2000 V70 XC--Request assistance reading VIDA data

Steve in Beacon · Post by **Steve in Beacon** » 06 Mar 2016, 06:55

Hi folks
My 2000 V70 XC frequently shows a MIL code for catalytic converter efficiency being below threshold. VIDA data shows the following--can someone help me interpret the data? VIDA shows:

ECM-4801 Three way catalytic converter (TWC) efficiency, bank 1

Fuel system status bank 1 LR Closed loop operating with 2 sensors
Fuel system status bank 2 LR Open loop operating, start condition not yet fulfilled
Calculated load 13.33%
Coolant temperature 87 C
Short term fuel trim, bank 1 3.91%
Long term fuel trim bank 1 16.41%
Short term fuel trim, bank 2 99.22%
Long term fuel trim bank 2 99.22%
Engine speed 1920 rpm
Vehicle speed: 58 km/h
Turbo pressure 42.75%
Battery voltage 13.52v
Throttle angle, desired value 23.05%
Mass air flow 75.6 kg/h
Ambient temperature 3.75 C
Total distance 292499 km

What might I be looking for as a problem?

Thanks for reading!!

Post by **jimmy57** » 06 Mar 2016, 08:49

The long term fuel trim at 16.41% is a possible problem. Short term at 3.91% also is a bit off.
Look for places leaks could occur between the MAF sensor and the turbo inlet and also the hose from crankcase breather box to turbo inlet hose. MAF could also be suspect. Check to see if it is 12-14 Kg/hr when idling out of gear with a/c off with engine warmed up. Less than that indicates MAF issue if there are no air leaks. Your values are not off enough for any DTC's for MAF but the catalyst would not function well and the efficiency could could readily set.
Does the engine run well and idle smooth?

You could have a weak/failed catalyst. Has the catayst ever been changed? How many miles on the car?

Steve in Beacon · Post by **Steve in Beacon** » 06 Mar 2016, 19:35

Thank you so much, Jimmy57! The MAF is new, which presumably takes that out of the equation. I've gone over the visible hoses pretty well and I am reasonably sure there are no vacuum leaks, but the crankcase breather box hose is one I will check next. It's such a headache to get into that area on that particular engine. I am certainly hoping that there is a vacuum issue vs. a problem with the catalytic converter, although I wouldn't be surprised if it is not in good shape. I had replaced the engine when I got the car as the original had a coolant leak in the head and overheated, presumably blowing a lot of coolant and who knows what else out the tailpipe. Can you tell me what sort of fuel trim figures I should be looking for? I am having a difficult time finding a coherent but reasonably simple explanation of the concept that translates to actual numbers (I know they vary by engine design). Thanks, again, Jimmy57! I really appreciate your taking the time to help!

Steve

Post by **jimmy57** » 06 Mar 2016, 21:16

The long term and short term fuel trims are effectively percentage. Your LTFT is 16.41% rich. The short term is usually +/- 2 % so that is a little high but troubling amount too high unless you knew it was staying that high with LTFT still increasing.

The ECM gets inputs from sensors and computes injector duration and the oxygen sensors read exhaust to check actual fuel mixture accuracy. STFT is the immediate fix and LTFT is the long term fix when the computation is off. 10% is about the normal limit of LTFT before something is up. 25% triggers fault codes for fuel trim. When there is a fuel trim problem that is cylinder specific the system corrects across the board and that results in average oxygen content being OK but there can be one very lean cylinder and 4 rich ones and the catalyst is not really getting a balance of oxygen and hydrocarbons that can be processed (catalyzed) properly. I asked about quality of engine running to dig into the lean cylinder/rich cylinder question.

Bad MAF will offset the info used for computation and result in LTFT that is out of expected range. New MAF should have eliminated that though some non-Bosch MAFs have dubious quality sometimes.
The head gasket deal may have poisoned the catalyst and your problem could be catalyst. There is an additive available at parts stores that can give temporary catalyst performance improvements and trying that might be the easiest way to an answer.

Steve in Beacon · Post by **Steve in Beacon** » 07 Mar 2016, 06:59

Thank you again! That is all very helpful. I'm going to search the oil separator and associated hosing to insure there is no intake leak, and maybe reinstall the old MAF (I replaced it just because I had another (which happens to be non-Bosch). I'll look into the temporary catalyst rejuvenatior--perhaps if the code desists for a bit I can fairly attribute the trouble to the catalyst and act accordingly. Thanks so much, brother!

Steve

Post by **precopster** » 07 Mar 2016, 13:19

This is probebly the best thread I've read on MVS regarding fuel trims and what they mean.

Post by **kallekula** » 07 Mar 2016, 17:12

If it wasnt mentioned before, revving the engine keeping the rpms steady at about 3-4000 and seeing the STFT drop drastically would point to a vacuum leak.

Steve in Beacon · Post by **Steve in Beacon** » 10 Mar 2016, 06:09

Thanks, Kalleula, I'll try that and see what I get! And ditto on the kudos to jimmy57!

Post by **kallekula** » 28 Apr 2016, 10:49

Did you get it running ok?