Possible MAF failure.

[PeterH]

Hi all, a few weeks ago I noticed my 2001 P38 HSE 4.6 thor hesitating now and then, was struggling up hills occasionally, I couldn't quite put my finger on what the problem was as I could not recreate it.
Other times it ran perfectly.
Then one morning it lost power, I managed to turn around and baby it home, the fuel pump had died.
I replaced that with a new Bosch one and it started straight up, all was well again.
Then I noticed it was idling a bit rough and smelled like it was running rich, I took out the plugs and they were carboned up, classic overfuleing sign.
Checked the fault codes and one of the O2 sensors was at fault.
As the O2 sensors are now 19 years old, I thought it was probably time to replace them both.
So with new O2 sensors installed, it was running very well while driving, but the rough idle and overfuelling is persisting.
I checked the fault codes, there are 5 codes present.

*P0135=Oxygen sensor heater upstream catalyst Bank1 Drive cycle C persistentely present
*P0155=Lambda sensor heater upstream catalyst Bank 2 Drive cycle C persistentely present
*P0175=Mixture adaption factor FRA Bank 2 drive cycle C (signal too high) persistentely present
*P0134=Lambda sensor upstream catalyst Bank 1 drive cycle C signal invalid intermittent
*P0175=Additive adaptive mixture correction TRA Bank 2 Drive cycle C (signal too high) persistentely present

I doubt I'd get two new faulty O2 sensors, so I'm thinking that's all pointing to a faulty MAF, but I'd be interested to know your thoughts on this.
The MAF I have is about 5 years old, I'm wondering if missfiring due to the old fuel pump has damaged the MAF in some way.
Thanks, Pete.

[prelude]

Not sure about the BOSCH engine but with gems at least the MAF is so far away (at the beginning of the air intake) that misfires are not likely to hit it.Just to check: did you erase the error codes after replacing the O2 sensors?

Cheers,
-P

[PeterH]

Hi Prelude, thanks for the response, yes I did clear the fault codes a couple of times.
The codes don't re appear straight away, it needs to be driven a bit for them to show again.
It could just be a failed MAF sensor regardless, as the MAF and the O2 sensors work together.

[biggin]

Do you need to do an adaptive reset as you would with a D2 after replacing O2 sensors?

[PeterH]

I did attempt to do an adaptive values reset, my faultmate worked really well with my old serial port laptop, but I have tried and tried to get it to work with my new USB laptop with no luck. I have updated drivers etc with no success.
While I can read and clear fault codes in stand alone mode, I can't do anything more advanced without it being connected to a lap top.
It is my understanding the adaptive values would adjust themselves over time anyway, it's been 3 or 4 weeks now with no noticeable improvement.
You are probably right though, I might keep trying with the new lap top, pity the old one died!

[biggin]

After replacing one of my sensors, I had a 1000km trip with terrible economy and bad fueling ratios. As soon as I did the reset, it all came good immediately, so worth a try.

[PeterH]

Thanks biggin, you were spot on!
After a bit of mucking around I managed to update my serial to usb drivers, got it hooked up and what do you know it connected.
I reset the adaptive values and it instantly started idling better.
I think that's done the trick, thanks for your help!
Saves me the cost of a new MAF.
Cheers, Pete.

[PeterH]

I have an update, it is idling better now and running well, but I'm still getting the error codes popping up for the 02 sensors.
I have cleared the codes twice and they keep returning after a drive.
Any suggestions on a next step here?
Thanks, Pete.

[Hoges]

Hi Pete
have you checked for vacuum leaks?
the following URL has a fairly comprehensive approach to testing the O2 sensors... including checking voltage fluctuation with a multimeter..
(O2) Oxygen Sensor - Function - Failure Symptoms - Testing (https://dannysengineportal.com/o2-oxygen-sensor-function-failure-symptoms-testing/)
hope it helps
cheers
Hoges

[PeterH]

Thank you for that Hoges, interesting read!
I have not checked for vacuum leaks, that will be my next step, I'll check that today.
Interestingly, the plugs on the drivers side bank are full of carbon, the passenger side plugs look pretty normal.

[PhilipA]

Interestingly, the plugs on the drivers side bank are full of carbon, the passenger side plugs look pretty normal
To me that says dud O2 sensor.
Did you use sealant on the threads? This is a nono.
Perhaps swap the o2 sensors and see if the main rich problem moves to the other side. The fact that the banks are different would seem to preclude the MAF. Exhaust manifold leaks can be a factor?

My experience says that in closed loop the MAF has little input . The O2 sensors control mixture almost totally. In fact on a 14CUX the MAF is adjusted rich for o2 sensors as it is apparently easier to take fuelling out than add it. If you are nailing it and going into open loop then the MAF will play a bigger part.

While a 14CUX is not as sophisticated as the GEMS and Motronic the principles are the same.
Regards PhilipA

[PeterH]

Thank you for your thoughts PhillipA, yes that does make sense, I'll try swapping them and see what happens.
Although the fault codes are currently showing both sides have an issue.
I only used anti seize on the thread, no sealant, was very careful to keep the sensor clean.
I'm not hearing any obvious exhaust manifold leaks, it's all pretty quiet.
The 02 sensors are aftermarket, I'm wondering if i should have put genuine sensors in?

