Strange misfire just showed up - Maserati Forum
 
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post #1 of 12 Old 07-06-2019, 09:22 PM Thread Starter
 
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Strange misfire just showed up

So the other day I took my 08QP Sport GT (91K miles) off the tender after a month I was away and did an oil change.


I then just turned it on and left it running while I went inside to wash up. When i came back out the engine was misfiring like CRAZY!!


I turned it off right away and hooked up a scanner. The only codes I got were for random misfires on literally every cylinder. Spark plugs were done couple months ago and coils are fine, so I ruled that out.



I happen to have another MAF and replaced it with the same results.



So after messing with everything and trying to figure out what is causing this I found a pattern.


Every time the engine hit operating temp, the misfire would begin and not go away.



One thing I did notice was then I turn the key to ACC, I didn't hear a buzz like I usually do (I believe that's the fuel pump sound).. But there is no problem with it since its starts right up and runs fine...



until it hits 195 deg.



I'm lost... the only thing I didn't do yet was look for vacuum leaks. I ordered one of those EVAP smoke machines off ebay to check for leaks, so that one more thing I need to do.


But If I had a leak I would assume I'd get some sort of code besides just misfires. I disconnected the battery over night and did the proper relearn process, with no change.


I'm stuck and Its so weird. Its smooth as any other day just until it hits 195 degrees.


It only happens when I'm stopped... if I'm driving there are no lights, no misfires, and the car runs just as powerful as it always has... but when i come to a complete stop its starts acting up.


In the last year I changed plugs, oil change, flushed radiator, and replaced the coolant temp sensors along with he thermostat.


Brand new up stream O2 sensors just cause I found them cheap.


I have FD DBW, Larini mufflers and x-pipe, 91K miles. I'm totally lost, please help
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post #2 of 12 Old 07-07-2019, 07:24 AM
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How long were the new components installed before the lay up?

C

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post #3 of 12 Old 07-07-2019, 05:05 PM Thread Starter
 
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Originally Posted by Catmanv2 View Post
How long were the new components installed before the lay up?

C

the last thing done were the O2 sensors back in January.. Other than that just the oil change the day the problem started. Used OE Filter and Mobil 1 10W-40.


And Its my daily, so I've put 4K miles or so since then.
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post #4 of 12 Old 07-08-2019, 06:21 AM
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Very odd. I'd be wondering if you'd disturbed something during the oil change? Other than that you're going to have to diagnose the old fashioned way I suspect.

C

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post #5 of 12 Old 07-08-2019, 08:43 PM
 
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Wild guess here, and it's only worth what you are paying for it... nothing.

Things change, but in early days of cat converters, etc. the car starts in "open loop", where it essentially is ignoring the O2 sensors. Only when warm did it go to "closed loop" and utilized feedback from the O2 sensors to regulate the injection system. Now, this was way back, and I don't know if there is still an "open loop" and a "closed loop" transition, nor when it might occur.

Where I'm going with this is perhaps those O2 sensors that you got "at a good price" might be the source of your problem.

Heading back into my cave......

Hans

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post #6 of 12 Old 07-09-2019, 06:12 AM
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I believe that your are correct on the open loop / closed loop piece.
I'd certainly wondered about the )2 sensors, but think the odds of them failing simultaneously (to give random misfires on all cylinders) was less likely.

I've been wrong many times before though!

C

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post #7 of 12 Old 07-09-2019, 09:57 PM
 
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Quote:
Originally Posted by Catmanv2 View Post
I believe that your are correct on the open loop / closed loop piece.
I'd certainly wondered about the )2 sensors, but think the odds of them failing simultaneously (to give random misfires on all cylinders) was less likely.

I've been wrong many times before though!

C
I was thinking more along the lines of incorrect - or maybe poor quality - sensors, rather than them failing. Or installation issues? I've heard of them getting contaminated from careless application of anti-seize etc.

If I were the OP, I think I'd try re-installing the old O2 sensors.

Hans.

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post #8 of 12 Old 07-09-2019, 11:09 PM
 
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Vehicle manufactures try to get engines in closed loops as quickly as possible...The start up and warm up are some of the dirtiest times emissions wise...You are normally in closed loop within the first 60 seconds...O2 sensors don't normally cause misfires...I would look at the fuel trims when it gets to 195 and also check the fuel pressure....Jason

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post #9 of 12 Old 07-10-2019, 07:22 AM
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Thanks, Jason!

C

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post #10 of 12 Old 07-10-2019, 07:54 PM Thread Starter
 
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I'm not too convinced that it would be the O2 sensors... I put like 4K miles since install. Could it be the downstream sensors?
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post #11 of 12 Old 07-10-2019, 07:59 PM Thread Starter
 
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Originally Posted by 4regt4 View Post
Wild guess here, and it's only worth what you are paying for it... nothing.

Things change, but in early days of cat converters, etc. the car starts in "open loop", where it essentially is ignoring the O2 sensors. Only when warm did it go to "closed loop" and utilized feedback from the O2 sensors to regulate the injection system. Now, this was way back, and I don't know if there is still an "open loop" and a "closed loop" transition, nor when it might occur.

Where I'm going with this is perhaps those O2 sensors that you got "at a good price" might be the source of your problem.

Heading back into my cave......

Hans

I ordered the temp sensors and thermostat from ferrparts.com, I asked if he could hook me up with the price if i take O2 sensors as well and he gave me a discount.



Its not that they were bad, just figured i'd swap them as preventative maintenance since the mileage is up there.
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post #12 of 12 Old 07-10-2019, 08:03 PM
 
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O2 sensors don't make misfires...Especially downstream which are used to monitor the catalytic converters...Follow my advice from my earlier post...Check your fuel trims before and after it starts running poorly and also check the fuel pressure...Jason

ASE Master Tech. 29 years experience
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