My 82 928 has a no start problem...

I traced the problem to either the Temp II Sensor or the AFM....I did this by running a hose through the AFM and sure enough I got a start...YES...however..

I noticed the PO has monkeyed with Temp II Sensor before and I noticed that the cap to the sensor was severly cracked.

I unwrapped the black electical tape and this is what I found....


I have ordered a replacment cap and sensor...what do I about that resistor...?

 

The resistor is not supposed to be there. It has been added to make the ecu think that it is colder than it is, and force it to run richer. They may have done this because there is another problem causing it to run lean.

 

Someone may have also added the resistor because the "acceptable" range of sensors is so wide, a sensor that tests out good may be on the lean or rich side.

I played with about a dozen Temp II sensors on my 81 (tested in boiling water, cold water, ambient etc...) and going from the highest resistance sensors versus the lowest made a noticeable difference in air / fuel and all of them were well within the range listed in the Work Shop Manual.

It became accepted practice by the dealers back in the day to add a resistor because the cars were far pickier than the sensors were.
Talking to a 928 tech a while ago, he said they often couldn't find a temp sensor "rich enough" after ordering a batch so they just add a resistor......problem solved. And yes, he worked at a dealership.

There is also the CO adjuster on the AFM, but that doesn't make nearly as big of a difference as a temp II sensor that's at the extreme end of the spectrum.

I'm not saying this is your problem, just pointing out that a resistor on the Temp II sensor could be there for other reasons.
Test the sensor with a meter and see where it is

 

I posted the samequestion Wednesday about my 83. Except there was also a Klixon thermo disc wired in for good measure. I found it laying on the passenger side head. I replaced the the sensor right after I got the car 4 years ago. After removing the resistor/thermo didsc I have a rough running problem, but that may be due to somethingelse. Car acts like it running on 7 cylinders, but haven't taken the time to run it down.

 

Here's what I found

 

Wow, guys thanks alot, ... going to leave it in place. The car will fire up once I unplug the Temp II sesnor and when I plug it back in and seated properly, I get a no start.

I should get the cap and sensor today from Roger (928srus)...will post if that solves the problem...

 

Wait a minute.....the runs with the Temp II unplugged???

My L-Jet is a bit rusty, but I remember my car wold not run with the Temp II unplugged and if I pulled it while the car was running it would die.

 

If you unplug t2, the car should die

 

+1

 

Maybe we should back up a bit. The L-jet has three temperature sensors in the coolant bridge that are rather close to each other.

The temp II the one on top, standing vertical with a standard, Bosch / Tyco fuel injector style plug on it. Usually the connector is blue. If this is disconnected the car should not run, at all.

The temp sensor next to it feeds the gauge in the dash, has two wires on top with spade terminals, no plastic connector

The temp sensor sticking out the front of the coolant bridge laying horizontally, with a brown? connector is the temp time switch used during cranking only to trigger the cold start injector.

 

My '81 had a similar unseen resistor which I found by breaking it accidentally, which caused a no-start.

 

Take a look...your thoughts. Mind you I could not get my 928 to fire. Now that stumbled across this Temp II Sensor subject, now it will start...

 

this is odd.....when the temp II reads infinte resistance it goes STUPID rich....for example when the sensor was bad in my 84 it WOULD run with a little wire jumping it to near zero resistance....the second you pulled the wire it would go silly fat and die.....

 

All of this suggests that there is a problem with something else, and the resistor was added to compensate for the other problem. Much better to find the other problem and fix it.

I have no experience of L, just K and LH, and from K I know that the mixture adjustment according to temperature varies in the warm-up range, but once the engine is warm (above 65 C), the mixture is not adjusted any more when it goes from warm to hot. This suggests that mixture adjustment is not desirable at these temperatures, and that to fool the ecu into richening the mixture, we have to fool it that the temperature is down in the warm-up range. What this will mean is that the slight variations in temperature as driving conditions change will be constantly causing mixture changes when it is not desirable.

 

Anyone reading this please offer some suggestions...

We know the car will fire up....
The 928 will start up two different ways..
1) Running a hose down the AFM keeps the flap open and car starts (The Temp II is connected)
2) With the hose removed from the AFM, the car starts but with the Temp II Sensor disconnected...

We know it only fires up when the Cap to the Temp II Sesnor is removed...
We know the cap to the sensor is severly cracked...
We know a resistor was added to compenstate for other related issues...
We know the car was running fine without any issues before...

What will I do tomorrow...
I will replace the sensor and cap....should arrive tomorrow at noon but I have to work so I wont get to it until after 5