Good old Bill

Are there any other codes besides the MAF. I have a 02 4.2 with no issues. I know your 98 has a different intake set up then mine, but your symtoms say intake leak. If you haven't inspected the elbows to the PCV valve as torkum suggested, do it. Still don't like the MAF as the cause, just doesn't feel right. Was playing with wifes 5.0 and had the intake elbow with the MAF removed and it idled fine. Threw a code at me so had to erase it, but no problem with idle at all.

JohnF150

Just to make it clear - English is not my native tongue -

There should be 2V coming of the PCM to the MAF sensor.
But there is not anything measured on that connector

John

JohnF150

Ok, here is some further information.

Car is not running idle properly and cuts off regularly.
IAC is constantly changing the RPM's
Only code is P0102 (Mass airflow circuit low input).

MAF sensor has been replaced.
At the connection at the MAF senson max 0.02V
At the PCM maximal 0.02 V aswell

PCM has been replaced (twice).

Note that other sensors have been checked and cleaned.

According to the information there should be 2V at the connector.
Seems that there is something (not the PCM) else that may influence the voltage on the connector of the PCM.
Maybe another sensor?

Hope someone can think of something !

Thanks

John

tory3

There is battery voltage input to the mass airflow sensor which your mechanic should check to see if it is available at the sensor connector . If this checks out good to ground (and there is a ground connection in the sensor connector) then they should check for voltage coming from the mass airflow signal terminal with the sensor plugged back in the connector with the engine at idle. The PCM does not provide a signal to the mass airflow sensor - the sensor provides a signal to the PCM. At idle you should measure between 0.2 to 1.5 volts between the signal terminal and ground. If there is voltage at the signal terminal at the mass airflow sensor connector and none at the PCM then you have an open circuit somewhere in your wire between the mass airflow sensor and the PCM. If there is no voltage at the signal terminal at idle and assuming a new sensor has been installed, then you may have a problem in your ground circuit or possibly a bad mass airflow connector.

No MAF signal at the PCM will cause the idle to surge. Hope this helps.

JohnF150

Sorry , took a bit to get this checked. Appreciate the suggestion !

My mechanic explained that there are four wires at the MAF sensor not three as it looks like you work from?
It is driving him nuts as he spent a lot of time on it and he can't pinpoint it.

Now he says that he has read that there should be current coming from the PCM (but that was a while ago and he doesn't remember where he read this ) and perhaps the 4th wire would then be for reference of the voltage (hope I explain this right!).
He checked the ground etc.

So it seems that the MAF sensor doesn't get the battery voltage direct but from the PCM (and this doesn't happen).
Could it be that I have a 4 wire MAF?

I have read also:
Mass Airflow Sensor
The Mass Airflow (MAF) sensor uses a hot wire sensing element to measure amount of air entering the engine. Air passing over the hot wire causes it to cool. The hot wire is maintained at 392°F (200°C) greater than ambient temperature, as measured by a constant cold wire.
The current required to maintain hot wire operating temperature is proportional to the intake air mass flow. MAF sensor outputs an analog voltage signal to Powertrain Control Module (PCM) proportional to the intake air mass. PCM uses this signal to calculate the fuel injector pulse width in order to provide the desired air/fuel ratio.

Ok, let me know if someone has an idea on this on or if you need specific answers?

Thanks

John

Skunkcontrol

At the connection at the MAF senson max 0.02V
At the PCM maximal 0.02 V aswell

PCM has been replaced (twice).

Note that other sensors have been checked and cleaned.

According to the information there should be 2V at the connector.

Call me crazy but if that mechanic is using a Auto ranging fluke brand meter to look close at what range the meter is testing in.... if not make sure he is on the lowest possible setting above 2 volts..

sensing 0.02 V consistent when looking for 2v is pretty odd in electrical work and a flip of the **** can move that decimal ..

I will Venture to say there is nothing wrong with the parts you are reading 0.02 on and that he either is trying to use a POS auto ranging meter or setting his selector incorrectly..

tory3

There are 4 wires to the MAF. ONe is battery voltage, one is ground, another is MAF input, the last is return to PCM . These last two wires are what the PCM senses from the MAF. You need to have your mechanic look at the possibility of a wire either being broken somewhere in that harness or the possibility of a short to ground on one of those wires. Again I do not think the PCM supplies a signal to the MAF - it is the other way around.

JohnF150

Ok, got the readings:

The sensor has 4 connections

- VPWR (red) =13.6 V =o.k.
- GND (black/white)=o.k.
- SIG RTN (brown/blue) = 0.01 V when engine is running ( PCM PIN# 36) should be : 0.34-1.96 V
- SIG (blue/red) = 0.017 V when engine is running (PCM PIN# 88) should be : minimal 4.5 V (meassured in the PCM! so no broken wire.

Thanks

John

JohnF150

Went by the shop and checked with the mechanic.

There is 13V on the wire, the ground is tested and ok.

The two other wires have a function too.
But what are these functions and how do they work?

My mechanic tells me that it should be 4.5 V and coming from the PCM.
(this is backed up on a page where I read : "The air flow sensor generates a pulse so it repeatedly opens and closes between the 5V voltage supplied from the engine control module.")
Again, on another engine with a four wire MAF sensor the 4.5V was measured on the MAF Connector while not connected to the MAF sensor.
So we think the 4.5V comes from another source and we think that this is the PCM (same wire color and no resistance between the MAF Connector and the PCM port).

The last one would be the signal from the MAF sensor to the PCM but I think this would only provide a signal if the 4.5V is on the other wire.

The PCM is replaced (twice) and I don't think that that can be the cause.

Does anyone knows whether there is another device in between or maybe a device that will trigger the PCM to give the 4.5 V to the MAF Sensor?

Thanks.

John

tory3

John,


I have looked at this and as far as I can tell the MAF is a sensor that uses the battery voltage to generate a analog signal to the PCM which measures the amount of air flowing through the air intake. It is great you have 13V to the sensor and also to ground. Those other two wires are the ones that give the signal to the PCM.

I would suggest plugging in a OBD II fault code reader that can read sensor input values and seeing if the MAF is generating any input to the PCM. See what readings you are getting from the sensor if any at idle and when the engine is revved up a little and see if the readings change (they should). From what you have described I am betting you don't have an input from the sensor. The PCM uses that signal to compute the correct amount of fuel to obtain the correct fuel/air mixture.

From the readings you gave before on the voltage at the PCM there may be a problem either at the connector of the MAF or somewhere in those two wires running to the PCM.