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96 4.6
23rd January 2009, 12:26 AM
My P38 is idling at a very fast 1200-1400 RPM, and it is becoming very hard to drive, not to mention the cost for the fuel at the moment!!
I have removed the stepper motor and cleaned it, I have cleaned the carby body, and I have attempted to clean the MAF. It did this a few months ago and I did all of this as well as replace the stepper, but it was only after carefully blowing out the MAF with a compressor that it returned to normal. Is there a better way to clean it? I have a can of MAF cleaner, but it does not seem to get any into the sealed tube because of the wire mesh. It seems to disipate the spray before I can get it to go where I want it to... The wire mesh had some fine dust on it, so I am assuming that this is the problem, but besides a very expensive replacement, the actual MAF seems to be non serviceable... But I am sure that there are some genius's that have encountered similar problems and have a work around.. PLEASE!!!

Thanks in advance...
:angel:

CowsGoMoo
23rd January 2009, 05:04 AM
My can of cleaner has a little plastic tube that can be attached to the nozzel. Tube can be poked it through the wire mesh and directed where you want the cleaner to go.

Or do you mean the wire mesh won't let you get the tube in?

My TD5 MAF only had fine mesh at one end.

p38arover
23rd January 2009, 07:13 AM
THe wire mesh was blown out of mine with an LPG backfire. Seriously!

PhilipA
23rd January 2009, 11:24 AM
The wire mesh is there to ensure that air flow into the MAF is uniform, if there is not about 30CM of straight tube in front.
In the 14CUX, you can remove the mesh by levering on a spring retainer.
In any case, where you want the cleaner is in the sampling tube of the MAF on older ones (hot wire type) or on the film surfaces of later type ones (hot film type).
There are two small wires in the sampling tube which you should be able to see when they are clean. The hot film type has a double sided "blade" sitting in a holder in the middle of the MAF tube.
Spraying the mesh in either case does nothing but make it look nice.
Regards Philip A

Tank
23rd January 2009, 11:27 AM
My P38 is idling at a very fast 1200-1400 RPM, and it is becoming very hard to drive, not to mention the cost for the fuel at the moment!!
I have removed the stepper motor and cleaned it, I have cleaned the carby body, and I have attempted to clean the MAF. It did this a few months ago and I did all of this as well as replace the stepper, but it was only after carefully blowing out the MAF with a compressor that it returned to normal. Is there a better way to clean it? I have a can of MAF cleaner, but it does not seem to get any into the sealed tube because of the wire mesh. It seems to disipate the spray before I can get it to go where I want it to... The wire mesh had some fine dust on it, so I am assuming that this is the problem, but besides a very expensive replacement, the actual MAF seems to be non serviceable... But I am sure that there are some genius's that have encountered similar problems and have a work around.. PLEASE!!!

Thanks in advance...
:angel:
First, take out the wire ring holding the wire mesh into the MAF body, paint it (the mesh) green and throw it into some tall grass, I have no Idea why L/R put the screen there, it must create havoc with the airflow and if it is needed to filter particles out of the airstream then the air filter is a waste of space.
Every Fuel injected L/R I have ever owned, the first thing I did was remove this mesh, it has made no discernible change to the performance of the motor.
If you have dust on this bit of mesh, then your air filter is allowing it through, not good.
In the top left hand corner (just inside) of the opening of the MAF is a small hole with the Hotwire wires inside, you need to spray in this hole to clean the wires, do it with the engine running, or not.
I would also be checking for a vacuum leak at all of the many Vacuum hoses, a vacuum leak can cause the problems you describe, Regards Frank.

Tank
23rd January 2009, 11:30 AM
THe wire mesh was blown out of mine with an LPG backfire. Seriously!
Shows how much resistance to airflow if it can be blown out, Regards Frank.

96 4.6
24th January 2009, 07:38 AM
So the consensus would seem to be that the mesh which is too fine to get the little tube from the can through is just there to keep the flys out... I do have a new air filter element, and just to make matters worse, it is a genuine one... The dust that was on the mesh was very fine, but that's gone now thanks to the can of cleaner (At least it has done something!).

So I'll check all of the vacuum hoses I can find for holes / cracks, and see if I can get the mesh out. One way or the other, I'll get access to the inner tube and get some cleaner in there.
Just as a thought, is there a replacement or addition to the tube for the can that I could use that would allow me to bend the end, and actually attack it from the rear? I could come in from the back if there was a 180deg bend and spray in there easily... That way I would not have to touch the mesh. I don't have a problem pulling it out, but LR must have put it there for some reason.

Thanks for the suggestions, I'll try them ASAP and let you all know if I've been successful successful...

