Hesitation

[911JC911]

Hi,

1992 911 C2 with exhaust and aftermarket chip. When I'm cruising (doesn't matter at what speed) and I have my foot lightly on the throttle, sometimes when I press the gas pedal to accelerate, there are rare instances where the car doesn't go, but seems to stumble (car doesn't stall) for a second or so, then accelerate. Most times, acceleration is instantaneous....any ideas? Thanks in advance.

[Dan J.]

Hi,

It may be a bad o2 sensor.

I had a similar throttle response issue with my c2. To diagnose, unplug the o2 sensor connection (located on the driver's side, back of engine compartment just above the valve cover, follow the wire up from the o2 sensor through the engine sheetmetal) and drive the car around. If the car runs better and doesn't hesitate, than your o2 sensor is likely the culprit.

Hope this helps.
Dan J.

[dependencies]

I have EXACTLY the same symptoms on a 1990 C2

Could somebody indicate on this picture where I should begin looking for this sensor please




could you also describe what I'm looking for in terms of shape as well please

[ilko]

I had the same issue and it was the O2 sensor. The O2 sensor is located in the catalytic converter housing, behind the driver side rear wheel.

You can get an OEM O2 sensor for $150, or an aftermarket one off Ebay for $25. I got the cheap one and have had no issues with it.

To install it you would need a 22mm (I think) flare nut wrench or the equivalent cut out socket.

[dependencies]

My thanks,

Following your advice I traced lead forward from its sensor on the cat' drivers side,

through the wheel arch, and into engine bay alongside valve covers,





and up until this connector....



pulled them apart,

took car out for an hour, and its fine now.

It would indeed appear to be the culprit, I'll take a look on E-bay this evening and find a good one

thanks very much,


Richard

[911JC911]

Many thanks too. I haven't done anything yet but I'll yank the cable to see how she runs. I only get this hesitation on a very infrequent basis. Second question is, will this O2 sensor cause any major problems if I don't take care of it right away? Or is it best to change out the part ASAP before any more road trips?

[dependencies]

I was wondering this as well
Although I'm going to replace the part as soon as I find one anyway.

On a further note, I would say I've not turned up anything
in the UK as yet on E-bay or otherwise,
although I shall ring around on Monday morning as I suspect theyr'e not appearing in web-sites,
as such a common part, a bit like the DME relay I bought first the other week

[911JC911]

Anybody? Is driving with a 'faulty' O2 sensor a bad idea?

[dependencies]

I've used mine for a week so far, and and nothings dropped off yet,


mind you i've picked up a replacement to put on
although it came without the plug on end, so had to chop tail off existing part and link it together before swapping it.

I imagine long term without feedback supplied by the sensor at tail end of motor, something at the business end might suffer

perhaps a boffin will be along directly to explain

[ischmitz]

Originally Posted by 911JC911

Anybody? Is driving with a 'faulty' O2 sensor a bad idea?

you'll loose power since the DME is going into "limp mode" if the sensor is missing. A degraded sensor usually has a much longer response times. As a result the mixture will be off. Fuel ecconomy might suffer and power will be reduced. I would fix it to up the fun.....

[gizmofixer]

Removing the O2 sensor signal will generally force the mixture full rich.
Extended usage in this condition will foul the plugs and kill your expensive catalytic converter.
Most folks are not aware that the O2 is a wear item, they should be replaced regularely, i change mine every 50K.

[ischmitz]

I have to revise my previous comments and here is why: My 3.6 conversion was running flawlessly for more than 4 years. I put in a brand-new O2-sensor about a year ago. All of a sudden a couple of weeks ago I once felt a slight hesitation. "Strange...." I thought but didn't further follow up on it.

This past weekend on a longer trip down the 101 all of a sudden the car started to intermittently cut out. I was late in the evening and I was about 80 miles from home with no tools and nothing. I was afraid I would not make it home. Every 5 to 10 minutes the engine would just completely loose it and I was preparing for a full stop. It felt like someone cut power to the ignition. Well, I did make it home. I checked the DME relay and did not find anything obvious.

The CEL (check engine light) never came on. Today out of curiosity I hooked up the hammer (Bosch tester) and sure there was one fault stored in memory. It was "O2 sensor shorted to ground/not present" and the additional information indicated that it happened at 3170 RPM engine speed with 4.0ms load signal. This indicates cruising speed at a leisure 70 mph with light throttle.

So my issues were caused either by bad contact at the O2 sensor connector or a bad splice. I disconnected and reconnected the O2 sensor and have not noticed anything since. What leaves me baffled is that this caused the engine to completely go dead for periods of 10 seconds or more. My guess is that the DME gets really upset (read: it resets and stops putting out a spark signal) when the O2 sensor signal has intermittent shorts or opens....

Ingo

[911JC911]

Thank you all for the responses. I'm planning on getting it fixed up ASAP (we only have about 2 weeks left in the Porsche driving season) and will probably replace it as I get new fluids in before the she goes to sleep for the winter. I have 2 trips left before I put her away.

[dependencies]

Ischmitz

That was interesting to read actually,

I agree it was usually within that rev range actually.

Went to fit my new One today (sensor)
had devils own job removing old one, only to find new probe, resists threading in properly.
The thread pattern looks similar, although the thread on the old one is a bit damaged,
suggesting its left a bit of itself in the cat' which is annoying.

For now I've replaced the base of the old one in place untill it reaches the garage next week
(and some expert hands)

the tin-ware shielding that wheel from the cat is a bit fiddly BTW,
and best apply some oil overnight to soak the bolts
hope this helps

[bigchillcar]

had similar symptoms, but disconnecting the o2wasn't the fix. first replaced the cht sensor and then got it right with cleaning the light corrosion off of my maf sensor at its connection. on these cars, so far for me it's all been about sensors. didn't have these to deal with the years i wrenched on my '74. the '90 is a whole other animal.

[dependencies]

Following my tracking my hesitation down at least in part in to the o2 probe
Unplugging it from the harness in the engine compartment removed the symptom (hesitation)

however removing the apparently duff sensor from the Cat'
with a dull tool......... ME

causing further unscheduled expense as I stripped its threaded hole.

Drove around with old sensor base screwed back in to stop it blowing, for a good few weeks without much problem.


Today took it to a specialist who heli-coiled me a new thread and located replacement sensor in it, & plugged it all in for me.


Couldent help but notice SOME hesitation from the start,

although its not as often doing it as before, its quite apparent theres a relation between the sensor plugged in HESITATING
& not plugged in FINE

anyone else fammiliar with this, and what might I try next


PS couldn't detect any obvious change in cars performance whether its probe is in or out

[dependencies]

Well,
over the last Three days its been hesitant on a perhaps A couple of occasions with new sensor fitted,

bear in mind I've run perfectly for a Month without any problems or o2 probe in place


...........fit new sensor and suddenly an intermittent problem,
still it is at the moment just an intermittent fault so I can live with that,


unless of course anybody knows this fault themselves?

[craig001]

You might want to disconnect the battery for 20 minutes or so to reset the DME's memory. Then let it "learn" again. Don't know how much this will help though.

[dependencies]

I was wondering when to expect this option TBH

While I suspect it might do some good,
Might be best if I consult my alarm fitter for possible side effects first,

However given its new component as the old looked to be 'problematic' this new twist MUST be something else right?