[PhilipA]

The 02 sensors are aftermarket, I'm wondering if i should have put genuine sensors in?

Bosch Motronic can be fussy over sensor brands.
I would recommend Bosch sensors .
You do not really have to pay a ransom for the sensors with the correct connectors. You can buy a general Bosch sensor and swap over the plugs by cutting them off the old one and attaching to the new.

I have found that you have to crimp connect the wires rather than solder .
Regards PhilipA

[PeterH]

I cleared the fault codes, went for a drive and the codes that pop up are for both sensor heaters and a mixture adaption error.

*P0135=Oxygen sensor heater upstream catalyst Bank1 Drive cycle C persistentely present
*P0155=Lambda sensor heater upstream catalyst Bank 2 Drive cycle C persistentely present
*P0175=Mixture adaption factor FRA Bank 2 drive cycle C (signal too high) persistentely present, (which would result in the overfuelling and carboned plugs on that side).

Then I swapped the sensors over, cleared the fault codes, reset the adaptive values and went for a drive.
After resetting the adaptive values it idled so smootly you could barely tell it was running, by the time I got back, it was idling a bit roughly again.
Checked the fault codes again, it came back with the same codes as above, with an additional code

*P0175=Additive adaptive mixture correction TRA bank 2 Drive cycle B, (signal too high), currently present.

So it appears both 02 sensor heaters are not operating correctly.
I read on another forum sometimes aftermarket sensors do not heat up fast enough and the ECU logs a heater fault.
I checked fuse 26 and that is ok (02 sensor heater circuit)

Interestingly the overfuelling errors stayed on the same side after swapping the sensors over.
I removed both sensors again to find the same side had carbon showing, even though it was another sensor in there.

[PhilipA]

So there is something about bank 2 that is causing a rich condition.(ie the bank is running lean but being compensated by the O2 sensor) It cannot be MAF related or would affect both banks.

I still wonder about either an exhaust leak or an inlet leak on that bank. The oil vent system comes out of the drivers side rocker as does AFAIR the vacuum hose for the brakes and the evap system. Inspect all of the pipes and suck on the brake booster hose. The crankcase vent system can get blocked and the spring thingy has to be cleaned or replaced , but IMHO the vacuum pipes are the answer.
Check the operation of the evap system valve.
Regards PhilipA

[PeterH]

Brilliant advice as always Phillip, thankyou, I will investigate your suggestions and let you know how I go.
I ordered 2 genuine bosch sensors today, they will go on when I get them.
Thanks again!

[prelude]

Just a tip for hunting vacuum leaks:

I made hunting for vacuum leaks a bit easier by using an old smoke generator and a pressure hose. It would basically push smoke into the air intake of the car (after the maf :P) and smoke would come out where there are leaks.

Chears,
-P

[PhilipA]

On further reflection the vacuum lines come from the "bar' across the front of the Thor manifold and would affect both banks but the thought is still valid.
Regards PhilipA

[PeterH]

That's very inventive prelude, good thinking!
I did try the old carby cleaner spray trick around the vacuum hoses, but didn't find anything.
I might give that another go and see what I can find.

[PeterH]

I have it solved!
After waiting what felt like an eternity for the Bosch sensors to turn up, they arrived today, so I got straight to it.
Replaced both sensors, cleared the fault codes and did an adaptive values reset, which resluted in it sounding much better straight away.
I've been for a bit of a drive and checked for fault codes with none present.
It's idling so much better now without the vibration that was occuring.
I replaced the carboned plugs on bank B and noticed the existing ones were still showing carbon, but they were all clean on the tip where the spark would be, which is a pretty positive sign to me.
I'll replace the plugs on the other bank so they are all new.
So the moral of the story, only use genuine Bosch 02 sensors!
It wasn't happy at all with aftermarket sensors.

While I was waiting for the sensors to arrive, I also checked around for any vacuum leaks, one thing I did find was the vacuum hose that runs from the plennum to the rocker cover (where the oil seperator is) was a bit loose at the plennum end. I was able to move the black plastic connector slightly with my hand, so i tried to pull the hose off and it broke in half straight away.
So be aware those connectors become very brittle and fragile with age and break very easily.
The hose itself seemed ok, so I replaced the connector and also replaced the oil seperator which was a bit gunked up with oil.

I probably should take it for a bit of a drive now to try and blow out the carbon deposits.
Thank you for your help eveyone, Cheers, Pete.

[PeterH]

Just thought I'd post a follow up to this thread, after 4 weeks, it is still running beautifully, the best it has ever run since I've had it.
Fuel economy has vastly improved as well, getting a lot of extra kms out of a tank.
It's such a pleasure to drive I look for excuses to drive it!
So to summarise, new genuine Bosch 02 sensors (stay well clear of aftermarket sensors), plus a new set of plugs solved the problem for me.
Thanks again for all the help.
Cheers, Pete.

[prelude]

That is good to hear mate :)

I have been seeing very low mileage figures myself lately but buying new bosch O2 sensors just to see if it makes a difference... Not sure ;)

Cheers
-P