MAF Replacement

[TONUP]

Towing the caravan home from Devon last week along the A361, which in places is like a roller coaster ride, I thought that the Terrano was struggling a bit. Nothing serious, but I found myself reaching for lower gears than usual.

Whilst parked up at Taunton Dean services a guy pulled in next to me with exactly the same model as mine (colour, year and everything) towing a caravan, and he said that he had the MAF replaced on his at a garage (cost £200.00) and that performance had really improved.

On sunday I removed the MAF, with a view to cleaning it and checking its general condition. Unfortunately it has some special screws in the top, which I dont have a driver for. I could see the little wire, but I couldn't get to it as there is a gauze in the way.

I have looked on line, and it appears that I can get a (Bosch) replacement for £103.00, but do I have to replace the whole sub-aassembly, or can I just get the actual sensor?

Image below...

Regards

Alan

 

[BIGSEAN]

Concerning the "special" screws mine were modified very quikly with a junior hacksaw, now they are just plain old slot heads much less messing about

 

[rayf3262]

Before you chuck a hundred quid or so at the car....
For the sake of 10 mins.
With a meter it would be worth checking the output from it first, as per PAGE EC-360. 1.0 V engine stopped & ~ 2.2 V engine idle.

In addition to that check, the output from it should rise fairly linearly as engine revs increase. The maximum output of ~4 volts will probably be achieved at around 2500~2900 rpm.
If this checks out ok then a clean with a solvent spray (pcb cleaner etc.) is in order.

You can remove those Bosch 5 spline screw with a good pair of pliers around the screw head. There is about a 1mm land around the head that you can just get a grip on.

 

[Timbo_1975]

Before you chuck a hundred quid or so at the car....
For the sake of 10 mins.
With a meter it would be worth checking the output from it first, as per PAGE EC-360. 1.0 V engine stopped & ~ 2.2 V engine idle.

In addition to that check, the output from it should rise fairly linearly as engine revs increase. The maximum output of ~4 volts will probably be achieved at around 2500~2900 rpm.
If this checks out ok then a clean with a solvent spray (pcb cleaner etc.) is in order.

You can remove those Bosch 5 spline screw with a good pair of pliers around the screw head. There is about a 1mm land around the head that you can just get a grip on.

I would want to see a solid 4.4-4.5v under full load to guarantee absolutely full power on these. 4v would be 'good enough'.

 

[clivvy]

do the above certainly, but i am fairly sure i have seen MAFs of your type for £100 ish and less, and you only need the MAF, not the whole assembly, that would cost a lot more money.

et voila

http://www.ebay.co.uk/itm/NEW-Air-F...arts_Vehicles_CarParts_SM&hash=item3caf50e72f

 

[makeitfit]

Hey Clivvy can you find me a Hitachi one for that sort of money please?

 

[clivvy]

Hey Clivvy can you find me a Hitachi one for that sort of money please?

hahhahhahhahahhahaaaahahah ,,, you crack me up matey.....:thumbs

 

[TONUP]

Before you chuck a hundred quid or so at the car....
For the sake of 10 mins.
With a meter it would be worth checking the output from it first, as per PAGE EC-360. 1.0 V engine stopped & ~ 2.2 V engine idle.

In addition to that check, the output from it should rise fairly linearly as engine revs increase. The maximum output of ~4 volts will probably be achieved at around 2500~2900 rpm.
If this checks out ok then a clean with a solvent spray (pcb cleaner etc.) is in order.

You can remove those Bosch 5 spline screw with a good pair of pliers around the screw head. There is about a 1mm land around the head that you can just get a grip on.

Ray/Timbo, et al,

Thanks for contibuting this thread and for your detailed explanation of how to test the MAF, unfortunately and at the risk of annoying you, I am going to have to ask you to eloborate a bit more as I don't understand the technical terms.

Below I have created an image of the MAF, in-situ, and labelled all of the wires by colour i.e. B & W = Blue & White, R & B = Red & Black, G & R = Green & Red and Y = Yellow.

I have also indicated the P = Positive & N = Negative on the meter.

Would you be able to, in idiot fashion for me, explain where I need to place either of the probes from the meter and what I need to look for. Also how do you get the probe onto a wire (if needed) with the plug connected.

I hope you can help. Saving a £100.00 right now would be most welcome. I'll also get some PCB cleaner from Maplins today.

Thanks & Regards

Alan

 

[rayf3262]

Pin 1 = Unused
Pin 2 = YW
Pin 3 = GN/RD
Pin 4 = RD/BK
Pin 5 = BK/WT.. This is the MAF output signal you need to check.

Connect the Black meter probe to a known good earth point on the engine/body.
Connect the red meter probe to pin 5 (BK&WT) on the MAF connector.
Measure as previously shown.

As for making a connection; I have a set of meter probes with very sharp points, with these I can just pierce the cable insulation and obtain a reading. If you do not have meter probes like, you can achieve similar by use of a sewing pin just pushed through the cable insulation and the meter probe connected to this.

Happy measuring.

 

[supergnome]

There are pics of all this in the workshop downloads section. they make it look straight forward so I'll have a test on mine.

