running rich with lots of black smoke

mott6904 · Post by **mott6904** » 23 May 2016, 16:20

Alright volvo gurus im in need of lots of help with this one. Im a long time reader but never registered till now. Im the lead tech at a smaller indy shop in Indiana and i have a 99 s70 that i just cant seem to figure out. Car had 159,000 miles with the 2.4t b5254t engine. So car came to me for being flooded out and running extremely rich with black smoke and soot out the tailpipe. First thing i did was charge the battery, pull and erase codes and then went for a test drive. After a short test drive at idle the maf was reading 30kg/h which is twice as much as it should and ecm 261a reset. While it was smoke and running bad i disconnected the maf cleared the codes and drove again. Car did fantastic and the black smoke was gone. I have replaced tons of mafs, pretty typical. So i sold him a New bosch maf and ngk iridium plugs. Installed them, let the car idle for a bit then took it out for another test drive. Did awesome had perfect power maf and o2 sensors was reading correctly but because im very anal i let the car run idle more and took it out for another test drive. Same thing happened maf reading went from 14kg back 30kg at idle. Pulled over disconnected maf cleared codes and car drove fantastic again. So at this point im thinking someone returned a defective maf or i had a bad one. I ordered another bosch unit swapped it out and i still have the same issues. This time when it messed up i did the same thing on the side of the road but before i head back to the shop i the maf back in and started it up and the maf reading was back to normal and is still reading correctly in the back of my shop. What am i over looking for the maf to go from 14 kg 30kg at idle after a short drive that i can clear the codes and then read perfectly fine. I understand how a bad front 02 sensor could cause the rich condition after a short drive but i cant understand how it would make the maf read twice as much. While running bad i checked 5v, 12v and ground at the connector and all are present.

Original codes pulled with launch scan tool so descriptions might different from correct volvo definition

ecm-280a front heated oxygen sensor faulty signal
ecm-2a1a rear heated oxygen sensor aging
ecm 261a long term fuel trim
ecm 3502 miss on at least on cylinder
ecm 3552 miss on cylinder 5

Post by **abscate** » 23 May 2016, 17:01

Take a good luck at the induction pathway from air cleaner all the way to intake manifold. A split in the hose or intercooler will open and shut under Throttle and run rich in between

mott6904 · Post by **mott6904** » 24 May 2016, 06:41

I forgot to add i already smoked tested the intake system and found no leaks. I would also think that if it was a intake leak somewhere my maf reading should be lower and not higher like it is. When it runs bad the idle is very choppy and lower than normal because it is loading up. The idle never increases to account for the higher than normal maf reading. Im also getting zero etm codes and everything with the etm test out okay.

Sommerfeldt · Post by **Sommerfeldt** » 24 May 2016, 07:20

My 850 had occasional black smoke and soot - mostly after long-ish drives, but would sometimes leap right into it at startup. I assumed my MAF was slowly dying. On the heels of my wastegate actuator adjustment, the rich codes, smoke and roughness disappeared. Haven't had them since. Since I discovered that the WG most likely had a little play in the actuator, it was probably dumping air right out those millimeters.

I don't know if it helps, but it's certainly something to check off your list of possibilities.

- S

mott6904 · Post by **mott6904** » 24 May 2016, 09:13

In theory a bad turbo or lots of other things could play a big part in it but its mainly at idle when the turbo is making boost and a loose wastegate would make the turbo spin slower. So the idea of a bad turbo is a little far down on the list but im at the point with this turd that ill try just about anything within logical reason.

Post by **abscate** » 24 May 2016, 09:21

Duh - I missed this possibility

The MAF connector on these cars is known to go bad on high mileage/years (as in all cars in this Forum)

I bet the connector is wonky, which will put your MAF readings all over the place - even with a new one.

Post by **dosbricks** » 24 May 2016, 12:45

abscate wrote:Duh - I missed this possibility

The MAF connector on these cars is known to go bad on high mileage/years (as in all cars in this Forum)

I bet the connector is wonky, which will put your MAF readings all over the place - even with a new one.

^^^Agreed. Spray/clean the connector with contact cleaner and then do as many of us have already--zip-tie it diagonally to the MAF to keep it from wiggling around as the engine torques. A thin coat (wipe it on/wipe it off) of dielectric grease on the spades won't hurt anything either.

mott6904 · Post by **mott6904** » 24 May 2016, 13:22

when the car is acting up i have tried doing the good ole ford wiggle test and didnt see any change in the readings and there is no corrosion or wide terminal openings so im not sure what the typical failure of the connector is. I think that as a lot to do with people trying to pull of the connector since the tab doesnt like to release sometimes. I learned many years ago to use a pic to release the tab so it pulls right off. Im getting ready to pull the ecm and check for corrosion there and ohms out the wires. I have been working on volvos for years and have never had one kick my ass like this one has and of course i have a pissed off customer because its their only car. yay me