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Discussion Starter · #1 ·
Hi again JRV,

Noticed over


Hi again JRV,

Noticed over approximately the past month "popping" at idle and slight surging when car warm. During warmup period as drop from fast idle to normal runs rough @ 900 RPM for about 30 seconds then returns to 1000 RPM. No loss of power while driving. Turning on A/C (once warm) drops RPMs about 100 and seems to lessen popping sound.

Airflow sensor has silver plug (? factory) in mixture adjustment hole.

(1988.5 328 completely stock 9400mi started weekly/driven monthly)

To date my endeavors have included:

* Removal of all NGK plugs (~400mi/12mo old), blasting clean, then confirming proper gap (0.024").
* Removing caps and wires. Amazingly, could not demonstrate continuity on 5 of 8 (!) replaced with new wireset and extenders confirmed continuity before reinstallation. Wire-brushed cap/rotor contacts. Confirmed spark with timing light (rear bank only) tonight.
(thought this was defacto my problem but unfortunately not)
* Removed Microplex, checked reistances across terminals (not sure of individual meaning, but both identical). Cleaned, reinstalled & confirmed grounds.
* Frequency valve buzzing appropriately.
* Cleaned wiring harness plug contacts for cold start, warm-up regulator, frequency valve.
* Removed bellows hose and wiped out throttle body (not really dirty) and airbox & perimeter of air intake plate (same).
* Removed O-2 (lambda) sensor relay from ECU plate (ergo my earlier posting). Pulled fuse (good) and top didn't notice any burned connections, etc. Reinstalled with new fuse.

None of the above made any particular difference.

Starting to get somewhere tonight measured O-2 sensor voltage when warm-start: fluctuating 0.4 to about 0.9mV. However, once blipping the throttle for the first time and returning to idle digital voltmeter would flash 0.24-something- then "OL" for overload.

Disconnecting the O-2 sensor resulted in about a 200 RPM increase in warm idle (to 1200-1300) and complete resolution of popping in exhaust.

Not sure what I've stumbled upon here - dying O-2 sensor? Have refrained from playing with any other settings (throttle body stop, mixture). Only temporal event I can recall is dropping cat to replace gaskets about 2 weeks ago but as I recall symptoms were present prior to this. Went through old FC archives some symptoms similar others not would prefer not to throw parts at problem.

Suggestions where to proceed from here? (unforunately do not have exhaust gas analyzer nor easy access)

Thanks as always,
Carl
 
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Discussion Starter · #2 ·
Hi Carl,

there is a way to


Hi Carl,

there is a way to somewhat set the fuel mixture (very poor way, but possible) using the voltage oscilations at the frequency valve and an analog volt/dwell meter..

I'll have to get my Bosch Books back from JL to write the procedure inteligibly.

Yes the silver plug you referenced will need to be removed and the small screw beneath it. You'll also need a long 3mm Allen.

Actually there is a very long indepth conversation in the old FC archives about 308/328 Mixture setting procedures between myself and someone else (can't remember who).


Oh ....the relay is a standard Porsche part...it's a 928 overvoltage protection relay.

Regards, JRV
 
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Discussion Starter · #3 ·
I think method for resetting m

I think method for resetting mixture involves reading O-2 sensor voltage and adjusting to 0.5mV (?) It is in the Probst Bosch book (which I have been scrutinizing over the past 48hrs).

Do any of my symptoms suggest faulty component (O-2 sensor, relay) that I should replace?

Thanks again JRV,
Carl
 
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Discussion Starter · #4 ·
Oh PS JRV I printed out your d

Oh PS JRV I printed out your description of setting mixture (9 pages, very thorough) from FC archives yesterday.
Carl
 
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Discussion Starter · #5 ·
Hi Carl,

way to soon to sug


Hi Carl,

way to soon to suggest faulty part imo. The mixture itself will make the O2 Sensor Voltage vary widely. Mixture can & oes fall off on it's own, needing periodic corrections.

>>I printed out your description of setting mixture (9 pages, very thorough)<<

LOL...without flames I probably could have written it in 7 pages...
 
