Twins...another project

[carrera]

Well, here's the comparison.

They are different, but physically the same size. Note how the earlier one appears to have a larger cat on it, perhaps that's value engineering....

Anyway, as you can see both lambda sensors are off the Aero pipe. The 2.0 one has the rear one still in situ, and to be honest the only way that is coming off is with a grinder, so for now I will leave the old one on

In other news after many hours of using a dremmel, then needle files, then a small round file I got to the point where the threads were just becoming visible. I gave it a final flurry and the hole seemed ready for a tap to be run down it. Which is when I realised that the final flurry was far more efficient in terms of removing metal (because I suppose I had got to the cast iron, instead of the steel), which meant it wasn't really possible to retap the hole. So, time to drill it out & helicoil.

Tapping cast iron seems quite a bit more challenging than steel. It has hard bits and soft bits, seems quite capable of breaking the tap if used incorrectly, but I'm trying not to exert too much force & using oil to lubricate. The tap is just through the hole, but it's not fully threaded to the bottom yet

Still, the turbo has zero play, so it's worth saving

[sgould]

I would expect that modern cast iron is more uniform than old stuff. So you should be fine.

We used to drill and tap holes up to 2½ inches dia. in cast iron mains.  Some of the mains were vertically cast in the early 1800's and could be anything from ½" thick to 2 inches thick.  That work was done with the main full and under pressure!!

[carrera]

Some progress today:

Turbo was thread repaired & refitted, only for the feed from the pump to have a leak from the dowth washer someone had fitted. Which meant I had to remove ^ refit the cobra to put two new copper washers on 

Car started fine, did the CO reading, and after getting the cat up to temperature showed 0.15%... but it didn't return to the set point.

I watched the lambda reading on Opensid and voltages via Tech II

I have a feeling that the CO is still high, on idle the Opensid reading is almost always positive, in the 400-500 range, which seems higher than the original twin. More experimentation planned for tomorrow

I have effectively swapped cat and lambda sensor II. The cat test on Tech II showed the same O2S low capacity warning for the replacement, which doesn't help me move forward. Lambda 1 is not a Saab/Bosch part by the looks of things. I wonder if I have a spare lying around to test

If it isn't the pair of cats, or the front lambda sensor, I'm wondering what else it could be...

[sgould]

Do the readings change if you disconnect the MAF? If they do, I’m not sure what it would tell you.  I’m just wondering what the engine does if the info it’s getting is wrong. The backup checks should throw an engine light, but maybe not if it’s not a big error.

[carrera]

Thanks for the idea

I did some back to back checks yesterday, literally bumper to bumber so that I could swap the probe between the two tailpipes

It seems to be better, though not quite as repeatable as I would like.

Having done some reading around, in particular getting the understanding of what the Lamb reading actually means in Opensid (short term fuel trim in % x100, a positive value being additional fuel compared to map), I became comfortable that the o2 sensors were behaving as expecetd and the LAMB values were normal

Some times it was very close to the original twin, though it was often 0.15% higher. Then giving it 20 seconds at high revs to warm the cat up a bit brought it back down again.

I think I'll try again tomorrow, but as the Lamb values do seem to be a little higher on this car, I really should disconnect the MAF to see if that is detecting a little too much flow, which results in a bit of extra fuel being timmed in ...

[carrera]

Another visit to the exhaust analyser

She failed, no real change, and then passed after getting a bit more heat into the cat & disconnecting the MAF. It seems that it'll give good readings for a while & then it just increases CO. Lambda & HC are perfect

Back to my place to do some more back to back tests, tried another MAF, but that seemed worse. I'll try swapping fuel rail in the morning in case it's a variable / dribbling injector

[carrera]

Did some more swapping, MAF and fuel rail, in case they were the issue.

That improved things, but not because of the components, but because as part of doing the job I discovered that the spigot on the one way valve on the PCV system was broken, with about 2mm actually in the hard pipe. A jubilee clip was fitted, along with some glue as a temporary fix.

That was enough to reduce the variability in the emissions, so the car now has an MOT

However, I think it's a biy marginal, and to avoid the problem for next year I think I need to source a replacement cat.

Has anyone any experience of the aftermarket catalysts. I seem to be able to pick one up on ebay for ~£120 with a 5 year warranty, but at the back of my mind there's a voice saying "not as good"

I also just put a wanted ad up in case someone has a genuine one lying around, unloved, in their garage