Hopefully with the continued support of forums like this, we can all band together with our combined knowledge and keep these great cars going for a long time to come.
:)

Tank
24th January 2009, 10:41 AM
99% of the gunk that gets on the "Hotwires" is on the front of the hotwires, which is where they read the airflow, so you really need to clean the front through the little hole, there is a wire "circlip" that holds the mesh in, it is easily removed with a small screwdriver or O ring pick.
I would be checking, air filter, air filter box and any induction hoses to find where dust is getting in, there should be dust tracks to guide you, Regards Frank. P.S. please post up here any solutions to your problems for the benefit of others that may have same or similar problems, Thanks

PhilipA
24th January 2009, 11:59 AM
AFAIK, the MAF cannot cause a fast idle.
It is upstream of the throttle body.
As suggested , look for vacuum leaks after the throttle blade, or a faulty stepper.

Just block off both ends of the hose to the stepper and see what the idle does. It should be a slow idle at about 550RPM. If it is fast then you have a vacuum leak somewhere. BTW, If the stepper mount is like that of a 14CUX, check the tightness of the bolts that hold it to the Plenum. If the idle is slow then the stepper is suspect even though you cleaned it.

Regards Philip A

96 4.6
26th January 2009, 01:46 PM
Ok. It did this a few months back, and cleaning the MAF worked a treat after replacing the stepper did nothing.
I have borrowed a MAF from a mate, and no difference this time. I have used the carby cleaner again, I have cleaned the vacuum hoses from the rocker covers to the plenium all with no luck. The smaller diameter vac hose to the plenium on the RHS was well caked in gunge, and I have removed all of that with the carby cleaner, I cannot see any holes in the pipes. I have removed all of the multiplugs that I can see and sprayed them with contact cleaner, and still no change.

Does anybody else have any suggestions? The next step I can think of is to get the faults read/cleared at the local dealer, but there must be a cheaper method... Besides, I'd like to solve it so that if it does it again, I can fix it again..

Tank
27th January 2009, 10:31 AM
Ok. It did this a few months back, and cleaning the MAF worked a treat after replacing the stepper did nothing.
I have borrowed a MAF from a mate, and no difference this time. I have used the carby cleaner again, I have cleaned the vacuum hoses from the rocker covers to the plenium all with no luck. The smaller diameter vac hose to the plenium on the RHS was well caked in gunge, and I have removed all of that with the carby cleaner, I cannot see any holes in the pipes. I have removed all of the multiplugs that I can see and sprayed them with contact cleaner, and still no change.

Does anybody else have any suggestions? The next step I can think of is to get the faults read/cleared at the local dealer, but there must be a cheaper method... Besides, I'd like to solve it so that if it does it again, I can fix it again..
If you have totally ruled out a vacuum leak, then I would take it to a L/R specialist, could be the idle adjustment in the MAF or the Throttle Position Sensor, which I would suggest unless you know what you're doing would be best left to a specialist, unless someone here can instruct you on adjustment.
I don't know if a P38 has an Idle screw adjuster on the throttle linkage or not, but have a look and see, you may be able to adjust, BTW did you test the vacuum lines to see if they hold vacuum, you can suck on them and put your tongue over the end and see if it holds vacuum (sticks), Regards Frank.

LOVEMYRANGIE
27th January 2009, 08:50 PM
The PCV lines are a good start. These hoses crack.
The other thing with the stepper motor, at least on the Classic anyway, is there is a vacuum hose from the fuel regulator to the very back of the manifold. If this has cracked or fallen off, it allows enough air to lift the idle significantly.

Either that or someone has been playing around with the air idle bleed screw on the manifold. (Another Classic thing... Need to get a P38 me thinks....)

nobbyclrk
30th January 2009, 08:45 PM
From what you are saying, I'm going to assume you have a hot film type MAF sensor. That screen on the front of the unit plays an important part of fuel control. It is there to smoothen out the air flow. Take out turbulance. The same reason why the actual measuring part of the sensor is jammed inconvieniently in a tube. That tube is there to reduce the impact of engine pulsations (valve action ect).
On a scope this is all (including each engine pulsation) very visable. It is a very sensitive componant. When cleaning I would be (assuming it is hot film) very cautious. It is for this same reason they are liable to failure. As for confirming a faulty MAF sensor, I wouldn't rely on a sacanner. An exchange with a known good one will give you direction. A scope will point out bad ones before a scanner. Hope this helps.

cockie55
30th January 2009, 11:41 PM
The wire mesh is there to ensure that air flow into the MAF is uniform, if there is not about 30CM of straight tube in front.
In the 14CUX, you can remove the mesh by levering on a spring retainer.
In any case, where you want the cleaner is in the sampling tube of the MAF on older ones (hot wire type) or on the film surfaces of later type ones (hot film type).
There are two small wires in the sampling tube which you should be able to see when they are clean. The hot film type has a double sided "blade" sitting in a holder in the middle of the MAF tube.
Spraying the mesh in either case does nothing but make it look nice.
Regards Philip A

PhillipA or anyone out there ......if we are talking about how to clean these MAF sucker's ....then don't we need to know HOW THEY WORK or the sensing or sampling difference in MAF's between Lucas 14CUX, GEMS and Bosch Motronic???

