05-20-2021, 05:48 AM
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#1
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Registered User
Join Date: Apr 2021
Location: Montreal
Posts: 16
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Quote:
Originally Posted by Stl-986
Well if you have no clue then maybe you shouldn't say anything. And if YOU googled you would have known that isn't miss fire on 4 cylinders.
It's actually misfire on cylinders 1-3. I would start with just pulling the coils & plus and replacing the plugs. clear the codes and then take it for a drive.
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Woah there, calm down, I forgot about the general misfire 000 code. I actually have experience diagnosing a misfire I've just not yet bought/worked on a 986 and don't know if there's another common issue that could cause half the cylinders to fail, hence deferring to others
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05-20-2021, 06:28 AM
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#2
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Misfires all on the same bank.
pull the coils a look at them for hairline cracks.
If there are no cracks the coils should be ok.
Replace the plugs as STI-986 said.
Also look for any oil on the coils or plug insolator.
Oil on the plugs or coils can cause issues.
Let us know if that fixes the issue.
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05-20-2021, 06:36 AM
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#3
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Registered User
Join Date: May 2017
Posts: 1,180
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Also, check for oil leaks around the spark plug tubes on the cam cover. This is typical of dry/cracked spark plug tubes. Ok to replace, cheap but just time consuming. These can cause misfires also.
for coils unless the crack is very obvious it will be hard to see them usually. cracked coils typicall cause misfires when driving in rain or getting them wet.
If you dont know when either were last replaced, it may be best to just replace all the plugs & coils, it isn't expensive.
__________________
2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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05-20-2021, 08:56 AM
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#4
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Registered User
Join Date: Nov 2013
Posts: 17
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Solenoid?
Both plugs and coil packs are fairly new. I could understand if one failed, but not all three on one bank simultaneously. There has to be another problem causing this. Read about a possible solenoid issue known to cause misfire codes on bank 1. Any information on this subject?
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05-21-2021, 04:00 PM
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#5
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Rundtinden
Both plugs and coil packs are fairly new. I could understand if one failed, but not all three on one bank simultaneously. There has to be another problem causing this. Read about a possible solenoid issue known to cause misfire codes on bank 1. Any information on this subject?
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I some what agree with your line of thinking.
BUT 
The car sat for two years 
So the best thing to do is go with automotive tried and true diagnostic procedures.
That means simplest things first then work your way up step by step.
The plugs, coils, and any oil that could cause issues is the easiest first step.
If there is no issues with them then there's no cost.
Go to the next step.
Next would be the wiring harness to the coils.
Rodents like to chew the coating on wires for some damn reason.
You can test that out with a common Digital Multi Meter.
If these prove out all good then it's time to look for other causes.
Sticking to the basics helps prevent chasing your tail
Let us know how you go.
If the above does not fix the issue perhaps we can help you find the issue.
Last edited by blue62; 05-22-2021 at 04:50 PM.
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05-23-2021, 11:13 AM
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#6
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Registered User
Join Date: Nov 2013
Posts: 17
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Test drive
Will change the plugs and check the coils 
Cleared the faults and took it for a test drive today. It drives well. No hesitation on acceleration and no smoke or misfire. Drove approximately 60 km. I then decided to check the brakes and floored the pedal. The brakes are very good. But the cel came on again immediately! Coincidence? Turned around and drove 60 eventless km back again.
Hooked it up again and the same codes were present: P 300, 301, 302 and 303.
It was stored for two years with little fuel in the tank. Any possible problem here that will affect bank 1 cylinders only?
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05-23-2021, 01:34 PM
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#7
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Rundtinden
Will change the plugs and check the coils 
Cleared the faults and took it for a test drive today. It drives well. No hesitation on acceleration and no smoke or misfire. Drove approximately 60 km. I then decided to check the brakes and floored the pedal. The brakes are very good. But the cel came on again immediately! Coincidence? Turned around and drove 60 eventless km back again.
Hooked it up again and the same codes were present: P 300, 301, 302 and 303.
It was stored for two years with little fuel in the tank. Any possible problem here that will affect bank 1 cylinders only?