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Discussion Starter · #6 ·
(without flames...what a g

(without flames...what a great line!)

My thoughts on this two-fold: without change in mixture adjustment, this problem arose spontaneously (which is why I suspect faulty part). Or, old plug wires slowly failed until became symptomatic then replacing with new changed previous state of tune - in the other direction.

Certainly the former agrees with your assessment. JRV, what do you think of the relatively inexpensive exhaust CO testers (Gastester $230) on the market? Sufficient for home mechanic (obviously not as thorough as your 5-gas machine).

Carl

Also must comment on how *fast* you have responded to my problem - wonderful!
 
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Discussion Starter · #7 ·
Mixture can just fall out of a

Mixture can just fall out of adjustment for no apparent reason, although I would suspect normal wear & tear of use plays a part.

I'm not familiar with the Gastester, although I know we have discussed many types in the past.

As a setting tool many home testers may work. The thing I don't like about the testers that don't read Hydrocarbons (HC) is that they can't be used as a Setting Tool AND a Diagnostic Tool. To diagnois & isolate issues one needs HC readings as well as CO readings. If the Gastester reads HC then it will be a handy tool to have around.

Regards, JRV
 
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Discussion Starter · #8 ·
Sorry JR,

I'll get h


Sorry JR,

I'll get he Bosch books back to you tomorrow. Have been busy with the CV boots.



JL
 
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Discussion Starter · #9 ·
Carl,
On a properly set-up ca


Carl,
On a properly set-up car, with a properly funtioning 02 sensor, the voltage range should be between 0.2 volts (lean) and 0.8 volts (rich)...

A voltage reading, such as the what your measuring likely points to a bad O2 sensor...Steady state idle conditions should produce 500 milivolts. A voltage test is the confirmation step...Using a CO/HC meter is really the best way to dial in the mixture. The Gastester you refer to works reasonable well in terms of giving you a relative reading...though repeatability is suspect. Idealy, you would adjust for the lowest possible HC, which translates to the highest possible combustion efficiency.

Regards,
David
 
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Discussion Starter · #10 ·
JRV & David you guys are g

JRV & David you guys are great.

JRV, went though searches on FC archives for "HC", "PPM", "emissions" etc. didn't find anything specific regarding tester equipment. Gastester device only measures CO. But did realize (not sure others do) how much of a loss your departure was.

David, I cannot explain why I get such a fluctuating reading at idle after blipping throttle; but the fact that I do get a reasonable reading *before* blipping throttle makes me slightly hesitant to condemn sensor. Any other multimeter testing (resistances? voltage at higher RPMs?) I can perform?

That said, being in the middle of MS few resources exist locally. JRV if I still lived in Houston I'd be dropping by.

At this point have choice of funding a new sensor ($130) [or relay?] or pursuing proper diagnosis/equipment. Want to be a mechanic here...but also want to effect a fix. Any good sources for used 2 gas analyzers for <$1k?

(and in the back of my head remember reading incessantly on old board about ignorant savages who played with adjustments they didn't understand..!)

Carl
 
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Discussion Starter · #11 ·
Carl,

Although crude, remov


Carl,

Although crude, remove the O2 sensor...and clean with ScotchBrite. With an high impedence voltmeter, measure the voltage output of the O2 sensor, while heating the tip with a propane torch. The output voltage should approach 1 volt, as the tip comes up to temperature. This test only will determine voltage output, not reponse rate...which deteriorates over time.

As to the test gear question, without measuring HC, you're really shooting in the dark. The best, and least expensive two-gas analyzer is available from: http://www.bridgeanalyzers.com/9003%20Brochure.htm

When you blip the throttle, voltage on a suspect and good 02 sensor will rise, as the exhaust temperature go up, hence potentially higher 02 output. In that the frequency valve is buzzing, I would make the assumption that the rest of the O2 circuit is functioning properly.

With all this info in mind...you still nee to know, before proceding with 100% confidence, where the mixture actually is. Based on the 02 voltages you've provided, and the apparent lean misfire, it's pretty clear we're on the very lean side.

