AFM test results - can I be sure my AFM is defective?
Discussion
Sorry to bombard this site, but I'm testing my AFM as per:
"Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.5 Volts or higher, and take at least 2 seconds to come down to the correct voltage."
My meter does indeed shoot to 0.5 (1.6 in the very first instance!) and then falls down to 0.35 over a few seconds. So can I be confident my AFM needs replacing?
I have a video of the meter reading if it's possible to upload here?
"Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.5 Volts or higher, and take at least 2 seconds to come down to the correct voltage."
My meter does indeed shoot to 0.5 (1.6 in the very first instance!) and then falls down to 0.35 over a few seconds. So can I be confident my AFM needs replacing?
I have a video of the meter reading if it's possible to upload here?
Very common issue but i think it would pay you to get yourself Rovergauge and let one of the guys here have a look at the logs for you.
Its been said if its slow to respond on the test you performed its likely it will be inaccurate through the rest of its range.
Im trying to find a recent thread that involved a lot of afm testing so will post it up when i do!
https://www.ebay.co.uk/itm/315059052757?chn=ps&...
la-1814673648222&abcId=9303859&merchantid=6995734&gclid=Cj0KCQiAv8SsBhC7ARIsALIkVT3zJw_r7UiTZlOc0RSUicPUIuX2HYT9bPdqYjV9LDeCde6ly7BVzuUaApYtEALw_wcB
Its been said if its slow to respond on the test you performed its likely it will be inaccurate through the rest of its range.
Im trying to find a recent thread that involved a lot of afm testing so will post it up when i do!
https://www.ebay.co.uk/itm/315059052757?chn=ps&...
la-1814673648222&abcId=9303859&merchantid=6995734&gclid=Cj0KCQiAv8SsBhC7ARIsALIkVT3zJw_r7UiTZlOc0RSUicPUIuX2HYT9bPdqYjV9LDeCde6ly7BVzuUaApYtEALw_wcBBelle427 said:
Here is the thread, never overlook the basics!
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Ah, thank you so much! I'll have a thorough read. While I've got you here, just to pick your brains further, my coolant and fuel temp sensors (tested in situ) are BOTH giving resistance of approximately 1500 ohms when cold (11C). Going by the Steve Heath bible, these are way off (should be more like 4000?), but seems coincidental that they both read roughly the same.https://www.pistonheads.com/gassing/topic.asp?h=0&...
"The Coolant Temperature Sensor should change resistance with heat, per the following specs.
-10C (14°F) 9100-9300 Ohms
0C (32°F) 5700-5900 Ohms
20C (68°F) 2400-2600 Ohms
40C (104°F) 1100-1300 Ohms
60C (140°F) 500-700 Ohms
80C (176°F) 300-400 Ohms
100C (212°F) 150-200 Ohms"
I can help you with understanding RoverGauge data once you get it running.
Specifically with the MAF
Failing MAF's become erratic when the engine bay gets hot. Its easy for me to test for but I will need a RG log file created in a very specific way. What I do is take you data do a full statistical analysis which then gives a standard deviation for that MAF. Then if its >0.08 its defective. If its <0.05 its good in between its borderline.
Specifically with the MAF
Failing MAF's become erratic when the engine bay gets hot. Its easy for me to test for but I will need a RG log file created in a very specific way. What I do is take you data do a full statistical analysis which then gives a standard deviation for that MAF. Then if its >0.08 its defective. If its <0.05 its good in between its borderline.
Great news.
Set RG up as bellow then...use your COM port.....
Switch on ignition.
Click on "Connect" in RG
Click on "Start Log F5"
Then start the car (preferably from cold so I can see how the warm-up proceeds, but its not essential).
Leave the car to idle (no touching any controls)
Allow the car to reach full temperature and for the fans to cycle on and off at least twice.
Continue collecting data for a further 10 minutes. That should be about 20 minutes in total.
Send me the two txt logfiles. (I will msg you my email address)
Set RG up as bellow then...use your COM port.....
Switch on ignition.
Click on "Connect" in RG
Click on "Start Log F5"
Then start the car (preferably from cold so I can see how the warm-up proceeds, but its not essential).
