Thread: TD5 MAF Stuffed?

Hi all

Well after a couple of day's letting the problem sit and a bit more googling I've has another dig around the engine bay.

First check was unplugging the MAF. Nanocom reading was now a flatline 4.0 just as you observed JC.

Following Tombie's advice I also has a good look at the wiring loom running across the front of the engine. Well the conduit cover passing over the air cond compressor was pretty crumbly and falling apart but from the water temp sensor to the ecu looked fine. Removed all the crud conduit (it just fell apart in my hands!) and had a look at the actual wiring. I saw nothing untoward, no brittle insulation or abrasion. Whacked on some new conduit and then started the car. Still a flat line! Wriggled the wiring to see if that made a difference but no change.

I then decided to check the resistances across the pins of the MAF meter reasoning that this checks the MAF only, while the nanocom reading is a calculated figure from the electrons passing through a lot of wiring circuits. Pins 1-2 were right on at 16.75k ohms, but there was infinite resistance across both pins 2-3 and pins 1-3, ie no circuit.

So my conclusion is that the MAF is dud. This is very much a learning exercise for me (but an enjoyable one ) so I ask the question of more learned members, should I be checking anything else and is there anything in the above I have misinterpreted, before I hit the visa card?

Cheers

Steve

Originally Posted by Rok_Dr

Hi all

Well after a couple of day's letting the problem sit and a bit more googling I've has another dig around the engine bay.

First check was unplugging the MAF. Nanocom reading was now a flatline 4.0 just as you observed JC.

Following Tombie's advice I also has a good look at the wiring loom running across the front of the engine. Well the conduit cover passing over the air cond compressor was pretty crumbly and falling apart but from the water temp sensor to the ecu looked fine. Removed all the crud conduit (it just fell apart in my hands!) and had a look at the actual wiring. I saw nothing untoward, no brittle insulation or abrasion. Whacked on some new conduit and then started the car. Still a flat line! Wriggled the wiring to see if that made a difference but no change.

I then decided to check the resistances across the pins of the MAF meter reasoning that this checks the MAF only, while the nanocom reading is a calculated figure from the electrons passing through a lot of wiring circuits. Pins 1-2 were right on at 16.75k ohms, but there was infinite resistance across both pins 2-3 and pins 1-3, ie no circuit.

So my conclusion is that the MAF is dud. This is very much a learning exercise for me (but an enjoyable one ) so I ask the question of more learned members, should I be checking anything else and is there anything in the above I have misinterpreted, before I hit the visa card?

Cheers

Steve

Steve, I have a spare MAF you are welcome to use as a test if you are not too far away.

It really does sound like the MAF is dead. This is very very common, and shows in the fixed air consumption. Strangely they never do put up a fault code for this failure.

The MAF is mainly used to caclulate when to operate the EGR valve, and when the MAF dies it operates at the wrong time which leads to the stumbling when you try to pull off.

Originally Posted by Mark Adams

It really does sound like the MAF is dead.

The MAF is mainly used to caclulate when to operate the EGR valve, and when the MAF dies it operates at the wrong time which leads to the stumbling when you try to pull off.

So if you blank your EGR, what else does the MAF do?

Auto trans shift points are partially referrenced from it, as is engine loads etc and it works in conjunction with ambient air sensor for a density/ volume calculation of incoming air.

JC

JC the Td5 I've got here runs better with the MAF dis-connected,it blows black smoke so I'm thinking it's gone to the default setting?. Pat

Hi All

Well the old sensor was dead. Bought a new sensor (Siemens), fitted it last night and now I'm getting readings on the nanocom as per normal, mid 50's at idle etc, etc. On the test drive the car felt subtlety different. Less lag at takeoff and it revs out more cleanly and less strangled at high RPM. It may be my imagination but the auto shifts seem a bit crisper as well. I'll be interested to see how my fuel economy goes now......

So the outcomes for me were:

1. A flat line reading in the 4-4.5 range indicates a dead sensor (at least in my case).

2. It is well worth checking the wiring back to the ECU, if only to replace the conduit cover before the heat destroys the wiring insulation and also check for any other damage.

3. While it helped I didn't find the resistance testing to be particularly reliable. Both the dead and new sensors showed 16.7kOhm across pins 1-2. New sensor showed mid 20's mOhms across the other pins which is a bit lower than other posts have noted. Interestingly a test of the dead sensor after a hour or so driving in traffic showed very low approx 1.8mOhm values across pins 2-3 and 1-3, which leads me to suspect a fracture in the sensor's circuitry somewhere that causes an open circuit when cold. All I can say is that high values across pins 1-3 and 2-3 good, very low or no values bad. I certainly wouldn't be using them to predict % life left etc.

Anyway thanks one and all for your help with my problem. Its amazing what you can do with modern electronic diagnostics and my nanocom is now well on the way to paying for itself

Cheers

Steve

I think the good measurements mturri has posted are too high. There are now three reports of brand new or known good mafs measuring around 20Mohm so you'd have to assume this is normal rather than "dodgy" as mturri suggested.