Here are some pics and test info for a hotwire MAF. The first picture shows the hotwire setup which is connected to the underside of the circuit board. The thin grey sensor in the foreground is the actual hot wire. Cleaning this with Contact Cleaner etc after it is heavily coated will probably not be successful though it might improve reading.

The second picture shows the circuit board. It is pretty simple as ItsNotWorthComplaing indicates. My view is the alloy casing on the 3AM and 5AM MAF’s while making it very robust does great things for transferring heat to these electronics and I think the reason why later MAF’s are plastic along with being cheaper to build. However as you can’t simply swap in a plastic (and larger throat) 20AM MAF from a GEMS RR without first changing the fuel map (to compensate for the different airflow to voltage ratio), we are stuck with these alloy MAF’s (or go Megasquirt etc). The only moving part is the variable resistor or “pot" seen on the right hand bottom corner of the photo and this sets the CO trim at idle. The “pot” is sending that voltage direct to the ECU and is not connected to the AFM/MAF electronics at all.

Many people confuse being able to achieve this CO adjustment with having a MAF that works??? This is not the case!!! You need to check the airflow signal from the MAF to the ECU in conjunction with a gas analyzer and preferably a dyno to see if your MAF is working OK. However as most people don’t have gas analyzer at their disposal and 4 wheel dyno time is expensive (and not necessarily in the hands of those who understand Rovers), you can still tell a lot about you MAF by the airflow signal output.

As most people don’t have an oscilloscope lying around a digital multi meter (preferably one that has a manual/auto range single digit DC voltages) is OK.

Peel back MAF boot connector. You will find on underneath that each connector is numbered. To check the airflow signal backprobe ground connector 2 (red with black trace or just black) and airflow signal connector 4 (blue with green trace or just green). Switch on ignition (but not starter) and expect to see 0.30 - 0.35 volts. Switch off wait 10 seconds and then switch ignition on again. Airflow signal should immediately go to 0.30 – 0.35 volts.

If it goes above this say to 0.5 - 0.8 volts and takes a few seconds to drop down to 0.30 - 0.35 volts this is a good sign a Rover hotwire MAF is on the way out or already defective. A defective MAF may also be producing at slow idle an airflow signal in excess of 2.0 volt instead of around 1.7 volts for a 3.9. The faulty airflow signal does not necessarily mean the ECU will trigger a fault code / go to limp home mode but more probably be picking a fuel map for a moderate load when it does not need it. This will equate to lousy fuel consumption.

By the way if you find your CO idle trim is set lean or down to around say 0.1 volts instead of around 1.4 volts (for non cat) someone may have set this to compensate for MAF setting a richer signal to the ECU. Note: Connectors 2 and 6 (or outside connectors) measure CO trim voltage and Connector 2 and 5 is 12v/battery supply voltage to the MAF. If you have an additional earth at connector 1 (or outside closest aircleaner), you probably have a harness from the MAF changeover period.

This test is a bit off my post topic however I will mention it in a “MAF Bulk Buy” post I hope to put up this weekend.

Attached Images

	hot_wire.jpg (5.1 KB, 67 views)
	5AM.JPG (27.5 KB, 66 views)

Can a Moderator please direct me to where I should post this AFM/MAF Group Buy as there is only a limited quantity and no profit involved so the Verandah does not seem an appropriate place, putting aside I can't post there as I am not a Vendor.

Its more a manufacturing cost thing. Heat transfer isnt an issue. The components are rated to a high temp and are also encased in a resin which insulates and dissipates heat. This is the problem with Chinese units flooding the market. The components tolerances are a lot lower, for example, resistor values, although they might be identical in resistance, a Lucas unit is 1 or 2% accuracy where as the chinese unit would be a much cheaper 5% or worse unit. The easiest way to tell is look at the resistors and the bands around them. A 4 band resistor is a 5% where as a 5 band resistor is 1%. The 5% are a carbon film, 1% are metal film.
This can be used in ANY electronic gear to check if its a quality item.

Not so. The main difference with the 20AM and 5AM is that the 20AM doesnt have a CO trim pot. The air tubes are the same but the internal ID is far bigger due to the MAF style. A few changes to the wiring plug into the MAF and the addition of a trim pot and you have a 20AM on a 14CUX system. This is a pretty common upgrade for hi performance 3.9's in TVR's etc.

