Difficulty starting when nearly warm or cooled down
03-08-2019, 03:35 PM
#1
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Thread Starter
Difficulty starting when nearly warm or cooled down
Hi, I wonder if anyone can help please.
I own a 1987 928s4 (manual) uk spec with around 80k miles on the clock. Just recently say in the last two or three months she has become slightly difficult to start when either warm although she will start instantly when cold or hot.
if I do a short run, and leave the car for an hour or so, it will churn on the key for several seconds before firing up, then run roughly for another two or three seconds, as if it’s only running on 4 or 5 cylinders, however, give her a boot full of excelerator and rev the engine, this will clear and run smoothly
however, if on a longer run, again she will start, but only after cranking for a few seconds.
but every now and then, normally after about 3 hours after a full hot run, she will churn on the key for at least 20 or 30 secunds, then starts on what feels like a few cylinders and try’s to stall, again a blip the throttle, the other cylinders join the party but this time with a great cloud of black smoke out the back and a very strong smell of fuel in the cabin (which clears almost instantly)
ive changed all the plugs, HT leads, distributor caps and rotor arms...... but no change..... any thought please.
I own a 1987 928s4 (manual) uk spec with around 80k miles on the clock. Just recently say in the last two or three months she has become slightly difficult to start when either warm although she will start instantly when cold or hot.
if I do a short run, and leave the car for an hour or so, it will churn on the key for several seconds before firing up, then run roughly for another two or three seconds, as if it’s only running on 4 or 5 cylinders, however, give her a boot full of excelerator and rev the engine, this will clear and run smoothly
however, if on a longer run, again she will start, but only after cranking for a few seconds.
but every now and then, normally after about 3 hours after a full hot run, she will churn on the key for at least 20 or 30 secunds, then starts on what feels like a few cylinders and try’s to stall, again a blip the throttle, the other cylinders join the party but this time with a great cloud of black smoke out the back and a very strong smell of fuel in the cabin (which clears almost instantly)
ive changed all the plugs, HT leads, distributor caps and rotor arms...... but no change..... any thought please.
03-08-2019, 05:23 PM
#2
Chronic Tool Dropper
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Your symptoms point to a leaking injector or a leaking diaphragm in the fuel pressure regulator or damper. After running the car, remove the air cleaner housing so you have access to the vacuum connections on the dampers and regulator. Pull the hose and check for fuel in the hose. A sniff test is usually adequate. Better is a test to verify that they hold vacuum OK, typically done with a hand vacuum pump.
Testing the injectors for leakage gets a little more involved, as it requires you to do a fuel pressure test with a gauge.
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Your symptoms say that there's extra fuel dropping into the intake after the engine is shut off. When the engine stops, you get the effects of both the extra-rich mixture and the lack of fuel pressure from the leak-down into the intake manifold. If the engine is at full temperature at shutdown, the fuel system will vapor-lock from evaporation, and take a bit of cool fuel flowing through the system to clear the vapor and restore full liquid flow through the injectors to support actually starting.
Testing the injectors for leakage gets a little more involved, as it requires you to do a fuel pressure test with a gauge.
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Your symptoms say that there's extra fuel dropping into the intake after the engine is shut off. When the engine stops, you get the effects of both the extra-rich mixture and the lack of fuel pressure from the leak-down into the intake manifold. If the engine is at full temperature at shutdown, the fuel system will vapor-lock from evaporation, and take a bit of cool fuel flowing through the system to clear the vapor and restore full liquid flow through the injectors to support actually starting.
03-09-2019, 04:11 PM
#3
AutoX
Thread Starter
Thank you for this,
The smell of fuel in the cabin has only happened 3 or 4 times (out of around 100 starts) when it churns on the key for a long time
someone has also suggested it could be the EZK is starting to fail (I hope not as it’s not going to be cheap to replace)
i think this is going beyond my ability but this at least gives me something to tell the mechanic to start with. She’s going in Monday, so I will update you.
again, thanks for your help
The smell of fuel in the cabin has only happened 3 or 4 times (out of around 100 starts) when it churns on the key for a long time
someone has also suggested it could be the EZK is starting to fail (I hope not as it’s not going to be cheap to replace)
i think this is going beyond my ability but this at least gives me something to tell the mechanic to start with. She’s going in Monday, so I will update you.
again, thanks for your help
03-10-2019, 05:52 AM
#4
Drifting
My money’s on leaking injectors.
