Warm start problem - ongoing investigation

[Ian C]

The long running saga of an annoying warm start problem continues. I started off here with vapour lock questions:

http://www.mkivsupra.net/vbb/showthread.php?254054-Hard-to-start-when-warm-vapour-lock-issue

 

Then went here with fuel pressure:

http://www.mkivsupra.net/vbb/showthread.php?282306-Fuel-pressure-retention

 

And recently here with a starting voltage question:

http://www.mkivsupra.net/vbb/showthread.php?289550-Starting-voltage-how-should-it-behave

 

All of which didn't really draw any conclusions. I read up a lot on alternators etc. since that and the ramp-up is apparently normal. The symptoms and what I've tried already are covered in those so I won't repeat them here, but I did notice something that finally made it change behaviour.

 

The place this usually crops up is at the petrol station. The car is fully warm when I get there (v-power only ) and it takes about 4 or 5 minutes to fill up and cough up. Sometimes it starts, sometimes it struggles, a lot of the time it fails to start and I have to key off, wait a bit, and try again.

 

So I figured I'd drive home and get and oscilloscope on a fuel injector, wait 5 minutes, try and start it, record what the injector did. Alas, as described here I couldn't reproduce the problem despite trying again another day as well. Then I realised I was parking up in the garage, popping the bonnet, attaching the wiring and stuff, and then leaving it with the bonnet open. It started just fine every time when all the underbonnet heat was allowed to escape.

 

So I've come full circle to heat soak/fuel vapourisation issues again. I got a multimeter with a thermocouple on it, the went and filled the car up with fuel, timing how long it took me. I got home and took some temperature measurements around the fuel rail and injectors. I checked the rail itself at the front and the back, a fuel injector near the head end and near the rail end, and one of the two fuel rail support cylinders at the head end and at the rail end as well. (It's a HKS purple alloy top feed rail and comes with two aluminium cylinders that the mounting bolts go through).

 

I checked these areas both straight after parking up, and after leaving it five minutes with the bonnet down. The reason I took head end and rail end temperature readings of the components that join the fuel rail to the cylinder head was to see what the temp differential was along them. The bigger the difference, the more of an insulation effect the component had.

 

I've not got the exact numbers with me at the moment, but I know that after 5 minutes standing, the fuel rail body temp went from around 45degC to 55degC, quite a significant heat transfer. The fuel injectors dropped about 25degC across them (head end was about 70degC, rail end was about the same as the fuel rail). But the two aluminium support cylinders dropped barely anything, about 5degC - they were merrily transmitting all the cylinder head heat into the fuel rail.

 

Something else that backs up this conclusion is that I let the engine idle for about 30 seconds at the pumps before switching off, and it fired up first go. Circulating the fuel like this probably has some initial cooling effect to the fuel rail and maybe the cylinder head itself a bit. I used to run a turbo timer for one minute until consensus on here that they weren't really needed these days what with water cooling jackets on turbos, DBB cartridges etc.. I think my warm start problems began because I stopped running the engine a minute before keying off, hence this test, and so far it's panning out.

 

So I'm now thinking I need to try insulating the fuel rail from the cylinder head heat via these two support cylinders, ideas welcome Doesn't have to be a permanent solution, just a temporary test (so no bespoke carbon fibre solutions just yet). Also, anyone else who has warm start problems like mine, try running the car for a minute after stopping, like you have a turbo timer, and see if it helps. It'd also be nice to know if you have an aftermarket fuel rail setup.

 

-Ian

[Ian C]

My fuel rail, the ally cylinders I'm talking about, and where I measured the temperature:

 

[Alex]

Nylon tube replacement is still my (patent pending) option - if it can take the heat.

[mellonman]

Thermal gasket from the block I fitted mine and must admit I havent had this problem as much, I did say heat soak in one of the other threads

[trebor69]

You know I'm itching for a turbo and more power but ALL of the supra's with big BHP are always having issues (or so it seems) .....I love my Supra , its styling and the fact that I can work on any part of it (not like the modern rubbish) ......where do I go from here ??????

By the way Ian C .....I'm sorry that this helps you in no way whatsoever

[JamieP]

Has you checked to see if your injectors are leaking? I've just had that issue on my GTR, hot starts started to become dodgy, turned out the injectors was leaking and flooding the engine.

