Air flow meter temp sensor

[nigel_350i]

Hi folks, I've got a flapper type airflow meter on my 350I and suspect that the air temp sensor within the meter is on the blink. Anyone know if these are available from a supplier for a DIY refurbishment?

[dickymint]

I'm pretty sure that that there isn't a temp sensor in your flapper AFM (stand corrected if i'm wrong).Unless you have a hot wire AFM - Post up your symptoms.

As confirmed here (about 1/3rd down the page)...www.rpiv8.com/carbs-3.htm

>> Edited by dickymint on Tuesday 26th October 15:08

[nigel_350i]

Hi, Theres a sensor just before the flap that is for incoming air temp (Needed so ECU can approximate for density on hot summer days Vs cold winter mornings). It's just a thermistor and I get a lower resistance than I believe I should, ECU thinks it is hotter than it is -> leaner.
I've been tracking down a poor idle(revs up and down)rough running fault for a while. I've done loads so far and am convinced it's running lean. Manually pushing the flap forward -> fool ECu into thinking it's got more air than it has -> inject more fuel -> better. Also both Co2 screw and IDle screw were screwed closed when I bought the car to make it run richer perhaps to disguise the problem.

(1) renewed throttle pot (new) and connections re-done
(2) Loads of electrical checks as per Rover fault guide, all fine apart from the air flow temp sensor
(3) New valley gasket -> in case of leaks
(4) all hoses checked for leaks
(5) Fuel pressure at around 30 is ok
(6) timing / spark all good

So currently thinking on new sensor to check this theory out without stumping up for a whole new air flow meter (which is a re-con Lucas unit fitted around two years ago).

Sorry for the long story!!

Nigel

[gsx600]

Dicky
You are correct no air temp done on flapper system

"and unlike the later Air Mass Meter as used on Hot wire injection, it is only able to give information relating to air speed.
It has no ability to give the ECU, air density or temperature information."

Could still be worn though this company might be able to help with hire of one to check where your fault may be

Allcar Electronics 01773836485 Alfreton, Derbyshire

>> Edited by gsx600 on Tuesday 26th October 15:34

[nigel_350i]

Think RPI are wrong here,

This site has good diagrams etc. for the flapper type meter, Check out bottom of airflow meter section,

www.roversd1.nl/sd1web/airflow.html

Mine is not "hotwire" but definately has this thermistor which does react to temp changes. My ex-Wifes hairdryer shot at it changes the resistance...

[gsx600]

Looking at the Rover website it does mention this air temp, but having had an afm apart I don't think that is a servicable item.

I have a spare one from my 400 that you are welcome to borrow to try if you are fairly local to me for pickup ?

[nigel_350i]

Thanks Paul, appreciate the offer , Unfortunatly I live up in Scotland (where BTW the wedge appears to be a relatively scarce species)so I think I'm going to have to try and source one on some kind of loan arrangement. Maybe even get one from a land rover breaker.

I've not had it apart only the top cover off and the pot track is fine. I can get my hand in the inlet and touch the sensor but not sure if it will come out without a fight. Just thought if I can get a new sensor and bodge up some wiring I could check it out.

>> Edited by nigel_350i on Tuesday 26th October 15:54

[dickymint]

nigel_350i said:

Think RPI are wrong here, This site has good diagrams etc. for the flapper type meter, Check out bottom of airflow meter section, www.roversd1.nl/sd1web/airflow.html Mine is not "hotwire" but definately has this thermistor which does react to temp changes. My ex-Wifes hairdryer shot at it changes the resistance...

Have seen this temp sensor on a few drawings.(The SD1 site mentions it as well). I'm thinking that, if it is there, its not connected to ECU

you out there Wedg1e and co...

[djc1001]

SD1 and Range Rover manuals do refer to the flapper meter also having air temp sensing the two together measuring air mass.
The Bible gives test figures (resistance) for air temp.

Whether TVR moded this or connected it to the ECU may be a different story.

David

[dickymint]

Interesting stuff. So is it pin 27 on the ecu that you're measuring a resistance change?
edited to say i found these figures for it........

air temperature sensor.
-10 deg c 9.2k ohms
0 deg c 5.9k ohms
20 deg c 2.5k ohms
40 deg c 1.18k ohms
60 deg c 600 ohms

But i'm still not conviced its apllicable to a Wedge )only because i cant find reference to it on this forum)


>> Edited by dickymint on Tuesday 26th October 18:56

[wedg1e]

dickymint said:

nigel_350i said: Think RPI are wrong here, This site has good diagrams etc. for the flapper type meter, Check out bottom of airflow meter section, <a href="http://www.roversd1.nl/sd1web/airflow.html">www.roversd1.nl/sd1web/airflow.html</a> Mine is not "hotwire" but definately has this thermistor which does react to temp changes. My ex-Wifes hairdryer shot at it changes the resistance... Have seen this temp sensor on a few drawings.(The SD1 site mentions it as well). I'm thinking that, if it is there, its not connected to ECU you out there Wedg1e and co...

