Warm start
07-07-2014, 09:24 PM
#1
Racer
Thread Starter
Warm start
I have an '03 996TT with an EPL tune. The car has developed a warm start problem. It starts just fine when cold, but if it's still warm, it cranks for 15 seconds before puttering to life.
I was told by my tuner that it was the little silver metal check valve on the octopus of lines coming off the fuel pump. Given that I have replaced two fuel pumps because the u-shaped rubber hose split, I had a spare check valve. I installed it thinking it would solve the problem, but no luck. There is another white plastic check valve in the same area, but I am reluctant to keep changing out parts guessing at the problem.
Anyone here solve a similar problem? I do think it's a fuel related issue, but I don't know how to solve it.
BTW, once started, hot or cold, it runs fine.
Thanks
I was told by my tuner that it was the little silver metal check valve on the octopus of lines coming off the fuel pump. Given that I have replaced two fuel pumps because the u-shaped rubber hose split, I had a spare check valve. I installed it thinking it would solve the problem, but no luck. There is another white plastic check valve in the same area, but I am reluctant to keep changing out parts guessing at the problem.
Anyone here solve a similar problem? I do think it's a fuel related issue, but I don't know how to solve it.
BTW, once started, hot or cold, it runs fine.
Thanks
07-07-2014, 11:58 PM
#2
could be vapour lock, if the engine bay is hot enough, there is lots of fuel system/lines/filter located in there...
07-08-2014, 11:13 AM
#4
^ +1
In addition to checking the pressure, watch how the pressure rises, the stability of the pressure, and if it holds that pressure once key/pump is off. Do this with the engine both hot and cold.
Cheers,
In addition to checking the pressure, watch how the pressure rises, the stability of the pressure, and if it holds that pressure once key/pump is off. Do this with the engine both hot and cold.
Cheers,
07-08-2014, 06:14 PM
#5
Race Director
Fuel supply/pressure is always a possibility. You've received good advice to check these.
Not sure though I'd agree in this case it is a fuel pressure/supply problem. But check the fuel system anyhow.
My WAG is it reads like a bad crankshaft position sensor that acts up -- quits working -- when hot for a few moments then comes to life.
The engine will crank just fine but will not start as there is no signal to know where the pistons are in their cycles.
But check the fuel pressure/supply first. I have to stress that you must check these under the same conditions as when the no start behavior appears.
Let me add that I assume there is no spitting back or backfires through the exhaust? Either of these would suggest too little (or too much) fuel. Instead the symptom is the engine cranks just fine, maybe even sounds like it is cranking with no compression (this is an illusion of course), but it just cranks and makes not one attempt to fire up, not even misfire?
Not sure though I'd agree in this case it is a fuel pressure/supply problem. But check the fuel system anyhow.
My WAG is it reads like a bad crankshaft position sensor that acts up -- quits working -- when hot for a few moments then comes to life.
The engine will crank just fine but will not start as there is no signal to know where the pistons are in their cycles.
But check the fuel pressure/supply first. I have to stress that you must check these under the same conditions as when the no start behavior appears.
Let me add that I assume there is no spitting back or backfires through the exhaust? Either of these would suggest too little (or too much) fuel. Instead the symptom is the engine cranks just fine, maybe even sounds like it is cranking with no compression (this is an illusion of course), but it just cranks and makes not one attempt to fire up, not even misfire?
07-16-2014, 10:05 PM
#6
Racer
Thread Starter
Thanks
thanks for the advice guys. I am away from the car until this weekend, but will take your advice and see where this goes.
Once the car starts, it runs fine.
I will try to post again once resolved in case someone else experiences the same thing.
Once the car starts, it runs fine.
I will try to post again once resolved in case someone else experiences the same thing.
07-18-2014, 10:02 AM
#7
Instructor
Similar situation with a different car I had. I added a fuel pressure gauge and saw that the fuel pressure bled off faster than spec after shutoff.
Turned out to be a faulty Fuel Pressure Regulator (FPR). easy replacement and about $100 part.
Turned out to be a faulty Fuel Pressure Regulator (FPR). easy replacement and about $100 part.
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08-04-2015, 07:06 PM
#9
Racer
Thread Starter
Problem Solved
After many many months of warm start problems and several mechanics trying unsuccessfully to diagnose the problem, I went on a hunch and it turned out to be right. My problem appeared initially to be a heat soaked or warm difficult starting problem. If the car was cold it started right up. If warm and turned off and restarted immediately it started right up. If warm and it sat for +10 minutes, it would hard start.
One day, I didn't start the cold engine, but simply turned the key to on to see how much gas I had in the tank thereby pressurizing the fuel system. 10 minutes later I tried to start it and got the hard start (long crank). As always, the smell of fuel was present on a long crank.
What I guessed was that the fuel pressure remained in the lines well after the engine was turned off and it was leaking into the cylinders and flooding the engine causing the hot start.