Leave the car to idle (no touching any controls)
Allow the car to reach full temperature and for the fans to cycle on and off at least twice.
Continue collecting data for a further 10 minutes. That should be about 20 minutes in total.
Send me the two txt logfiles. (I will msg you my email address)
Edited by blaze_away on Sunday 31st December 15:41
Quick update
OP sent me his logfiles, the temp sensors are all good coolant rises from 5 to 90's and stabilises/cycles, fuel temp rises from 5 to 25 slowly rising as engine warms up.
What we have found is the MAF looks good though reading low 26% at idle v normal 32% ish, it has good stability with StdDev 0.031 (good maf's are <0.05 at idle) sensor may need a clean.
The ICV is very low at near 0% vs normal 35% so suspecting base idle needs setting and/or vac leak.
In order of priority
set base idle, check for vac leaks, re-run logs, maybe clean maf sensor.
OP sent me his logfiles, the temp sensors are all good coolant rises from 5 to 90's and stabilises/cycles, fuel temp rises from 5 to 25 slowly rising as engine warms up.
What we have found is the MAF looks good though reading low 26% at idle v normal 32% ish, it has good stability with StdDev 0.031 (good maf's are <0.05 at idle) sensor may need a clean.
The ICV is very low at near 0% vs normal 35% so suspecting base idle needs setting and/or vac leak.
In order of priority
set base idle, check for vac leaks, re-run logs, maybe clean maf sensor.
Frank (and RoverGauge) has been so helpful!
We're making steady progress; I could never have done this on my own.
Vacuum advance diaphragm needs replacing, and we've also established that clamping this hose (with annotated yellow stripe) from/to the plenum will cause the revs to drop until stalling, so perhaps our vacuum leak.
We're making steady progress; I could never have done this on my own.
Vacuum advance diaphragm needs replacing, and we've also established that clamping this hose (with annotated yellow stripe) from/to the plenum will cause the revs to drop until stalling, so perhaps our vacuum leak.
Edited by PreCat Griffith on Monday 1st January 20:56
That looks like the crankcase vent hose from rocker cover which is un valved so may behave like that.
Id repair the vacuum advance and see how it goes but you can temporary clamp or plug the hose to see if the stepper responds and goes to its normal value.
Some info on how the crankcase vent system works here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Id repair the vacuum advance and see how it goes but you can temporary clamp or plug the hose to see if the stepper responds and goes to its normal value.
Some info on how the crankcase vent system works here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Edited by Belle427 on Tuesday 2nd January 07:05
Belle427 said:
That looks like the crankcase vent hose from rocker cover which is un valved so may behave like that.
Id repair the vacuum advance and see how it goes but you can temporary clamp or plug the hose to see if the stepper responds and goes to its normal value.
Some info on how the crankcase vent system works here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Great link about crankcase venting thanks.Id repair the vacuum advance and see how it goes but you can temporary clamp or plug the hose to see if the stepper responds and goes to its normal value.
Some info on how the crankcase vent system works here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Edited by Belle427 on Tuesday 2nd January 07:05
I was wondering if op might have leaky rocker gasket(s).
I am at my car later today will give that hose a squeeze see how much it knocks the revs. Mine has been fully vac sealed using smoke tester so I know there are no vac leaks), not yet done on op car.
Op did manage to get base idle to about 750rpm (tightened hose clips and blocked off leaky ign advance module) but iirc that was with adjuster fully shut. ICV now runs at 12%ish.
As a reference check I checked what happens on my engine when I clamp each of the crank case hoses to the plenum.
1. No impact on rpm
2. Moderate decrease in engine rpm
3 Moderate decrease in engine rpm
Concluding that (metered) air is drawn from outside the butterfly to plenum when butterfly is shut and plenum vacuum is at its highest.
1. No impact on rpm
2. Moderate decrease in engine rpm
3 Moderate decrease in engine rpm
Concluding that (metered) air is drawn from outside the butterfly to plenum when butterfly is shut and plenum vacuum is at its highest.
Edited by blaze_away on Tuesday 2nd January 20:32
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