1998 S70 T5 poor running [ECT connection]

Sommerfeldt · Post by **Sommerfeldt** » 28 Mar 2020, 06:37

Been said before, but 80% of weird engine running issues with these are vacuum leaks. The hose/elbow on the passenger side of the intake manifold is a known culprit. (you don't need an elbow, btw - push on a 4 or 5mm silicone hose, and run it "outside" the manifold if you want. Note that silicone will sweat here, since there is vapor going through this one. Won't leak for a loong time, but will be discolored.)

Contrary to what Micha says, a bad MAF won't necessarily mean your rpms will hunt. Symptoms are very varied. Some just make the engine choke, some will result in rough idle and only that, some will skyrocket your fuel consumption. I don't see you having a peek at your O2 sensor(s). I hunted a rough running/low power issue for a long time on the 850, and it turned out to be a combination of a bad MAF and a bad O2 sensor.

BUT - also take a look at your turbo vacuum/air connections. You mention that you have to "kick in" the turbo, and that sounds weird to me. There should be a smooth curve up from vacuum to boost, not a sudden onset with effort. I.e. it should be quite "difficult" to keep the car in vacuum, and quite "easy" to go over into boost. ECU maps confirm this very clearly.

Check that your wastegate actuator connection is good, and that it's moving like it should. Check that all hoses on/from/to the turbo are in the correct spots and not cracked - especially the "lower" connection (below to the left of turbo intake) is easy to miss, and prone to be jostled and damaged when removing the intake hose. It can cause some super weird behavior.

So, what I would do:
- Check/replace all hoses, small and large.
- Check/replace O2 sensors

Note that an off brand/aftermarket thermostat usually won't cause you grief. They're "dumb". ECT and MAF usually needs to be OEM, as others have stated.

- S

Post by **jreed** » 28 Mar 2020, 07:01

You've probably already checked these, but if not it would be worth removing the spark plugs and checking to make sure the gap isn't too wide.

Gerd · Post by **Gerd** » 18 Sep 2020, 10:37

Haven't been back in awhile a was out of town working. But found issue.
Turns out that no matter how many times I read it here, I just didn't believe I hadn't checked it well enough. The connection to the ECT was cleaned, set tight and then zip tied. Couldn't be that, right? I was Wrong.

After endless amount of time looking at other things, I bought the Bluedriver Code Reader. If you haven't seen one, have a look online. Amazing amount of info. Including coolant temp. Mine said 0C. So it is either a brand new faulty ECT or the connection. Did multimeter test on plug and it was good.
Back to the plug - cleaned it with PB Blaster and Baking Soda. And a small file and sand paper. Dielectric grease and put it back together and ... no good. Then I zip tied it so tight that if I cut that tie, I will probably lose an eye. started it and knew right away it was working. Scanned it and got 80C on coolant temp. Went for a drive and was thrilled at having power again.
Thanks for all the input/help here guys.
Now on to my next issue ... the cruise control brake switch. I'll start another thread

Post by **abscate** » 18 Sep 2020, 11:49

Thanks for follow up Gord

Changed title for search

850oldschool · Post by **850oldschool** » 18 Sep 2020, 20:34

The old school bullet connectors that it plugs into are often in a sorry state by the time you get in there to replace the ECT sensor. I'm kind of inclined to think that half the time the problem is a bad connection. This writeup shows some bad ones and provides details of spicing new ones in:

https://volvo850wagon.wordpress.com/category/ect/

Deoxit cleaner and protector works much better than PBlaster and baking soda. I've started treating every electrical connector I assemble on my 850 with it.

After doing this kind of troubleshooting with the ability to watch live data on a graph I could never go back. You're just groping around in the dark throwing parts at it.

If you ever feel like writing more about Bluedriver I'd love to see a more in-depth review. I was headed in that direction until I found a used iCarsoft for about 60 bucks.

Gerd · Post by **Gerd** » 18 Sep 2020, 21:11

Hey 85oldschool. Thanks for the input. I’ll go over the link tomorrow so that I can prepare for the eventuality of changing out those connectors. I’ll also have a look at Deoxit. Even the name sounds better than my stuff.
As far as BlueDriver goes, it is well worth it already but something that is a bit of a negative for those of us with ‘vintage’ vehicles is that we don’t have anywhere near all the sensors is scans for. But again, we’ll worth the 100 bucks as far as I am concerned.
Thanks again.

Post by **Chuck W** » 19 Sep 2020, 08:15

At some point, the wires where they're crimped to those terminals are frayed, and even a good cleaning of the connector isn't going to help. Ran through that on both of our cars. The wires on the harness end were 1/3-1/2 frayed apart.

I just cut both ends off and installed a WeatherPak connector in place of the factory one.

Gerd · Post by **Gerd** » 19 Sep 2020, 10:12

Hey. that is more good info. I'll make a note of that and be ready for next time.

Thanks Much