Thread: D2 V8 MAF sensor issue?

That does sound like a possible MAF issue. It's possibly leaning off due too poor reporting from MAF.

I do have some images that demonstrate exactly that (not on a Land Rover, but its the same engine management). If I can find a way of posting the images up, I can show what happens and goes wrong at the PCM.

HTH
Andrew

Right, figured it out.

Here we go part one. Good luck

I'm hoping to demonstrate how hard it can be to prove a faulty MAF but at the same time show why you feel some of the symptoms. It may look complicated but with a bit of time you will see what and why exactly the PCM behaves the way it does.

The first image is a good MAF. It just makes it easier to see what is wrong in the poor image (which I will post tomorrow). This is from a Subaru but the concept applies to every EFI engine with a MAF.

The brown line is the voltage output from the Throttle Position Sensor (TPS). At it's lowest point, my foot is off the throttle. At the highest point is Wide Open Throttle (WOT). And anything in between, well thats obvious.
The red line is the MAF output. Easy again. The higher the voltage the more air is passing through the MAF.
The blue line is manifold pressure in psi. Note this is a turbo, so that is why it shows positive pressure.
The green line is the Oxygen sensor. This gives a feed back to the PCM in closed loop (generally when the engine is at idle to light load) about the Oxygen content in the exhaust. 0.1volts is lean up to 0.8v which is rich (note, this not a smooth transition. In fact the PCM flip flops between the two about once a second in closed loop)

In the above image you can see me move my foot on and off the accelarator (the brown line). Even the gear change between 1st and 2nd is obvious and others if you look closely.

The area in second gear is the area I'm looking at.

I should point out you can see the time scale along the bottom is in seconds.

I'm interested (in this case) in what the engine does and how the PCM reacts to my demands for full power. Which in this case is me planting my foot in second gear (for seven seconds)

It looks good to me.... Why?
The MAF (the Red line) has reacted instantly to the throttle being pulled wide open and given the PCM a good response to the air passing through. And I know that because the O2 (the green line) has reported no free Oxygen in the exhaust as soon as it goes full throttle. So I know it is in enrichment mode and it is receiving a nice rich mixture (it is above 0.8Volts constantly during WOT) . Also I can see no misfire (the O2 would show that by dipping down).
NOTE: As the RPM increase and air flow increases, you can see the MAF voltage climb.

The result of this is the immediate increase in boost pressure. More power.

Just for the hell of it, I have out lined the area where the PCM has gone into closed loop and the Oxygen sensor cycles between rich and lean.

To anybody who is still reading this. Concrats. And thanks for your effort.
It can be a bit over wealming to start off but it explains why sometimes faults are hard to prove. But can be easy with the right tools.

Tomorrow I'll post the bad MAF which you will then easily see the fault. (Interstingly this fault I found, was not the complaint. It was another, also caused by the MAF).

Part two.

The reason I thought I'd post this case study up to answer Darians question, which basically is that his V8 just doesn't feel responsive, can it be the MAF? Well, yes it can, and I just want to show why.

As mentioned before this car was not in for this problem. It had a problem at idle which I will show later. I was testing the MAF's reponsiveness to further condem it as faulty. Funnily enough when I got the vehicle the bloke said "they're not very fast off the mark these Subaru's". LOL. We know better.

Again:
Brown is Throttle Position Sensor
Red is MAF voltage
Blue is Manifold pressure
Green is Oxygen sensor

This second test was done on the same stretch of road. And again we are looking at the second gear part of the image.




This image very closely follows the first. But there is one thing that stands out telling me all is not good. The Oxygen sensor is not staying full rich, in fact it starts to dip (go lean) shortly after peaking, before slowly climbing back up again. It is not in full fuel enrichment, the PCM is not putting enough fuel into the engine. But Why?

If we go back to where I stomp on the accelarator, where the TPS (brown line) shoots up we can see the MAF voltage has shot up to 2.91Volts. Doing the same test with a good MAF, it shoots up to 3.36Volts.
"But that's only 0.4Volts, surely it won't make that much differance" I can almost hear you say. It does. A massive differance and I will prove that later.
We can now see another result of this under reporting of air mass. The manifold pressure is also down to 5.23psi. With the good MAF the engine management is working well the pressure hits 5.84psi. More boost. This car was never going to go 'like a scalded cat', boost pressure is down and it's leaning out.
And remember this is not even the complaint.
I hope you guys can now see why sometimes your car just doesn't go like it should. Yet you can't find anything wrong.

One thing I have to point out here is that the manifold pressure it's self or the MAF voltage mean nothing in themselves. You're not going to get figures to compare in the real world. What is the tell-tale here is the Oxygen sensor reporting the exhaust is heading lean under WOT conditions.

Remember other faults can cause these lean outs during WOT. The one that comes to mind, of coarse, is the fuel pump. If your pressure and flow is under spec, you will get a very similar result. So before condemming your MAF. Check your fuel supply.

