performance issue with Carrera
06-01-2010, 12:17 AM
#46
I haddah Google dat
Rennlist Member
Rennlist Member
Ice, the CHT plug harness is the topmost of the three on the left hand side of the engine.
The O2 sensor has two connectors. One is the heating circuit, and it has two wires. The sensor wire harness is cylindrical, and should be a green wire.
The O2 sensor has two connectors. One is the heating circuit, and it has two wires. The sensor wire harness is cylindrical, and should be a green wire.
Last edited by rusnak; 06-01-2010 at 12:38 AM.
06-01-2010, 12:20 AM
#47
Team Owner
Thread Starter
yeah Russ I have the actual O2 sensor so figured I was looking for a round one . but i just can't find it .. this is a 3.2 put into a 78sc that never had o2 .. could it be that it dosn't even need to be connected ?
I found the CHT ensor thanks, checked out okay but it is a the old style single wire.
I found the CHT ensor thanks, checked out okay but it is a the old style single wire.
06-01-2010, 12:47 AM
#48
I haddah Google dat
Rennlist Member
Rennlist Member
If the O2 sensor is not plugged in, and the harness is receiving no votage from the O2 sensor, then the system will continue to operate in "limp home" mode, adjusting fuel and timing according to a pre-loaded map, taking temp and throttle pos inputs from various sensors, but not keeping the system at ideal fuel air. It will tend to run rich. If the O2 sensor is plugged in, but the O2 sensor itself is not installed in the exhaust header, or is improperly installed so that the sensor is sampling ambient air, then the car would be damn near undrivable.
WB is right....you can NOT run an SC fuel pump in a 3.2 911. The fuel pressure is roughly twice as high in the SC than the 3.2.
My own recommendation is to make sure all the sensors are good, and before plugging in the O2 sensor, connect up an LM-1, and adjust base mixture at idle to 14.4. Lambda is 14.7 to 1.
The reason to use a heated sensor is that they last roughly twice as long as unheated ones (100,000 miles or so).
It could be that a huge vacuum leak is causing the problem.
The fact that the engine dies when it's hot suggest to me that the O2 sensor needs to be properly installed.
WB is right....you can NOT run an SC fuel pump in a 3.2 911. The fuel pressure is roughly twice as high in the SC than the 3.2.
My own recommendation is to make sure all the sensors are good, and before plugging in the O2 sensor, connect up an LM-1, and adjust base mixture at idle to 14.4. Lambda is 14.7 to 1.
The reason to use a heated sensor is that they last roughly twice as long as unheated ones (100,000 miles or so).
It could be that a huge vacuum leak is causing the problem.
The fact that the engine dies when it's hot suggest to me that the O2 sensor needs to be properly installed.
06-01-2010, 12:02 PM
#49
"then the system will continue to operate in "limp home" mode,"
Actually then is no 'limp-home' mode in the 3.2 DME ECM.
A 'limp-home' mode denotes that the ECM makes a correction for a system
failure to allow continued driving to a repair facility. The 3.2 ECM just runs
open-loop and NOT necessarily in the rich condition, i.e. It runs at a set
AFR.
"The reason to use a heated sensor is that they last roughly twice as long as unheated ones (100,000 miles or so)."
Actually the reason for a heated O2 sensor is for better overall O2 operation
over a wide range of engine temps, i.e. better AFR control for colder temps.
"The fact that the engine dies when it's hot suggest to me that the O2 sensor needs to be properly installed."
A bad O2 sensor rarely if ever can cause the engine to die, i.e. It would have to short
to ground (very rare) and that would just cause a rich mixture but not cause the engine
to die.
"Tonight he took it out again and once it warmed uo it died ,, so I went over with my meter and checked the cht sensor ."
Since it's been indicated that the engine has a single wire temp sensor, this
could be indicative of your problem. That type of sensor tends to be intermittent
at its mechanical connection which provides the ground. A simple test to eliminate
the sensor is to jumper the white connector once the engine warms-up,
e.g. use a paper clip.
Actually then is no 'limp-home' mode in the 3.2 DME ECM.
