I have an '81 928 and I can smell fuel in the exhaust. I also noticed that the inside of my exhaust is coated in a nice thick layer of black soot. My plugs aren't black (more brownish-tan and the sparkwires are new) and I can smell a hint of fuel in my oil. I pulled the cat off in my garage and put a light to it, it seems to be clear and the baffles are in great condition. The O2 sensor was rusted into the cat so I couldnt really take a good look at it. I guess my question is, what else can I look at to figure out what is going on? Would it be wise to go to a shop and have them analyse the exhaust? Is there any testers out there for the 81's?

Thanks for the help !

 

You know it's rich, so there isn't much point takeing it to the shop. There are rather few shops that are comfertable working on the L-jetronic EFI system in the car, assumeing it's a US spec. car. There is a electronic computer testor, but it's extreamly expensive, and I'd say not very useful.

You know your eighter very rich, or you've got a cylinder that isn't fireing.

Do you have the WSMs? (at least a CD copy.) If not, you need to get them.

Basic things,

1. Pull your ignition components, see if any of the plugs, leads, cap, rotor, green wire, etc. look bad. If so, replace 'em. Even if that doesn't cure the problem, you should replace if it looks bad anyways. (it'll save you so much headace later.)

2. Check the "Temp II" sensor, use the values in the WSM. The temp II sensor is the one that stick out of the coolent manafold in the frount of the engine underneat the cross brace. Use the values in the WSM.

2. Check the fuel rail pressure in accordance to the WSMs. It should not excede a certain pressure, and it should not fall below another pressure after a given time peroid. Both are important, if you have falling fuel pressure, then you have a leaky injector, if you have too much fuel pressure something is wrong with the regulators, or the fuel return line. We can go about dignosing it from there later.

If you don't have the WSM, PM me, and I'll see if I can't e-mail you a copy of the relevent pages.

 

I had very similar symptoms with my S4 that are now resolved. First do all regular maintenance especially components related to the fuel system ie. air and fuel filters as well as ignition components. The fuel injection is controlled through the brain which is deciding on how much fuel the engine requires at a given moment from inputs of many sensors. It is these sensors that require diagnosing for correct operation as well as the injectors and then the brain itself.

Echo the WSM comments, they are very affordable just now from the big 3.

My problem was the MAF which was replaced with a John Speake rebuilt unit.........car now purrs at idle and revs freely, no soot at the tailpipe all at 3000ft above sea level.

 

Assumeing his car is an US spec, there is no MAF on the car. It uses an "AFM" instead. That really seems stupid when you see it in print, but the "MAF" is a Mass Air Flow sensor, which uses a hot wire element to determine how much mass of air the engine is injesting. The "AFM" is an Air Flow Meter which uses a barn door style meter to measure the volume of air the engine is injesting.

Generaly, the AFM should not cause a extreamly rich condition w/o someone first buggering it up. Ususaly when an MAF goes south, the engine starts missing. But of course, not always.

 

Right, probably not the AFM they are pretty rock solid. could be the o2 sensor. I would buy one of those cheapo Air fuel ratio meters and hook it up. if the o2 sensor is working, and so are the associates switches. (full throttle switch on throttle linkage is not stuck closed!) then, the fuel mixutre should be full rich and full lean 8-10times every 10 seconds. this averages out to 14-15:1 fuel to air and that is on the lean side. in order for you to smell fuel, one cylinder could not be firing and that would do it. (or the pressure is too high and the 02 sensor cant fight it , but thats unlikely) vacuum lines still attached to the fuel regulators????? they need to be hooked up to the head side of the throttle plate on the vacuum fittings on the throttle plate. reversing them with the vacuum advance makes the fuel regs put out full pressure all the time, and you get full advance at idle . probably not the case either.

MK

 

An O2 sensor seized in the CAT is a sign it should come out - and be tested, or replaced.
"Using a high impedence DC voltmeter, camp the sensor in a vice. Attach the negative lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. Remove from flame and you should see a drop to under 0.1 volt within 4 seconds. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age." ... a good summary paraphrased from a 'Google' search ....

You can find new single wire O2 sensors on ebay for ~$15 max ( Bosch or equivalent).

 

Thanks for all the help ! I am sorry for not getting back earlier with you all. I lost my water pump last week, and I have been on my back in the garage since then. Once I have the water pump installed, I will certainly investigate all of the options that have been posted. I feel confident now that I can find the correct solution. Thanks everyone !