Although it has been quite a few years since I worked on an O2 sensor car, I remember a test using a dwell meter...seems the O2 should read 45%-55% duty cycle. Maybe JRV remembers that quick test, in more detail...

See what the O2 sensor voltage is with the propane torch trick...and we'll go from there. Your meter should be on the 1 volt (1000 mv) scale, at minimum.

Regards,
David
 
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Discussion Starter · #12 ·
correct that the FV buzzing me

correct that the FV buzzing means the relay is fine.

I'll have the info on the Duty Cycle tests tonight. Using 'duty cycle', you can get he mxture close.

Actually there is a Co that sells used 4 gas analyzers...I'll try and find the info.
 
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Discussion Starter · #13 ·
Thanks again David. Will try a

Thanks again David. Will try and pull O-2 sensor tonight & (never pass on opportunity to own more tools) find propane torch.

One question though: I'm presuming to heat on bench (in vise) how will I get a voltmeter reading without power input?

Carl
 
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Discussion Starter · #14 ·
Carl,

The O2 sensor will ge


Carl,

The O2 sensor will generate a voltage, as it warms up...! No power connection is needed. One lead of your voltmeter on the output wire, the other on the O2 sensor case. That's it!

Regards,
David
 
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Discussion Starter · #15 ·
>>Actually there is a

>>Actually there is a Co that sells used 4 gas analyzers...I'll try and find the info<<

Well...seems the one I was familiar with went out of business.

At one time in a conversation with Henry I had found some other used GA sellers using google.

Regards, JRV
 
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Discussion Starter · #16 ·
OK here's tonight's re

OK here's tonight's results (I'm now the proud owner of a propane torch - neighborhood look out!)

[sensor Bosch #258003009 12V also marked 844 15 1]

Cold picture on removal (-80mV):

Cleaned up with Scotchbrite. Heating tip (max voltage .927 mV):

After cooling down (-80mV):


Which would seem to suggest O2 sensor functioning properly? (realizing this doesn't test response time). Porsche dealer can get relay 3-5 days for $127. Bought a set of Champion RA6HC #809 copper plugs tonight will install for testing purposes.

JRV, I called around in yellow pages to all shops in area offerring "computer diagnosis" one gentleman had heard of CO/HC tester neither he nor anyone else actually had (no emissions testing in MS).

Carl
 
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Discussion Starter · #17 ·
Some more data points on O-2 s

Some more data points on O-2 sensor readings:

* Reinstalled prior to start-up 0.1mV
* Start cold idle 0.531mV & steady
As the car warms up there is a brief (<5sec) "whirring" sound from the front then idles roughly for about 30-60 seconds. I'm presuming this is switch from open to closed loop input.
* Digital voltmeter then reads all over the place, flashing numbers in sequence until reaching "overload" in about a second. Hooked up my analog meter which oscillates between 0-1v. Revving the engine & holding at perhaps 2-3000 RPM results in faster oscillations.

Seems to pop slightly less after reinstallation, but this could be my imagination. Remains with slight idle surge.

Does this help?

Carl
 
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Discussion Starter · #18 ·
Carl,

At this point, withou


Carl,

At this point, without knowing the HC levels, we really can't go much further...Likely, cleaning the O2 sensor would produce a slightly higher output voltage, hence slightly richer condition. Yes, the swings in voltage are due to the change of open loop to closed loop conditions. I'd be curious to know the "warm" system pressures, as well...as the cold idle O2 reading seems about right.

From what you've found, IMO, it does seem like the O2 sensor, and associated circuits are working correctly.

Other than the poor idle, how does the car run?

JRV...Your thoughts here??

Regards,
David
 
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Discussion Starter · #19 ·
Are you sure that the plug wir

Are you sure that the plug wire extenders (our favorites) are all OK? Typically, 1 or 2 bad could cause this type of problem, inspect carefully up inside where the spark-plug plugs in.
 
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Discussion Starter · #20 ·
Thanks Brian. I replaced plug

Thanks Brian. I replaced plug wires & extenders right off & checked continuity in all before reinstallation. Changed out plugs to inexpensive Champions last night.

Carl
 
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