Yes, there is an air temp sensor in the flap AFM, connected between the Red/Black and the Blue/Red wires (or terminals 6 and 27 if you prefer).
Looks like it was epoxied in place, so should be possible to extract, but sourcing one with similar response characteristics may be problematic.

[dickymint]

Nice one Wedg1e. Now i'm a believer. Well done Nigel for bringing it up
So we i have another bl**dy variable to worry about!!!!! ah well live and learn....wheres me torch!

[djc1001]

dickymint said:

Interesting stuff. So is it pin 27 on the ecu that you're measuring a resistance change?

RR manual suggests testing by ohmmeter direct across sensor terminals. (battery disconnected & connectors unpluged)
Same resistance figures as coolant sensor but only ambient temps will be reached
-10c 9200ohms
0c 5900ohms
+20c 2500
+40c 1180ohms
Manual also says test each sensor term to sensor body - should be open circuit.
Can't see which ECU terminal No. - must be in book somewhere

[dickymint]

Same figures as i found then. Somebody tell me to shut up and accept i was wrong (again).
But whats the point in having the coolant temp sensor (same readings)? Is it that the density of air is dependant on temp and volume or vice versa? and why cant the ecu just use the water temp and mass?
ok i'll get me coat......and i'm off to adult education centre for physics top up!

[DJC1001]

dickymint said:

Same figures as i found then. Somebody tell me to shut up and accept i was wrong (again). But whats the point in having the coolant temp sensor (same readings)? Is it that the density of air is dependant on temp and volume or vice versa? and why cant the ecu just use the water temp and mass? ok i'll get me coat......and i'm off to adult education centre for physics top up!

For most UK based TVR's the injection system is probably too complex - don't forget the system is Rover / R.Rover and with minor spec changes designed to run in Artic thro' to Sahara conditions - a possible 60c temp differential.
However the flap & air temp together must give a better measure of air mass and the coolant sensor is linked to engine condition / cold start etc.
The coolant sensor has the same resistance for checking purposes but is not taking the same reading.
The Hot wire system does what you suggest - air mass & coolant temp.
Having said that - I am having problems getting a reliable 'idle' with my Hot wire system - but will start another thread shortly.

>> Edited by DJC1001 on Wednesday 27th October 09:09

>> Edited by DJC1001 on Wednesday 27th October 09:12

[nigel_350i]

Thanks for the help folks. Looks like my post stimulated some discussion! I'm testing it at the meter itself (easy to do by pulling the connector off and getting at the pins). Thanks for the figures they've given me a Eureka moment I've been measuring expecting a few ohms (as per the Rover SD1 site)that gives

-10 C +/- 0.5 C 8.26 to 10.56 Ohms
+20 C +/- 0.5 C 2.28 to 2.72 Ohms
+50 C +/- 0.5 C 0.76 to 0.91 Ohms

Looks like these are the same figures but he may have made an error with the magnitude! Should be looking for KOhms? Looks like I'll be taking the decent meter out to the garage tonight and checking through the higher ranges!

I'll let you know the outcome!

Thanks again.

[leorest]

nigel_350i said:

Thanks for the help folks. Looks like my post stimulated some discussion! I'm testing it at the meter itself (easy to do by pulling the connector off and getting at the pins). Thanks for the figures they've given me a Eureka moment I've been measuring expecting a few ohms (as per the Rover SD1 site)that gives -10 C +/- 0.5 C 8.26 to 10.56 Ohms +20 C +/- 0.5 C 2.28 to 2.72 Ohms +50 C +/- 0.5 C 0.76 to 0.91 Ohms Looks like these are the same figures but he may have made an error with the magnitude! Should be looking for KOhms? Looks like I'll be taking the decent meter out to the garage tonight and checking through the higher ranges! I'll let you know the outcome! Thanks again.

For testing purposes and untill you get a propper replacement, you can always solder a resistor of suitable value in series (to increase the resistance) or parallel (to reduce resistance) with the thermistor . Thermistors are cheap, have a look at the link.

For diagnostics you could always add a pot in series!

www.maplin.co.uk/Module.aspx?ModuleNo=2218&TabID=1&WorldID=&doy=27m10

Best of luck
Leo

[nigel_350i]

Cheers Leo, I'm taking home a bunch of resistors tonight though I suspect now that it may be be more to do with my measuring than the thermistor but you never know.

Thanks for the link, if it is the thermistor then looks likely I can rig something up to do the job.

Cheers

[nigel_350i]

Hi folks, well using the correct range on the meter got 4.06K at 10deg so looks like the thermistor is OK after all.(and I'm a professional electronic engineer maybe time to get away from the desk and improve my hands on skills!)

Anyway back to the drawing board to try and figure out this problem....

Thanks for the help