For instance everyone rolls off the tongue Hotwire 14CUX 5AM and or Bosch hot film MAF specs......they can or can't work with oiled/K&N air filters etc etc with confidence?? What about GEMS?????

It seems to me a GEMS 20AM MAF no one is quite sure about how they work???? For instance (and we are speaking MAF only).....is a GEMS 20AM a simple hotwire 5AM upgrade that everyone has forgotten about OR something more significant???

Is the bucketing Bosch hot film MAF's (10 years old) justified???? If so does this mean a GEMS MAF albeit 15 year old is far better????

Love to be illuminated

PhilipA
31st January 2009, 09:12 AM
PhillipA or anyone out there ......if we are talking about how to clean these MAF sucker's ....then don't we need to know HOW THEY WORK or the sensing or sampling difference in MAF's between Lucas 14CUX, GEMS and Bosch Motronic??

Well all MAF work by measuring the MASS of air entering the engine. A hot wire samples the air by taking a fixed proportion of it through a tube.

The measurement is done by measuring the resistance difference between a wire heated to a known temperature and another wire. The cooling effect of the incoming air cools the hot wire . Hot film works much the same but on all the air.

This automatically makes compensation for air temperature unlike the flapper which measures air by the mechanical lifting of a flap which only measures the volume of air.

The 14CUX is particularly unsuitable for use with a K&N because it is one of the only (or THE ONLY) ECU that does not pulse a burst of high heat through the hot wire as you turn off the ignition. This is designed to burn off any oil. The 5AM Hitachi MAF is used in many GM cars and they do not have the problem to such a degree as Range Rovers, but they still do have it.
I do not know about the GEMS ECU, but I would be surprised if it did not institute a burn off phase, so using a K&N would not be such a severe problem. Its not the MAF so much as the design of the ECU.

So, when oil or other stuff gets on the hot wire it acts as insulation which alters the temperature effect of the incoming air.
Enough???
Regards Philip A

cockie55
1st February 2009, 09:54 AM
Thanks PhillipA.

My 5AM is on the way out so intend wiring in a 20AM MAF for larger airflow and hopefully it has the burnoff feature you speak of. I need to source the right potentiometer to adjust CO signal as this not on the 20AM.

Same conversion could be done with the Bosch but I get the impression they are troublesome when you don't here of any problems with earlier MAF's

PhilipA
1st February 2009, 12:22 PM
It's not the MAF which determines the "burn off" it is the ECU, so unless you change your ECU you will not achieve that.
But the conversion to the later MAF seems straightforward ( on the RPI site), but really only useful if you have a big capacity motor and want max high rev power.
Regards Philip A

cockie55
1st February 2009, 09:04 PM
Thanks PhillipA. I am tossing up doing a gradual 14CUX to GEMs swap with a larger engine (stroking an GEMS donor) or sticking with the 14CUX (and stroke anything).

The simplicity of the dizzy 14CUX Versus of the GEMS kiss the dyno goodbye after initial setup is an interesting pros and cons exercise.

96 4.6
8th February 2009, 07:35 AM
Well my problem is sorted. After scouting round on the forums, I found a guy that other members could not reccomend highly enough. Ricks 4x4 at Nerang. I rang Rick and he suggested that it sounded like the base idle had adjusted itself. When I got there, he hooked up the computer, found that his suspisions were right, and as soon as he adjusted it back to standard, it now runs like a dream. And I got change out of 50 bucks too!!!
If anybody else gets a problem that they cannot fix, and they are around the Gold Coast, call Rick. The man is a magician and does not charge huge fees.
:D

The only question that remains is why did it fix itself last time it did this??? Computers in cars, what a good idea that was!

DAMMAG
12th April 2009, 12:04 PM
I cleaned the hole in the plenum that feeds the air bypass screw with throttle body cleaner the other day which seemed to help my D1's idle. I wonder how gunked up these get. A fair bit of black bits came out.

Damian.

LOVEMYRANGIE
19th June 2009, 12:43 AM
Well my problem is sorted. After scouting round on the forums, I found a guy that other members could not reccomend highly enough. Ricks 4x4 at Nerang. I rang Rick and he suggested that it sounded like the base idle had adjusted itself. When I got there, he hooked up the computer, found that his suspisions were right, and as soon as he adjusted it back to standard, it now runs like a dream. And I got change out of 50 bucks too!!!
If anybody else gets a problem that they cannot fix, and they are around the Gold Coast, call Rick. The man is a magician and does not charge huge fees.
:D

The only question that remains is why did it fix itself last time it did this??? Computers in cars, what a good idea that was!


Either that or someone has been playing around with the air idle bleed screw on the manifold.
:TakeABow: Looks like I was on the money!! :ehigh5: