Normy

Drew-

Despite my extreme rhetoric, I am thinking of replacing my twin S4 cats with a Louis Ott X pipe...

I'll make sure that this is the problem before I do this, and '85-86 US exhaust pipes will make an appearance on your's truly's car before anything happens.

[I cannot believe I am contemplating removing my cats; quick- someone talk me out of it~]

N!
'85 S2 5 Speed

Drewster67

Dude - I'm just going with test pipes. My emissions is good to 05. You'll be WAY happy you did. The sound man, I tell you ...the SOUND.

That's all I need is more power -

PeteS

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Normy:
<strong>Despite my extreme rhetoric, I am thinking of replacing my twin S4 cats with a Louis Ott X pipe...</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"><img border="0" title="" alt="[Eek!]" src="eek.gif" /> <img border="0" title="" alt="[Eek!]" src="eek.gif" /> <img border="0" title="" alt="[Eek!]" src="eek.gif" />

Welcome to the dark side.

A number of 928s have passed emissions tests without cats, so it's not as big of a deal as you probably think it is. One good smokey burnout probably puts more emissions into the air than a well running 928 without cats probably would in a long time.

Richard S

Drew, that blue box looks similar to the box spliced into my 84 Euro wiring harness. My box was made by Neutronics, and connects the O2 sensor to the computer (no pins on a Euro harness). You can then measure the voltage and adjust the fuel mixture by adjusting the pots in the box. I guess it was required for federalization, only way to get the O2 sensor to work with the computer.
Rich

John Speake

Hi Thomas,
The problem with your car could well be the MAF sensor. I can refurbish and repair for you. Please check my website's FAQs. at

<a href="http://www.jdsporsche.com" target="_blank">www.jdsporsche.com</a>

Mark

Thomas -

I had a similar prob w/my '85 ROW...when I replaced the air tubes (that were quite leaky) - the problem went away...I think at the slow sppeds it was sucking in warm/dirty air thru the cracks in the old tubes.

reno928s

I also had a new MAF sensor installed and the problem is still. Drew, if the ceramic honey comb was broken in pieces in the cats wouldn't it make a vibrating noise at idle. Sal

Old & New

"One good smokey burnout probably puts more emissions into the air than a well running 928 without cats probably would in a long time."

One day of volcanic eruption probably puts more emmissions into the atmosphere than all the 928's ever built, ever will. Being a green weenie is more of a matter of perception than reason... Go for it N!

Reinhardt

Thomas, I wish I knew more about the workings of the throttle position switch but, sadly, I don't.
Why is it only the Euro models that seem to have this problem?

Drewster67

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by reno928s:
<strong>I also had a new MAF sensor installed and the problem is still. Drew, if the ceramic honey comb was broken in pieces in the cats wouldn't it make a vibrating noise at idle. Sal</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Yes and No - No if the peices are wedged in the pipe - I had that happen to me in my 87 Mustang LX 5.0. -

drnick

hey normy,

my car still has that same problem with the higher rpm miss at part throttle and like you say it isnt there so much when the car is cooler say on a cold day or evening.

what is most frustrating is the way the car does 'rocket forward' once the miss clears and the fact that up to that point it hasnt been, i feel like im missing outon heaps of extra horses!!

maybe its the throttle position switch? i will add this to my 'to do' list.

_Thomas_

Hi

@Bruce: found and cleaned one ground (thick black wire) in middle of the cam cover and another one (thin brown) at front of cam cover, near timing belt cover. Is there another one?
Actually it might have helped a bit, problem seems to get smaller ...

@Reinhardt: I ordered the intake gaskets and O-rings for the throttle position switch so that I can put everything back without a leak after testing.

@John: thanks for info if the MAF sensor will turn out to be the culprit (out of calibration, it is certainly not entirely gone) I will send it to you.

I would still like to have some more info about the throttle position switch ... anybody?

Cheers Thomas

Normy

Nick-

I've wondered about the TPS a little too. One of my friends has an '87 RX-7 and has had all sorts of trouble getting it to run right. He's brought it over to my house a few times, and the diagnosis for its horrid fuel mileage [these have something like 145 hp, yet his car is only getting about 13 mpg/ 20 litres per 100km] has centered around the TPS. There is a test procedure from a Mazda website which involves a voltmeter, and despite the fact that it does not test properly at all [indicating a bad part in my opinion], my friend continues to try to adjust it back to normal.

Apparently, the TPS can be adjusted. If you look at ours, you'll see there are screws that can be loosened, and the whole unit will move on the axle of the throttle plate [I think- I haven't tried this]. What this adjustment apparently changes is the ratio of voltage transmitted to the injection computer to the actual throttle plate opening. The Mazda test procedure actually gives data on how this is to be set; I don't think the Porsche manuals say anything about it for our cars. I did test my TPS with a multi-tester as per the manuals, and it tested correctly.



Then again, it is possible for something to test perfectly in your quiet driveway, and yet fail when under power...

<img border="0" alt="[crying]" title="" src="graemlins/crying.gif" />

Normy!
'85 S2 5 Speed

WallyP

The 928 uses two Throttle Position SWITCHES, and does not have a Throttle Position Sensor.

The Idle Switch tells the ECUs that the throttle is closed. It should show continuity (very low Ohms) with the throttle closed, and should open as soon as the throttle moves. This switch enables the 1200RPM fuel cut-off (no fuel injected above 1200 RPM with the switch closed) and signals for timing and mixture changes to improve the idle.

If the switch doesn't close, the idle will be less smooth, and fuel economy will be reduced slightly.

If the switch doesn't open, the engine won't run above 1200 RPM.

The WOT (Wide Open Throttle) Switch tells the ECUs that the throttle is open more than about 70%. It richens the mixture and retards the timing. The switch should be open below about 70% throttle, closed above that.

If the switch never closes, WOT performance will be degraded slightly. If the switch never opens, fuel economy and part-throttle performance will be degraded slightly.

_Thomas_

Thanks Wally

I followed your great list of how to sort out electrical gremlins. I think you should add the grounds mentioned by Bruce (plus maybe the injection jet connectors). I am starting to think that it might have sorted out my problem ... but I am still going to check out the throttle position switches (thanks again for clarifying) and maybe set the MAF slightly richer.

Cheers Thomas