granprixweiss928

Hi all

Recently completed engine out refresh on my 88 S4 automatic with 155+ miles.

The engine was in sad state when I got the car (not running actually) but i did get it going soon after. The engine was leaking oil everywhere and numerous vacuum leaks were easily located.

during the engine out refresh, I refinished the intake and replaced all the seals/gaskets/vacuum lines/elbows/hoses/injectors/fuel lines/fuel regulators/dampers/spark plugs/coils and rotors/temp 2 sensor and more. thats been documented here.
https://rennlist.com/forums/928-foru...on-thread.html

Everything was assembled carefully on the engine on the stand and then installed in the car. A positive pressure test using dwyanes method was done prior to the installation, we got at least 2psi to hold and found several little leaks like the dipstick and vent line at top of oil filler.

once installed it fired up fine, after a small fuel leak and throttle cable issue. and it would idle at 750-800 steady.

when I took it to smog I drove it on the highway for about 20 minutes and then let it idle once I arrived, so it was good and hot.

The exhaust does not smell rich.

the temperature gauge reads just above the normal mark- higher than on my 81.

Hi Nox= lean condition I know, and I have read many threads on this so far. hard to determine if there are any post maf air leaks, I would find that hard to believe...

I tested my o2 sensor today and after warm up it would fluctuate between 0 and about .45 volts. the test tells me it is working...and telling me the car is lean. possibly replaced by PO in 2003

I checked my MAF also, its not original from 88, it was replaced by PO in 2001 at 105K miles. I did the resistance tests on pins 6/4 and 6/3 and I am in spec- although pin 3/6 should be 0-1000 ohms...I got 990 ohms!

unplugging the o2 and starting the car had limited effect- it seems to run ok, but idle was not as smooth.

unplugging the MAF it will also run, but poorly, it wont rev and decel well at all.

Ive disconnected the vacuum line to hvac to rule that out as a source of leaks- and vacuum tested the vacuum canister- its good.

and plugged line to the fuel vapor value to rule that out...no change

Flappy works at 4000rpm, the shaft moves

I have not tested fuel rate or pressure, should I ?

need help here, where to go next.

Bmw635

May be another failing MAF ? Do you have report from previous test ?

granprixweiss928

I need to add:

The car has aftermarket cats, installed in June 2013 purchased from here

http://www.automotion.com/catalytic-...1985-1995.html

when the car had them installed, it had also failed previous to that for the same reasons.
NOX was reduced by like 500 ppm then.

here are my results

15 mph Co2 13% o2 2.4% HC 47 max allowed 110, CO% 0.03 max allowed 0.72, Nox 1170 max is 773

25mph Co2 13% o2 2.5% HC 46 max allowed 85, CO% 0.02 max allowed 0.59, Nox 945 max is 712

Bmw635

I've heard from other Bimmer owners that aftermarket cats only last more than 2 yrs. I know of couple folks replacing cat every smog or 2nd smog. My cruiser has 49 state aftermarket cat 5 yrs ago but still pass smog. Not sure if maintenance regimen affects longevity on these cats or just inferior material. I suspect your cat is dead from the reading and stories I've heard.

worf928

Your idle is higher than the spec 675. High idle is usually due to false air. You know all these things though.

High idle can also be due to an inaccurate TEMP-II reading. Have you tested the TEMP-II resistance at the ECU pins?

Did you powder coat or paint the water bridge? If you did, run a temporary auxiliary ground wire from the base of the sensor to a ground point (cross brace bolt will do) and see if the idle changes.

outbackgeorgia

"750-800 steady"
My idle is steady. 750-800 is not "steady". There is a hint here, it should be rock solid at the spec RPM and not move more than a few RPM. May not affect the smog, but are the IAC and hoses working correctly? No leaks?
Dave

jcorenman

Mark,

High NOx (and low CO/HC) does indicate a lean mixture, so that's the first place to look. However if that were the only problem then I would expect HC to be lower, also. So I think it is likely to be a couple of problems: Lean mixture, and worn-out cats. Aftermarket cats don't have a lot of material in them, and (as mentioned above) a couple of years is a reasonable expectation.

The O2-sensor voltage should be moving between approx 0.1v and 0.8v, your 0.45 means it is never getting to the "rich" side of stoich (14.7 AFR). This could be a bad O2-sensor, or an out-of-cal MAF.

So how many tries do you get, and at what cost? There are two approaches here:
1) Start with the cheap stuff (O2-sensor) and replace things one at a time until it passes, or:
2) Refresh all of the possible suspects at the same time: O2-sensor, MAF and cats, then re-test.

O2-sensors are good for around 50K miles, and tend towards lean mixtures as they age. The Bosch part# is 13048, available lots of places. I would replace this first in any case.

MAF's also age towards lean mixtures, and are good for 50-100K miles before needing to be rebuild and re-calibrated. The LH2.3 will compensate within limits, adding (or subtracting) fuel to keep the mixture around the 14.7 stoich value as measured by the O2-sensor. The resistance checks don't mean much, they would only indicate a gross failure. What happens is that the burn-off cycle slowly erodes the platinum hot-wire over time, causing a shift in calibration. The wire must be replaced, a simple cleaning or re-cal won't last.

Rebuilt MAFs are available from JDS Porsche in the UK, via Louie Ott in Oregon: http://performance928.com
There are other suppliers for rebuilt MAFs, not all are created equal.

Also check the Temp-II sensor as noted above, it is grounded to the engine block and powder-coating can insulate that. Measure resistance from the Temp-II sensor body to the chassis (should be zero ohms), or measure the resistance of each element at the LH and EZK connectors, as noted in the WSMm (section 24/28).

Hilton

Things I'd be checking first in order of easiest.


1. Are the chips original inside the LH ecu?
2. Spray brake cleaner or starter fluid (ether etc) around the intake gaskets, injector lower o-rings, etc. to see if rpm fluctuates (i.e. vacuum leak)
3. MAF - borrow a known-good one from another 928'er, or send yours off to Louie Ott for testing.

Your MAF tests are inconclusive. Pins 3/5 just tests that the circuit resistor is in spec, not the voltage output of the wire itself. Pins 3/6 are not used by your car (S4's don't use the potentiometer in the MAF). As MAF's age, they tend towards lean, altho an O2 loop will compensate for the aging, up to a point.

I think most likely culprits are a vacuum leak, and the MAF.

As a last resort, some used/borrowed stock cats - but first, work through the likely symptoms, as the OEM cats are good enough to mask a fair amount of running issues.

On idle speed - after initial cold start, idle will be higher than spec, but will drop to 675 after a couple of minutes as the engine warms up. If you have a digital tacho (on a multimeter for example), you can get tacho info to verify the actual idle speed from the diagnostic connector on pins 2 (ground) and 3 (rpm) - set the meter to 4-cylinder mode, as the pulses are taken from a single ignition bank.

dr bob

Did you clean or replace the injectors as part of your refresh?

All it takes is a few weaker injectors to trash the NOx readings, even with good oxy sensor readings and a good MAF. The oxy sensor reads and corrects based on the average CO it sees from all the cylinders. If CO indicates the mixture is right, the weak-injector cylinders can easily spew enough NOx to fail you.

My car passed easily when I bought it with 22k on it. Over the years and the miles the NOx gradually got higher, to the point where it would barely pass. The car ran fine. New injectors as part of the intake refresh smoothed out the idle that seemed fine before the work. Most important though the NOx numbers were back down to as-new levels.

granprixweiss928

Bob,

the injectors are new. Ford Racing 19 lb.

Ive ordered an 02 sensor since what is on there is either at least 50K or more miles on it.

Ill keep going over the motor and look for leaks, but I really doubt there are any due to the tests we did prior to the install.

and I need to take a look at the fuel system. and put in a complete fresh tank of gas. whats in there is a mix of old and new.

Mark

Bill Ball

As I told Mark yesterday, I had similar results with a failed aftermarket cat. Failed NO only.

Last year I failed smog with my original cats, so I installed aftermarket cats and passed easily. I replaced the MAF after that and decided to put my original cats backs on thinking that may have been a major contributor.

Here are the results this year

1. Original cats with 275K miles...
15mph CO2 13.7% O2 3.9% HC 137 max allowed 110 (FAIL) CO 0.13% NO 748 max is 772
25mph CO2 13.7% O2 3.9% HC 81 max allowed 85 CO 0.62% NO 672 max is 711


2. Put the aftermarket cats back on, 1 year old...a year earlier NO was 200 with them installed...
15mph CO2 13.2% O2 4.6% HC 19 max allowed 110 CO 0.01% NO 1295 (FAIL)
25mph CO2 13.1% O2 4.7% HC 11 max allowed 85 CO 0.00% NO 1299 (FAIL)

Now, this would normally lead anyone to think I had a lean condition, but with the original cats only a week earlier I didn't see that. So....

3. Used Porsche cats with only 150K miles...
15mph CO2 13.8% O2 5.0% HC 93 max allowed 110 CO 0.09% NO 579
25mph CO2 13.8% O2 4.8% HC 76 max allowed 85 CO 0.06% NO 473

Now, everything is not all good. The high O2 and high (but passing) HC leads me to believe I may have a (lean) miss in one cylinder, but my main conclusion is that the aftermarket cats failed in the NO stage.

Speedtoys

Good data Bill.

Mark, there is a large brown box at my front door, it contains a Y pipe with good OEM cats.

I will see if wife can take it to the RHV airport where you can get it easier there this week.

granprixweiss928

hooked up wideband today and took car up the highway.

getting in hwy and then cruise a bit

highway cruising around 70 mph

Full throttle accell on hwy

residential 35 mph crusing

Hilton

Looks to me like your WOT switch isn't working. AF should enrichen at full throttle.

Koenig-Specials 928

.....What Hilton said.

Last year I failed the Canadian smog and when I did my final re-check it was the WOT not working right. I corrected it and passed next day. I actually needed an automotive stethoscope to hear it correctly (comes with age ).

Btw, in my signature it shows that I am running with X-Pipe and free-flow Cats that are now 6 years old. Still passed.

Tech at the shop also told me that a lot of German Cars with aftermarket rad fans/fans controller fail because they are not set up right i.e. they are set to run too cold. Most of them change the setting in the parking lot to get the engine nice and hot but still safe and pass on re-test.

Good luck