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Does your scanner show freeze frame data?
That is data showing the conditions or some of the conditions when the codes were set.
If I remember correctly most all OBDII scanners that show freeze frame data show data for the last code only.
But Since all your codes are related there may be a clue to whats triggering them in the freeze frame data.
Still need to look at the coils, plugs and wiring harness though.
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05-20-2021, 09:10 AM
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#8
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Registered User
Join Date: May 2017
Posts: 1,180
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You would have other codes for a solenoid issue. I know, have a 2000 doing it.
if all you are getting is misfire for 1,2 3 then it's going to be plugs/coils....or wiring. Having sat for a while it's possible something got in and started to chew on wires.
I would still do new plugs. 1 hour of your time and under $40 in parts. Never hurts to do plugs.
You can just get it out and start driving it, put about 100 miles on it, clear the codes and then see if they come back.
__________________
2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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05-29-2021, 10:37 AM
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#9
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Registered User
Join Date: Nov 2013
Posts: 17
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Update
Checked for vaccum leaks and found a hole on the underside of the right rubber sleeve connecting the plenum to the right hand side intake manifold (as seen from behind the car) Will fit a new one ASAP. It was quite a big hole too. Can this explain the codes on the bank 1 cylinders?
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05-29-2021, 10:52 AM
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#10
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Registered User
Join Date: May 2017
Posts: 1,180
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yes, it can. Once you fix that, check for more leaks. I would grab a vacuum gauge from HF (they are cheap) and then see what you are getting with the car running. You can also use one of those handheld mini vacuum pumps that some use for doing brake bleeding. You should be able to hold vacuum if there are no leaks. Just T it into the line off the check valve.
One thing a smoke test wont tell you always is if the reservoir is cracked. They can crack on the underside which only shows up when there is vacuum.
__________________
2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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05-29-2021, 11:17 AM
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#11
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Stl-986
yes, it can. Once you fix that, check for more leaks. I would grab a vacuum gauge from HF (they are cheap) and then see what you are getting with the car running. You can also use one of those handheld mini vacuum pumps that some use for doing brake bleeding. You should be able to hold vacuum if there are no leaks. Just T it into the line off the check valve.
One thing a smoke test wont tell you always is if the reservoir is cracked. They can crack on the underside which only shows up when there is vacuum.
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How are you going to hold vacuum with a handheld mini vacuum pump on the intake system?
Your going to pull air past the throttle plate (butterfly).
So you would have to seal the throttle body.
Last edited by blue62; 05-29-2021 at 11:19 AM.
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05-29-2021, 11:25 AM
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#12
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Registered User
Join Date: May 2017
Posts: 1,180
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sorry, got my steps wrong. Just did this a month ago should of remembered.
put the vacuum on the side of the check valve that goes into the plenum. that will test all the lines & vacuum canister and check valve.
__________________
2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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05-29-2021, 12:39 PM
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#13
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Stl-986
sorry, got my steps wrong. Just did this a month ago should of remembered.
put the vacuum on the side of the check valve that goes into the plenum. that will test all the lines & vacuum canister and check valve.
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so your using it to check EVAP system not the intake system:
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05-29-2021, 12:53 PM
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#14
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Registered User
Join Date: May 2017
Posts: 1,180
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That isn't the evap system, at least not the complete one. It's still the intake. All you are doing is using the vacuum pump in place of the engine creating the vacuum. The check valve at the plenum is just a 1 way valve so air can't go back into the intake. This is pretty standard way to check for a vacuum leak as well a smoke test.
__________________
2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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06-08-2021, 08:38 AM
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#15
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Registered User
Join Date: Nov 2013
Posts: 17
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Update
Tried to different throttlebodies. To sets of throttle position sensors and two different idle control valves. Same symptoms.
Hooked it up again to the Bosh Motronic. Seems like I have a lot fewer parameters to view than in a more modern car?
Get some info from the OBD, but little in depht on engine management etc.
This is a professional tool. Any ideas what to look for?
Also tried the Texa scanner. It can not scan boxster 2.5. Works from 2.7 onwards.
Will order a new AOS and change it, just in case.
Any thoughts?
