98 Boxster with intermittent misfire - Rennlist Discussion Forums



98 Boxster with intermittent misfire

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Old 02-10-2017, 11:43 PM   #1
Greg S
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Default 98 Boxster with intermittent misfire

Hi all,
I have a 98 Boxster with 50k, all stock. A few weeks ago, I heard a misfire while driving around town. It made a stuttering sound for a few seconds, triggered the CEL, then went away after about 15 seconds. The code was a 0301, a cylinder 1 misfire. I installed all 6 new plugs and a new coil on #1. The car has always been maintained well and has a fairly new fuel filter in place.

I drove the car today on a 65 degree day. I drove 25 miles highway, then after 10 minutes in traffic, the CEL flashed for maybe 30 seconds, then stopped flashing, remaining on. The car was obviously running on five cylinders and made a stuttering sound. After being parked an hour, it started and ran perfectly all the way home, in traffic and on the highway. I read the codes when I was home and saw a 0301, 1314 and 1317 code, showing misfires.

I'm puzzled as to the cause, even more so since it is an intermittent problem. My plan is to check the connections on the coils and at least the #1 plug. I suppose the next step would then be to check for a dirty or clogged injector. Has anyone else had the same problem or have other suggestions? Other than this issue, the car has always run very well and has no other symptoms.
Thanks,
Greg
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Old 02-11-2017, 01:28 PM   #2
Schnell Gelb
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When you reconnect the coil wiring connector - push back the boot and make sure the clip fully engages and the retainer latch snaps closed. If you do not push the boot back, you can neither see nor hear the 'snap' to verify a good connection.
You can always try the swapping of coils/plugs/injectors to see if the problem follows the changes. "Read " each plug to confirm if it is a lean or rich misfire?
For the benefit of others who may respond, I suggest you define the other codes for them and search the Forums for that combo of codes.

Last edited by Schnell Gelb; 02-11-2017 at 02:01 PM.
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Old 02-11-2017, 03:50 PM   #3
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Originally Posted by Greg S View Post
Hi all,
I have a 98 Boxster with 50k, all stock. A few weeks ago, I heard a misfire while driving around town. It made a stuttering sound for a few seconds, triggered the CEL, then went away after about 15 seconds. The code was a 0301, a cylinder 1 misfire. I installed all 6 new plugs and a new coil on #1. The car has always been maintained well and has a fairly new fuel filter in place.

I drove the car today on a 65 degree day. I drove 25 miles highway, then after 10 minutes in traffic, the CEL flashed for maybe 30 seconds, then stopped flashing, remaining on. The car was obviously running on five cylinders and made a stuttering sound. After being parked an hour, it started and ran perfectly all the way home, in traffic and on the highway. I read the codes when I was home and saw a 0301, 1314 and 1317 code, showing misfires.

I'm puzzled as to the cause, even more so since it is an intermittent problem. My plan is to check the connections on the coils and at least the #1 plug. I suppose the next step would then be to check for a dirty or clogged injector. Has anyone else had the same problem or have other suggestions? Other than this issue, the car has always run very well and has no other symptoms.
Thanks,
Greg
P0301 is # 1 cylinder misfire. P1314 is emssions related misfire on # 2 cylinder and P1317 is emission related misfire on # 5 cylinder.

"emission related" misfires are rich misfires. I suspect you have failed to properly connect (at the plug or at the wiring harness) the coils for #1, #2, and #5 cylinders. But check that all the coils are securely connected to their respective plug and each plug's wiring harness connection is secure as well.

Be sure each coil is properly bolted down too.

Before you installed the plugs did you verify all the plugs were the correct plugs? Not just that the box had the right marking but that the plug marking was correct? And that the gaps were all correct?
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Old 02-11-2017, 06:12 PM   #4
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Here's the update so far. My brother in law, who is a real mechanic, brought his scan tool and verified the codes. Macster's definitions of the codes are correct. All coils were properly attached but the plugs appear to be incorrect. They are Bosch FR8DPP33 plugs that seem to be a fit for a Mercedes. They came from Pelican, but this is the first goof in 20 years, so I can't rant about it. Still ... annoying.