Just a couple of points and numbers I noticed while playing around with this post was in the bad image.
It took 0.446 seconds to go from closed throttle to WOT
The MAF had finished reacting in 0.155 seconds. This is where it probably started to go wrong.
The lower boost level took 0.881 seconds to reach.

On the good MAF.
0.631 seconds to WOT (this was due to the tyres trying to break traction)
0.37 seconds for the MAF to react (these times don't match throttle movement due to engine dynamics, the 'gulp' etc)
But only 0.626 seconds to reach a higher boost. Almost following the TPS.

If I get a chance I will show what was thw actual fault with this MAF, what differance 0.4V make and why I don't believe adjusting the MAF output should be done (in my opinion).

And too anybody still reading. Thankyou and well done. Hopefully you have gained a little bit of understanding about engine management and fuel control.

And to answer your question Darian. Yes, possibly, but check your fuel supply.

HTH
Andrew.

Thanks Andrew, its been a great insight to a few different areas of the engine. Thank you very much for your time.

You must have been wanting to get that off your chest for a while?

So two questions remaining-
If the fuel pump is a possible issue, can it be partly 'off colour'. I thought these things either run or when they die, thats the end of them - but hey, I'm no mechanic.

Many reports I've read here have people wrecking the MAF sensor by attempting to clean it. Is this due to 'home mechanics syndrome' (sorry guys, not intended to offend as I'm in that boat too!) or is it a really fussy bit of equipment? If so, should I budget and expect to have to replace the whole unit or just the sensor (if you can re-fit it?)

I do have a VERY trusty and 'street smart' mechanic, but would you recommend seeing a LR specialist?


Thanks again for your help, time and effort.
regards
Darian

Thanks Andrew, its been a great insight to a few different areas of the engine. Thank you very much for your time.

You must have been wanting to get that off your chest for a while?

Not a problem Darian. Good to get some feed back
I've been looking for a captive audience for a while now (Woah-Hahaha ). I will get round to putting up the complaint (not quite as exciting) just for more info about MAF's and kicks. But hopefully it explains why you get those 'just doesn't go like it should' cases, why they can be a buggar to nail down, but with the right tools and approach you can. But equally you easily spend a fortune if the wrong approach is taken.

If the fuel pump is a possible issue, can it be partly 'off colour'. I thought these things either run or when they die, thats the end of them - but hey, I'm no mechanic

I should of said fuel system, not just pump. Because a blocked fuel filter or a faulty fuel pressure reg ,etc will give you similar problems. I'm not exactly sure what you mean when you say 'off colour'.
Pumps can fail in many ways and unfortunatly some just won't give up without a few death throws (NRMA guy bangs the tank and off you go). If I suspect a fuel delivery problem I'll test pressure (regulated and max by breifly clamping return), flow, and if need be I will look at how well the pump operates electronically- looking at current draw and the state of the commutator bars. If there is a problem with the fuel system, I will find it.
But colour won't come into it unless the fuel was contaminated, off.

Many reports I've read here have people wrecking the MAF sensor by attempting to clean it. Is this due to 'home mechanics syndrome' (sorry guys, not intended to offend as I'm in that boat too!) or is it a really fussy bit of equipment? If so, should I budget and expect to have to replace the whole unit or just the sensor (if you can re-fit it?)

Thats a whole can of worms. Some people say if you need to clean your MAF, it broken. Buy a new one. Pesonally I believe if you're happy with the results. Go with the clean.
I'm not sure how they are getting broken, but they shouldn't be touched by anything at all. Sprayed with MAF cleaner, that is all. Although I do use brake clean.
And yes it's one fussy sucker. You have seen one result of it going lean by 0.4Volts and thats at about 3Volts. I'll show the other end of the scale, on how sensitive these thing can be.
In my opinion, I would replace just the sensor if possible (the results above were from just sensor replacement). I have no doubt quality varies in aftermarket componants and that is the risk. If you're concerned, go genuine. But personally I don't think it's worth the money.

I do have a VERY trusty and 'street smart' mechanic, but would you recommend seeing a LR specialist?

If he's a good mechanic, he should be able to fix it. It's not really about LR's, it's just understanding engine management. If he knows where his limits are. The better.
And the same goes for LR specialist's. They may be specilalist but they may not be sharp. I have ignition waveforms and pics that show (IMHO) why those Rover modules are unreliable, yet a LR specialist gave up on the job after many weeks.
So if he is good and honest, stick with him.

Anyhoo Darian, I'll shut up now (thank the lord, he says. Yawn, Yawn). But I hope it helps. I will try and get round to posting and explaining those other waveforms. And hopefully it will put some more pieces in the engine management jig saw, and show some more facets of fuel control.

HTH
Andrew.

There is a history of the cheaper Ebay aftermarket sensor only replacement units having issues where the genuine Bosch assembly (or LR boxed unit) don't seem to have the issue. The Bosch sensor only is within a few dollars of the whole unit anyway.

Finally got my orignal Bosch sensor in the mail yesterday, Replaced it last night and the car idles perfectly now and the gear change is smooth and crisp. thanks for the good read