What I replaced is the fuel return check-valve, which I confirmed was clogged, with a new one from ebay for
One day, I didn't start the cold engine, but simply turned the key to on to see how much gas I had in the tank thereby pressurizing the fuel system. 10 minutes later I tried to start it and got the hard start (long crank). As always, the smell of fuel was present on a long crank.
What I guessed was that the fuel pressure remained in the lines well after the engine was turned off and it was leaking into the cylinders and flooding the engine causing the hot start.
What I replaced is the fuel return check-valve, which I confirmed was clogged, with a new one from ebay for
08-05-2015, 03:59 AM
#10
After many many months of warm start problems and several mechanics trying unsuccessfully to diagnose the problem, I went on a hunch and it turned out to be right. My problem appeared initially to be a heat soaked or warm difficult starting problem. If the car was cold it started right up. If warm and turned off and restarted immediately it started right up. If warm and it sat for +10 minutes, it would hard start.
One day, I didn't start the cold engine, but simply turned the key to on to see how much gas I had in the tank thereby pressurizing the fuel system. 10 minutes later I tried to start it and got the hard start (long crank). As always, the smell of fuel was present on a long crank.
What I guessed was that the fuel pressure remained in the lines well after the engine was turned off and it was leaking into the cylinders and flooding the engine causing the hot start.
What I replaced is the fuel return check-valve, which I confirmed was clogged, with a new one from ebay for
One day, I didn't start the cold engine, but simply turned the key to on to see how much gas I had in the tank thereby pressurizing the fuel system. 10 minutes later I tried to start it and got the hard start (long crank). As always, the smell of fuel was present on a long crank.
What I guessed was that the fuel pressure remained in the lines well after the engine was turned off and it was leaking into the cylinders and flooding the engine causing the hot start.
What I replaced is the fuel return check-valve, which I confirmed was clogged, with a new one from ebay for
08-05-2015, 10:15 AM
#11
Racer
Thread Starter
Check valve
Maybe my theory is wrong, but it absolutely fixed the problem.
There are check valves in both directions, no? One white plastic (to engine) and one metal (from engine). The one on return, and pictured, is the check valve that allows flow back from the engine, not to the engine. It was completely clogged. I replaced it with a new one, allowing flow from the engine.
If the white plastic check valve was clogged, I agree that you would not get fuel to the engine.
My experience was that once started, the engine would run fine, but after sitting after fuel system pressurization, it would hard start. So, a clogged return seems like it would let the engine run, no?
There are check valves in both directions, no? One white plastic (to engine) and one metal (from engine). The one on return, and pictured, is the check valve that allows flow back from the engine, not to the engine. It was completely clogged. I replaced it with a new one, allowing flow from the engine.
If the white plastic check valve was clogged, I agree that you would not get fuel to the engine.
My experience was that once started, the engine would run fine, but after sitting after fuel system pressurization, it would hard start. So, a clogged return seems like it would let the engine run, no?
08-05-2015, 03:41 PM
#12
Maybe my theory is wrong, but it absolutely fixed the problem.
There are check valves in both directions, no? One white plastic (to engine) and one metal (from engine). The one on return, and pictured, is the check valve that allows flow back from the engine, not to the engine. It was completely clogged. I replaced it with a new one, allowing flow from the engine.
If the white plastic check valve was clogged, I agree that you would not get fuel to the engine.
My experience was that once started, the engine would run fine, but after sitting after fuel system pressurization, it would hard start. So, a clogged return seems like it would let the engine run, no?
There are check valves in both directions, no? One white plastic (to engine) and one metal (from engine). The one on return, and pictured, is the check valve that allows flow back from the engine, not to the engine. It was completely clogged. I replaced it with a new one, allowing flow from the engine.
If the white plastic check valve was clogged, I agree that you would not get fuel to the engine.
My experience was that once started, the engine would run fine, but after sitting after fuel system pressurization, it would hard start. So, a clogged return seems like it would let the engine run, no?
08-07-2015, 11:29 AM
#15
Racer
Thread Starter
revised
I stand corrected. I looked again today, and the metal check value is outbound to the engine. So my theory seems flawed. The interesting thing though, is that the car would run properly with this clogged check valve (maybe the fuel pressure was enough to push through?) but the clogged valve did create warm start issues, as replacing it is the only thing I did and it immediately cured the problem. Better to be lucky than smart.
BTW, this check valve is attached to the fuel lines coming off the fuel pump, which is located in the gas tank. While that might sound somewhat intimidating, this is a level 2 of 5 skill job. Accessing the pump is easy and the only tricky part is heating up the lines to soften them enough to get the press fittings on and off and reclamp them.
See this link for details and great pictures: http://www.6speedonline.com/forums/9...-pictures.html
BTW, this check valve is attached to the fuel lines coming off the fuel pump, which is located in the gas tank. While that might sound somewhat intimidating, this is a level 2 of 5 skill job. Accessing the pump is easy and the only tricky part is heating up the lines to soften them enough to get the press fittings on and off and reclamp them.
See this link for details and great pictures: http://www.6speedonline.com/forums/9...-pictures.html