Hot=will not start
08-22-2021, 11:39 AM
#16
Rennlist Member
Thread Starter
Will start with simple stuff. I hope it's not the ISV , I would mean removing intake on 85/86 and not looking forward to removing again!!
08-22-2021, 01:55 PM
#17
Team Owner
Mike to get to the ISV remove the center T manifold and the MAF.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
Last edited by Mrmerlin; 08-22-2021 at 02:00 PM.
08-22-2021, 03:09 PM
#18
Rennlist Member
If it restarts right then, that's because you still had fuel pressure. So far, so good. Turn off. Wait 10 minutes. Now restart. No restart at this point, even though some minor cooling has occurred means no fuel pressure, hence odds are your fuel pressure regulator is leaking back.
So if those conditions align, replace your FPR. Easy test. Just drive, turn off, turn back on works, turn off, wait 10 minutes attempt to turn on again.
08-22-2021, 04:51 PM
#19
Rennlist Member
Thread Starter
Mike to get to the ISV remove the center T manifold and the MAF.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
Thrust bearing was checked and there was no bowing on flex plate, I unbolted and "no clunk" in the flywheel..
The ISV was changed approximately 25,000miles ago and doubt its defective.
How can you check to ensure ISV is working properly?
08-22-2021, 04:55 PM
#20
Rennlist Member
Thread Starter
Mike to get to the ISV remove the center T manifold and the MAF.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
NOTE the ISV on your car is a wear item and after about 60K miles the armature can be holed by the brushes.
this causes the unit to stick, this then will damage the drivers in the computer and thus cause collateral damage.
\NOTE the ISV for the 85/ 86 USA cars is no longer a Bosch made part, ( 87 on uses a completely different unit with no brushes)
LOWE is the new MFG and it seems that they have idle issues and if using a Lowe part your new idle will be about 1100 RPM.
NOTE since you didnt answer the question of the thrust bearing ever being checked,
this should go to the top of the list.
Make sure that the rear pinch bolt is also inspected and retorqued, use blue loctite on the bolt threads set to 66 ft lbs.
NOTE as a maintenance item, every year auto should have the drive line pinch bolts checked if their is no record of this task being performed,
as most will be found to be loose, also make sure that you can hear the clunk in the flywheel when moving the flywheel front to back,
if no clunk then the thrust bearing is preloaded.
NOTE the 84 on years will be more susceptible to the thrust bearing preloading due to the increased torque being made.
I had that "no hot start" problem on my Ferrari and it was one of its 2 fuel pressure regulators (easy fix, fast and cheap). The way to test your FPR is to start your Porsche cold, drive until operating temp, stop, turn off the motor and IMMEDIATELY restart your car.
If it restarts right then, that's because you still had fuel pressure. So far, so good. Turn off. Wait 10 minutes. Now restart. No restart at this point, even though some minor cooling has occurred means no fuel pressure, hence odds are your fuel pressure regulator is leaking back.
So if those conditions align, replace your FPR. Easy test. Just drive, turn off, turn back on works, turn off, wait 10 minutes attempt to turn on again.
If it restarts right then, that's because you still had fuel pressure. So far, so good. Turn off. Wait 10 minutes. Now restart. No restart at this point, even though some minor cooling has occurred means no fuel pressure, hence odds are your fuel pressure regulator is leaking back.
So if those conditions align, replace your FPR. Easy test. Just drive, turn off, turn back on works, turn off, wait 10 minutes attempt to turn on again.
I also tried restarting seconds after hot shut down and no restart.
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no doubt (08-22-2021)
08-22-2021, 05:01 PM
#21
Rennlist Member
Thread Starter
08-22-2021, 05:06 PM
#22
Rennlist Member
Thread Starter
Michael,
If you have a problem with the diaphragm on one of either the FPR or dampers when you switch off the engine the fuel rail will lose pressure quickly and with the heat soak present the fuel can vapourise inside the rail and then the car will not start until the thing cools off and the fuel condenses once more. Cranking the motor theoretically should reinstate the pressure but i suspect being at a high point in the system the vapour gets high point locked and does not wash out. Similar thing if an injector is leaking
If opening the bonnet sees the problem resolve itself "quicker" that might confirm the above.
i doubt it is a TBF issue but then you should know for a fact such is not happening and if that is not the case then you need to ensure you know for a fact that all is well.
If you have a problem with the diaphragm on one of either the FPR or dampers when you switch off the engine the fuel rail will lose pressure quickly and with the heat soak present the fuel can vapourise inside the rail and then the car will not start until the thing cools off and the fuel condenses once more. Cranking the motor theoretically should reinstate the pressure but i suspect being at a high point in the system the vapour gets high point locked and does not wash out. Similar thing if an injector is leaking
If opening the bonnet sees the problem resolve itself "quicker" that might confirm the above.
i doubt it is a TBF issue but then you should know for a fact such is not happening and if that is not the case then you need to ensure you know for a fact that all is well.
What others symptoms other than no hot restart?
The engine turns over freely with no strain on hot restart.
08-22-2021, 06:19 PM
#23
Rennlist Member
Starter turns motor over freely when restarting hot, but motor doesn't catch, so the easy free next test is starter fluid (I love it, but lots of people hate it thinking it causes damage).
Even a small squirt of starter fluid will tell you upon hot restart attempt if you have a fuel or spark issue, based on what you hear. If she briefly fires up with starter fluid when motor is hot, then she only fired up because you gave it fuel (starter fluid), which means that she isn't getting fuel = obvious fuel issue. Otherwise, if no difference in your hot restart attempt, then the fuel/starter fluid made no difference so you've identified a spark problem.
Easy test.
08-22-2021, 07:09 PM
#24
The majority of guesses here are on the FPR or Dampers. Just because something was replaced X number of miles ago or the car restarts immediately after shutdown (that’s the first I’ve read about that one), those are not tests that people usually perform in this instance.
Pull the vacuum lines and smell for fuel. Even better take a tiny diameter Allen wrench and gently dip it in and remove to see if gasoline is on its tip.
Good luck.
Pull the vacuum lines and smell for fuel. Even better take a tiny diameter Allen wrench and gently dip it in and remove to see if gasoline is on its tip.
Good luck.
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928NOOBIE (08-24-2021)
08-22-2021, 08:40 PM
#25
Team Owner
Note you should hear a clunk as the crank bottoms on the thrust bearing while prying the flywheel back and forth
NOTE if you don’t hear a clunk / thud then the thrust bearing may have welded itself to the crank
NOTE if you don’t hear a clunk / thud then the thrust bearing may have welded itself to the crank
Last edited by Mrmerlin; 08-23-2021 at 12:34 PM.
08-23-2021, 12:25 PM
#26
I had the exact same issues as you described. I replaces the fuel dampers and the problem was resolved.
Checking vacuum on them does not necessarily tell you anything.
I pulled vacuum on both of them and it held.
Follow Greg's advice and replace the dampers.
Art
Checking vacuum on them does not necessarily tell you anything.
I pulled vacuum on both of them and it held.
Follow Greg's advice and replace the dampers.
Art
08-23-2021, 07:25 PM
#30
Addict
Rennlist Member
Rennlist Member
Seems like replacing the fuel pump relay might not be a bad idea; this was already mentioned in post 15. Might not engage when warm, but will when cold and will continue to operate once energized.
I had one hell of a battle similar to this many years ago that I'm pretty sure was ultimately resolved by replacing the fuel pump relay.
I had one hell of a battle similar to this many years ago that I'm pretty sure was ultimately resolved by replacing the fuel pump relay.