930 tuning mess..

scmguru · 10:58 PM

Had the car over at a non Porsche specialist shop to address some oil leaks and to check timing/tune.

Car is returned "tuned" and they "adjusted it" and put in a new wideband o2 sensor in it..

The car was running great 2 weeks ago, it just had some leaks and had been driven less than it should have. We wanted the car to have a quick once over..

As part of the tune it had the O2 sensor replaced with a wideband o2 sensor. Afterwards, it ran noticeably less smooth when cold (i.e. you'd hit the gas and the car would barely accellerate), but it was relatively driveable.

At this point, I was pretty concerned that we were in going the wrong direction, so I did what I should have done in the 1st place and took it to a specialist..

They dialed down the CO from 8 to .3 and verified the timing as 26 degrees at 4k rpm.

It is now completely undriveable when cold.

If it sits outside in 70 degree weather for an hour, the car won't accellerate, backfires, stumbles and stutters for at least 15 minutes.

Also, on a cold start it no longer fires up and runs at 1100 or 1200 rpm like it used to.. it runs at 600-750 rpm until it warms up.

Once it warms up it still stumbles on accelleration randomly or if I hold it at a fixed RPM. It does seem to run better from 3000RPM up... FWIW.

I've noticed it's guzzling gas and the exhaust is smelling pretty strongly.

It's been suggested the WUR has gone, can this happen seemingly "instantly" and would it be exacerbated by leaning out the idle? The old O2 sensor was allegedly dead, could the new O2 sensor be responsible for some of this?

I'm baffled how we've gone so quickly from a car that more or less ran really well to what seems like a mess.

Thanks guys!

JFairman · 05-07-2009, 08:14 AM

The oxygen sensor should be the correct part number bosch narrow band with heater element, not a wide band for the CIS lambda system.
Other than that it sounds like the warm up regulator is way out of adjustment or broken.

MURF · 05-07-2009, 09:14 AM

Co is set way too lean richen that puppy up and all your problems will disappear

mark houghton · 05-07-2009, 10:09 AM

Quote:

Originally Posted by JFairman

The oxygen sensor should be the correct part number bosch narrow band with heater element, not a wide band for the CIS lambda system.
Other than that it sounds like the warm up regulator is way out of adjustment or broken.

+1. Get rid of that wide band sensor.

With your CO at .3% you certainly shouldn't be experiencing the pig rich conditions that you describe (strong gas smell, stumbling, guzzling gas). I would first isolate the WUR as being the culprit....check (or have someone check for you) the control pressures. It's very simple, provided you have the gauge setup to do it. Also check to see that the electrical connection to the WUR is good. Without that connection, it won't heat up as fast as it should and will run rich until the engine heat itself soaks the bimetalic spring inside the WUR.

NathanUK · NathanUK's Garage

If you're not confident hooking up fuel gauges and know how to use a meter then check for a resistance at the WUR.

Edit your signature so we know what year car you have etc etc. Your location would be useful too.

scmguru · 05-07-2009, 04:08 PM

Thanks for the tips folks.. I went in and checked for any loose/bad vacuum hoses and replaced the AAR hose because it was old and cracking.

While I was in there, I checked the WUR Resistance and it was 26 Ohms with the car off for about an hour or so.

Fired it back up and not much improvement..

mark houghton · 05-07-2009, 07:14 PM

Quote:

Originally Posted by scmguru

Thanks for the tips folks.. I went in and checked for any loose/bad vacuum hoses and replaced the AAR hose because it was old and cracking.

While I was in there, I checked the WUR Resistance and it was 26 Ohms with the car off for about an hour or so.

Fired it back up and not much improvement..

Your resistance is fine, so the heating element is working. But that doesn't necessarily mean that the bimetalic strip is still intact. You're just going to have to check those control pressures in order to completely rule out the WUR. The badly cracked AAR hose....especially if it was the hose connected to the intercooler, could allow a leak where that lost air was supposed to go to the intake manifold. That would result in rich conditions across the board. But if not leaking, then the culprit still resides elsewhere.

Aren't these cars fun? Stay with it; you'll eventually have an "aah-haa" moment.

dsiegel360 · 05-07-2009, 10:04 PM

Not sure the exact diagnosis....
Make sure your spark plug wires are secured to the plugs as well as to the distributor. Also make sure the wires are in the correct firing order (which they probably are).

If by chance you started the car several times and did not drive it, the plugs may be fouled.

The airflow meter is a tricky little clit. If the car is not completely warmed up while messing with it, it will give you inaccurate idle/fuel. Also, there is a screw beside the throttle body that adjust idle/air.

Best to have your own o2 sensor to both diagnose and tune. PLX is good. Dave from inyourfacegauges.com makes cool stuff for plx applications.

Good luck

911st · 05-08-2009, 08:35 AM

Are your saying they removed the O2 and replaced it w a wide band and hooked it back up to the wiring harness?

