nwehtje944

I finally got my car mostly running, but I still have one problem. the car runs very poorly when its cold, I think its running lean. As soon as the engine is warmed up its runs great. I thinking that the temperature sensor that is for the DME has gone bad, or a wiring issue with that sensor.

Which of the two temperature sensors is for the DME; A or B.


question 2; in second picture, I have the two temperature sensors. the top, smaller one, is from my new engine. the lower, larger one, is from my old 86 engine. the wiring is different from the older and newer sensor, is there a way I can wire the old sensor to work with the newer wiring.

thanks,

944Play

The blue plug (A) is the DME Temp II sensor.

The newer gauge sender (lower) has a terminal for the idiot light (closes at 125C) in addition to the gauge terminal. HTH....

Perry 951

There is also an inlet air temp sensor in the AFM, but they rarely go bad. A bad coolant temp sensor can cause cold start issues, so I would replace to be sure.

Ski

Isn't the arrow pointing to A being the NTCII/DME sensor? The blue one with the electrical connection.

If you pull the retainer clip and just barely break the connection, you should hear the air meter jolt closed and the car will almost die. If this happens the sensor is good.

944Play

[quote]Originally posted by Ski:
<strong>Isn't the arrow pointing to A being the NTCII/DME sensor?</strong><hr></blockquote>

Woops! Just assumed that the lower one would have been the later one labeled, I guess. Edited.

Granite 944

I too may have an issue with the temp sensors above in the lower picture. The small sensor: draws its temp source from a dead headed hole in the block(block temp). The larger,(2 prong sensor): draws its temp source from inside block, from the water around the cylinders. My question is......does this make a difference at the gauge? Calibration issue? And then in the above example, assuming he has a 2 prong wire connector going to this sensor location, if sensors are interchangable, than all he needs to do is determine which prong of the two goes to the gauge,use this connector, and forego having an idiot light?
I'm very interested, as I have an earlier block going to the machine shop for rebuild, and will have the unused boss in the block drilled and tapped out to accomodate the newer style sensor if above really could be an issue. Thanks!

Danno

The two coolant-temp sensors are not interchangeable. The one shone as A is a NTC-negative temperature coefficient sensor that decreases in resistance as temperature rises. That is the one used by the DME computer.


The other sensor B further back on the head has the opposite response curve; it increases in resistance as temps rise. This one is used for the gauge on the dash.

Also in that second photo above, stick with the larger sensor. Don't know where that smaller one came from, but I think it's the actual 'older' style sensor.

nwehtje944

thanks for all the replies. so sensor (A) is the temp sensor for the DME. I'll try and see if I can figure out if this sensor is good or not tomorrow.

from what I tell the (B) sensor is for the gauges, and nothing else, correct?. after doing some testing I figured out that the wire that is nearest to the sensor is for the analog gauge, where as the wire that is further away is for the "idiot light." so basiclly I won't have "idiot light," which is fine by me.

Granite 944; I tend to think your correct that the different length of the sensor does play a importent role in their measurement of the temperature, or that the sensors measure differently. by the temp gauge, my car is running much hotter than it used too, even with a new water pump, etc, etc. there should still could be some air in the system, but my current line of thought is that the 'calibration' isn't correct for the older sensor. furthermore I no idea how I'm going to fix this. hmmmm. <img src="graemlins/c.gif" border="0" alt="[ouch]" />

if the temperature sensor isn't my problem, what else could cause my poor idle when the engine is cold.

SpeedyGonzalez

Just wanted to ask one question ...

If the wire for the wider prong is for the idiot light and the one with the narrower prong is for the temp gauge - are they measuring the same thing?

This might sound stupid but in traffic my idiot light comes on but the gauge needle remains near the first mark. On the highway, the light tends to go off after I've been going for a while.

This is not a loose wire issue since I just crimped the connectors installed them properly ...

Am I missing something here?

Thanks
Jawad


I have a question

nwehtje944

?!? <img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/c.gif" border="0" alt="[ouch]" /> ok you got me. other than bad sensor or a wiring short somewhere I don't know.

944Play

[quote]Originally posted by SpeedyGonzalez:
<strong>If the wire for the wider prong is for the idiot light and the one with the narrower prong is for the temp gauge - are they measuring the same thing?
</strong><hr></blockquote>

No. If you connect them backwards, your gauge will not register and the temp idiot light (and (!)) will glow dimly.

The idiot light is supposed to come on at 125 degrees C. Sounds like yours is closing at around 90, so it's probably a good idea to test this out in a pan of boiling water.

Granite 944

Nathan, I dropped off my engine blocks at machine shop yesterday, and went over to talk to a Porsche mechanic in a nearby shop. In regards to the the two different styles of temp sensors (not the DME sensor), the mech. said he has experienced the "problem of the gauge reading higher when using the '83 block in a latter model car, yes they are different reading sensors. He says he has corrected the problem by drilling the sensor hole open bigger for the new style sensor when old block in newer car, and has had a brass bushing made when a newer style engine is placed in an older ('83/'84?) car. He was rather busy , so I could'nt get into more detail with him. thought ya might like to know!

M758

OK I just did my engine rebuild so I know all about these temp sensors.

Firstly the large blue connector and sensor is basicly the same in all NA's. In my race car I am using an 84 block with 87 DME. It plugs in and runs fine.

The second plug is different between the early cars and the late cars. The early cars like my 84 block have a short round connector. The later cars have large plug with a single spade connector. Now as I am using the 87 DME harness in the car I have simply plugged it in to the early plug. Seems to work fine. Now the early and late plugs are NOT interchangeble. There is different size holes in the block.

nwehtje944

most helpful, thanks.

SpeedyGonzalez

Hey thanks for the help guys ...

One more question though:

The light IS coming on much sooner than it should so does that mean a new sensor or can recalibrate it somehow?

Thanks