 

[andrewk]

In addition to that check, the output from it should rise fairly linearly as engine revs increase. The maximum output of ~4 volts will probably be achieved at around 2500~2900 rpm.

The workshop manual for the Patrol says the output should rise linearly to about 4v at 4000 rpm. Whoever wrote the manual must have forgotten that the operation of the turbo and the egr valve affect the readings (or more likely, they tested the MAF on a testbench, not in an engine). If you measure the MAF, if it is good, the output volts will rise as engine revs rise (but not particularly linearly) and it'll flatten off a bit over 3v around 3000 rpm.

Mine look like this ......

I tested two MAFs and they are virtually identical. The one labelled "Hokey1711" was measured using ECUTalk, not a DMM and was at sea level, whereas mine were measured with a DMM at about 1000ft above sea level (where I live).

If yours look anythink like this, they should be OK. As an aside, you can get security Torx bits at most tool shops - I bought some dead cheap off Ebay.

Andrew

 

[andrewk]

but i am fairly sure i have seen MAFs of your type for £100 ish and less, and you only need the MAF

Much less than £100, I think. The one labelled "Ebay_MAF" in graph above was about £60. As you can see from the graph, it measures pretty much identically to the factory original - so test first. Even £60 might be a waste of money if the original is fine.

Andrew

 

[TONUP]

All contributors,

Thanks for your ongoing help.

I didn't think to look in the downloads section, but you are correct that there is an excellent resorce for this problem available.

I now have some special screw driver bits and a tin of PCB cleaner.

I will also have a go at testing it.

Do you think the eBay ones will be OK?

Report back soon... probably after the weekend.

Best Regards

Alan

 

[Timbo_1975]

The workshop manual for the Patrol says the output should rise linearly to about 4v at 4000 rpm. Whoever wrote the manual must have forgotten that the operation of the turbo and the egr valve affect the readings (or more likely, they tested the MAF on a testbench, not in an engine). If you measure the MAF, if it is good, the output volts will rise as engine revs rise (but not particularly linearly) and it'll flatten off a bit over 3v around 3000 rpm.
Andrew

Unless you are measuring the output from the MAF under load conditions, rather than just revving the engine, you wont get a hugely usefull result, other than output is rising according to airflow. If the turbo is boosting at (say) 1 bar going up a hill, we need the MAF to register that. If it maxxed out at ~3v under those circumstances, you'd have a truck with about 80hp, on a good day!

 

[andrewk]

Unless you are measuring the output from the MAF under load conditions, rather than just revving the engine, you wont get a hugely usefull result, other than output is rising according to airflow.

Identifying the rate at which the output voltage rises with airflow is exactly what you do need to know. The means for measuring that is specified in the workshop manual - and it doesn't require it to be done under load.

Attempting to test under load (not that it is really possible to do that anyway) just introduces more variables and would make any results meaningless.

Andrew

 

[Timbo_1975]

Identifying the rate at which the output voltage rises with airflow is exactly what you do need to know. The means for measuring that is specified in the workshop manual - and it doesn't require it to be done under load.

Attempting to test under load (not that it is really possible to do that anyway) just introduces more variables and would make any results meaningless.

Andrew

I'm not quite sure you understand how a working MAF VS one thats drifted out of spec has such an impact on performance then.

 

[andrewk]

I'm not quite sure you understand how a working MAF VS one thats drifted out of spec has such an impact on performance then.

There is no spec for what the output voltage should be under all possible load and engine speed conditions - so it just isn't possible to test under load. If you think otherwise - please explain how.

Andrew

 

[Timbo_1975]

Two ways, either tape the DVM to the passenger side windscreen and go for a drive with an assistant, and secondly on the later trucks, MAF output is available in serial data, in both voltage, and ECU calculated airflow in cuft/min. (depending on scan tool)

A healthy MAF on a healthy 2.7 should pull at least ~90cuft/min, given you need at least 1.5cuft /min of air per HP on a diesel to burn clean at around 17:1.

 

[andrewk]

Two ways, either tape the DVM to the passenger side windscreen and go for a drive with an assistant, and secondly on the later trucks, MAF output is available in serial data, in both voltage, and ECU calculated airflow in cuft/min. (depending on scan tool)

All you've done is tell me how you would measure the MAF output volts. You could readily do that with a Consult (or ECUTalk or any other Consult-alike). That is a (dead) easy part.

The difficult part is replicating some test condition for which Nissan have published expected results. The only condition for which they have published expected results - and its in the workshop manual if you care you read it - is on no load - i.e. in neutral.

I think you are simply flying a kite - and I don't see the point.

Andrew

 

[BIGSEAN]

Am I wrong then that when using ecutalk for diagnostic purposes that the "air flow" column is not in fact taking it`s reading direct from the MAF?
After all it is a voltage measurement and it correlates pretty much exactly with what the w/shop gives as voltage outputs at given RPM readings.
If I am not wrong, it is entirely possible to check outputs whilst under load and under various driving conditions (which is why ecutalk/consult was developed in the first place)
One final question, if not tested under load conditions, how is it possible to get accurate readings at standstill when the ECU detects no load and cuts fuel at 2500 RPM after a set time?(15 seconds is it?)