944 cuts off and hiccups
02-22-2011, 01:18 PM
#1
944 cuts off and hiccups
cutoff:
in cold weather, it starts ok. After I drive a few minutes it cuts off in neutral. takes a few starts to get going, a few miles down the road it cuts off again,
doesn't do this in warm weather or after having driven for a while
hiccup:
this first started in pittsburgh during a few cold days. I'd be driving on the highway and the car would lose power (almost as if a strong wind were pushing it back) and regain power. sometimes only once in a while, other times as frequent as every dozen seconds or so.
Took it to the dealer, they couldn't reproduce the problem after three days of trying . Been ok in the week since (warmer weather) but today (colder morning) even though it was fine starting up, after 20 minutes of smooth driving, it shut off in mid drive. It started back up ok and shut off at the next stop twice more, then it was fine for the rest of the drive.
The local (non-Porsche shop) opined that it was the idle control unit. A forum member thought it could be either the fuel pump or fuel pressure regulator, any other ideas?
in cold weather, it starts ok. After I drive a few minutes it cuts off in neutral. takes a few starts to get going, a few miles down the road it cuts off again,
doesn't do this in warm weather or after having driven for a while
hiccup:
this first started in pittsburgh during a few cold days. I'd be driving on the highway and the car would lose power (almost as if a strong wind were pushing it back) and regain power. sometimes only once in a while, other times as frequent as every dozen seconds or so.
Took it to the dealer, they couldn't reproduce the problem after three days of trying . Been ok in the week since (warmer weather) but today (colder morning) even though it was fine starting up, after 20 minutes of smooth driving, it shut off in mid drive. It started back up ok and shut off at the next stop twice more, then it was fine for the rest of the drive.
The local (non-Porsche shop) opined that it was the idle control unit. A forum member thought it could be either the fuel pump or fuel pressure regulator, any other ideas?
02-22-2011, 01:22 PM
#2
Nordschleife Master
Air flow meter, TPS, or DME coolant sensor.. but those are just shots in the dark, and this is a very dark room...
http://www.clarks-garage.com/shop-manual/elect-22.htm
http://www.clarks-garage.com/shop-manual/fuel-06.htm
http://www.clarks-garage.com/shop-ma...ure-index3.htm
http://www.clarks-garage.com/shop-manual/elect-22.htm
http://www.clarks-garage.com/shop-manual/fuel-06.htm
http://www.clarks-garage.com/shop-ma...ure-index3.htm
02-22-2011, 03:05 PM
#3
Three Wheelin'
Join Date: Jan 2010
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Sure sounds electrical to me. Crusty connectors, bad grounds, brittle cracked wire, loose wires, bare wires shorting? etc.
More details? Does it happen under load, or just crusing? certain speeds? after hitting bumps in the road? Have you done any work to the car immediately before this started occuring?..etc Hard starting and dying out while driving could also be a plugged fuel filter. What has your mech done or checked so far?
More details? Does it happen under load, or just crusing? certain speeds? after hitting bumps in the road? Have you done any work to the car immediately before this started occuring?..etc Hard starting and dying out while driving could also be a plugged fuel filter. What has your mech done or checked so far?
02-23-2011, 10:28 AM
#4
cutoff (or unable to start) when starting with key only (no gas): last running is the main factor (the longer it's been since it ran last the more likely to not start/cutoff). Outside temperature is a close second. On warm days this problem doesn't exist, the colder, the more likely this is to happen.
This may be a coincidence but light seems to be a factor as well. Parking on a cold street that gets bright sunshine in the morning is better than a warmer parking garage with no light.
starting: once it cuts off, attempting to start with just the key is an exercise in futility. at this point, the only way to get it/keep it started is to give gas along with the key, slowly decrease the rpms to 2000 and then even more slowly drop below 2000. on a really bad day it'll sputter and cutoff just under 2000 rpms. it's never cutoff at >=2000 rpms which idling or driving.
driving: within the first 10 mins and under 2000 rpm is the highest cutoff risk, usually happens when coming to a stop. every now and then I'll be in mid drive, no change is speed or rpms, it just won't take gas and cutoff in mid drive. no sure if this is related but every now and then (again, earlier in the drive) I'll hear a noise much like the long soft "beep" when the airplanes indicate the seatbelts should be fastened.
no relation to speed or bumps in the road. I bought the car in October '10 from intersport who said it was thoroughly checked and needed nothing. about a month or so later the clutch master cylinder went out so I took it to the dealer and told them to check/fix it from nose to tail along with a yearly maintenance. $4500 later (ouch!) I was back on the road until this issue (that the dealer can't reproduce) surfaced.
This may be a coincidence but light seems to be a factor as well. Parking on a cold street that gets bright sunshine in the morning is better than a warmer parking garage with no light.
starting: once it cuts off, attempting to start with just the key is an exercise in futility. at this point, the only way to get it/keep it started is to give gas along with the key, slowly decrease the rpms to 2000 and then even more slowly drop below 2000. on a really bad day it'll sputter and cutoff just under 2000 rpms. it's never cutoff at >=2000 rpms which idling or driving.
driving: within the first 10 mins and under 2000 rpm is the highest cutoff risk, usually happens when coming to a stop. every now and then I'll be in mid drive, no change is speed or rpms, it just won't take gas and cutoff in mid drive. no sure if this is related but every now and then (again, earlier in the drive) I'll hear a noise much like the long soft "beep" when the airplanes indicate the seatbelts should be fastened.
no relation to speed or bumps in the road. I bought the car in October '10 from intersport who said it was thoroughly checked and needed nothing. about a month or so later the clutch master cylinder went out so I took it to the dealer and told them to check/fix it from nose to tail along with a yearly maintenance. $4500 later (ouch!) I was back on the road until this issue (that the dealer can't reproduce) surfaced.