[mellonman]

You know I'm itching for a turbo and more power but ALL of the supra's with big BHP are always having issues (or so it seems) .....I love my Supra , its styling and the fact that I can work on any part of it (not like the modern rubbish) ......where do I go from here ??????

By the way Ian C .....I'm sorry that this helps you in no way whatsoever

This is just because we are using the old method of ecu, now things are alot better with stand alones and ecus in general, dont let it put you off a single turbo 500-600bhp supra is where the party is lol, but cars this old will always need things doing to tgem regsrdless of power

[mellonman]

Has you checked to see if your injectors are leaking? I've just had that issue on my GTR, hot starts started to become dodgy, turned out the injectors was leaking and flooding the engine.

 

This could also be true as when I changed to the thermal gasket I replaced the injectors

[Ian C]

Has you checked to see if your injectors are leaking? I've just had that issue on my GTR, hot starts started to become dodgy, turned out the injectors was leaking and flooding the engine.

 

I have indeed, I fired it up with as much removed from the top end as possible, then turned off and pulled the plugs. No wetness on any of them and no fuel on the piston crowns.

 

This is just because we are using the old method of ecu, now things are alot better with stand alones and ecus in general, dont let it put you off a single turbo 500-600bhp supra is where the party is lol, but cars this old will always need things doing to tgem regsrdless of power

 

I'm still happy with the EMU. I know fingers have been pointed at this as the reason for the duff warm start, but if it's just heat soak via the fuel rail supports, it's hardly an ECU issue. Maybe a Syvecs could do some trick that works around the issue, but it's only masking the actual problem.

 

This could also be true as when I changed to the thermal gasket I replaced the injectors

 

This thermal gasket, where does that live? Between block and lower intake manifold? Sounds promising, got any linkies?

[mellonman]

I have indeed, I fired it up with as much removed from the top end as possible, then turned off and pulled the plugs. No wetness on any of them and no fuel on the piston crowns.

 

 

 

I'm still happy with the EMU. I know fingers have been pointed at this as the reason for the duff warm start, but if it's just heat soak via the fuel rail supports, it's hardly an ECU issue. Maybe a Syvecs could do some trick that works around the issue, but it's only masking the actual problem.

 

 

 

This thermal gasket, where does that live? Between block and lower intake manifold? Sounds promising, got any linkies?

 

Yep thats it thats exactly where it goes, also stops heat soak to the intake temp sensor, I will try and dig out some links , not sure how easy they are to get think they was specail made

[mellonman]

http://www.mkivsupra.net/vbb/showthread.php?178422-Intake-temps&highlight=intake+thermal+gasket

http://www.ebay.co.uk/itm/OBX-Intake-Manifold-Thermal-Heatshield-Gasket-93-98-Toyota-Supra-3-0L-Mark-IV-/171061801931?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3ASupra&hash=item27d413f3cb

 

There is a obx gte thermal gasket, not sure if its the same as I have as I brought mine from ryan g from his build

[Digsy]

Something else that backs up this conclusion is that I let the engine idle for about 30 seconds at the pumps before switching off, and it fired up first go. Circulating the fuel like this probably has some initial cooling effect to the fuel rail and maybe the cylinder head itself a bit. I used to run a turbo timer for one minute until consensus on here that they weren't really needed these days what with water cooling jackets on turbos, DBB cartridges etc.. I think my warm start problems began because I stopped running the engine a minute before keying off, hence this test, and so far it's panning out.

 

I'm wondering whether it might be down to the fact that running the engine for an additional 30 secs / 1 minute keeps the cooling fan running, which as well as the temperature of the engine itself will help lower the overall engine bay temperature - more like the open bonnet would allow the hot air to vent out.

 

Circulating the fuel in the rail will probably help prevent the fuel from vapourising, but it won't be because the fuel is cooling the head, it will be because you are presenting a higher mass of fuel for the heat to soak into (thus lower imcrease in temperature). The question is whether the heat is conducting up the ali supports, from the surrounding air or from direct radiation off the engine.

 

Would be interesting to see an air temp measurement from the fuel rail vicinity with and without the fan running, and with the bonnet open.

Edited July 15, 2013 by Digsy (see edit history)

[Alex]

...as well as 30secs of coolant cycling.

