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Old 22 September 2009, 22:57   #1
Tucker82
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Default Car wont start when its warm. Suggestions?

Right. This has been ongoing for nearly two years.

I have:
Replaced spark plugs
Checked coil packs for cracks/splits.
Replaced Crank/Cam and BOTH water temp sensors (with resetting ecu)
Its also had a new battery.

Its starts EVERYTIME from cold, without fail.

When its had a chance to get a bit warm, it turns over, smells of fuel but just wont fire. No engine check light.

I am flat out of ideas. Scoobyclinic said replace the smaller water temp sensor as that could be the problem. Fitted that today and it wouldn't start straight after fitting it lol.

Do you lot have any ideas/suggestions or somebody had this before?

I need a reliable car
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Old 23 September 2009, 02:27   #2
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What usually causes bad warm starting (on any petrol-fuelled car, not just an Impreza) is what's known as vapour-locking. Basically, the fuel in the lines on top of the engine evaporates from the heat, so there's none there to prime the injectors (or carb) when you go to start it back up. You won't notice anything with the engine running, because the pump's continuously replacing any lost fuel then. With the Impreza's engine layout and the fuel lines all running literally right across the top of the block, the potential for this might well be a bit worse than on a conventional in-line 4-cylinder, admittely.

The only way I could think changing a water temp sensor might help is by keeping engine temp slightly lower, if the old sensor was misreading (less heat = less evaporation), but I doubt very much this is the main problem. The root cause is still going to be either a weak fuel-pump, and/or something in the manifold end of the fuel delivery circuit (fuel lines, fittings, gaskets, o-rings, etc getting marginally porous from age, or a weak FPR), all of which would be totally consistent with the smell of fuel you mentionned.

Of course, if you're going to work your way through figuring out exactly which of those components is to blame, this might be the perfect time to upgrade to a Walbro and/or do a parallel fuel line mod while you're at it
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Old 24 September 2009, 00:25   #3
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Quote:
Originally Posted by markjmd View Post
What usually causes bad warm starting (on any petrol-fuelled car, not just an Impreza) is what's known as vapour-locking. Basically, the fuel in the lines on top of the engine evaporates from the heat, so there's none there to prime the injectors (or carb) when you go to start it back up. You won't notice anything with the engine running, because the pump's continuously replacing any lost fuel then. With the Impreza's engine layout and the fuel lines all running literally right across the top of the block, the potential for this might well be a bit worse than on a conventional in-line 4-cylinder, admittely.

The only way I could think changing a water temp sensor might help is by keeping engine temp slightly lower, if the old sensor was misreading (less heat = less evaporation), but I doubt very much this is the main problem. The root cause is still going to be either a weak fuel-pump, and/or something in the manifold end of the fuel delivery circuit (fuel lines, fittings, gaskets, o-rings, etc getting marginally porous from age, or a weak FPR), all of which would be totally consistent with the smell of fuel you mentionned.

Of course, if you're going to work your way through figuring out exactly which of those components is to blame, this might be the perfect time to upgrade to a Walbro and/or do a parallel fuel line mod while you're at it
Interesting, thanks! So basically, a ****e fuel system could be the cause, could also explain why my car drinks the stuff for fun, constantly smells like a petrol station and empties my wallet regularly. I was also told today that becuase the Maf is close to the turbo, this can cause starting probs and to try a heat shield.

Would fitting braided fuel lines help? TBH I have no idea of how the fueling system actually works and wouldn't know where to start with fitting parallel fuel lines and FPR's, although I have thought about it in the past. I know a walbro can be had for about 70, but what about the rest? Would I need to think about ecu settings if I modded the fuel system?

Thanks

Tucker
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Old 24 September 2009, 12:13   #4
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Common issues causing warm start problems are the 3 following sensors :
Coolant temperature
Crank position
cam position
I had this issue, swapped the sensors in the above order, was only when I installed a new cam position sensor was the problem resolved and it then started fine every single time from then on.
That sensor was thought, I beleive, NOT to be used during the start-up process but it was certainly the one that did it for me.
Coolant temp sensor was the worst to replace (at the rear to the left of the engine block) so I'd maybe start with the cam or crank position sensors and see if they resolve your issue.
Not mega bucks brand new (30 - 40-ish) but you might try to source a s/h one if you want.
If I recall, when the problem happened for me, if I unclipped then put the sensor back on it would often clear the problem.
Crank sensor is at the front of the engine, cam sensor to the right hand side.

