Greg_L

Sorry , this is a bit longwinded.

3 weeks ago i took my car to a specialist for a 24k service.
They changed the oil to Halvoline Extra 10w40 (was Magnatec 10w40),
new plugs and filters, plus replaced a slightly leaky cam/powersteering? seal.
They told me my cat was knackered and offered me a bypass pipe.
I took them up on it and asked if it had an O2 sensor. They said no but
it makes no difference, as they jumper the DME.

For the first 150 miles i noticed an oily / rich smell, i checked the level, it
was 6mm over the max line of the dipstick, i called the specialist & they said
its ok but if i want i could drain some off - i did, via the oil fill pipe. No oil had
been spilt around the oil filter area during the service, the RHS heads were
nice and clean.
3 weeks on and the car still smells of oil / rich mixture and i've noticed on
occasion, a faint waft of dark smoke from the exhaust. I don't see it on startup,
but do see a slight waft when coming to a standstill after a few miles. Cant
see stains as car & exhaust are black.
Also, the idle is intermittently unstable. Now and then it searches upto
100rpm either side of normal (800rpm if i remember).
I top up the oil by about 1 litre every 1000 to 1500 miles. No drips ever
although i have the undertray on (cars done 180k km's). Over the last 3
weeks i've seen the oil level drop more than usual, but i might be imagining it.
I can't really tell if fuel consumption is worse.

Lastly, the engine feels as strong as ever, a little quicker than before even.

I've read everything i can here about cat bypass pipes and running rich.
But i could not find a conclusive answer to my problem.

Am i simply running rich? is this at all damaging? Could a DME reset help?
Could this be due to badly reset valves or a tweak to the idle stabilizer
at service?
Was the cat hiding the smoke beforehand?
Would a cat bypass pipe with an O2 sensor stop me running rich?
Could this be something more serious - ie. tired piston rings?

or should i stop worrying as old engines just do this

Christer

IMHO, I think you are on the money on some points:

1. Was the CAT hiding the smoke before. Quite possibly.
2. You will most probably run rich without an O2 sensor. I know I do.
3. Woudl a cat by pass with an O2 sensor stop ruch running? Yes it should do, but you may still get smoke and unstable idle of course.
4. Could this be something more serious? Well, yes but not necessarily.

I would check the possibility of oil overfill properly first, then go down the list. Perhaps you can borrow an O2 sensor from someone to check things out? Good luck, hopefully it is nothing too serious...

Adrian

The only 964 delivered without an O2 sensor was option M150. If you do not have this engine installation you must have an O2 sensor installed. Even the M150 engine had the altitude compensator fitted to assist in mixture control. The mechanic is not telling the 100% facts here.
So firstly check if you have M150 which means you are running on 98 Octane leaded fuel (which is not possible) so you will be using 98 Octance unleaded with special additives.
If you are running on 95 Octance unleaded fuel you need the O2 sensor otherwise you will run rich all the time.
Ciao,
Adrian
964C4

Adrian

Lorenfb

You really need to put the car on a gas analyzer to determine whether
the engine is runninng rich or not. Also, it's not a good idea to leave the
O2 sensor input open, especially on a 964 engine as the DME is very
sensitive to spark plug wire RFI. Make sure that the DME doesn't have
a chip in it.

axl911

I wouldn't go back to a shop who would recommend removing the O2 sensor.

It's always a bad idea to run with no O2 sensor. The sensor provides a feedback to the engine management on whether the car run rich or lean. Without it, I think the car would run rich to protect itself from an overlean condition.

---
anthony

Greg_L

Thanks Christer, i'll look into the overfill issue first.

Adrian, i don't have the M150. The DME was jumpered as the bypass pipe has no hole for an O2 sensor i think. I've read about this here many times,
i assumed it was ok.

Loren, what is "spark plug wire RFI" ?

robmug

Greg - I think you can get Cat bypass pipes with the holes for O2 sensors...

(btw, sold the E30 M3 last night)

robmug

this from type911

robmug

Oops - sorry, that's a cat, not a bypass...

Greg_L

Hi Rob,

Yep i had looked into this before i was told i needed it done. The specialist told me there was no difference in O2 / non O2 pipes. They sold the non O2 sensor version and have fitted it to loads of cars with no problems. As they had the cat off for the service i thought i'd go ahead with it and have it fitted for free. I'd like to know if there's a noticable difference in smoke/smell between a pipe fitted with an O2 sensor and one without.

(bet it hurt to see the E30 go, shame i never got to drive it. I'll own one at some stage hopefully!).

Greg_L

Just a quick update . i had a friend at work come and have a sniff. He insists its not burning oil, its just running rich.

I spoke to the specialist and they were surprised it was running rich after their DME tweakery. They asked that i take it in to plug it into their computer. Tomorrow hopefully.

cheers,
Greg

mark lintott

Greg,
Coincidences - I got my car back about 2 weeks ago after having about the same work done ie

Replace a 10$ oil seal on the power steering drive shaft - leaking onto the RHS exhaust and causing a burnt oil smell at each red light.
As the clutch needed looking at anyway - juddering at moving off - the engine came out to change the seal at the same time.
Also changed the cat. conv. to a "sports cat" from design 911 (made by Bursch I think and with an oxygen sensor)
Did a major service including valve adjustment also made easier as the engine was out.

Anyway apart from the very noticable performance increase I also noticed a little smoke from the exhaust and definate exhaust smell. The smoke was explained as being the film of protective oil burning off the new Cat which would dissappear within a few miles. This seemed plausible to me and I haven't noticed it since. I also assumed the stronger exhaust smell is a reminder of why we have Cats and unleaded fuel in the first place - to reduce pollution.

I followed my own car the other day for the first time as I tried a 930 turbo belonging to a friend and he drove my car. There was a waft of smoke coming from mine as we stopped at lights - not much but definatley there. I'd also like to know if this is to be expected with a conversion like this or should I be worried..... My car only has 20,000 miles on though so its hard to imagine it could be anything serious internally.

Thoughts?

Madridcab

I think you may have problem as well with smog test if you run without the oxygen sensor, I failed mine because the sensor connector had come loose (with the cat in, mind you)

Adrian

If you do not have an O2 sensor fitted you will run in open loop mode all the time and you will run rich. This will cause fuel consumption to be higher, it will reduce the life of your exhaust components, you will FAIL emissions tests, you will end up staining the rear of your car, you will possibly cause coking on the top of the pistons.
The 964 is designed to use an O2 sensor. Anyone who says you can remove it and everything is fine is not telling you the truth.
Ciao,
Adrian
964C4

PS: If you intend to drive overseas on holiday keep out of countries that have random exhaust gas testing.

Lorenfb

You don't jumper the O2 sensor. Whoever said that needs "help" (out of the auto
repair business). Jumpering the O2 sensor causes the engine to run very rich or
lean depending how it's jumpered. It should always be connected.

RFI means radio frequency interference. Spark plug wires can radiate "noise" even
though they are shielded causing DME faults. This is a very common 964 problem,
e.g. lower spark plug connectors which have not been fully pushed on the spark
plug. Since the O2 input to the DME is a very high impedence input (sensitive),
it can be affected by the RFI causing changes in the mixture.