Its connected. Its trims the overall setting of the MAF scaling and controls the signal into the ECU.
The main reason these have a trim pot is they can be used with or without and O2 sensor. All 14CUX in Rangies for example, don't have O2 sensors as they are low compression engines. From '94-95 onwards with the GEMS onwards, all have O2 as they are 9.35:1.

Yes and no.... you can quite successfully achieve a good tune without an analyser, however an analyser will tell you more accurately how its set and for those lucky enough to have one...
Dyno's are expensive but really arent that important. You will feel the difference after resetting if your MAF's been set wrong and your fuel gauge will be nicer to you!

The base setting is anywhere from 0.2v - 0.7v for the MAF to be serviceable and the trim pot alters this.

See my post HERE

Cheers

Andrew

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LOVEMYRANGIE/Andrew good observation about the electronics but I don't think all Chinese MAF's are necessarily crook. It'sNotWorthComplaining seems to be happy with his for the last 2 years. Also I am told Rover OEM Replacement Hotwire MAF's are now made in China and not by Lucas/Hitachi any more!!

However first noting I have no difficulty with open debate, with all due respect your comments about MAF operation and testing are simply not correct.

Firstly I say “The only moving part is the variable resistor or “pot" seen on the right hand bottom corner of the photo and this sets the CO trim at idle. The “pot” is sending that voltage direct to the ECU and is not connected to the AFM/MAF electronics at all”.

Andrew you say “It is connected. Its trims the overall setting of the MAF scaling and controls the signal into the ECU”

The CO idle trim pot is only located in the body of the MAF for convenience. The CO trim voltage does not change under revs or change in airflow. More importantly once out of idle the ECU fuel map kicks in and that is what drives fuel injector pulses. You can even install the CO trim pot inside the cab and connected direct to the ECU using the wiring going from pin 22 on the ECU having no connection to Connector 6 on the MAF at all (just as you have to do when doing a 3/5AM to 20AM conversion as the 20AM has no CO trim pot or connector 6). Therefore the CO trim pot has no bearing in the MAF’s functionality or determining whether a MAF is defective or not, (which is the entire point of my thread and post).

Secondly I say “To check the airflow signal backprobe ground connector 2 (red with black trace or just black) and airflow signal connector 4 (blue with green trace or just green). Switch on ignition (but not starter) and expect to see 0.30 - 0.35 volts. Switch off wait 10 seconds and then switch ignition on again. Airflow signal should immediately go to 0.30 – 0.35 volts. If it goes above this say to 0.5 - 0.8 volts and takes a few seconds to drop down to 0.30 - 0.35 volts this is a good sign a Rover hotwire MAF is on the way out or already defective.”

Andrew you say “The base setting is anywhere from 0.2v - 0.7v for the MAF to be serviceable and the trim pot alters this”

For the reasons I have outlined above, adjusting the “Co trim pot” will not alter the “airflow signal”. Airflow signal is the MAF’s prime job and the only way the ECU can select an appropriate fuel map position. Also if you have a "base airflow signal" with ignition on (not running) with less than 0.3v or greater than 0.4v then I suggest your MAF is not right as the ECU fuel map tolerance can't really exceed 0.10v. However any difference will be hard to perceive I suspect. Therefore a far better guide to MAF serviceability is the "stability" of the "airflow signal" immediately from the time the MAF receives power (via connector 5) as I mention above.

Finally Andrew you say “Dyno's are expensive but really arent that important. You will feel the difference after resetting if your MAF's been set wrong and your fuel gauge will be nicer to you!”

I agree you must get CO trim correct and a gas analyser is far better than the default CO trim voltage signal to ECU to determine that mixture at idle. However as I have already indicated adjusting the Co trim pot has no bearing on the “airflow signal” the ECU receives. Measuring the "airflow signal" the ECU receives at tickover is a good sign of MAF serviceability and I agree a Dyno is not essential however the only way you can be really certain of the "airflow signal" is to measure it under load (and injectors being controlled accordingly) on a Dyno. However for those who want to try it at home, hardwire your Digital Multimeter to the MAF so you can see the readout from the cab and go find a nice steep hill. A functioning MAF in a 3.9 should show a "airflow" voltage in the order of 4.75v at full load, bit less for a 3.5. If not your MAF is probably not producing the appropriate "air signal" voltage at lower loads. It is the low load area which most concerns me as a defective MAF will send an "airflow signal" corresponding to a higher load and with the commensurate amount of wasted fuel, but not so high it will trigger a ECU fault signal / limp home mode.