If you you can get hold of fuel rail pressure gauge (or find competent shop to do the test), then you can confirm and/or find alternative diagnosis easily and quickly.
Had similar warm start issues on my old 88 S4 Auto. Diagnosed leaking injectors with gauge, and fixed problem with set of equivalent Ford Motorsport injectors (I don’t think they’re available now, but there are other options including rebuilding existing injectors).
If you you can get hold of fuel rail pressure gauge (or find competent shop to do the test), then you can confirm and/or find alternative diagnosis easily and quickly.
Had similar warm start issues on my old 88 S4 Auto. Diagnosed leaking injectors with gauge, and fixed problem with set of equivalent Ford Motorsport injectors (I don’t think they’re available now, but there are other options including rebuilding existing injectors).
03-10-2019, 07:06 AM
#5
Team Owner
I would put a bottle of Techron in the fuel
do this after you have performed the sniff test to verify the dampers and FPR are not leaking
instead of leaking injectors it could also be a leaking check valve in the fuel pump so this check valve should also be part of the replacement protocol
NOTE when working on the fuelpump you should have a new filter a new short rubber feed hose and the short hardline and a new check valve it comes with 3 new sealing rings on hand
This to insure that the repair doesn’t cause a future leak
do this after you have performed the sniff test to verify the dampers and FPR are not leaking
instead of leaking injectors it could also be a leaking check valve in the fuel pump so this check valve should also be part of the replacement protocol
NOTE when working on the fuelpump you should have a new filter a new short rubber feed hose and the short hardline and a new check valve it comes with 3 new sealing rings on hand
This to insure that the repair doesn’t cause a future leak
03-11-2019, 04:55 PM
#6
Nordschleife Master
Thank you for this,
The smell of fuel in the cabin has only happened 3 or 4 times (out of around 100 starts) when it churns on the key for a long time
someone has also suggested it could be the EZK is starting to fail (I hope not as it’s not going to be cheap to replace)
i think this is going beyond my ability but this at least gives me something to tell the mechanic to start with. She’s going in Monday, so I will update you.
again, thanks for your help
The smell of fuel in the cabin has only happened 3 or 4 times (out of around 100 starts) when it churns on the key for a long time
someone has also suggested it could be the EZK is starting to fail (I hope not as it’s not going to be cheap to replace)
i think this is going beyond my ability but this at least gives me something to tell the mechanic to start with. She’s going in Monday, so I will update you.
again, thanks for your help
Everything you wrote points to very, very rich on startup. Stumbling until you 'goose' it (wet plugs), big black cloud of smoke, fuel smell.
03-11-2019, 05:05 PM
#7
Team Owner
Its the LH thats that failing computer not the EZK
LH is for the fuel injectors
EZK is for the spark control.
I would add the fuel injector cleaner first.
LH is for the fuel injectors
EZK is for the spark control.
I would add the fuel injector cleaner first.
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03-12-2019, 01:07 PM
#8
Nordschleife Master
Stan - Would a failing LH exhibit those symptoms?
Super rich only on 'kinda warm' startup ?
I don't pretend to know a whole lot about the LH brain, but that doesn't sound like a computer problem to me.
I would expect to see a failing computer cause issues on a variety of start up conditions (warm, cold, hot, ect).
But I could certainly be wrong about that.
Super rich only on 'kinda warm' startup ?
I don't pretend to know a whole lot about the LH brain, but that doesn't sound like a computer problem to me.
I would expect to see a failing computer cause issues on a variety of start up conditions (warm, cold, hot, ect).
But I could certainly be wrong about that.
03-12-2019, 09:08 PM
#9
Team Owner
Well this was a general statement about what computer is actually failing on the S4 series
in post 3 the OP states the EZK might be failing, Thus what i posted.
At this point it sounds more like a damper, FPR, check valve, or injector
in post 3 the OP states the EZK might be failing, Thus what i posted.
At this point it sounds more like a damper, FPR, check valve, or injector
03-14-2019, 01:17 PM
#10
Rennlist Member
