few mins if idiling it started to hunt to point of almost stalling.

[Phil-R]

 

Tps 0.68v
Map 100.97
02 1.977       <-------what unit ?

 

 

MAP is fine. TPS looks 'ok' to me. Can you confirm what unit the O2 reading is ? The lambda sensor can only output approx 0 - 1 Volts, and you didn't specify volts, so this measurement is a little confusing.

 

What is the lambda value with the sensor unplugged? ( Yes, I know that sounds like a stupid test).

Edited by chrome, 01 November 2014 - 08:33 PM.

[LukeH]

It is reading in volts and I know it does look an odd value and I wonder if that's the snap-on reader getting confused. With the o2 unplugged it was reading 1.943 which seemed odd, should it not be 0v?

The readings drop to 0.595v briefly then spike to 1.9-3v

[Phil-R]

Anything over 1V is not right.

 

You may want to trace that wiring back to the ECU and check it's condition and make sure it's not shorting with one of the other wires. With the sensor unpluged and the engine off, see if you can move the wiring around and get the voltage to change.

[FlyingScot]

The O2 sensor is a voltage generation cell it is complete with a heater coil. Try measuring the voltage from the O2 with a multimeter if you can.
I have come across this before on here but it has not been clear is this is due to voltage leakage from the heater coil in the sensor or the code reader being used. ( or as chrome is suggesting above a wiring fault, the wiring can get cooked due to it's location)
Same type of reader too, see here http://www.theminifo...-oxygen-sensor/
You will see in the thread the details of the wiring.
We could do with solving this as this isn't the first one of these....and I don't like unknown issues with fuel injection motors

FS

Edited by FlyingScot, 01 November 2014 - 09:21 PM.

[LukeH]

I'll get the multimeter on it hopefully tomorrow as I want to get to the bottom of this also. I have a spare sensor that I can try if I can fit from above.

Thanks for the help so far.

[Fast Ivan]

just to clarify the tps and map sensors - the tps steadily increases in value as you rev? 

the map rises as you rev up to 100kpa at full throttle?

do the spark plugs indicate a running rich or lean engine?

[chrisking2021]

Hi
How much was skimmed from the head I've known of issues with mpi engines when they have had their heads skimmed. As the timing is fixed the engine hits top dead centre earlier and fires later thus causing rough running.

Chris

[LukeH]

I have taken a short video of a multimeter vs snap-on measuring the o2.

http://i237.photobuc...1102_162224.mp4

It appears to be switching OK on the multimeter and a bit slow on the snap-on

[Phil-R]

It appears to be switching ok until about 7 seconds in, then there's a high reading on the volt meter of 1.37V. Not sure if the snap-on is showing the peak voltage or an average, but they look to be showing the same thing.

 

I would have suspected the sensor itself, but you've said the unusual voltage is still present without the sensor. Generic replacement sensors usually don't have the correct plug, (if they have a plug at all), so start checking the wiring at the sensor end to see if someone has altered the loom close to the sensor. Also hunt around the engine bay for places where the wiring loom is earthed (EDIT: I would suspect there could be than one place). A bad earth on a signal wire can cause signal voltages to float higher than the really are. 

Edited by chrome, 02 November 2014 - 08:10 PM.

[LukeH]

just to clarify the tps and map sensors - the tps steadily increases in value as you rev? 

the map rises as you rev up to 100kpa at full throttle?

do the spark plugs indicate a running rich or lean engine?

 

The map sensor seems to steadily climb but the TPS seems a bit more erratic. The spark plugs indicate rich engine.

 

 

Hi
How much was skimmed from the head I've known of issues with mpi engines when they have had their heads skimmed. As the timing is fixed the engine hits top dead centre earlier and fires later thus causing rough running.

Chris

 

 

I'm afraid I do not know but I guess I could call the engine shop and ask.