onionpatchkid

I bought a 1979 Porsche 928 US 5-speed 3 years ago and it's been a great car. It has 98K on it. A few weeks ago a strange problem showed up and I'm grabbing at straws to fix it. After the 1st 5 minutes or so and when the temp gauge gets over 1/4 or so, the cars starts to spit and sputter and bogs down and loses power. It doesn't sound like it's backfiring but sounds close to it. If I push in the clutch and rev it up to 3500-4000 RPM's, it spits and sputters too. When I stop, I can smell rich fuel from the exhaust. It seems to be getting plenty of fuel but it feels like it's not burning it correctly.

The voltage gauge shows just above 10 volts and when I rev it, it moves up slightly. The alternator was replaced right after I bought the car 3 years ago. I do have a small valve cover leak that drips oil onto the alternator. I've had to clean the connections before but I did it less than 500 miles ago. I used a Fluke digital volt meter and the volt meter gauge isn't reading quite accurate. Voltage at the battery and hot post when not running is 12-13 and when the car is running, it reads 14 volts. The air filter is a 3 year old K&N.

Before the problem started, I was driving on a hot day and the temperature gauge got really high. I had to turn off the a/c, roll down the windows, and crank the heater to get the temperature to go down and make it home. No idea if this is related or not but it was not bogging down on that trip.

I've changed all the spark plugs (they looked bad), rotor and distributor cap. It didn't fix it. I have a new voltage regulator and fuel filter but haven't replaced them yet. I've heard it could be the Temp2 sensor, WUR, vacuum leak, green wire issue, voltage regulator, air/fuel mixture issue. Does anyone have any advice on what to check next?

I'd like to rule out the easy things 1st. I don't mind replacing parts that are good unless it's a huge expense. I'll keep the car forever anyways. I've always had a good mechanic but I moved and no one will touch it here except a place 5 hours away. I don't mind trying to wrench on it myself and learn about it. I'm no mechanic though. Any thoughts???

Guy

Sounds like you may have a little blockage somewhere in the CIS system. This would increase your pressure in the WUR which effectively throws your mixture too lean as your engine warms up. Granted, there's a lot more troubleshooting to do but it sure shoulds like it.

onionpatchkid

That doesn't sound easy to fix. What should I rule out next?

Guy

If you have access to cis gauges, break them out and check your pressures cold and as the car warms up. 928CLASSICS.com has some good information on it.

Or, simply remove your fuel line from the WUR and check that screen. That would be a quick down and dirty way to see if it could be an issue.

onionpatchkid

Is this the WUR? Which hose has the screen? Is it a black rubber hose or the hard line steel ones?

Petza914

The hard steel one. Could also be the Auxiliary Air valve not closing as tge car warms up making it lean. What did the plugs look like - got pics?

Both the connectors to the WUR and the AAV should get 12v all the time when the key is in the run position. Check that too.

onionpatchkid

Unfortunately, I don't remember which one came from which cylinder. I didn't place them on the cardboard in order.

Petza914

Those actually don't look terrible. They do look like you might be lean though and not rich. Check the AAV function and also the timing. Lean combined with timing advance is not a good combination.

onionpatchkid

Where's the AAV? Do you have a link to the 928 Workshop Manual for the earlier version engines? I'm missing that one.

Petza914

It's the assembly just to the left of the WUR with larger diameter hoses going in and out of it. When the engine is cold, the Plat inside is slid to the left allowing more air to pass into the intake. As the 12v applied to it warm it up the plate inside slides to the right and closes.

Remove it, put it in the freezer so it opens. Then apply 12v to it and make sure the plate inside closes over the next few minutes. Make sure the plug that goes to it has 12v when the key is on.

onionpatchkid

Interesting. Does the 12V make it heat up?

Petza914

Yes, that's what makes it heat up and close. Engine warmth alone won't close it much without the electrical connection.

onionpatchkid

So you think the car is possibly getting too much air by the looks of my plugs and the symptoms? And possibly that door in the AAV is stuck open all the time allowing extra air to continue to enter even when the engine gets warm and doesn't need it right?

Petza914

I think that's one possibility though I don't think AAVs fail all that often. The WUR is a more likely culprit as is an issue in the fuel distributor.

onionpatchkid

The connector does have 13V to it when the car is running. I can't get one of the hose clamps loose to be able to pull AAV out. I put some PB Blaster on it. What if I plug up the air intake hose to the AAV and mocking like the AAV door is closed? Will it start? I could plug up the hose and then drive it to see if the car bogs down.