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06-08-2021, 10:34 AM
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#16
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Rundtinden
Tried to different throttlebodies. To sets of throttle position sensors and two different idle control valves. Same symptoms.
Hooked it up again to the Bosh Motronic. Seems like I have a lot fewer parameters to view than in a more modern car?
Get some info from the OBD, but little in depht on engine management etc.
This is a professional tool. Any ideas what to look for?
Also tried the Texa scanner. It can not scan boxster 2.5. Works from 2.7 onwards.
Will order a new AOS and change it, just in case.
Any thoughts?
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Can you look at:
Short and or long term fuel trims??
O2 sensor signals??
Throttle position sensor signal??
MAF sensor signal??
Camshaft deviation??
Actual camshaft position??
Does it have freeze frame info on the codes??
Also a Vacuum test with a vacuum gauge would be helpful.
Not only the reading of the needle but the action of the needle.
Last edited by blue62; 06-08-2021 at 10:38 AM.
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06-08-2021, 12:38 PM
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#17
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Registered User
Join Date: Nov 2013
Posts: 17
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Update
I will try to take a picture of the oxygensensor values and other interesting readings on the Bosch system.
A short summary: The car idles bad. Deviating with a hundred or so up and down from about 800 when cold. When hot the idle is from 1200-1400.
Have changed plugs, checked coils, cleaned maf, switched throttlebody with both sensors, replaced a broken rubber sleeve and checked multiple times for vaccum leaks in the engine compartement. Changed fuel filter and air filter, engine oil and filter.
Both old oilfilter and plugs looked in good condition.
Car still throwing random codes on misfire, on different cylinders each time.
It pulls strong when on heavy throttle, but misfires on light throttle and idle.
Next is AOS. Ordered today.
A thought came to my mind. After deleting codes and driving for 70km I hit the brakes hard to test them. The CEL immediately came on again. Could I have a vaccum leak in a brake booster hose or something? Just a thought.
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06-08-2021, 01:35 PM
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#18
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Registered User
Join Date: Aug 2018
Location: Woodland Wa
Posts: 1,309
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Quote:
Originally Posted by Rundtinden
I will try to take a picture of the oxygensensor values and other interesting readings on the Bosch system.
A short summary: The car idles bad. Deviating with a hundred or so up and down from about 800 when cold. When hot the idle is from 1200-1400.
Have changed plugs, checked coils, cleaned maf, switched throttlebody with both sensors, replaced a broken rubber sleeve and checked multiple times for vaccum leaks in the engine compartement. Changed fuel filter and air filter, engine oil and filter.
Both old oilfilter and plugs looked in good condition.
Car still throwing random codes on misfire, on different cylinders each time.
It pulls strong when on heavy throttle, but misfires on light throttle and idle.
Next is AOS. Ordered today.
A thought came to my mind. After deleting codes and driving for 70km I hit the brakes hard to test them. The CEL immediately came on again. Could I have a vaccum leak in a brake booster hose or something? Just a thought.
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Yes you could have an issue with the brake booster.
Clear the codes go out and do your brake test again see if it repeats.
You could hook up a vacuum gauge for a vacuum test then step on the brakes, that will tell 100% if there is a vacuum leak in the brake booster.
A vacuum test gauge only cost around $20.00
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08-14-2021, 01:50 AM
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#19
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Registered User
Join Date: Nov 2013
Posts: 17
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New update
Changed the MAF for a new Bosch unit and replaced the AOS together with new piping.
Now I have changed MAF, AOS, new oil, filer, airfilter, plugs, fuel filter, inspected coils and checked several times for air leaks using start gas. Also cleaned throttle body and tried two different idle control valves and throttle position sensors. Same problem.
Today I changed the MAF disconnected the battery, reconnected after a few minutes. Ignition on for 60 sec, off 10 sec then started the engine. Idles up and down 100 rpm or so, can hear some misfires. Will hook it up, but suspect the codes are the same. Misfire on cyl 1, 2 and 3. Any ideas?
PS: When I changed the AOS I found a rubber hose hanging down next to the right wheel well. Is this end supposed to be loose?
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