Have you run through the CEL procedure - I recall the CEL lights gave me some slightly unreliable results.
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Old 24 September 2009, 13:25   #5
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Tucker
The fuel system basically consists a pump at one end, in the tank, that sends fuel up a long pipe to the engine bay, through the filter, then round a circuit of pipes to the injectors at the other end. For it to work properly though the fuel in the pipes has to be maintained at a continuous pressure, so that when the injectors are activated by the signals from the ECU there's enough fuel actually in the feed pipes to squirt into the cylinder head and power the pistons. If the pump isn't strong enough, or something is allowing fuel to escape out of the feed pipes prematurely, that will cause a drop in fuel pressure, which in turn will cause poor or unreliable engine firing. In your case the continuous smell of fuel is probably giving enough of an extra clue that the problem is more likely fuel escaping, so that's probably where to start looking first. Assuming you've changed the fuel filter recently, the next thing to do would be to check:
- condition and fitting of your fuel lines. All rubber can get slightly porous with age, so it might be just as simple to replace them regardless. If you're doing that, you might as well go with braided if you can afford it.
- fuel rails. Not often heard of them failing, but you can't rule out that one of them has a very small hairline crack, or just isn't fitted properly.
- injectors seals. More rubber, in the form of o-rings. If you're going to pull these out, the best option is to have a reconditionned spare set ready to go straight back in, with new o-rings. Plenty of places do them on an exchange basis, the main points to look out for are that the set they'll give you is flow-matched, ultrasonic-cleaned, and comes with new o-rings. Figure on around 15-20 per injector, plus a little for post, but check locally if there isn't a specialist near you who does them for less.
- fpr (pressure regulator). Again, not often heard of them failing, but any original part on a classic is going to be at least 10 years old, so you can't rule it out. You could try to pick up a low-mileage one that someone's sold off when they upgraded, to save cash - usually a fair few around either on here or Ebay.

Walbro is never a bad idea, especially if you've already got any power-mods on your car.
Parallel fuel-line mod has plenty of how-tos and guides on here and other sites, but isn't a good idea if you're not confident you'll do it exactly right. Pi$$ing fuel and hot engine parts are a very, very bad and potentially dangerous/expensive combination.
Neither the walbro or parallel mod would need a remap or new ECU.

Heatshield on Turbo not a bad idea either, generally, but I honestly don't think it's directly causing your problem, from everything you've said.

cheers
Mark
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Old 24 September 2009, 14:46   #6
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Quote:
Originally Posted by andyr View Post
Common issues causing warm start problems are the 3 following sensors :
Coolant temperature
Crank position
cam position
I had this issue, swapped the sensors in the above order, was only when I installed a new cam position sensor was the problem resolved and it then started fine every single time from then on.
That sensor was thought, I beleive, NOT to be used during the start-up process but it was certainly the one that did it for me.
Coolant temp sensor was the worst to replace (at the rear to the left of the engine block) so I'd maybe start with the cam or crank position sensors and see if they resolve your issue.
Not mega bucks brand new (30 - 40-ish) but you might try to source a s/h one if you want.
If I recall, when the problem happened for me, if I unclipped then put the sensor back on it would often clear the problem.
Crank sensor is at the front of the engine, cam sensor to the right hand side.

Have you run through the CEL procedure - I recall the CEL lights gave me some slightly unreliable results.

Thanks, Andy, but as I have said in the OP, I have already replaced these sensors and more with new parts and still have no luck.
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Old 24 September 2009, 14:56   #7
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Quote:
Originally Posted by markjmd View Post
Tucker
The fuel system basically consists a pump at one end, in the tank, that sends fuel up a long pipe to the engine bay, through the filter, then round a circuit of pipes to the injectors at the other end. For it to work properly though the fuel in the pipes has to be maintained at a continuous pressure, so that when the injectors are activated by the signals from the ECU there's enough fuel actually in the feed pipes to squirt into the cylinder head and power the pistons. If the pump isn't strong enough, or something is allowing fuel to escape out of the feed pipes prematurely, that will cause a drop in fuel pressure, which in turn will cause poor or unreliable engine firing. In your case the continuous smell of fuel is probably giving enough of an extra clue that the problem is more likely fuel escaping, so that's probably where to start looking first. Assuming you've changed the fuel filter recently, the next thing to do would be to check:
- condition and fitting of your fuel lines. All rubber can get slightly porous with age, so it might be just as simple to replace them regardless. If you're doing that, you might as well go with braided if you can afford it.
- fuel rails. Not often heard of them failing, but you can't rule out that one of them has a very small hairline crack, or just isn't fitted properly.
- injectors seals. More rubber, in the form of o-rings. If you're going to pull these out, the best option is to have a reconditionned spare set ready to go straight back in, with new o-rings. Plenty of places do them on an exchange basis, the main points to look out for are that the set they'll give you is flow-matched, ultrasonic-cleaned, and comes with new o-rings. Figure on around 15-20 per injector, plus a little for post, but check locally if there isn't a specialist near you who does them for less.
- fpr (pressure regulator). Again, not often heard of them failing, but any original part on a classic is going to be at least 10 years old, so you can't rule it out. You could try to pick up a low-mileage one that someone's sold off when they upgraded, to save cash - usually a fair few around either on here or Ebay.

Walbro is never a bad idea, especially if you've already got any power-mods on your car.
Parallel fuel-line mod has plenty of how-tos and guides on here and other sites, but isn't a good idea if you're not confident you'll do it exactly right. Pi$$ing fuel and hot engine parts are a very, very bad and potentially dangerous/expensive combination.
Neither the walbro or parallel mod would need a remap or new ECU.

Heatshield on Turbo not a bad idea either, generally, but I honestly don't think it's directly causing your problem, from everything you've said.

cheers
Mark
I think you could be right about the fuel system, Mark.

I have an understanding of the fuel rails/injectors and feed pipes etc, just not sure on how and what a FPR does and how I would go about fitting parallel rails etc. I have replaced the injector o-rings before (last yr) and found a broken injector, which I also replaced. Im only running 380's. I have in the past replaced one of the fuel rails too as one had a bolt snapped off and didn't have a good proper seal. So I am pretty confident that the engine bay area is all cushty, but cannot be 100% sure.

One thing I have never done is replace the fuel filter. Could this be a factor?

I may go down the braided fuel line route but that would only be from the filter to the lines themselves which isn't very much, so am not sure if it would offer any protection from heat.

So for now it looks like:

a) Fit a 255lph pump
b) Change fuel filter
c) look at braided hoses?

Thanks for the help mate

Tucker
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Old 24 September 2009, 15:23   #8
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Are you running an aftermarket ECU?

It could (just throwing ideas in the air) be dumping too much fuel in the cylinders when it is warm and flooding itself.

AFAIK, you need more fuel when cold so this explains why it starts okay cold. Then, when warm, it is putting the same amount of fuel in and flooding itself...

Just a thought...
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Old 24 September 2009, 16:40   #9
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FPR is a valve that allows fuel above a certain pressure to flow back into the tank, once it's completed the pump -> filter -> injector feeds circuit.


Quote:
One thing I have never done is replace the fuel filter. Could this be a factor?
How long have you had the car? Change interval is 30K-ish (not sure without checking manual), or 48/60 months (maybe less, again not sure without checking manual), whichever comes first.


Quote:
c) look at braided hoses?
The point with the hoses isn't so much to get stronger/better ones, just to get new ones. I personally prefer to upgrade if I can rather than replace like-with-like, if I have part go bad, but that's just me.
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Old 24 September 2009, 19:28   #10
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Originally Posted by rossi_p View Post
Are you running an aftermarket ECU?

It could (just throwing ideas in the air) be dumping too much fuel in the cylinders when it is warm and flooding itself.

AFAIK, you need more fuel when cold so this explains why it starts okay cold. Then, when warm, it is putting the same amount of fuel in and flooding itself...

Just a thought...
Its running on a Z5 which is from a Type RA if im correct.

So the ecu has to use less fuel when priming warm than it does cold? It does often seem like its overfuelling/flooded after a few turns. Sometimes it'll get going after 30 secs, sometimes 10 minutes. Just depends what mood its in!
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Old 24 September 2009, 19:35   #11
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Quote:
Originally Posted by markjmd View Post
FPR is a valve that allows fuel above a certain pressure to flow back into the tank, once it's completed the pump -> filter -> injector feeds circuit.




How long have you had the car? Change interval is 30K-ish (not sure without checking manual), or 48/60 months (maybe less, again not sure without checking manual), whichever comes first.




The point with the hoses isn't so much to get stronger/better ones, just to get new ones. I personally prefer to upgrade if I can rather than replace like-with-like, if I have part go bad, but that's just me.
Ive had the car for nearly two yrs now, and have never changed it. So probably should. I have no idea when it was changed last.

I think im going to gather a few prices of modding the fuel systam with some parallel rails and a new pump with replacement hoses.

Thanks Mark
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Old 25 September 2009, 11:20   #12
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d'oh, sorry my bad
Best of luck getting it sorted.
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Old 25 September 2009, 13:17   #13
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Originally Posted by Tucker82 View Post
Its running on a Z5 which is from a Type RA if im correct.

So the ecu has to use less fuel when priming warm than it does cold? It does often seem like its overfuelling/flooded after a few turns. Sometimes it'll get going after 30 secs, sometimes 10 minutes. Just depends what mood its in!
That is my understanding although I stand to be corrected.

Think of it like a manual choke. You need to open it fully when cold but leave closed when warm.

To be honest, I doubt spending sums of money on parallel configuration etc will solve your problem. It is a good mo though and cheap to do if you do it the budget way.

Re fuel filter, again I doubt this would cause warm starting problem.

Like I said, I'm not really sure but it could well be flooding itself.
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Old 20 October 2009, 19:17   #14
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Did you get to the bottom of this mate as i have the same symtoms as you?
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Old 20 October 2009, 22:16   #15
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Well I haven't driven the car an awful lot as I've had some problems:

1) A new born baby!!
2) new battery & alternator
3) 1 leaking injector O ring
34Steering pump went & new one leaked so had to make the new pump good after stripping it down.
5) New fuel lines & filter
6) More engine component spraying.
7) Fitting another header tank.

BUT after changing fuel lines, clips, and filter I drove it to a mates. It did start when hot, 4 times.

I haven't driven it since and putting it all back together again tomorrow so fingers crossed Its sorted. Once its all in 1 piece I will drive about for a couple of days and see how it goes. I'll update this thread so you know how I get on.

What symptoms have you got? Have you checked for fault code? What have you replaced/tried?

Tucker
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Old 20 October 2009, 22:16
 
 
 
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