Jump to content

The RennTech.org community is Member supported!  Please consider an ANNUAL donation to help keep this site operating.
Click here to Donate

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Poor running after spark plug replacement?

Recommended Posts

2004 C2, 57K miles.

Just did some service work on my C2 and replaced my spark plugs. Car was running great, but did it as part of 60K service.

[*]No history of CEL's prior to change.

[*]Plugs removed were BERU Ultra R6-336.

[*]All looked fine with good color and minimal electrode wear.

[*]All coil packs/wires/connectors looked great and were reused.

[*]Spark plugs were replaced with Bosch FGR5KQE0. Gapped as set from factory, not mis-handled or dropped.

[*]Plugs were torqued to spec.

Since I removed the mufflers for improved access, I took them to a local shop while they were out and had a gundo/fister type 2 modification done on them, essentially connecting the input and output pipe with a new piece of 2" tubing. This shop has done many of these before...

Car is back together and running... I've had it out for a few drives since the work, and to me it feels rougher, particularly during warmup and maybe even less power. Maybe even detecting a minor misfire when cold? I'm not getting any CEL lights. Rechecked connectors, all are tight.

Some thoughts and questions:

[*]Obviously it could be the exhaust, and perhaps the ECU not yet adjusted to a slightly increased airflow or just feeling the roughness of more exhaust resonation?

[*]How quickly should the ECU remap to any changes to fuel mixture due to exhaust and/or plugs? Can I speed up the process by removing the battery terminal?

[*]If I am getting misfires, how tolerant is the ECU before it will trigger a CEL? Can i assume that if I'm not getting a CEL, the engine isn't misfiring and fuel trims are fine?

[*]Is there any way to log any ECU data short of buying a durametric?

[*]Could the Bosch plugs be making the difference? I'm sure I could do the job a second time much faster, but cylinder 4 seems like a major PITA even now that I know the procedure!

[*]Any other thoughts? I'm always hyper-sensitive to how a vehicle is running after I work on it, and perhaps it's all in my head...

Also, I'm not sure I love the louder exhaust.... I really miss hearing the intake howl (had previously done the silicone tubing intake od) and it makes me feel a bit like a tool now when I open her up on an entrance ramp or something. Am the only person in the world that doesn't like the Fister exhaust??

Edited by pfbz
Link to comment
Share on other sites

Just my two cents... I replaced the plugs on my Boxster (Beru) with Bosch last fall. Had the same impression of less response, low idle burble, etc. No codes shown. Just replaced them with Denso Iridium and there seems to be a noticeable difference!

Link to comment
Share on other sites

I doubt the exhaust mod would be causing the problems. I would double check that the plugs are all seated properly and all of the coil connections are solid. I had a CEL after doing my plugs and I would have bet money that all of my connections were good. I went back in and sure enough, one of the coil wires came off when I tugged on it. I used the OEM Beru plugs and I see a noticable improvement after the change. The old plugs were Bosch but I can't say whether the improvement was due to the brand or just the age of the old plugs. My guess is the latter.

I have the Fister mod too, but I had it done by Fister. I love the sound and I have a Cab. I guess it depends on how faithful your local shop was to the Fister mod. Maybe you just need to get used to it. I've had mine for 2 1/2 years and I still get a kick out of them.

Edited by wyovino
Link to comment
Share on other sites

I would have bet money that there would be no noticeable performance difference between different brands of quality spark plugs that are of proper spec and not defective... but I guess I'll replace the plugs and see if it makes a difference.

I'm sure the job will be much easier the second time, but honestly I'm not looking forward to dealing with Cylinder #4 again. I picked up some new tools that should make it a bit easier, a ratcheting bit wrench for the coil pack torx bolts and ratcheting external torx wrench for the covers, but those muffler mounts make the plugs and coil packs a bit hard to get to, with or without the mufflers on!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.