P_Lav

I've had this happen to my car about 5 times now, and it only ever happens when I'm on a road trip some where, and its flipping annoying...

S4 GXL has 105,000 kms, original NA 13B, cone filter, exhaust, air pump removed, walbro pump (new last summer with new sock, and fuel filter), runs minty 99% of the time, smooth idle, pulls nicely, runs a tad hot till the t-stat opens and then temps never go past half after.

I drove the car for about 2 hours highway driving, temp gauge right in the middle, perfect operating temp, it's around noon, August, hot day, like 35 degrees Celsius outside, on my way to a drift demo, and first stop light I hit, down shift into 3rd... 2nd... and slip it into neutral, revs drop normally like its going into idle, but it doesn't stop at 800 rpm, just falls right off the tach and the engine dies. I try to start it back up, and it won't. I pump the pedal, it starts briefly, but I can't keep it running with the pedal... This was in traffic by the way.

I get it going, drive to the next light, same thing...

This time it really won't start. Thinking maybe it's flooded, pull the egi fuse, crank it, put it back in and try again... Nothing. So now thinking the worst I pull the 1st rotor trailing plug, and it's white, like it's running lean as f*ck. I cranked the engine over and listen to the puffs, all the pulses sound even. Same on the rear rotor, plug is white, even pulses.

After awhile a tow truck passes by, tells me he can come back and tow me in 15 minutes, and I just so happen to get it going, and drive to the drift event. Car sits 4 hours whilst I'm getting peppered in tire dust, and runs fine after.

Later on that evening still hot as hell out, go for a cruise with some friends, and it's running fine again, city driving, stop and go traffic, no problems. Pull over in a parking lot after 1 hour of cruising, to decide where to eat, idle it for a bit, watch some idiots in irocs do burn outs and get busted. Get back on the road, first stop light, dies, on the busiest street in the city, ON CRUISE NIGHT. Just so happened a cop was 3 cars behind me, and helped me get it off the road safely. And it started back up after a short time of sitting.

To me, this can only be vapor lock, it happened to me last summer a couple times, and it only ever happens after the car has been driven for a extended period of time, and it's hot out.

Is there anything else I might be over looking, coolant temp sensor having a dead spot? Or is this just a result of Mazda putting the fuel rail right above the exhaust mani?

And if it is vapor lock, what can I do to prevent it? Could my pulsation dampener be the cause? It doesn't leak, so I never really put any attention to it.

My cooling system seems to be doing its job, I'm not running any serious mods, or racing the car, so I figured upgrading my rad isn't necessary yet.

I'm debating on putting washers on my hood bolts to give it a bit better ventilation.

Just wondering if anyone has had any experience with this issue, or some ideas to shoot around, because when I'm 200 clicks from home, and on the side of the road in traffic, and getting police to help push my car out of harms way, it is a tad inconvenient.

misterstyx69

iTrader: (142)

The hood thing won't work as the hinges attach from the sides of the hood.That would only make the hinges spring outwards and the hood would stay where it is...Take a look,you'll see what I mean.

Have you tried a new gas cap?

clokker

iTrader: (2)

I think you have a heat related fuel delivery problem but not vaporlock.

My current Z car project is the poster child for vaporlock issues, the intake-over-exhaust is an open invitation to boil fuel out of the lines when the car sits after running (humorously, the first factory "fix" for this problem was clamping wooden clothespins to the fuel lines to act as heatsinks!).

Your car loses fuel and dies while it's actually running and to me that would indicate a pump issue.
Maybe the relay/resistor pack is acting up or as Styx proposed, a problem with tank venting but in either case, it's probably not that the fuel rails are hot enough to vaporize fuel.

RotaryEvolution

iTrader: (30)

1/2 on the gauge is not normal, though i doubt this is your root problem is probably a contributor as a problem sign of something else.

86-88 cars should run 1/3 on the gauge normally, if it is going beyond that then there is a problem within the cooling system.

if you happened to get a knockoff walbro instead of a true walbro then this could be your problem, i have seen the knockoff pumps seize up when warmed up after about a year of use. test fuel pressure when the problem presents itself.

P_Lav

I'll try a new gas cap, the only problem is testing this condition is it happens very rarely... Just horrible when it does happen.

RotaryEvolution

iTrader: (30)

if you have the original fuel pump still and it is functioning put it back in. there's very little reason to use a walbro on an n/a car.

if the problem goes away then you can probably point at the fuel pump being faulty.

P_Lav

The NA fuel pump was fault, I was planning a turbo swap later, so thats why I opted for the Walbro... It just happened again, it's like 40 degress Celsius out... Took the gas cap off to see if that made a difference, not so much... Just had to let it sit for 3 minutes or so and it started again.

RotaryEvolution

iTrader: (30)

i would try to get your hands on a fuel pressure test kit and see what the fuel pressure is when the problem occurs.

you could probably even make one with a generic liquid pressure gauge 0-100psi with a tee adapter for about $10 from a plumbing store if you can't afford to rent one. i would only use it temporarily since most don't use seals designed for fuel.

normal readings would be 40psi cranking but the walbro usually bumps it up to about 50psi. anything below 40psi would be a pump pressure issue or blockage in the system. a sound from the pump and rushing from the fuel lines doesn't necessarily mean the pressure is sufficient.

P_Lav

The pump is pretty quiet anyways, I'll look into getting the fuel system pressure tested, I just googled vapor lock fixes, and if my fuel system is running normally this shouldn't be an issue. I might also look into heat wrapping my fuel rail and lines.

RotaryEvolution

iTrader: (30)

your problem isn't vapor lock, stop trying to convince yourself that it is.

vapor lock was usually a problem associated with low pressure carbureted cars in extreme ambient heat. vapor lock is a very very seldom occurence with fuel injected high pressure system vehicles, also a problem i have never once seen on any RX7. the fuel tank can't build enough pressure to stall a high pressure pump.

clokker

iTrader: (2)

How is your pump wired?

This has been bugging me since I first read it:
I won't even get into the futility of discussing temp problems when the only data comes from the stock gauge but the bit about the t-stat is odd.
If all is right, engine temp does not spike high before the thermostat rescues it...the 'stat should be opening progressively and the temp will hit and maintain in the normal range without edging high first.

P_Lav

It's just a very strange problem and is really boggling my mind, it just seems like vapor lock because once it cools it starts up and runs fine. But where to go from here... I just wired it up the same way the stock pump was wired, all soldered and heat shrunk. unless the wiring has been molested in the past.

It doesn't always run hot at first, sometimes the temps will go a bit above half when I drive it hard and it's only been running 5 or 10 minutes, but I take it easy, temp will return to half after a minute or two, and it never goes past after regardless how I drive it.

RotaryEvolution

iTrader: (30)

the symptoms may be similar to vapor lock but a seizing pump is not really vapor locked.

i'd consider checking pump voltage, since the only n/a pumps i have seen fail were ones that sat in varnished fuel for years.

j9fd3s

iTrader: (3)

+1 its not vapor lock, and a fuel pressure test will tell you where you need to look next