The plug had a slight fuel smell. Resistance on both coils, one new, one original, was at 0.6 to 0.7. I can get OE Bosch 7402 at my local parts store, so I am headed there next. Next update will be tomorrow.
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Old 02-12-2017, 02:07 PM   #5
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The plugs my 2002 Boxster uses have 4 ground electrodes.

While some plug manufacturer charts list their plugs as being compatible with the "right" plug there have been times when this is not the case.

I remember on another board a Cayman owner was experiencing engine problems -- msifires or something else I can't recall now -- and long story short he had installed plugs that had a recessed center electrode. The plug maker's cross reference chart listed this plug as being a suitable replacement for the real McCoy but that was not the case. The Cayman owner bought the right plugs and after replacing them all the engine problems were gone.
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Old 02-12-2017, 06:28 PM   #6
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Latest update:

Macster: the OE Beru plugs I replaced a few weeks ago had two electrodes. They appeared to me to be the original plugs, showing some use but not fouled or damaged.

Yesterday my BIL noticed the fuel trims were sometimes >10%.
We removed and checked the air flow meter. No signs of damage or dirt. It registered valid temps in operation. I cleaned it w/ AFM cleaning spray anyway.
All coil leads were firmly connected

Today I replaced the incorrect Bosch plugs with the correct, two-electrode Bosch plugs (7402). I swapped the #1 and #2 coils to see if the misfire moved, if it reoccurred. I verified coil wires were firmly connected and heard them snap into place.

After replacing plugs, I drove the car for about 20 minutes. I monitored performance using the Dash Command app. Perhaps three or four minutes after a cold start, I thought I heard a few seconds of "stuttering" as I approached a stop sign and the engine returned to idle. It wasn't pronounced and didn't trigger a CEL. The fuel trims at the time were in the -3 to -5 range. After blipping the throttle, the idle sounded normal. There were no other anomalies for the remainder of the drive.

Here are some of my observations:
  • Intake and coolant temps were normal the entire trip.
  • Fuel trims varied less than yesterday, generally from -4 to +4. There was more variation than I have seen with some previous cars, especially my now-gone Jaguar XJ8, which seemed to be in the + or - 2 range.
  • O2 sensor voltage spiked up and down continuously, from 0.1 to 0.8v. From what I've read on this forum, that seems normal. Both banks showed the same degree of voltage change.
I'm not convinced I'm out of the woods yet. I've learned I can data log on the Dash Command app, so I will do that for the next few weeks or until a misfire returns. I will report back if that happens.

Thanks to Macster and Schnell Gelb for the input.
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Old 02-22-2017, 12:46 PM   #7
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Wow - so it was just a question of fitting the best/correct spark plugs?
If you get more problems - check the resistance of the coils against spec and each other.Easy to do.
The data logging is a great diagnostic aid -well done!
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Old 03-20-2017, 07:48 PM   #8
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Default Misfire returns

As I feared, the misfire returned. Today it was the P1313 code and happened after exiting the highway after a 30-mile run on a 75-degree day. It was the same symptom of stumbling, losing power, the CEL lighting up, but this time the engine died since I was putting the gear into neutral as I approached a stop sign. I restarted the car immediately and it ran fine again and the CEL turned off.

The car now has the proper plugs and a new coil on #1 cylinder. The issue seems to be heat-related and occurs only on warmer days after running 30 minutes or so. All of the connections are tight. I verified they clicked together and checked visually, too. The heat and time combination tells me this an electrical component problem, but a new coil makes that less likely (still possible).