02-24-2011, 10:31 AM
#5
One other thing of note. If, when trying to get it/keep it started, if I gradually decrease the rpms I have a better chance of it not cutting off. If I spike the rpms and then let off the gas immediately causing a sharp drop in rpms, it'll almost always cut off.
02-24-2011, 12:03 PM
#6
Three Wheelin'
Join Date: Jan 2010
Location: Durham Region/GTA East, Canada
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cutoff (or unable to start) when starting with key only (no gas): last running is the main factor (the longer it's been since it ran last the more likely to not start/cutoff). Outside temperature is a close second. On warm days this problem doesn't exist, the colder, the more likely this is to happen.
This may be a coincidence but light seems to be a factor as well. Parking on a cold street that gets bright sunshine in the morning is better than a warmer parking garage with no light. Nothing to do with light, but more to do with the sun warming the car (think of how warm your car can be inside when it is sunny but cold out)
starting: once it cuts off, attempting to start with just the key is an exercise in futility. at this point, the only way to get it/keep it started is to give gas along with the key, slowly decrease the rpms to 2000 and then even more slowly drop below 2000. on a really bad day it'll sputter and cutoff just under 2000 rpms. it's never cutoff at >=2000 rpms which idling or driving.
driving: within the first 10 mins and under 2000 rpm is the highest cutoff risk, usually happens when coming to a stop. every now and then I'll be in mid drive, no change is speed or rpms, it just won't take gas and cutoff in mid drive. no sure if this is related but every now and then (again, earlier in the drive) I'll hear a noise much like the long soft "beep" when the airplanes indicate the seatbelts should be fastened. this noise could be a relay buzzing as it is turning on and off very quickly. Could be fuel pump wiring/relay?
no relation to speed or bumps in the road. I bought the car in October '10 from intersport who said it was thoroughly checked and needed nothing. about a month or so later the clutch master cylinder went out so I took it to the dealer and told them to check/fix it from nose to tail along with a yearly maintenance. $4500 later (ouch!) I was back on the road until this issue (that the dealer can't reproduce) surfaced.
This may be a coincidence but light seems to be a factor as well. Parking on a cold street that gets bright sunshine in the morning is better than a warmer parking garage with no light. Nothing to do with light, but more to do with the sun warming the car (think of how warm your car can be inside when it is sunny but cold out)
starting: once it cuts off, attempting to start with just the key is an exercise in futility. at this point, the only way to get it/keep it started is to give gas along with the key, slowly decrease the rpms to 2000 and then even more slowly drop below 2000. on a really bad day it'll sputter and cutoff just under 2000 rpms. it's never cutoff at >=2000 rpms which idling or driving.
driving: within the first 10 mins and under 2000 rpm is the highest cutoff risk, usually happens when coming to a stop. every now and then I'll be in mid drive, no change is speed or rpms, it just won't take gas and cutoff in mid drive. no sure if this is related but every now and then (again, earlier in the drive) I'll hear a noise much like the long soft "beep" when the airplanes indicate the seatbelts should be fastened. this noise could be a relay buzzing as it is turning on and off very quickly. Could be fuel pump wiring/relay?
no relation to speed or bumps in the road. I bought the car in October '10 from intersport who said it was thoroughly checked and needed nothing. about a month or so later the clutch master cylinder went out so I took it to the dealer and told them to check/fix it from nose to tail along with a yearly maintenance. $4500 later (ouch!) I was back on the road until this issue (that the dealer can't reproduce) surfaced.
So many questions to ask here, that I suggest really looking over connections and wiring since your mechanic is not finding anything obvious, and is unable to recreate the symptoms. Inspect and clean connections..don't assume it is ok because it looks ok. check the actual harness for damage. Over the years, someone may have used a sharp probe test light to test the wiring, causing small pinholes in the protective covering, which can lead to corrosion/cracking of the wire inside the insulator.
One last thing, document what you have checked/found, what you cleaned up/replaced etc. This will help further troubleshooting and reduce the chance of doing things twice or missing one alltogther.
Goodluck
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02-26-2011, 08:05 PM
#8
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Unplug the TPS and see if the symptoms go away. The car will run rich, but should be okay. If symptoms go away your TPS is bad. Another possiblity is a cracked wire in the ref sensors, but that usually shows up when things are warm or hot, not cold. With the car running grab the ref sensor wires and move them around. If the car dies one of the ref sensor wires is bad. The temp sensor could be bad, but that should result in hard starting when cold, not cutting out once started (but it may stall at idle).
I had similar symptoms (not temp related) at a track event. It turned out to be a bad TPS, even though it passed the voltage test. Did I ever mention where the sub strap ends up when the car cuts out at full throttle down a straight? No? Well it involves the voice going up a few octaves! :-)
I had similar symptoms (not temp related) at a track event. It turned out to be a bad TPS, even though it passed the voltage test. Did I ever mention where the sub strap ends up when the car cuts out at full throttle down a straight? No? Well it involves the voice going up a few octaves! :-)
