Jazz running rich - MAP sensor faulty?

[Multiplier7]

Hi everyone,

I have a Honda Jazz 2007 and it is running rich (can smell it and it fails the emission test). I have replaced the 2 oxygen sensors before and after the catalyctic converter. The one after reads around 0.45-5 V and the one below fluctuated between 0.1 to about 0.7-0.8ish (Graph attached).

The MAP sensor, when I am revving the engine in neutral to about 2000 rpm (at relatively low altitude) is about 20-22 kPa and when I rev it up to 3000 rpm it is about 25 kPa. Does this sound correct or faulty?

If this isn't the case, does anyone else know what could be the reason? Engine Coolant Temperature seems quite normal around the the low 80s (degrees C). There was the EGR code but we cleaned the EGR valve and cleared the code and now it didn't come back. The gasket is, however a bit dodgy and old (new one ordered), is it possible this could be leaking and causing the running rich?

There were also error codes P0130 and P2271 prior to changing the O2 sensors but after they were changed they were cleared and haven't come back.

Does anyone have any advice?

Any help is greatly appreciated!

[CRC]

There are a couple of things I would investigate further, but not sure how much information is available from a scan tool on a Jazz.

The amount of fuel that is injected into the engine is determined by the ECU calculating the mass of air that is being pulled into the engine.

To do this, it uses the MAF sensor (Mass Air Flow Sensor) which actually works be measuring the VELOCITY of the air in the intake, then uses other data such as air temperature, inlet diameter, air pressure to calculate the MASS of air accordingly.

See if you can see data from the MAF sensor and the air temperature sensors as those are the first things to suspect .... also look around for splits in hoses etc that can allow unmetered air to enter the engine without passing by the MAF sensor.

You could try unplugging the MAF to see what happens. You would probably get an error code, but the ECU should revert to a default map if it senses that the MAF is no longer present. Also, try gently cleaning the MAF sensor with some electrical contact cleaner (that completely evaporates) and a cotton wool bud to remove any residue that might be coating it.

This is the primary method that the ECU uses to calculate injecttion times etc. The  O2 sensors take a while to warm up and get going, but when they do, the ECU looks at the data to determine how succesful it has been in producing the right mixture at the front end of the engine, and adjusts accordingly.

[Multiplier7]

There are a couple of things I would investigate further, but not sure how much information is available from a scan tool on a Jazz.

The amount of fuel that is injected into the engine is determined by the ECU calculating the mass of air that is being pulled into the engine.

To do this, it uses the MAF sensor (Mass Air Flow Sensor) which actually works be measuring the VELOCITY of the air in the intake, then uses other data such as air temperature, inlet diameter, air pressure to calculate the MASS of air accordingly.

See if you can see data from the MAF sensor and the air temperature sensors as those are the first things to suspect .... also look around for splits in hoses etc that can allow unmetered air to enter the engine without passing by the MAF sensor.

You could try unplugging the MAF to see what happens. You would probably get an error code, but the ECU should revert to a default map if it senses that the MAF is no longer present. Also, try gently cleaning the MAF sensor with some electrical contact cleaner (that completely evaporates) and a cotton wool bud to remove any residue that might be coating it.

This is the primary method that the ECU uses to calculate injecttion times etc. The  O2 sensors take a while to warm up and get going, but when they do, the ECU looks at the data to determine how succesful it has been in producing the right mixture at the front end of the engine, and adjusts accordingly.

Hi,

thanks a lot for the reply. As far as I understand, the Jazz II doesn't have a MAF sensor but just a MAP sensor which the ECU uses to calculate the Mass Air Flow. I will again next week check the values of this with a diagnostic tool and see if they align with recommended values corresponding to different RPMs. Update since this post was made: we recently checked the fuel injectors and they seem to be spraying ok and don't seem broken in any way. We will also do the smoke test to check for any leaks in/before the intake manifold. Is it common for the MAP/MAF sensors to fail? There also isn't any hissing sound for vacuum leaks but I guess this isn't always the case right? The diagnostic tool doesn't show any errors since the Oxygen sensors were replaced; it runs rich but not super rich.

[guest334]

What changed last ?
If oxygen sensors are from internet or Amazon then start there.
OE sensors or Denso NGK at a push

[CRC]

I'm more than a bit puzzled now. Certainly the Haynes manual makes absolutely no mention of a MAF sensor on the dsi engine, and yet, if I go to one of the numerous online components companies (Autodoc, GSF etc) and enter our registration ( a 53 plate 1.4 car) they seem to have numerous MAF options that they are all keen to sell me.

Do you have the MOT emissions test page that shows the readings from the analyser ...... quite often it can give good pointers to the problem

[CRC]

I realised that I was lacking in knowledge on how the Jazz fuel injection system actually works, so decided to plug in my Foxwell NT530 scanner and see what it would tell me.

Warmed the car up fully with a few miles drive and then plugged to see what was happening.

Firstly, I'm sure you're right that there is no Mass Air Flow sensor on the Jazz, only an Manifold Absolute Pressure sensor, which I believe works in conjunction with the throttle posistion sensor and the "pre-cat" oxygen sensor to determine the amount of fuel to inject.

The MAP sensor reads "absolute pressure", and as standard atmospheric pressure is around 100 kpa, anything less than that value indicates a vacuum. With a closed throttle, the engine running and the pistons sucking, this gives the MAXIMUM vacuum, which equates to the MINIMUM kpa value.

With a coolant temperature ranging from 84 to 90 during the test (the fan was starting to come on at times).

At tickover (680 rpm ish), the kpa value was ranging between 24 to 27 kpa.
At 2,200 rpm, the kapa value was ranging between 21 to 22 kpa.
At 3,000 rpm, the value was fairly constant at 23 kpa.

The highest kpa value I saw was a brief 34 kpa as the throttle was being opened.

My absolute throttle position ran at around 12-13% without me touching it, and would rise to around 20% when I put my foot gently on the throttle to raise the revs.

The "pre-cat" O2 sensor was showing the classic wave form and was varying from 0.11 to 0.7 volts over a period of around several seconds. It looked very much like your O2 sensor graph that you attached, so I would doubt if that was your problem.

The "post cat" O2 sensor was very constant at 0.67 volts - which is what you would expect as it shows the cat is doing its job correctly (this O2 sensor is purely there to determine if the cat is working correctly and isn't used to control the injection as far as I know. You say that your post cat sensor is reading "0.45-5 V) .... do you mean that it's between 0.45-0.5 volts or is it actually going to 5 volts. If it is going to 5 volts then that's very suspicious??

Short and long term oxyen trim levels were small (though stupidly, I forgot to take a note of the readings)

Good luck