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Unread 08-17-2014, 08:05 PM   #31
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Hilton . Just a quick update . i did as suggested . Checked all ignition leads / coil . No faults i can see . Swapped leads from box in nose cone , no change . Made a jumper wire for computer block left hand side and jumped relay . Car runs on 8 cylinders but is very rich / fuel smell . I have a m5 e34 that i have been told has same Maf sensor , so next is to swap the two and see if it makes any difference . Car blows thick black smoke @ idle . Any other suggestions greatly appreciated . Michael
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Unread 08-17-2014, 08:50 PM   #32
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So it runs on all 8 with the ignition monitoring relay bridged? that's good news, means the ignition side of the equation is working, and the relay is tripping because of a misfire introduced by mixture.

Simple MAF test is to unplug the MAF and see if the car runs the same or worse.

With no MAF signal, the LH ecu defaults to limp-home mode, which is a fixed injector pulse width more designed to allow you to move the car off the middle of the road, but not much more than that ("home" is wildly optimistic). So with it unplugged, if it runs the same as with it plugged in, then the MAF is cactus.

If the car runs worse (barely idles, and dies if you rev it), then the MAF is functioning.

I still think the O2 sensor is the likely culprit based on the hunting idle.

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Originally Posted by hilton View Post
my money's on an O2 loop issue, either sensor, or frayed wiring due to rubbing where it passes around the heatshield and then into the passenger footwell, or LH ecu dying (the o2 loop circuit is on the part which dies after about 25 years).
First test is to unplug the O2 sensor, and use a multimeter to check for continuity between the signal and the other two wires.

The O2 sensor connector is usually tucked at the base of the elec panel - its a 3-pin sureseal connector type like the middle row in this pic:

Click the image to open in full size.

The sensor is a standard 3-wire Bosch sensor - you can pick up the sureseal connectors and pins from element14 if you already have a sensor around in your spares for the bimmer. It enters the passenger footwell from the front-right of the tunne - I'll dig up a photo of the location in case you need to find the lead.
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Unread 08-17-2014, 08:56 PM   #33
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Here's the o2 sensor lead location in an RHD car - guessing yours is in the same place as it sounds like the conversion from LHD on your car was done pretty thoroughly.

Also - its worth reading this page at JDS Porsche about MAF diagnosis/function:

http://www.jdsporsche.com/faq.html

John Speake of JDS is a very reliable rebuilder of both MAF's and LH ecu's - his agent in Oz is Matt Nicholson referred to in a previous post, and whose phone number is on the http://www.landsharkoz.com/ page (or PM me for it).
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Unread 08-17-2014, 09:26 PM   #34
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Hilton . If i unplug exhaust sensor will this have any effect on running . I expect it uses this to judge fuel input so my guess is it would run richer again . ???
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Unread 08-17-2014, 10:30 PM   #35
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Quote:
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Hilton . If i unplug exhaust sensor will this have any effect on running . I expect it uses this to judge fuel input so my guess is it would run richer again . ???
Yep, unplugged O2 sensor causes the car to run way rich. Although from the sound of you'll have a hard time telling as you're already making lots of black smoke.
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Unread 04-10-2015, 09:45 AM   #36
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Hilton , if your still here was wondering if you could help . Have now purschase da 78 manual . Is it possible to do a vin check , so that I may know what I have . Thanks in advance . Michael . Vin no 9288101049
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Unread 04-13-2015, 01:08 PM   #37
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Did you fix the yellow S4? What was the problem?
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Unread 04-26-2015, 10:13 PM   #38
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Quote:
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Hilton , if your still here was wondering if you could help . Have now purschase da 78 manual . Is it possible to do a vin check , so that I may know what I have . Thanks in advance . Michael . Vin no 9288101049
Hi Michael - I don't check this site much.. Rennlist is much busier and I"m there pretty much daily.

Sorry, the data available for VIN's only starts with 1980. The only way to get more info is directly from Porsche.

Its a reasonably early example however - made in late 77 I believe. The person to ask for more info would be Jim Doerr of 928 classics. He won't have option codes for it, but he tracks all the early VINs and will know roughly when your car left the factory, and which unusual early features it has.

I'm curious to know whether it has the center vent with horizontal slats, instead of vertical slats like your S4 has.. the change to the later slat style happened part way through the 78 model year

Is it LHD or RHD? Was this the one that Martin had for sale with the Pascha interior he added to it?

Pics and more info would be awesome
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