sanadrustom

Anyone know how can someone test to see of the MAF is faulty?

I'm trying to trace down a rough idle that I been having and looking for info to collect before I throw money up in the air without definitive direction on where to go

Thank you

UrS4boy

Click on the link to the live version of my Engine Bay Device Map. Bookmark for future reference. Click on the G70 MAF label in the lower right corner (all the other links are live links too). Should give you your answer.

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

UrS4boy

For the G70 MAF harness connector the female pins are only in positions 1 through 5; No. 6 the one at the left end of the connector is empty. For the AAN MAF harness connector, the five pins are as follows:

Pin 1 = Brown with red stripe, goes to a ground (16) (on the cylinder head (cam) cover)
Pin 2 = Red with black stripe, goes to pin T26/55 in the ECU
Pin 3 = Green with white stripe, goes to pin T7/55 in the ECU
Pin 4 = Green with purple (violet) stripe, goes to pin T25/55 in the ECU. This is the burn-off signal wire from the <a href="http://forums.quattroworld.com/s4s6/msgs/102009.phtml">Holding Relay</a>
Pin 5 = Black with red stripe, connects to the <a href="http://forums.quattroworld.com/s4s6/msgs/90802.phtml">fuel injector harness</a>

Here is a photo showing those five AAN wires:

<img src="http://12v.org/urs/AANMAFPlugShowingWiringPinoutColours.jpg">

Testing the G70 MAF is found in the Bentley in section J24, Volume One, pgs. J24-77 to J24-85. The following is a short-form summary of this info and is not complete:

1. Testing for ground: Disconnect the harness connector from the MAF. Set your DMM to 20 ohms and look for continuity between Pin 1 (Pin 6 is the empty position) and ground on the engine or chassis. Not continuity = you have a ground issue involving that Brown/red wire. Start tracing back, looking for a broken wire. Won't be fun.

2. Testing for connection to the injector circuit: Turn the DMM to 20 VDC. Connect to Pin 5 and ground. Turn on the ignition. You should get some positive DC volts.

3. Checking MAF function: With harness connector removed, switch DMM to 200 ohms. Connect DMM probes to terminals 1 and 2 on the MAF (1 is on the right, 6 is on the left). Record the resistance. Disconnect leads and "Short" the circuit (press probe ends together). Display value must equal value recorded previously.

If the difference is greater than 0.1 Ohm, replace MAF.

Re-connect the MAF sensor harness connector. Peel back the rubber boot on the connector to expose the terminals. Switch the DMM to 20 VDC. Connect the DMM to the back side of Terminals 1 and 3. Turn the ignition switch to "ON" (run) but don't start the engine. Should be 1.2 to 1.5 Volts. Start the engine and let idle. Voltage reading should now be 2.5 volts. Increase the engine speed briefly (manually move the throttle position to more open). Voltage should increase to 3.0 to 5.0 volts (depending on engine speed). All the of the specified voltages must be obtained. If NO = replace MAF.

There is more re: Holding relay/burn-off wire but that shouldn't directly affect running and idling.

sanadrustom

as always Dave you are most appreciated indeed!.

i would have sold this car with out this forum and Dave's insightful words ( no im not brown nosing haha)

cheers

UrS4boy

Still tracking down my hot restart issue so I decided to follow the MAF testing info to eliminate it from "further enquiries". Here are the results (from this AM):

1. Testing for ground: Disconnect the harness connector from the MAF. Set your DMM to 20 ohms and look for continuity between Pin 1 (Pin 6 is the empty position) and ground on the engine or chassis. My result = 0.5 ohms = continuity = there is a ground for the MAF = good to go so far

2. Testing for connection to the injector circuit: Turn the DMM to 20 VDC. Connect to Pin 5 and ground. Turn on the ignition. You should get some positive DC volts. My result: 11.1 V = good

3. Checking MAF function: With harness connector removed, switch DMM to 200 ohms. Connect DMM probes to terminals 1 and 2 on the MAF (1 is on the right, 6 is on the left). Record the resistance. My result: 0.000 ohms
Disconnect leads and "Short" the circuit (press probe ends together). Display value must equal value recorded previously. My result: 0.000 ohms = same = good

If the difference is greater than 0.1 Ohm, replace MAF. (Nope. All is good so far)

Re-connect the MAF sensor harness connector. Peel back the rubber boot on the connector to expose the terminals. Switch the DMM to 20 VDC. Connect the DMM to the back side of Terminals 1 and 3. Turn the ignition switch to "ON" (run) but don't start the engine. Should be 1.2 to 1.5 Volts. My result: 1.25 V

Start the engine and let idle. Voltage reading should now be 2.5 volts. My result: 2.50 V

Increase the engine speed briefly (manually move the throttle position to more open). Voltage should increase to 3.0 to 5.0 volts (depending on engine speed). My result: 3.05 V

All the of the specified voltages must be obtained. If NO = replace MAF. (Nope, all good)



Bad news is the search for the hot-restart solution continues. Next up: revisiting the TPS because I can get it to restart easier if I crack the throttle, i.e. take it off the idle switch. News at 10.

sanadrustom

I will be doing this today, couldnt get around to it last night was painting the house .

will update values with what i find on mine

Cheers

sanadrustom

So I checked the MAF everything checked out with same values as your did + .1 here and there on all values. MAF is good

Time to continue the hunt for rough idle next is fuel pressure regulator the N71 and the G69 are on my list of things to do

UrS4boy

Info about all those devises can be found at: http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

Isolating the problem cylinder during an episode of rough idling can be done by disconnecting the injector electrical connectors temporarily, one at a time, and noting whether disconnecting makes the idle rougher or not. When you get one that doesn't make the idle much worse, you've found the cylinder with the issue.

Rough idle can be caused by many things:

1. Burnt valve(s) on one or more cylinder = lower compression = poorer combustion = a "bump" when you feel the exhaust at the tail pipe outlet. Confirm via warm engine compression test.

2. Bad spark plug(s) - at least check to see if they are tight. Tighten only 22 lb-ft

3. Bad spark plug to coil boot on OE ignition system, check and replace

4. Bad coil

5. Bad POS channel

Again info about all those items will be in that hyperlink engine bay device map.

Good luck

sanadrustom

Not sure what this means but when I disconnect the N71 the idle levels out at around 900rpms does this mean it's faulty? Or just the car compensating?

UrS4boy

Probably means that your N71 needs cleaning with throttle body cleaner because it is sticking open or something. It is used mostly when A/C is on and you are idling. Also on throttle off conditions, to stabilize the idle before actually stopping and statically idling.