[Digsy]

That will help, but in terms of engine geography the water jacket is a long way from the fuel rail, and the conductive path into it is quite small.

 

What we really need is a datalog of the fuel rail temp, the underbonnet air temp and the coolant temp to see which are most closely coupled after key-off. :-)

[Ian C]

I dismissed ambient air temp under the bonnet warming up the fuel rail because air is actually quite a good insulator, so the cylinder head heating the air and then heating the fuel rail external surface and then the fuel inside surely can't be the cause of it heating up, especially when those cylinders are cheerfully piping over 70degC of heat directly into the fuel rail

 

Plus a stock Supra has just as hot an engine bay, but they don't suffer from this problem. However they do have a different fuel rail made of cast ally with a non-shiny surface, which might transfer the heat less.

 

Datalogging multiple air temps at once with the bonnet shut is a bit of a problem as I've only got the one temperature reading multimeter

[Ian C]

Also, I am thinking it's underbonnet temps/heat soak and the running of the engine before key-off probably contributes in various ways as you say - cycling air through the engine bay, running fuel through the rail, coolant and oil through other hot bits. Might be enough to lower underbonnet temps enough to the point it has more capacity to soak up the block/head heat without affecting the warm start.

 

That manifold gasket is cheap enough, I'll see what the postage is like and bag myself one if it's reasonable

[Digsy]

I dismissed ambient air temp under the bonnet warming up the fuel rail because air is actually quite a good insulator, so the cylinder head heating the air and then heating the fuel rail external surface and then the fuel inside surely can't be the cause of it heating up, especially when those cylinders are cheerfully piping over 70degC of heat directly into the fuel rail

 

Heat transfer is a function of three factors, two simple and one complicated. The simple ones are: the surface area in contact between the "hot" and "cold" elements, and the difference in temperature between them. The compllcated one is the heat transfer coefficient (HTC), which is just a number which represents how well heat energy can jump from one to the other. Appropriate figures for HTC are usually looked up in a book or passed down from father to son through the media of poetry and dance

 

Suffice to say that you have a cylinder head which is joined to the fuel rail through two junctions which have a high HTC. but a small surface area (the supports). You also have a junction which has a low HTC but a much larger surface area (the fuel rail body / air interface).

 

I'm hypothesising that on shut down the major castings in the engine will have soaked to pretty much the same temperature - about 80degC. I woudn't be surprised if after a minute these metal temps were virtually no different if the engine was left running or switched off.

 

Interestingly, the specific heat capacity (the measure of the amount of energy it takes to heat up a kilogram of something by 1deg) for air and aluminium are quite similar (0.91kJ/kg.K for aluminium and about 1.00 kJ/kg.K for air) but there is a hell of lot less air surrounding the fuel rail by mass which means it will heat up very fast. Air is a good insulator because it heats up quickly and then doesn't pass that heat on. I'm hypothesising that keeping the air moving over the fuel rail by either natural convection (opening the bonnet) or forced convection (keeping the fan running) will have a greater cooling effect than keeping the coolant running through the head (which in engine geometry terms a very long way away from the fuel rail).

 

The other big factor is the movement of fuel in the rail by keeping the fan running. This will help transfer energy heat away from the rail amd also help stop the fuel from vaporising by maintaining the fuel pressure in the rail.

 

Despite you having discounted the air temp as being a possible cause I think you may have some evidence to the contrary because when the bonnet is open your problem can't be re-created to order. It might be interesting to rig the fuel pump to run on for a few seconds after engine shut down to see if that on its own will also probide a fix.

 

For a practial example, have a look at how a pan or metal tea pot handle is attached. Its usually by a single bolt or several very small spot welds. This is because the small contact area limits the heat transfer from the hot pan to the handle. You could boil water in the pan all day long and the handle would not get hot. This is because the surrounding air can extract heat from the handle faster than the small contact area with the hot pan can supply it. Even though the heat extraction from the handle is less efficient (lower HTC), the larger surface area more than compensates. By contrast, if you played a hot air gun on the handle it would heat up very quickly as the heat could not conduct away from the handle into the pan fast enough through the same small contact area.

Edited July 16, 2013 by Digsy (see edit history)

[Ian C]

I love science I haven't used SHC since A-level physics

 

I think we're looking at two different aspects here. The first is "why does my fuel rail get too hot when stock ones don't" and the second is "what can I do to prevent this". I don't think underbonnet air temps cause #1, because as you said, air doesn't give up heat easily. But keeping the engine running (and therefore the fan) helps with #2, yes?

