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Well it might be an opportunity to try and line up someone with Vagcom to shoot over and do the output tests!
That might give us some answers.
Must admit I seem to have broken everything I have touched this month as well!
Right,the car is up and running again,complete with a new set of oe plug leads aswell,just to be sure.
Here are the results from the three tests.
Car was running during this test for voltage.multy meter set to dc voltage.
ISV 13.7 volts
Carbon canister 13.6 volts
N75 13.6 volts
I thought tese seemed high so I tested the battery which was 12.4.
Next test with ecu dissconnected. multy meter set to ohms.used other pin on each connector.
ISV connector to pin 4 on ecu connector,fluctuates from 00.7 to oo.E
Well at least we have confirmed that we have power at the ISV, which means that the fuel pump relay is powering those components up. As they are all fed from the same terminal, then give or take a bit, thet should have the same voltage.
I guess you tested the battery without the engine running. With the car running the alt will put move than 12.6V back in. Thats why the voltages seem higher than the 12.6V you might expect. Unless regulated it will be nearer 14V!
Would have thought that all those connection would have a solid continuity. Depends on the sensitivity of the DMM I guess. However if the UL means infinity (open circuit) then the N75 is not connected to the ecu, which it should be if we are only testing the loom. Obviously needs to be rectified but I doubt whether its the cause of the idle problems, unless of course it is!
The N75 is plumbed back in as stock right?
Lou,
Does you MM have a duty cycle or dwell setting on it? We might be able to use that to verify that the ISV is being controlled by the ecu. Again in an ideal world we would have all the desirable diagnostic equipment available and would be able to do something like this!
I hooked my scope up to the ISV on my ur-S4 to capture some data for Marc. Maybe this will be useful for someone else too. Conditions are 40F ambient temperatures, the car has been parked overnight.
The ISV is driven on the low side (i.e. constant +12 on one side, switched ground on the...
From reading between the lines it looks like the following is correct:
1000 RPM idle (cold) 49% duty cycle
800 RPM idle (warm) 43% duty cycle
As we would expect, more duty equals more air!
Still we might be able to verify that the ecu is at least trying to control the ISV. From what we have checked, it should be ok. The idle switch circuit seems intact. We have power to the ISV and the control wire back to the ecu looks intact as well. That only leaves the circuitry within the ecu or as discussed previously another source of air!
The car does the same with two different ecu's which casts doubt on an ecu problem and points to something on the car. Yet the car appears to be leak free. The only question mark being the way the N75 was plumbed in.
According to that post there is still activity on the ISV after its idle functions have been discharged. So irrespective of the idle speed we should be able, given the right tools measure it! Unfortunately we all don't have a scope in the garage!
John,
So should he check each pin in the ecu for continuity with the ISV to see if its shorted?
According to that MG thread there is ISV activity even up to 2000 RPM. In that case he might be able to connect a spare one up electrically and observe whether it has moved from the default unpowered condition. Depending on how its orientated there should be a noticable gap at top/bottom unpowered. If its shorted to earth it will open fully. If its receiving some ecu control, I think that it will shut that gap off. That should all be visable.
As we know that idle speed is symptomatic of a unconnected ISV. We have power, so it can only be the control somehow.
It's not really a continuity reading. A short circuit is where two wires are connected together which shouldn't be.
If you read my post, points 7/ to /10 I say with the ecu disconnected, meter between the 2 pins of the ISV etc.. ie. one probe of the meter to pin 1 of ISV the other to pin2 of the ISV post the meter reading in Ohms. There should be no connection.
We do have a broken wire between the ECU and the WGFV though it would seem which is why the car is only giving spring boost. This is weird because I'm pretty sure I did the ghetto output test on it when the car was here (flick the throttle from idle to WOT and listen for the valve to click) and I seem to remember it worked, mighht be wrong though... Also we didn't get a code for it either. So a good idea would be to pull the rubber boot off the back of the connector and inspect the wires for damage.
Robin, the multy meter I have is a digital ISOTECH IDM67 I think it is autoranging.
John the test 7/10 between each connector with the ECU dissconnected show no ohms.
As far as the n75 is concerned it is back to the vented to air position as before but it must be working because on testing it yesterday after fitting the new leads the car ran realy well both hot and cold and I had full boost with no misfire or popping as before.But on return the idle problem came back,1050 at idle.occilating at 1450 revs jumping from 1450 to 1150.
I have checked the wires at the plug ends by pulling back the rubber boot and ther is some copper showing on a few wires but no wires touching.
I checked all the vacumme hoses again and even blocked each one individually with a pair of molegrips,but the idle and occilation remained the same.
Hmm.. doesn't look like that MM has that particular cabability. Obviously if we can establish that the ISV is working then we can eliminate it from our enquires! Some MM are more automotive based.
Same with the N75. If the wire has no continuity back to the ecu it cannot be working. Yet if the car boosts it must be working unless you have a stronger wastegate spring! Unless its broken and making an intermitment connection.
Of course we may have been barking up the wrong tree all along. When John disconnected his ISV he gets the same idle speed and more or less the same symptoms you have. It seemed logical to suspect the ISV/Idle circuit. If its not, we will need to re-evaluate the cause.
Again the output tests would confirm the function of the ISV and indeed the N75 to a certain extent. Perhaps John can run you through the manual process. It would be a lot easier with Vagcom.
Unfortunately due to the pipes its difficult to choke or restrict the air out of the ISV. If we can restrict it and the idle drops at least we would know the air is from the ISV if you see what I mean.
Now going back to something you said previously about the earths. What did you do, and how does it differ from standard?
The n75 is working and the wires have continuity back to the ECU.
I have a stock spring in the wastegate.
The earth strap comes from the battery to two locations,one to the passenger side engine mounting the other to the battery tray.The one that I ripped of was the one to the shassy on the driver side.
Lou,
In post 107 you said that N75 connector to pin 23 of ECU connector OL. Both myself and John have taken that to mean an open circuit!
Where exactly have you connected this other earth wire. What part of the engine mounting?
Quickly test the continuity between the battery neg terminal and the smaller earth wire terminal on the inlet.
Robin the small earth on the inlet to the negative of the battery has continuity.
The earth strap from the battery connects to one of the bolts that bolts the engine mountin braket to the engine.
When I tested the three sensors John mentioned and got OL on the n75, the multy meter was set on ohms, the n75 was the only one to show this the other two did not.when I tested the wireing for continuity the meter was set on continuity. ie the buzzer on the top, and all the sensors had continuity.
sorry for any confussion,but I simply thought OL was nothing or no ohms, not open circuit.
.
Ok!
Obviously the original earth strap earthed the engine to the body. The battery is also earthed directly to the body. I am not sure whether its an issue or not to earth the engine directly to the battery and not the body. I had a problem once on a 200 where the car would not start because the tiny earth strap from the cam cover to the body had a bit of corrosion on it!
Perhaps you can try and stick a jump lead directly from the car body to the engine to act as a temporary earth and see what happens.
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