c didy

EDIT:

As this evolves this thread is focusing on topics including Scantool code interpretation, cylinder head temperature sensors, throttle switches including WOT, air/vacuum leaks, and AFM AirFlowMeter evaluations. Any knowledge of these systems is appreciated.


Hi Guys,

The car runs great, and always has, but it smells rich and measures high with an exhaust sniffer.

My only error code is: 23=Oxygen regulation at stop (intake air leak?). I have cleared the code and will check it again but there is no question that I am running rich.

What are the most likely culprits?

Steve Weiner-Rennsport Systems

The first place I'd look is the cylinder head temp sensor and associated wiring/connector.

After that, I'd check out the throttle switches.

Then, look for a vacuum leak in the intake system that the O2 sensor may be trying to compensate for.

I'm assuming that everything in and on the engine is in top shape and a tuneup has been recently performed,...

c didy

Thanks Steve. That's my '72 down by the train tracks in Lake Oswego in my avatar photo from back in the day.


Well, interesting that you would point at the Cylinder Heat Temp sensor as someone else thought that. If the CHT is bad it seems like you would have problems not running rich enough when not warmed up. Shouldn't I have problems with cold starts/idle? It starts fine cold, always has. Yesterday it was chilly, less than 10F and it started fine each time.

Steve Weiner-Rennsport Systems

Neat car,...

Generally speaking, when cylinder head temp sensors fail, their resistance doesn't change with temperature as its supposed to and the car continues to run on a cold starting/running fuel mixture.

Thats one reason for the rich (and stinky) running. This really jacks up cat temps and accelerates failure so this should not be ignored at all. Further, the excess fuel washes the cylinder walls and accelerates ring wear.

You can measure the sensor's resistance from cold to hot to check its functionality. The values are in the little Bentley 964 Technical Data book.

Lorenfb

"You can measure the sensor's resistance from cold to hot to check its functionality."

Or you can simply jumper the CHT connector with a paper clip for testing.

Also, the rich running condition can result from:
1. high fuel pressure
2. a shorted O2 sensor wire
3. a bad O2 sensor
4. a mis-adjusted AFM
5. electrical noise entering the DME ECM harness from the spark plug connectors/wires.

c didy

Interesting. Stinky is right. And I don't need any more cylinder wear than I've already got for Pete's sake. Nor do I need any fuel contaminating/diluting my oil. I'm looking forward to a solution.

I ran the Scantool again today and this time it threw a "14 error, Engine temp sensor." Oooh, that would be nice if it was that simple. I'll have to move that up on my list of suspects.

c didy

I have cleaned the O2 sensor contacts and re-connected, (kind of a bear because the car-side cable has a very short tail, very difficult for me to do one handed, so the second time I did it I removed the heater blower for better access, allows 2 hands), then replaced the O2 sensor with a new one not knowing the history of the previous one. Since that was not a cure I have a spare O2 sensor now.

I also purchased the Scantool interface from Tore, (and have it partially running), to help direct further repairs and avoid unnecessary replacement of functioning components.

As for the paper-clip jumper idea, that's very interesting. I really like that you are suggesting both sophisticated and simple strategies for diagnosis. There are so many ways to make things more complicated than they have to be.

Thanks to both of you I am understanding more about CHT sensors.

c didy

More info for those who follow:


"Do CHT sensors usually fail high or low resistance and therefore give hot or cold start problems -- or can they go either way" - Marc Shaw -

"Temp sensors usually fail in the open condition." -Lorenfb-"

In other words:

CHT failures can result in poor cold starts, if they short, (closed failure)
or
CHT failure (open) can result in running rich, possible difficult hot starts, and more concerning very hot cat temps, cylinder washing and oil dilution, in which case jumping the connector after the engine is warm should correct the rich condition.


What I have not seen yet is an accurate description of the actual removal/replacement of the CHT sensor. It has been alluded to however, and there are vague warnings about the difficulty of doing so despite it's apparent simplicity.

Remove wheel.
Remove blower.


Then, things get a bit foggy:
Remove grommet.
Remove CHT. (Cut wires to allow a deep socket?)
Install CHT. (Slotted 14mm deep socket or some start the threads with needle nose pliers?)


Reconnect.
Replace blower.
Replace rear wheel.
Drive.

How is it done? Why is the difficulty underestimated?

Lorenfb

"What I have not seen yet is an accurate description of the actual removal/replacement of the CHT sensor."

Why waste time considering that when the CHT may not be the problem?

c didy

Good question. I have learned more but didn't post.

Here is my scan after a drive Tuesday.

c didy

My actual value for CHT during driving was a max of 117 degrees. It is my understanding that they should go to 240+ so it appears that we are not getting there.

Engine on the idle switch is activated at idle.
Engine off the WOT is activated with the throttle floored.

Would it make sense that AFM mal-adjustment would seem less likely at this point?

Would it still make sense to perform the jumper test for the CHT?

Lorenfb

"My actual value for CHT during driving was a max of 117 degrees. It is my understanding that they should go to 240+ so it appears that we are not getting there."

Not really! The 117 is degrees C. That's about 243 degrees F, and that should be hot effort, right?

c didy

Good point! And true enough.


After further searching I am finding that 115C / 244F are the highest readings I have seen. Here is a link that Loren was involved in on RL.
https://rennlist.com/forums/964-foru...-thread-5.html


Does this imply that the CHT error code is false?

c didy

Well, let's see what the scantool can tell me.

Here are my actual values. What does AFM indicate and what should the range be? If it is an air fuel mixture does it confirm a rich condition?

ALEX P

Sorry I can't help with your question but when mine was running really rich it turned out to be the AFM. The (barn door) flapper was just sticking slightly and not quite snapping closed.

May be worth a quick check as it's easy to remove and would be a nice easy fix.

Good luck.