Andrew your tutorial on “CO trim signal” is excellent however it does not deal with “airflow signal” at all and hence has no bearing on the serviceability of a MAF. As I could not find anywhere on this forum anything about MAF suppliers and serviceability checks I generated this thread.

By the way I would not recommend a 3AM/5AM to 20AM conversion without first re-chipping ECU to correspond to the new "air signals" (different air ratio/voltage) coming from the larger throated 20AM. I have tried it and found it runs too rich and too lean at some points, the latter doing engine damage with the hotter temps.

Cheers

I know it's a difficult answer to a simple problem , but adding o2 sensors overrides the MAF signal.

When you drive along you can see the mixture changing rapidly up and down to average 14.7, if you have a suitable tool.

My tool is a Jaycar LED mixture meter fed by a Zirconia (3rd) sensor. I must admit that the meter is not calibrated but the o2 sensors only work at one A/F ratio so if the mixture is cycling then it must be around 14.7:1.

Despite what many people say this even works at idle, by the cycling evident on the meter.

I can see no real reason to up the trim to 1.8 volts as LR recommend , other than it may give a more stable idle if the O2 sensors are taking out fuel rather than adding it in. I have upped mine from 1.2 to 1.8 but do notice much difference.

So AFAIK the MAF is only working when the 14CUX goes to open loop at over 1/2 to 3/4 throttle. When at those openings I would expect a rich mixture anyway.

BTW, another check for the MAF is to disconnect it while having a colourtune in a plug. You will see the mixture immediately go orange from blue/orange fleck as the ECU goes into limp home. I would imagine an exhaust analyser would also be quite evidently richer. Of course this will not tell you whether it is reading incorrectly within the ECU parameters, but will show if it is actually giving an output.

I must have something right as my economy can be 14.5L 100Kms towing a 600 +Kg camper at 100-105.

BUT dammit it still gets 20L 100Kms around my local area which has BIG hills everywhere.
Regards Philip A

I presume this Limp home thing must only apply to Autos?,My manual wouldn't even crawl home with the aid of crutches when the MAf was faulty

For the sake of ensuring the subject of this thread is not lost which is one of MAF suppliers and determining if you have a faulty MAF or not, I reiterate that both O2 sensors and the CO trim pot (the pot just happens to be located on the MAF body) have nothing to do with MAF serviceability and airflow measurement.

However if we are going to digress it is my understanding that using O2 sensors with a catalyst map, the CO trim value is ignored and ignored to the extent the sensor/ECU stays within range even if the CO trim pot is cranked up to 3.6v max. I assume 1.8v of trim pot is selected for catalyst maps as a safe halfway house position just in case sensors fail but you’re still stuck with a catalyst map.

While the fixed trim pot system on the non-cat 14CUX is pretty good and able to cope with engine modifications etc (within limits), I envy your cat set up PhillipA with its ability to continually trim the mixture within the correct range. One day I will remap with a 20AM MAF and cats.

I will have the MAF Group Buy details up tonight or tomorrow. It is looking very good for those interested.

For Info: I've just ordered a replacement MAF (part No. MHK100800) for Bosch 4.6V8 (P38 MY2000) for A$105 from Jag Landrover parts in the UK Jaguar | Land Rover spare parts at British Parts UK... with the A$ now worth 0.6 GB Pounds there are some bargains to be had...

Thanks Hoges but this Supplier, then Testing thread is for 3.5 or 3.9's ie D1 and Classic V8’s using a 3AM or 5AM Lucas/Hitachi style Hot Wire MAF's, not Rangie GEMS or later D2 and Rangie 38 Bosch MAF's (which are trillions $ cheaper you lucky buggers).

this post goes STRAIGHT to the Pool Room cockie55

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