Cranks but doesn't start!
06-03-2020, 08:17 PM
#1
Cranks but doesn't start!
Hi fellow members, This is my first post so thanks for having me as a member! I have done a fair bit of searching both here and on other forums and I have been unable to get the answers I am looking for with my google fu so I have decided to ask the question here and see if I can get my pig running again!
I own a 2005 Porsche Cayenne Turbo, I have owned it about 6 months now and its a project car I am building as an off road and long distance unsealed road weapon! I live in a very remote part of Australia, 700km to the next town on unsealed roads. I have fitted BFG Mud Terrains on 18" rims to the car.
So far I have managed to fix any issues I have run into myself, but recently the car developed what I diagnosed as a fuel problem with intermittent loss of power, then intermittent stalling. I replaced both fuel pumps, the filter & the PCV, but the problem was unresolved.
As I started to try to isolate the cause of the poor running I found a couple of electrical issues that sort of developed as I was working on the car - the starter relay appeared to have become intermittently faulty and I tried swapping it for the only one of the same spec I could find in the car, which was the relay under the seat, beside the battery. Things started getting weird at this point! That relay had tiny Argentinean ants (a local pest) in it and after cleaning everything up and treating for the ants, I ordered 2 new relays for the starter and whatever this one beside the battery is!
Now they have arrived and been fitted, but the same problem exists, the car will turn over fine, but no sign of firing. I can hear the fuel pump run when I open the drivers door, but I have confirmed the fuel pumps are not running when I try to start the engine (fuel delivery hose disconnected from PCV and a hose run into a container.) But I have also tested both fuel pumps by jumping the fuel pump relays and they both pump fine, I have also swapped the relays for others of the same spec just in case one or both were faulty. I Have also tried starting the engine with one of the fuel pumps relays jumpered so that I know there is a low pressure fuel supply. Still no firing.
So the diagnosis seems to be that the car cranks but something electrical is telling it not to supply fuel to the engine? Potentially there is also no spark although I haven't checked that yet and I am unsure as to the easiest way to do so.
To me it seems a bit like the sort of behaviour you would expect when the immobiliser was active?
The only factor that seemed to move the problem from one of starting and running (albeit, not very well), to cranking but no firing was when I started playing with the relay under the seat, beside the battery. This may be coincidence though, and I am relying on my memory of the sequence of events because it took a couple of weeks to get the replacement relays.
Other potentially relevant info is that prior to any problem developing I had changed the plugs and coils, so they are basically new. I don't have any scanning hardware ATM, but have a LAUNCH X431 on the way so will be able to run some checks then. When the problem of rough running first appeared I ran a mechanic's OBD Scanner on it and it didn't have any fault codes.
If anyone has any ideas of what could be causing the issue, or can help with suggestions for trouble shooting from here it would be appreciated.
I own a 2005 Porsche Cayenne Turbo, I have owned it about 6 months now and its a project car I am building as an off road and long distance unsealed road weapon! I live in a very remote part of Australia, 700km to the next town on unsealed roads. I have fitted BFG Mud Terrains on 18" rims to the car.
So far I have managed to fix any issues I have run into myself, but recently the car developed what I diagnosed as a fuel problem with intermittent loss of power, then intermittent stalling. I replaced both fuel pumps, the filter & the PCV, but the problem was unresolved.
As I started to try to isolate the cause of the poor running I found a couple of electrical issues that sort of developed as I was working on the car - the starter relay appeared to have become intermittently faulty and I tried swapping it for the only one of the same spec I could find in the car, which was the relay under the seat, beside the battery. Things started getting weird at this point! That relay had tiny Argentinean ants (a local pest) in it and after cleaning everything up and treating for the ants, I ordered 2 new relays for the starter and whatever this one beside the battery is!
Now they have arrived and been fitted, but the same problem exists, the car will turn over fine, but no sign of firing. I can hear the fuel pump run when I open the drivers door, but I have confirmed the fuel pumps are not running when I try to start the engine (fuel delivery hose disconnected from PCV and a hose run into a container.) But I have also tested both fuel pumps by jumping the fuel pump relays and they both pump fine, I have also swapped the relays for others of the same spec just in case one or both were faulty. I Have also tried starting the engine with one of the fuel pumps relays jumpered so that I know there is a low pressure fuel supply. Still no firing.
So the diagnosis seems to be that the car cranks but something electrical is telling it not to supply fuel to the engine? Potentially there is also no spark although I haven't checked that yet and I am unsure as to the easiest way to do so.
To me it seems a bit like the sort of behaviour you would expect when the immobiliser was active?
The only factor that seemed to move the problem from one of starting and running (albeit, not very well), to cranking but no firing was when I started playing with the relay under the seat, beside the battery. This may be coincidence though, and I am relying on my memory of the sequence of events because it took a couple of weeks to get the replacement relays.
Other potentially relevant info is that prior to any problem developing I had changed the plugs and coils, so they are basically new. I don't have any scanning hardware ATM, but have a LAUNCH X431 on the way so will be able to run some checks then. When the problem of rough running first appeared I ran a mechanic's OBD Scanner on it and it didn't have any fault codes.
If anyone has any ideas of what could be causing the issue, or can help with suggestions for trouble shooting from here it would be appreciated.
06-04-2020, 03:28 AM
#3
Thanks mate, I will do that and report back!
EDIT - Basically no movement from the taco even when cranking fast. Looking like you might have found the culprit, hopsis!
EDIT - Basically no movement from the taco even when cranking fast. Looking like you might have found the culprit, hopsis!
Last edited by Galumay; 06-04-2020 at 04:29 AM.
06-19-2020, 09:14 PM
#4
My replacement Crankshaft Position Sensor arrived this week and after fitting it the pig is running better than ever, so huge thanks to @hopsis for pointing me in the right direction. In hindsight all the problems I experienced were probably related to the slowly failing CPS, but never mind, I ended up with new fuel pumps, filter and PCV as well as a better understanding of many parts of the car.
I also now have my LAUNCH iCarScan and have cleared the service reminder and at least have a basic fault finding service for the car!
I also now have my LAUNCH iCarScan and have cleared the service reminder and at least have a basic fault finding service for the car!