That would be daft. Just try unplugging it from the harness. This will lock out the Lambda function so you can see if all is well.

Also, I hope they did not adjust CO with a cat in place after the cat or with out disabling the Lambda function because it can not be done.

It is ok to set a 930 w a Lambda system a bit fat. That may help or hurt cold start but will get you a bit more fuel on boost if needed. The Lambda computer will pull back the extra fuel on idle and cruse once warmed up.

Most 930 owners seem to want to just leave the O2 disconnected it runs more like a Euro model. If you are running a cat I would not do that.

The best.

krasuskyp · 05-08-2009, 11:40 AM

Quote:

Originally Posted by dsiegel360

The airflow meter is a tricky little clit.

Sorry for the threadjack, but indulge me if only for a moment:

bwhahahahaa

ahhahahah

haahhaha

hahahaaa

*Funniest quote on Pelican yet* Tx for the laugh. My new sig!

Now, 911st (puhleeeeze incorporate a name in yer sig, I always like your posts but feel like a toolbox calling you 911st! 8-))... you're suggesting those who'er sans kitties could / should run mit 02 unplug'd???

I've got a stock '87 save for RL8 exhaust and an EBC. Runs real strong, too strong since the exhaust (0.95bar). Should I unplug der 02???

Thoughts greatly appreciated.

Now, back to the thread at hand - good luck scmguru (another no-namer!)... what is scm and what guruship do you posses? (not being smartass, well, sort of, but srsly?)...

scmguru · 10:44 PM

Ok guys.. did some more digging.

Even though the invoice said a wideband O2 Sensor.. I don't believe it is one because it has 3 wires.

I checked the O2 sensor w/ a voltmeter and it's still good.. warmed up at idle it was around .40 Volts.

I disconnected the O2 Sensor and it didn't change the idle either way.

I replaced rubber hose from the AAR to the intercooler.. no improvement.

I dug up a narrow band air/fuel meter that I used a while back on another car.. I'm going to hook it up and at least see if I'm in the ballpark mixture wise tomorrow.

I used starter fluid to see if the cold idle changed any when sprayed near vacuum lines etc..

No real change anywhere except around the mass air flow.

I dug around and noticed there was a little bit of oil staining at the end of the mass air flow where it is attached to the lower part with the "spring loaded" hex screws. Airbox had some oil in it at one point.. will look into it further.

Thanks!

Mike

NathanUK · NathanUK's Garage

I think you're gonna need to hook up some CIS gauges like mark suggested.

mb911 · mb911's Garage

narrow band for a cis car should be a 1 wire o2 to my knowledge, the 3 wire would be for carrera cars

JFairman · 05-09-2009, 08:52 AM

'87 turbo's have a 3 wire narrow band oxygen sensor.
Single wire O2 sensors have no heater element and rely on exhaust heat to heat them up and get them working.
That takes too long for the EPA...

Generic bosch single wire ones go for around $25.

3 wire ones cost alot more and have a built in heater element which gets them up to operating temp faster so they start controling the mixture sooner.

scmguru · 05-09-2009, 10:58 AM

Hi Guys,

I hooked up the air fuel ratio gauge to the o2 sensor and determined I'm runing a touch rich at idle.

I also discovered that when I accellerate (lightly) or cruise, the fuel ratio drops like a rock below 17.1:1.

About the only time I can get a reading above "less than lean" is at idle or if I push in the clutch and coast.

Is this a limitation of the narrow band sensor?

Thanks!

Mike

JFairman · 05-09-2009, 11:17 AM

Don't know what you're using but narrow band oxygen sensors can only read a very narrow area plus or minus 14.7:1
They won't read above 15:1 or below 14:1 and may not even read that wide a range.
You need the more expensive wide band oxygen sensor and the electrical controller to use it, to be of any use with a 0-5 volt wideband AFR gauge.

Those old style inexpensive narrow band AFR gauge kits are useless for tuning a turbo engine where you need to know a much wider range of mixture ratios than stoichiometric idle and steady cruise AFR's.

They are little more than gadgets marketed for... gadget freaks.

scmguru · 11:35 AM

Good to know.. So I logged O2 sensor voltages as well.. will these be useful?

At Idle, the O2 Sensor is around .65 volts, on accelleration (light) or steady no load cruise, it is at .1 Volt..

The gauge is designed to run from .1 to 1 volt.

Documentation for the gauge indicates the following:

LED 10 - 0.97V - 12.1:1 -
LED 9 - 0.88V - 12.7:1
LED 8 - 0.78V - 13.2:1
LED 7 - 0.69V - 13.8:1
LED 6 - 0.59V - 14.4:1
LED 5 - 0.49V - 14.9:1 -
LED 4 - 0.39V - 15.4:1
LED 3 - 0.30V - 16.0:1
LED 2 - 0.20V - 16.5:1
LED 1 - 0.10V - 17.1:1 -