850r failing emissions miserably (HC and CO) Topic is solved

[scot850]

What happens if you disconnect the MAF?

Neil.

[JayPea44]

Next to no difference with the MAF plugged in. I’ve started it with or without and it’s the same.

I know you’re not supposed to do this but I unplugged it while it was running and there was no real difference just dipped a little and kept running.

[scot850]

Have you checked the trims with the MAF disconnected? The ECU starts to estimate running requirements with no MAF data input. It may help to identify if this is the issue or possibly the upstream O2 sensor needs replaced?

Neil.

[JayPea44]

So with the MAF disconnected if the trims are the same it’s likely to be the MAF that’s bad?

[scot850]

MAF failures can cause different issues from no change to stumbling engine and stalling to rough running.

Did you check the readings on your ECT (coolant temperature) sensor as was suggested?

I would suggest doing that before swapping the MAF out. If you can, check the Volvo and/or the Bosch part number on the MAF. As I mentioned earlier, the one that ends in the Bosch part number last 3 digits 107 (it is something like, 0 280 XXX 107) then it is only available new from Volvo. Bosch no longer sells them so unless you can find an NOS unit you are looking at Volvo OE New $$$ or used if you can find one. Used at least may help eliminate the MAF at less $$$.

Neil.

[JayPea44]

Ok this is gonna be a long one.

So I did check with my OBD and it seemed fine. But I just went on a drive (about 20 mins) and monitored my OBD and took resistance at the sensor before and after.

Before start (cold). OBD=8 degrees C ohms= 4.75k

At start and on drive OBD steadily climbed up to 88-92 average. Highest I saw was 96. Temp gauge was sat a slight touch over “3 o’clock”. Took around 5-10 mins to get to warmed up temp. (A little fast?)

Back home (warm) OBD=91 (c) ohms 0.173k

Does that seem right? Seems ok to me. At least not drastically out of spec. Didn’t notice if that fan came on or not.. wasn’t on when I switched it off at home.

For the MAF. I disconnected it and it started, took maybe a few cranks more. CEL light came on for MAF fault. As I was driving away it bogged down hard off the line and almost stalled out with it disconnected. Pulled over and reconnected it. Drove fine and the CEL went out after a minute or so. I think the MAF is good.

Fuel trims. STFT was again either solid at 0.0 or 29.7. The 29.7 only seemed to appear during accel/decel which seems logical. LTFT Dropped down to 21.1 from 25. So it seems it’s finding its “correct” point after the reset. Still this is really high.

I think I’m going to throw an o2 sensor at it.

[scot850]

I think you are on the right lines. The engines in these cars do warm up to running temp pretty quickly. 5-10 minutes is actually slow to me for an 850 depending on the outside temp. NA motors with the warm air tube into the airbox do it even quicker.

I would say your themostat is ok, ECT sounds ok, and MAF ok.

O2 sensor would be the next on my list.

Did you check the intercooler for leaks or cracks? I think it is ok by the vacuum you were able to pull.

Neil.

[JayPea44]

I think the intercooler pipes and such are definitely next on my list once this is sorted. They’re old for sure, plus it’ll be a nice upgrade.

Ok cool thanks for help. And yeah I agree from what I can tell or what it seems like, the rest of it seems ok and if o2 sensors can go bad without throwing codes I think it’s my best bet right now. Knowing my luck it won’t fix it ha!

[scot850]

Well apart from the money, if you don't know how old they are, it is a worthwhile Stage 0 service to replace the O2 sensors, at least the upstream one if not both. Make sure they are genuine Bosch parts and not copies. So careful where you source them from!

If you don't have any junkyards near you where you can pull a MAF, let me know the Bosch or Volvo part number and I can see if I have a used one. They cost me around $60 CDN ($45 US) these days at the junkyard. Maybe there is someone south of the border that has one they can loan for testing or sell you. Shipping is way cheaper south of the border.

Neil.

[WhatAmIDoing]

OK another update - I got a vacuum gauge and tested my vacuum, I was getting 15 inhg vacuum before I replace my TCV vacuum lines and now it's slightly lower, between 14 and 15, after replacing them. I also inspected and swapped out some worn-looking elbows but everything else looks relatively decent. I also did the "spray brake cleaner around all the connections to see if the idle changes" trick and it didn't budge.

So my question is, is that a normal reading? The needle is solid and doesn't move at all at idle, and to me, that seems like a decent reading for an engine this old that is also turbo'd (but I don't know - also bearing in mind I'm a mile above sea level). A little bit of googling tells me anything over 14 is "normal" on these, but not sure if I can trust that. Also, if it is a little low would a leak this small really put my emissions readings so high?

I'm starting to think I'm chasing my tail on this vacuum leak and thinking it's more a sensor, probably the o2 or MAF. (I had an old classic mini that had a bad MAP sensor and it ran rich as a pig which is making me think this is sensor related..)

Any input is greatly appreciated.

On both my 98 T5s, I usually get around 16-17 mmHg at cold start idle, then around 21 mmHg at hot idle. But I'm also much closer to sea level.

Can you read voltage for the O2 sensors? Or MAF data on your scan tool? Would help more with diagnosis if it is indeed a sensor issue.