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Old 11-30-2016, 10:55 PM   #1
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Hesitation at 4k and over when warm

Hi,

So I started my (cold) 2004 Boxster S without any issues, normal turn of the key and engine fired normally. If I foot the gas, the engine revs up to wherever I press up to full rev counter.

But once the engine starts to warm up, the engine will not rev up to more to approx 4-K revs and starts to hesitate if I keep trying to rev it up. Also noticed that once warm, the restarting of the engine takes a bit more turning than normal to start. I have not yet checked for any codes, but o lights came 'on' on the dashboard. Car is not used daily and has still only 25,000 miles on it.

I was think of plugs and coils, but not sure what else to look for.

Any input would be appreciated.

Thanks to all

Jojo
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Old 12-01-2016, 12:02 AM   #2
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Could be the CPS sensor, they tend to cause warm startup issues when they are failing, but I am not sure that would explain the inability to rev past 4k when warm. Hopefully someone will more knowledge can chime in.

Not sure if you know, but you mentioned revving the engine after a cold start. It's better for the engine to not rev past 4k RPM until the engine has fully warmed up to the 180 coolant tick.
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Old 12-01-2016, 12:58 AM   #3
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Thanks for the reply. Yes agreed not to over rev it when still cold, but had to try this out to try configure what's happening....

Cheers

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Old 12-01-2016, 11:17 AM   #4
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Does it hesitate at 4000 rpm but then rev through, almost like a stutter, if so could also be MAF.
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Old 12-01-2016, 11:21 AM   #5
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No it seems that it hesitates from say 4k upwards. To me it looks like misfiring. I'll try to see if I have any codes, but not sure since no engine warning came on yet!

JJ
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Old 12-01-2016, 11:25 AM   #6
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I had similar issue earlier this year when abroad, car would run and rev, but hesitated almost like a misfire at around 4000rpm.

Indie diagnosed as failing MAF and durametric showed a number of fuelling issues, new MAF all sorted.

Suggest codes read by someone knowledgeable, I had thought coils but he diagnosed over phone and was spot on!

Get codes read, don't really on my experience, mind you mines Ocean Blue Metallic too so it must be that (sic).
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Old 12-01-2016, 07:27 PM   #7
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So a bad or dirty MAF could work fine on a cold engine and give wrong readings when engine is warm? Resulting to the symptoms that I have and also what you have experienced??
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Old 12-01-2016, 10:03 PM   #8
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On my 98 it was the MAF. When the engine is cold it runs on fixed fuel trims and once warm it switches over to sensor driven trims. Failed MAF sensor = poor performance
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Old 12-02-2016, 03:45 AM   #9
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If you want an easier way to see if it's the MAF, open up the engine bay and unplug the wire from the sensor. If the car works fine with it unplugged, you'll know that it's the sensor. Don't drive for long with it unplugged, however.
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Old 12-02-2016, 08:50 AM   #10
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Variocam sensor? That kicks in around 3200 rpm...
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Old 12-26-2016, 03:31 AM   #11
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Hi so I cleaned the MAF and went for a ride, seems all fine for a while. Then parked car and came back about an hour after, when I came to start the engine I noticed that it took a few more than normal amount of turns for the engine to start, it then started and immediately knew that once I try to rev it more that 4500 rpm the engine will hesitate at that point which it did!! Plugged in a Scan Gauge and do not see any error codes, in fact no warnings on the dashboard also.

Not sure what's the best next logical step to take

Any input from you guys is appreciated.

Thanks,

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Old 12-26-2016, 04:17 AM   #12
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Hesitation at mid-throttle can be caused by cracked spark plug cables or cracked coils. The best way to diagnose whether this is the cause try to give it full throttle when you first notice the hesitation. If the hesitation goes away when you floor the throttle while driving you have found the problem.

The explanation is that the voltage needed to generate a spark is highest at mow load and mid revs. That will cause the spark to jump the cracks instead of the plugs.
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Old 12-26-2016, 05:19 AM   #13
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Hi thanks for your thoughts, however I am not sure about what you say since the hesitation only starts when the engine is warmed up.

I also noticed that hesitation is present even when no load, i.e. car is on hand brake and revved up.

when cold, no hesitation and starting the engine is very quick (minimal amount of turns).

I beleive that if it is a leaky coil, it should do it even when cold....

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Old 12-26-2016, 06:38 AM   #14
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Actually it is consistent. When the engine is cold the mixture is richer and the spark resistance is lower. As the engine warms up the mixture leans and the spark resistance goes up.

Under low loads, including no loads the resistance also is high.

All that you describe is consistent with the spark going around one or more plugs.

I had a Buick with exactly the same issues, took ages to convince the garage that the problem was in the spark plug wires. They kept insisting that it had to be injectors. When they finally gave up I had them replace the spark plug wires and bingo, the problem went away.
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Old 12-26-2016, 06:49 AM   #15
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Hi

Thanks for your reply, again.

Ok so did some further investigation hoping to eliminate some of the possibilities:

Noticed that at idle sometimes engine stalls as idle is sometimes hunting and rough.

TB is clean as a whistle.

Unplugged the MAF, engine still hesitating at 4500 and over, so probably MAF is not related.

Noticed that there is a small difference when the oil cap is removed, in fact engine revs go up a tiny bit however engine still hesitates with the oil cap is off and engine revved up to above 4500. so probably AOS not involved too.

Hot engine makes it needing more turning to start it up, but starts. Driving no further than approx 4500 rpm car seems to be fine.

So my next guess tends to be pointing at a defective coil/spark plugs so might need to inspect physically each one and see...

JJ
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Old 12-31-2016, 07:15 AM   #16
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Hi Anker, 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 now I am more lost than before. I am assuming that if the hall effect sensor CPS is faulty or maybe defective then it should not be related to engine temperature and should be troublesome even when the engine is cold, no?
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Old 12-31-2016, 08:10 AM   #17
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Hi JoJo. I have no experience with CPS issues and am running out of ideas and getting over my head. All I can offer is that remember reading that if the CPS fails the car will refuse to start.

A lot of issues are engine temperature sensitive. Something that works when the engine is cold and the mixture is rich may not work when the engine reaches temperature and the mixture leans out.

If I were in your shoes I'd pursue the CPS error and get that resolved.

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Old 12-31-2016, 08:47 AM   #18
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At minimum I would remove sensor, clean and reconnect. Then reset the code and see if it comes back. Some codes will store but may not throw a Cel until so many drive cycles. Intermittent electrical gremlins are the worst. You don't know when that code was active. There may be debri there you can't see. There is no adjustment on that sensor so you can't get it wrong by just removing and reinstalling. Check the crank pulley itself too for irregularities.

Last edited by Lapister; 12-31-2016 at 08:54 AM.
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Old 12-31-2016, 09:31 AM   #19
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Originally Posted by Jojo View Post
I am assuming that if the hall effect sensor CPS is faulty or maybe defective then it should not be related to engine temperature and should be troublesome even when the engine is cold, no?
Generally resistance increases with temperature, so it is fairly common for electrical problems to initially become noticeable at higher temps. As the component continues to degrade, then the problem becomes more common at lower temps. Eventually, the component degrades to a point where it essentially becomes a hard failure at all temps.

The P0335 code is your first real data point. I'd clear it and see if it returns. If it does, start your troubleshooting and diagnostics there.
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Old 01-02-2017, 04:11 AM   #20
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Ok and thanks.

Will physically check.

however maybe someone can tell me what ohm meter readings I should read and also the pin numbers of the sensor?

Thanks,
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