 

If leaving the engine running a minute via my still-installed turbo timer means I can fill up with fuel and relax, that's a great workaround. But it bugs me that millions of cars have that much heat under the hood and don't need to run a minute before keyoff to ensure a good start after 5 minutes, so I'm interested in nailing why the HKS fuel rail boils up when stockers don't. Those ally cylinders seems to merrily pipe the heat in, so I'm thinking that's the big difference here. Either that or the sculpted nature of the stock fuel rail presents a greater surface area to conduct heat out into the underbonnet air, perhaps.

 

Insulating the ally cylinders seems like a good fix attempt, but using an existing insulating gasket for the whole lower manifold seems like a more logical thing to as a permanent fix.

Edited July 17, 2013 by Ian C (see edit history)

[dandan]

Have you measured any rail temps?

[Ian C]

"after 5 minutes standing, the fuel rail body temp went from around 45degC to 55degC"

[Digsy]

...so I'm interested in nailing why the HKS fuel rail boils up when stockers don't. Those ally cylinders seems to merrily pipe the heat in, so I'm thinking that's the big difference here. Either that or the sculpted nature of the stock fuel rail presents a greater surface area to conduct heat out into the underbonnet air, perhaps.

 

Can we get a picture of the stock fuel rail and the HKS one side by side? Some approximate dimensons would be good too.

 

In OEM world we add extra volume into the fuel rail to offset the effects of vapour lock, which itself is a paradox because I was assuming that the interior volume of the HKS rail would be higher than the stocker?

[CanisLupus]

I've had a similar Problem while running the emanage... Since i've switched to Syvecs it starts no matter how long the engine has been switched off

Another thing to consider is that with the Stock pump and Fuel System the Fuel Pressure is retained over a long time as there are check valves. With 2-3 Bar of Pressure in the Rail higher Temps without vaporising can be reached. Maybe a starting point for your problem if you don't want to change the ECU?

[Ian C]

After going down the electronics route and finding nothing untoward, I'm still thinking it's heat soak to a (£2500) change of ECU is going to work around the issue using some tweak rather than actually fix the vapourisation in my opinion. A twenty quid thermal gasket sounds like a better first step to me

[BOB B]

Hi Ian, I think I get the same problem, mine only seems to happen within the first 10 - 20 mins of starting, (until fully warmed up) if I stop in that time period then I struggle to get it started again.

 

The main reason for me posting though, is I am stock BPU UK engine.

[Andy Blyth]

After going down the electronics route and finding nothing untoward, I'm still thinking it's heat soak to a (£2500) change of ECU is going to work around the issue using some tweak rather than actually fix the vapourisation in my opinion. A twenty quid thermal gasket sounds like a better first step to me

 

You could quite easily test your theory without changing the gasket. Install a switch in the cabin that replicates the "paper clip" method of forcing the fuel pump to operate (bridging the FP and B+ terminals in the diagnostics port connector).

 

Wait until you are expecting the car to have trouble starting. Before you try to start, give the fuel pump a 5 second blast (using the switch), which should be enough to force any vapour out of the rail and into the tank.

 

I think the following caveats would apply:

 

1> You would have to try this many times before beng able to have confidence that priming the fuel rail "fixes" your problem (you can't accurately predict the behaviour before it happens).

2> Doing this would replace the fuel in the rail with cool fuel from the tank. This may have an effect on the behaviour of the fuelling system. Hot fuel is lower in density; also the response times of injectors goes up with temperature (higher resistance).

3> Priming the fuel system will ensure that the fuel rail is at a sensible pressure at the point at which you start cranking. It's possible that your fuel rail has no pressure after 20 mins if you're running an aftermarket FPR. this could have an effect on the cranking behaviour.

 

Do you have the ability to measure the temperature that the IAT sensor sees after a long heat soak? I'm running a stock ECU at the moment and after a hot start, the AFRs are very lean when idling, until the closed-loop fuelling starts. When running a standalone, I can see the stock IAT sensor sees some crazy intake temperatures after a heat soak. That said, I'm not sure if the stock ECU looks at the IAT to calculate the fuel needed for cranking.