Low Power When Cold
03-08-2017, 08:19 PM
#1
Low Power When Cold
This problem started a couple of months ago and was first noticed when the car stalled when cold and did not want to restart. I had posted this as a non-start issue and followed the advice given (replaced the FP, LH, EZK and X-bus relays, checked fuel pressure and the various signals at the computers, did not like the tempII values and replaced the sensor - the old one fell apart on removal - and noted that the cam Hall sensor seems to be dead - a problem for another day - but the rest seemed all right).
The current problem, and I think the original problem, is as follows: (note that this only occurs on the first start in the cool California mornings...) the engine starts fine and idles well ; if the clutch is immediately engaged, the car reacts normally with smooth power, but after a few seconds it acts as if it had a carburettor with a failed automatic choke - it will still idle fine and smoothly accelerate with no load, but wants to stall with any load (if it does stall, it does not want to restart - the reason for the earlier post...); it is drivable with revving the engine and slipping the clutch to start moving; and everything seems fine after normal operating temperature is reached with no recurrence during the day even after not running for hours. Additionally, and only during the warm up driving, there are occasional sudden momentary losses of power.
As always, any suggestions are much appreciated.
Bob
The current problem, and I think the original problem, is as follows: (note that this only occurs on the first start in the cool California mornings...) the engine starts fine and idles well ; if the clutch is immediately engaged, the car reacts normally with smooth power, but after a few seconds it acts as if it had a carburettor with a failed automatic choke - it will still idle fine and smoothly accelerate with no load, but wants to stall with any load (if it does stall, it does not want to restart - the reason for the earlier post...); it is drivable with revving the engine and slipping the clutch to start moving; and everything seems fine after normal operating temperature is reached with no recurrence during the day even after not running for hours. Additionally, and only during the warm up driving, there are occasional sudden momentary losses of power.
As always, any suggestions are much appreciated.
Bob
03-09-2017, 02:30 AM
#3
Rennlist Member
Bob,
It sounds as though your system is basically functioning OK but there is an intermittent issue during the warm up period when additional enrichment is required and something is disrupting this process. Given temp2 is new and functioning correctly [have you checked the current resistance values?] my suspicion would initially be to investigate the wiring/contacts.
In your case the first place I would look would be at the MAF connector. The loom passes through a swan neck and into the connector. This area is infamous for degradation issues. I revamped mine but the best approach is probably a new connector and splice new tail wires to the existing loom further back. This presumes that at that point the wiring is in reasonable nick.
Problems elsewhere cannot be ruled out but investigate the more likely suspects first. Whether or not the MAF might cause your symptoms remains to be seen- swapping in a known good one for test is the more obvious way to eliminate that possibility.
Rgds
Fred
It sounds as though your system is basically functioning OK but there is an intermittent issue during the warm up period when additional enrichment is required and something is disrupting this process. Given temp2 is new and functioning correctly [have you checked the current resistance values?] my suspicion would initially be to investigate the wiring/contacts.
In your case the first place I would look would be at the MAF connector. The loom passes through a swan neck and into the connector. This area is infamous for degradation issues. I revamped mine but the best approach is probably a new connector and splice new tail wires to the existing loom further back. This presumes that at that point the wiring is in reasonable nick.
Problems elsewhere cannot be ruled out but investigate the more likely suspects first. Whether or not the MAF might cause your symptoms remains to be seen- swapping in a known good one for test is the more obvious way to eliminate that possibility.
Rgds
Fred
03-09-2017, 07:04 AM
#4
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History of mass-air sensor.
Have you verified correct resistance of new Temp-II at ECU pins?
History of Speed Sensor (aka Crank Position) Sensor?
Have you verified correct resistance of new Temp-II at ECU pins?
History of Speed Sensor (aka Crank Position) Sensor?
03-09-2017, 12:58 PM
#5
Thanks for the replies.
MAF - Unverified as long as I have had the car. The wires looked good and were flexible last year when MAF was removed to reset throttle cable. I will inspect them again in the next few days.
Temp-II - Resistance values of new sensor good at ECU.
CPS - Unchanged by me, but I believe was new ~7 (?) years ago. I did not monitor this signal....
I will be unable to monitor Rennlist for the next day or so, but I will see if I can come up with a MAF to borrow for next week (can't work on it before then...). Any chance these are symptoms of a failing LH?
Bob
MAF - Unverified as long as I have had the car. The wires looked good and were flexible last year when MAF was removed to reset throttle cable. I will inspect them again in the next few days.
Temp-II - Resistance values of new sensor good at ECU.
CPS - Unchanged by me, but I believe was new ~7 (?) years ago. I did not monitor this signal....
I will be unable to monitor Rennlist for the next day or so, but I will see if I can come up with a MAF to borrow for next week (can't work on it before then...). Any chance these are symptoms of a failing LH?
Bob
03-09-2017, 04:19 PM
#6
Rennlist Member
LH failure follows some general symptoms but failure can manifest itself in some relatively atypical ways. John Speake is doubtless the best person to comment in this regard.
As a matter of interest, is your 928 the one that has a lot of miles on the clock but much less on the Devek motor? Sounds similar spec to one I was offered about 12 years ago.
Rgds
Fred
As a matter of interest, is your 928 the one that has a lot of miles on the clock but much less on the Devek motor? Sounds similar spec to one I was offered about 12 years ago.
Rgds
Fred
03-18-2017, 01:50 PM
#7
The problem was a bad MAF.
Bill Ball graciously helped again: he brought spare ECU's and a MAF and isolated the problem to the old MAF, and testing on consecutive cool mornings confirmed that mine was bad. It will be taking a trip to Louie Ott in the near future.
Many thanks again for the helpful replies, and of course to Bill Ball.
Fred R. - It might be the same car: low miles on the engine, etc.,
Bob
Bill Ball graciously helped again: he brought spare ECU's and a MAF and isolated the problem to the old MAF, and testing on consecutive cool mornings confirmed that mine was bad. It will be taking a trip to Louie Ott in the near future.
Many thanks again for the helpful replies, and of course to Bill Ball.
Fred R. - It might be the same car: low miles on the engine, etc.,
Bob