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In Reply to: V12 warm up puzzle posted by Kevin on May 20, 2001 at 11:10:37:
More details on the warm up characteristics.
1. When the car first starts, it is certainly running on all 12 cylinders, but it drops back to the driver's side 6 withing about 2 - 3 seconds.
2. While the car is warming up, the passenger's side bank warms up VERY slowly. To give you some idea, I can still put my hand on the exhaust headers (at the O2 sensors) after 10 minutes of idling. Through this time, the car does start to run better... it's like the passenger's bank is slowly, slowly coming to life. Once they do, the car runs fine.
Based on these findings, I'm focusing on things that would cause the DME to shut down a bank of cylinders. I'm not certain of this, but I'm guessing that the inductive sensor on the spark plug wires may act as a go/no-go signal to the DME... that is to say... if there is no spark, don't send any fuel. Can anyone verify this? Has anyone ever had any problems with this sensor? I ohm'd out both sides and they read near dead shorts... very low impedence sensors, it seems. If I am right about the way that the DME uses this sensor's information, then even a bad plug wire or fouled plug could cause the kind of behavior I am seeing. Any youghts? Thanks.
Kevin
Hoping some of you more familiar with the warm up cycle of the V12 can figure this one out. It has me stumped!
Here are the symptoms.
1. During warm up, the engine idles very rough and produces no power (sluggish response, TRANS PROGRAM warning etc.) I get no codes at all if I just let the engine sit and warm up without driving.
2. Power, responsiveness etc. all get progressively better as engine warms up. After about 10 minutes of idling, I can turn the key off and on and the car will run perfectly until it cools down for 6 - 8 hours and then the whole cycle repeats itself. Without turning the key on and off (after warm up), even though the engine is running better than when it was cold, it is still not 'normal'... power is reduced and still runs a little rough.
This is what I have been able to verify:
1. Spark exists on both sides at all times the engine is running
2. When the engine is warming up only one fuel pump and ECU seems to be supporting the engine. I can pull the fuse or relay on one of them and the engine continues its rough warm up, but if I pull the other (with the first one in or out), the engine dies. Odd thing is that both sides of the engine seem to be experiencing combustion (I get burned fuel in the exhaust, which is warm on BOTH sides during the warm up process...doesn't this violate the design philosophy of having two independent, siamese systems??). Both fuel pumps are drawing 4.1 amps while operating.
3. After the engine has warmed up for the requisite 10 minutes and has been stopped and started (read, is now running normally...lots of power), either fuel pump relay (or fuse) causes the engine to go into 6 cylinder mode.
4. I can start and restart the engine repeatedly after this warm up sequence and it runs beautifully, however, it occassionally refuses to idle (RPM drop to zero) for no apparent reason (does not seem to be related to temp, operating time, driving style etc). Engine can be kept running by keeping foot on throttle. After being driven for 2 or three minutes operation returns to normal.
What I've replaced so far while trying to diagnose:
1. Engine Coolant Temperature senors (both)
2. Fuel filters
3. Have disconnected the power to the ECUs and reconnected
4. O2 sensors are about 20K miles old
5. Have verified vacuum manifold is about 17" of mercury at idle on both sides.
6. Distributor caps and rotors have 2K on them
7. Car has 120K miles on it
Any ideas?
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