What does that leave? Wiring? Connector? Anything I'm missing? Of course today I didn't have my iPad to do any data logging, so no help there.
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Old 03-20-2017, 07:54 PM   #9
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Quote:
Originally Posted by Greg S View Post
As I feared, the misfire returned. Today it was the P1313 code and happened after exiting the highway after a 30-mile run on a 75-degree day. It was the same symptom of stumbling, losing power, the CEL lighting up, but this time the engine died since I was putting the gear into neutral as I approached a stop sign. I restarted the car immediately and it ran fine again and the CEL turned off.

The car now has the proper plugs and a new coil on #1 cylinder. The issue seems to be heat-related and occurs only on warmer days after running 30 minutes or so. All of the connections are tight. I verified they clicked together and checked visually, too. The heat and time combination tells me this an electrical component problem, but a new coil makes that less likely (still possible).

What does that leave? Wiring? Connector? Anything I'm missing? Of course today I didn't have my iPad to do any data logging, so no help there.
P1313 is an emissions related (aka rich) misfire at cylinder #1. You did say above you swapped cylinder #2 and #1 coils. If this is the case then it reads like the misfire sort of followed the coil to the #1 cylinder.

This suggests the #1 cylinder coil is bad.
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Old 03-20-2017, 08:06 PM   #10
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True, I did swap the coils. That slipped my mind. I will verify the new one is still on 2. If so, I will get another coil. Or more than one.
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Old 03-20-2017, 08:14 PM   #11
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Greg,
Consider replacing all the old coils. You may think they are O.K. but if you examine them for cracks under a bright light and lens ,you may find hairline cracks developing.
There is an improved 'thicker" coil available. Just be careful with the part numbers.
Are you sure those are the correct plugs? Macster is correct ! If they are the wrong heat range, they may work - just not very well.
Be careful you haven't swapped #1 & #2 coil connectors.They will easily fit the wrong way around .Ask me....
Can you read any other data to see if it is a lean misfire or rich ?
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Old 03-20-2017, 09:36 PM   #12
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The new plugs are the correct ones, a platinum, dual-pronged Bosch plug. When I replaced the plugs and one coil, I worked one cylinder at a time so I wouldn't risk making a bad connection.

The new coil is the thicker one you mentioned, a Beru from Pelican. I ordered two more this afternoon. You're right, it's smart to replace all at once, but I didn't want the extra expense right now. I did check the old coils for cracks and didn't see any that were visible to the eye, which is not to say there couldn't be an internal crack or something.

When I find my wireless obd connector, I will watch the data log again. Nothing to report on that front at the moment.
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Old 03-21-2017, 11:32 AM   #13
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Maybe Porsche changed the plug part #?

Here's a pic of a new and old plug from my 2002 Boxster. I haven't checked with the parts department for the part # so I can't say for sure the 4 electrode plug is still the "right" one.

The Boxster (and other Porsche models) use an "extended" tip plug. As I understand it the plug tip stays cleaner at low RPMs because it is exposed to more of the combustion heat. At higher RPMs it is cooled by the incoming charge.
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Old 03-31-2017, 06:43 PM   #14
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According to the research I did and the dealer parts guy, the 2.5l cars use a two-electrode plug. My car has Bosch 7402,which should be a direct replacement.

My problem may have been self-induced this round. I pulled the coil and plug from #1 to check condition. The coil looked fine and ohms measured between 0.6 and 0.7. The plug is shown below. It wasn't fully torqued to spec, hence a self-inflicted problem. Rather than clean it and try again, I replaced it with another Bosch 7402 and used a torque wrench to tighten to 22 lb/ft. It may be a few days before I can drive the car any distance, but I will report back when I can.
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Old 03-31-2017, 08:24 PM   #15
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The 2.5l engine may indeed use a different plug than the 2.7l engine. If you are sure the plugs you are using are the right ones that's what matters, not the # of electrodes.

It is good practice to check the gaps. Some plugs come pre-gapped but all it takes is one that is wrong to ruin your plug change day.
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