Jojo Bonett

Hi,
I have a Boxster S (2003) which when cold starts normally and also revs up to full revs without any issue. However once the engine is warm the engine hesitates at 4500 RPM and over. In fact it will not go above the 4500 mark as it starts like misfiring? I also noticed that when the engine is warm and I try to start the engine, it takes a few more cranks than normal to have the engine started.When the engine is warm the idle is not so stable (throttle body is clean). I also tried unplugging the MAF but no difference noticed.

I also took off the oil cap and although you do notice the engine a bit faster, the hesitation remains, so I guess that the AOS is not related also.

No engine warning lights on the dashboard and when I plugged my Scan Gauge II with the car, I do not see any recorded error codes.

Could it be the coils or maybe spark plugs?

Any input would be appreciated.

Thanks to all

Jojo



i

lee101315

Try swapping in a MAF insert.

Jojo Bonett

Hi
thanks for the reply. However do you still think it could be a bad MAF even though I unplugged it and the engine still hesitated at 4500 rpm?

Jojo

extanker

ssssoooo many different things could cause this. You really should start with a scan tool ....not a code reader and look for readings out of spec. You should have got a cel when you ran the car with the maf off. yes plugs could do this......and coils,crank sensor,if app varo cam,bad fuel,fuel system etc. the list is long so rather than poke n hope use a pro scan tool eg snap-on .let us know

Macster

Hope I'm reading your post wrong. I hope you don't rev the engine real high when cold. If so that's not a good idea and I would advise you to stop doing that.

"Misfire" to me requires the CEL come on either solid or flashing. Whether it remains on or goes dark as soon as the misfiring condition ends is Ok. If it remains on then there should be one or more error codes and misfire error codes should be among them.

Since you don't report the CEL coming on solid or flashing and have obtained no error codes so when you say "misfire" I take it the engine is hesitating/refusing to run above 4500 when warm?

The removal of the oil filler tube cap is to see if the cap can be removed with the engine idling. In some cases, a bad/failing AOS can subject the engine crankcase to so much low pressure while one can unscrew the cap he can't remove it against the pressure difference.

That the engine speed up a bit with the cap removed is normal. With the cap removed the open tube is an air leak and with more air the DME is going to add more fuel and this can increase the engine's RPM's a bit.

The fact you were able to remove the cap does not let the AOS off the hook.

Did this behavior appear out of the blue or did it appear after something was done the car? Some recent servicing? Mod's? Has the car sat unused for some time? What about the freshness of the gasoline?

The slight delay at starting could be the battery is just getting low. Low from the engine being started but the car not being driven long enough to replenish the battery.

When the MAF is suspected the technique is to disconnect the MAF at the engine wiring harness. Then using an OBD2 tool erase the error codes, even if there aren't any. This clearing of the codes (whether there are any or not) resets all the fuel trims and other learned settings back to their defaults.

Then just start the engine and road test the car, drive it normally, and no high RPMs when cold! Then see if the same behavior is present. The CEL may come on but this can arise because the MAF is disconnected. You have to read the code but do not clear it at this time.

Back home then reconnect the MAF and read the codes if any. Write them down. You can do a search to see if they are related to the MAF being disconnected or possibly something else.

Clear the codes and road test the car. If the behavior is present with the MAF removed and present then the odds are the MAF is not the problem.

Extanker said it best. If you are going to attempt to diagnose this yourself you need a tool that you can use to monitor/view engine telemetry in real time to try to spot something out of the ordinary.

Unless you are experienced in this you may be better off taking the car to a professional tech for his diagnosis.

Schnell Gelb

The short version is to connect Durametric

sniperonhigh

You are having this problem driving, as in under load? Or free revs? Anyway, have you ever checked your fuel supply pressure? That and cps would be a couple of things that can cause problems but not throw a code. Fuel pressure rules out a lot of variables....

Macster

No. Not really. No error codes. The OP is probably not experienced enough to identify a possible MAF problem by viewing engine/MAF telemetry. The OP probably doesn't have a Durametric and probably unwilling to spend that kind of money for what he preceives will be a one time use of it.

The true short version is take the car to a professional.

Jojo Bonett

thanks for your thoughts and I do see what you explain. Today I reconnected the ScanGauge II and managed to see a P0335 code!. Checked on the forums and found that its the Crank or camshaft position sensor. So I physically took a look at the sensor in the car and also checked the connector wire but all seem to be fine. I started the engine and since it was cold it started without any issues, waited a while for it to warm up a bit and confirmed that the engine can rev up till red, so I left the car to warm up fully and as anticipated the car started to have a rough idle and also will not rev up more than 4500 rpm. When at idle and warm, the car also stalled. So I left the car for a while with engine off and re attempted to restart, it was cranking (so no battery issues) but will not start!. Waited for a further say half an hour and tried restarting and in fact although took some cranking it did start.It was also hesitating when revving more than 4500 rpm.

So could this mean that it can be the CPS being faulty or maybe defective and therofore the CPS can create these symptoms that I am experiencing, i which are:-

all normal starting and revving at cold engine.(although not recommended.)

when engine is warm, idle hesitates a bit and does not rev above 4500 rpm. When engine is warm, sometimes engine stalls when at idle.

when warm engine does not start immediately but needs extra cranking battery is good.

tried to restart the engine after say 30 mins, but to no avail, engine will not start. waited for an hour and engine started but still with revving problem showing and rough idle.

So could all the above be due to a bad CPS?

Thanks for your patience!! and happy new year!!

JJ

extanker

i see you are going the poke n hope route.................well change the cps and hope .

Schnell Gelb

A gamble of Less than $100 for BOSCH 0261210204

Schnell Gelb

...who has a Durametric or PIWIS

Macster

And the know how to make the most of it.

Jojo Bonett

Yes it seems to be pointing in that direction CPS that is, but I shall anyway try to get an experienced Durametric owner and get some more detailed readings before.

This morning I had a go and tried to start the car, which started immediately, but still can see P0335 error on the ScanGauge, but no engine light on the dash...

What I cannot understand is why does this sensor not affect the engine when cold?,

Cheers and thanks

JJ

extanker

it is very common for sensors to fail when they get hot but behave when cold.