A 'limp-home' mode denotes that the ECM makes a correction for a system
failure to allow continued driving to a repair facility. The 3.2 ECM just runs
open-loop and NOT necessarily in the rich condition, i.e. It runs at a set
AFR.
"The reason to use a heated sensor is that they last roughly twice as long as unheated ones (100,000 miles or so)."
Actually the reason for a heated O2 sensor is for better overall O2 operation
over a wide range of engine temps, i.e. better AFR control for colder temps.
"The fact that the engine dies when it's hot suggest to me that the O2 sensor needs to be properly installed."
A bad O2 sensor rarely if ever can cause the engine to die, i.e. It would have to short
to ground (very rare) and that would just cause a rich mixture but not cause the engine
to die.
"Tonight he took it out again and once it warmed uo it died ,, so I went over with my meter and checked the cht sensor ."
Since it's been indicated that the engine has a single wire temp sensor, this
could be indicative of your problem. That type of sensor tends to be intermittent
at its mechanical connection which provides the ground. A simple test to eliminate
the sensor is to jumper the white connector once the engine warms-up,
e.g. use a paper clip.
06-01-2010, 02:58 PM
#50
I haddah Google dat
Rennlist Member
Rennlist Member
[QUOTE=Lorenfb;7619060
A bad O2 sensor rarely if ever can cause the engine to die, i.e. It would have to short
to ground (very rare) and that would just cause a rich mixture but not cause the engine
to die.
[/QUOTE]
Loren, I appreciate your responding to my post, but I didn't say it was a bad sensor. Think about it a second longer. If the O2 sensor is plugged into the harness, and is not installed or is bad, it is sending incorrect voltage signals to the dme, which would throw it off.
I don't care to get into semantics about running in constant open loop vs limp home mode. I think you relish this type of pointless debate, but I'll just ignore your point.
You're saying a faulty CHT would cause the engine to die? And not fire back up?
It seems to me a likely combination of more than one problem is at work here, including the fact that the motor is running in open loop, has a (possible) intermittant signal from the CHT sensor due to faulty ground, and possibly incorectly adjusted base CO%, all of which needs to be checked.
Don't veer the OP off base with your comments, he needs to focus on step by step diagnosis.
A bad O2 sensor rarely if ever can cause the engine to die, i.e. It would have to short
to ground (very rare) and that would just cause a rich mixture but not cause the engine
to die.
[/QUOTE]
Loren, I appreciate your responding to my post, but I didn't say it was a bad sensor. Think about it a second longer. If the O2 sensor is plugged into the harness, and is not installed or is bad, it is sending incorrect voltage signals to the dme, which would throw it off.
I don't care to get into semantics about running in constant open loop vs limp home mode. I think you relish this type of pointless debate, but I'll just ignore your point.
You're saying a faulty CHT would cause the engine to die? And not fire back up?
It seems to me a likely combination of more than one problem is at work here, including the fact that the motor is running in open loop, has a (possible) intermittant signal from the CHT sensor due to faulty ground, and possibly incorectly adjusted base CO%, all of which needs to be checked.
Don't veer the OP off base with your comments, he needs to focus on step by step diagnosis.
06-01-2010, 03:32 PM
#51
Race Car
Looks like a benz you have there Rusnak LOL. I think you are right though, This may be a snake-headed medusa, multiple problems. The only way to proceed is to identify one at a time.
I have to wonder what wiring harness was used in the conversion. I know it sounds simple that a Carrera harness had to be used, but Proper power and ground points are up in the air. No reason to think this is a problem, just an observation that could be pertinant down the road.
I am more concerned however with the varied ohm readings of the CPS. That could be a problem. The O2 sensor should not cause these symptoms. I would consider that secondary to the main issue.
CPS can have strange failure modes which are heat sensitive, but I am used to checking them with a graphing scope that will show their analog swing in detail - ohms may be misleading. Have you ohmed the referance sensor? ohms should be similar(the two plugs are the same and should be right there next to one another. Changing these senders may require at least a partial engine drop because they are a pain to reach.
I have to wonder what wiring harness was used in the conversion. I know it sounds simple that a Carrera harness had to be used, but Proper power and ground points are up in the air. No reason to think this is a problem, just an observation that could be pertinant down the road.
I am more concerned however with the varied ohm readings of the CPS. That could be a problem. The O2 sensor should not cause these symptoms. I would consider that secondary to the main issue.
CPS can have strange failure modes which are heat sensitive, but I am used to checking them with a graphing scope that will show their analog swing in detail - ohms may be misleading. Have you ohmed the referance sensor? ohms should be similar(the two plugs are the same and should be right there next to one another. Changing these senders may require at least a partial engine drop because they are a pain to reach.
06-01-2010, 05:27 PM
#53
Race Car
Man what utter confusion I have. I am sorry for the mistake on my part. Ice had talked about the CHT(Head temp), and for some oddball reason I took that to mean CPS(crank Position sensor).
rusnak you are dead-nuts on, and thank you for posting the DME test values for my edification. I guess my post made no since at all - and it started with a weak joke.
Please don't send me to the 944 forum,please PLEASE, not the 44 forum.
rusnak you are dead-nuts on, and thank you for posting the DME test values for my edification. I guess my post made no since at all - and it started with a weak joke.
Please don't send me to the 944 forum,please PLEASE, not the 44 forum.
06-01-2010, 05:30 PM
#54
I haddah Google dat
Rennlist Member
Rennlist Member
NO WB....I de-coded your post and knew you meant CHT. It seems you and Loren probably agree, so I thought I'd post my notes that happen to be written in a book. I don't know the title........
06-01-2010, 05:32 PM
#55
Team Owner
Thread Starter
Again some great info guys .
This would explain why the car is actually running with no O2 sensor - doubt it was ever connected with the 3,2 upgrade . Although not ideal it will in fact run this way and i should leave this issue till later. The connector I had was a more modern O2 sensor with the the heater wires ( white) and the black wires sensor all in one connector just lying there.
That is some great info Loren thanks. As it is a a single wire system i will jumper the single wire to ground with an aligator this should represent total short or fully warmed up.
Thanks for the pics Russ . i can't get perspective on those shots of where the O2 connectors are as they are too close .
So i will look again.
Today he will hopefully have that pipe fixed and we may be one steop closer.
This would explain why the car is actually running with no O2 sensor - doubt it was ever connected with the 3,2 upgrade . Although not ideal it will in fact run this way and i should leave this issue till later. The connector I had was a more modern O2 sensor with the the heater wires ( white) and the black wires sensor all in one connector just lying there.
That is some great info Loren thanks. As it is a a single wire system i will jumper the single wire to ground with an aligator this should represent total short or fully warmed up.
Thanks for the pics Russ . i can't get perspective on those shots of where the O2 connectors are as they are too close .
So i will look again.
Today he will hopefully have that pipe fixed and we may be one steop closer.
06-01-2010, 05:33 PM
#56
I haddah Google dat
Rennlist Member
Rennlist Member
Ice, that area is under the fuel filter, on the left hand side of the engine. The single wire cht grounds inside the head, which is what Loren is referring to (mechanical connection). I agree with a jumper wire. A good reliable ground is the engine mounting bolt. A paper clip might only reach the intake plenum.
fix the pipe and jumper the sensor ..
06-01-2010, 05:56 PM
#58
Race Car
I think Loren is hung on the O2 sensor - of which I agree more with you - not a direct issue causing the motor to die. to eliminate or confirm a faulty temp sensor is an easy test.
06-01-2010, 06:02 PM
#59
Team Owner
Thread Starter
Man what utter confusion I have. I am sorry for the mistake on my part. Ice had talked about the CHT(Head temp), and for some oddball reason I took that to mean CPS(crank Position sensor).
rusnak you are dead-nuts on, and thank you for posting the DME test values for my edification. I guess my post made no since at all - and it started with a weak joke.
Please don't send me to the 944 forum,please PLEASE, not the 44 forum.
rusnak you are dead-nuts on, and thank you for posting the DME test values for my edification. I guess my post made no since at all - and it started with a weak joke.
Please don't send me to the 944 forum,please PLEASE, not the 44 forum.
voted off Advice island ..
..no advice for you ..... ! YEAR !!!!
