Warm start issue

[txhokie4life]

2.7 Boxster:

 

Crank Position Sensor already replaced.

 

Cold start -- no problems at all

Hot start -- no problems at all

If car sits for 30-60 minutes or longer -- car turns over, but doesn't seem to fire.

 

I've noticed that I either have to feather the gas pedal while cranking, or sometimes just crank longer.

 

As soon as it starts once -- seems to start every time immediately there after.

 

I haven't checked fuel pressure yet.

 

Acts as if fuel pressure bleeds off?  I.e. if you immediately -- or say 5 minutes later try to start it -- no problem.

But wait 30-60 minutes or so -- hard start.

Cold start never seems to be a problem.

 

So what is the difference between a cold start and warm start?

 

Runs awesome once going.

 

Mike

[Ahsai]

Does sound like an air/fuel mixture issue. Do you have a scanner that you can check the coolant temp sensor reading? I think it's a good idea to verify fuel pressure first. Then maybe check if the evap purge valve is leaking (it should have tripped the CEL though)?

[timbo]

When you turn on the ignition do you hear the initial buzz of the fuel pump to pressure up, would have thought it should hold its pressure anyway though, once cranking I think the pump should be on. if not it could be a relay problem. However, Im not sufficiently up to speed with the details of this system to understand why it should start cold if this was the problem unless it was temperature related. I'm sure someone will be along who knows the answer.

[boxster_nut]

2.7 Boxster:

 

Crank Position Sensor already replaced.

 

Cold start -- no problems at all

Hot start -- no problems at all

If car sits for 30-60 minutes or longer -- car turns over, but doesn't seem to fire.

 

I've noticed that I either have to feather the gas pedal while cranking, or sometimes just crank longer.

 

As soon as it starts once -- seems to start every time immediately there after.

 

I haven't checked fuel pressure yet.

 

Does tach read 500-700 rpm while cranking?  if not, CPS not working

As others mentioned, do  you hear the fuel pump spin up on turning key?  at 122k miles that is, IMHO, fuel pump starting to go.  This symptom is exactly same as saabs with approximately the same mileage on the fuel pump. 

If possible, attach a pressure gauge on the fuel line and watch it during periods of cranking with no start.

 

Good luck

 

J

 

[txhokie4life]

Looked at it this morning.

 

Tach bounces to 4-500 rpm when cranking.

 

fuel pressure at 60psi while starting and running, drops to 50psi after sitting a little bit.

 

swapped throttle body and cleaned MAF, replaced fuel pump relay.

 

Smoke test -- no apparent leaks

 

It's hard to duplicate the warm start (takes time) -- but there seems to be ever so slightly a hot start behavior -- maybe 2 or 3 cranks required, longer

than what I remember.  Maybe the slightest hesitation -- then it kicks over and runs great.

 

monitored ECU -- everything looks just fine -- and it runs great.

 

head scratcher.  left it with my mechanic to try a few other things (but we're running out of ideas).

 

Mike

Edited October 7, 2015 by txhokie4life

[Ahsai]

A few more things maybe worth checking:

 

- vacuum leak

- evap purge valve leak

- idle stabilizer needs cleaning

- fuel pressure when it's struggling to start

- fuel filter?

- fuel injector(s) leaking

[txhokie4life]

A few more things maybe worth checking:

 

- vacuum leak

- evap purge valve leak

- idle stabilizer needs cleaning

- fuel pressure when it's struggling to start

- fuel filter?

- fuel injector(s) leaking

 

I think he checked for vacuum leak with both smoke test and vacuum gauge -- I wasn't looking at the time.

I don't think there is an idle stabilizer on drive by wire

There is no fuel filter.

 

We had the FP gauge on -- I didn't specifically look when cranking.

I think we would have noticed a fuel injector leaking -- but I'll ask.

 

M

[Ahsai]

I see so you have a lot less to check. For the FP gauge, I meant wait till the engine is warm where you expect to see a hard start, then hook it up or it was hooked up that way already?

 

How about the evap purge valve then?

[Ahsai]

BTW, since it's e-gas, have you tried throttle body recalibration yet?

[txhokie4life]

A little more info.

 

FP doesn't droop during startup.

Battery voltage solid during startup

evap valve seems fine

MAF good.

TB good.

 

will check fuel connections, starter cable, purge valve test and cps (Again).

 

Mike

[txhokie4life]

FP is 55 when running, drops to 30psi in 1 hour -- what is expected drop?

 

Tried disconnecting MAF -- run for 30 minutes, sit for 30 minutes.  Still slow to catch, then once it fires, it immediately fires next time.

 

Checked Dealership with VIN -- no software updates for this car needed.

 

Swapped starters, checked battery connections.

 

this is driving me batty,

 

Mike

[txhokie4life]

I think when it starts fine -- the RPMs run to 1500 or so and then drop immediately back down.

 

When it struggles to start -- it doesn't have that quick RPM surge -- it just settles at or around the idle mark.

 

As soon as it starts once -- it will start everytime.

 

Swapped the fuel pump today -- think its better -- but might not have run it long enough to heat soak it on the way into work -- will try again this evening.

 

M

[Ahsai]

Did you check if the coolant temp sensor and intake air temp sensor report the correct readings during hard start?

[txhokie4life]

Fingers crossed -- we swapped fuel pumps and it appears to be happy.

 

Since it can be difficult to "recreate" the failure -- I'm still being somewhat reserved.

 

The interesting behavior is the Fuel Pressure readings always looked good.

 

The other issue was that the car only has 12.5K miles -- however -- it is not known just how long it sat when the engine suffered an IMS failure prior

to acquisition on my part.

 

The theory is that the pump was worn -- maybe due to bad gas -- and as it warmed -- it wouldn't always turn on -- however, when hot, there

might have been enough gas in the rail/lines/etc to fire the engine -- and once firing -- the pump worked fine (vacuum pull on fuel?, higher voltage after cranking?, DME sending more fuel request then just starting at idle?) -- at cold, pump worked fine.

Warm -- the fuel pressure had bled down, and the pump didn't run (or run well),  Allowing it to crank allowed it to build pressure or if that was not good enough -- blipping the throttle enticed the pump to work a little harder.  In the end -- who really knows....

 

So I'm hoping this is the issue -- and will guide some other poor schmuck who stumbles across this thread......

 

Mike

Edited October 14, 2015 by txhokie4life

[Ahsai]

Good luck and do let us know if that fixed the issue for good.

[txhokie4life]

No issues for 3 days -- thick we nailed it.

 

M

[Ahsai]

:thumbup: