christallon

Guys, wondering if anyone can help. I just did new plugs and coils (Beru plugs and Beru 997 coils) I took it for a spirited drive and felt it was hesitating and popping under light load. As I poured throttle on it seemed to be OK, but when I came to a stop it sounded rough and backfired a bit. When I got home I walked around and could smell un burned fuel. Car is def running very rich. Any ideas what it can be? The car was running well before I changed the plugs/coils. The plugs had 25k miles on them and coils were original w 53k miles. Plugs were Bosch green stripe now Beru. The car is not running well at the moment.

TIA....

993GT

faulty plug(or maybe a very large gap is set) or coil
could also be installer hasn't got the intercooler plumbing tight/blown off

extanker

go back over your work. cel ?

christallon

I actually never checked the gaps, I simply installed them from the box. I will go over the coil connections again and confirm the connectors are seated. I'm usually thorough. No Cel's present. It's def running too rich given the smell and the hesitation and backfire on low RPM's. Any other thoughts?

Rob, no inter coolers as it's a GT3.

Thanks for the responses so far! Much appreciated.

Rob S

Chris,

The obvious "brute force" DIY way of narrowing this down is to start swapping parts back. Maybe start with the coil packs -- all six of them. If there's no change, then put in the old plugs as well. There are electronic diagnostic techniques that can help you locate which cylinder(s) are suspect, either by looking at misfires cylinder by cylinder or by looking at lambda readings on one cylinder bank versus the other. This may help narrow down the problem. But doing so will require some equipment you may not have. Of course, it could be that the problem is unrelated to your plug/coil change and that its just a coincidence. But like you I'm sure, I don't like coincidences! Is there anything you may have disrupted (especially sensors or something in the intake) that may not have been put back correctly?

Are you running catalytic converters? And you're smelling unburned fuel? That's a little concerning. In my experience, the cat will cleanse (or attempt to cleanse) unburned fuel from the exhaust stream, but may get very hot in the process. Have you noticed if one or both of your cats are overheating?

Rob

christallon

Thanks Rob, I'm sure it's either plugs or coils. The car was running fine prior to that. I'm hoping that as I remove each plug and inspect it, I'll be able to tell if one of the plugs is suspicious. When I say I burned fuel, I mean that I can smell the exhaust much more than I could before. Fabspeed bypass. I'm going to go through each one again and check gaps against gap of previous plugs. Previous plugs were Bosch platinum and all 6 were nice a grey and looked just right, albeit aged. The new Beru plugs seemed slightly longer than the Bosch platinums for some reason. I will confirm. Many Thanks

993GT

GT3..ahh! brain fart moment, should've had a coffee before posting..lol
Try plugging in a OBD2 or Durametric and see what codes are in there (no CEL needed)...narrow it down to what cylinder(s)

christallon

Ha, coffe always helps, but I understand, all good. I have a standard dura metric tool I use for my truck, will that work or will I need to go to a shop that has one specific to Porsche? Thanks Rob

993GT

Any basic OBD2 scanner, like the one for your truck, will give you cylinder-specific misfire codes. Makes life a little easier

christallon

Cool, I'll give that a try first. Thanks

christallon

So I gave the obd2 scanner a try and it came back with no stored codes. I decided to pull all the coils and plugs out & do a thorough inspection, check the gaps etc and go from there, hoping something would present itself. The gaps on both the old plugs (Bosch Platinum double electrode) and the new (Beru 14FR-6LDU) were at .71 or 0.28 instead of the .80 or 0.32 that seems to be recommended. I left the gaps alone because both old and new are the same. I decided to swap the old plugs back in the car and re install the new coils first. Voila, it's back to its happy mechanical self and runs great! I am going to leave well enough alone for now and run it as is.

After looking at the profiles of both plugs, I found that the Beru plugs, once seated into the cylinder will be approx 1/16 to 1/8 inch deeper into the cylinder. I'm not sure if that made a difference or not but that is really the only visual difference I could see. I know the Beru's are the OEM plugs, but for some reason, my car runs much better on the Bosch Platinums. My curiosity is piqued! Thanks for the help guys and if anyone has an opinion on the plugs, please post up here.

Cheers!

AudiOn19s

Weird but glad you figured it out. I know there were 2 different hear range plugs in the Beru curious if you had the 5's or the 6's.

I run the Beru sourced from the dealer but specifying heat range just to be sure. Never had issues.

christallon

Heat Range 6 on the Beru's. The Bosch Platinum +2's are heat range 7 so a hotter plug. My car prefers the Platinums for some crazy reason. I just ordered a new set, so hopefully they will be even better than the 25K miles set in there now.

The interesting thing is that these plugs are not spec'd for the car.

christallon

I replaced the 25K miles Bosch Platinum +2's with a fresh set just now and absolutely feel the difference. Amazing. The car is very responsive, lively, very smooth and this all makes me very happy. They are a heat Range "7" so 1 heat range up from the BERU's. For some reason, my car loves these.