Thread: Installed PLOG, now studders under boost. Please help!

I have been working on getting some things done with my 2000 GTP (wheel bearing, sway bar, etc) and it has been "out of commission" for 2 days while I've been working on it. My fixes/mods have been going well, but I installed a ZZP stainless steel PLOG yesterday, but didn't drive the car until today and now, all of a sudden, I get studdering under boost. Light studdering under low boost, and not a ton under WOT, but very noticeable at about 50% boost. This doesn't matter if I am going 25mph or 65mph.

The PLOG is the only engine upgrade I've done in several days, and I don't recall ANY studdering prior to it going in place.

Earlier this week I put on my TDC FWI and drove the car for 3 days without issue before starting this current batch of repairs/mods.

I don't get any SES light at all, not even a flicker. I pulled into the garage after my test drive and without load, I can hit the throttle pretty good without anything negative happening. Of course, the supercharger doesn't seem to be "engaged" when I am in park/neutral, so if it is a boost issue, that would make sense. Of course with no load, it isn't really a great test either.

A couple of weeks ago I upgraded to a 3" catted downpipe. My goal was to let the car breath and remove any * KR. I wasn't noticing anything, but I am just trying to get ready for a pulley drop later this year.

Other details related to the engine are as follows:

Vehicle has 55,400 miles (yeah, that isn't a typo).

Oil change/filter completed 6 weeks ago.

Spark plug wires were replaced a year ago as my one coal pack had a little rust that trashed a wire. Coil pack is still original, but rust was removed from it.

New battery was installed 4 weeks ago (I know, probably not the issue, but just being thorough.)

Coolant was flushed 4 weeks back.

"Dog Bone Flip" done 4 weeks ago.

180* T-Stat put in with the coolant flush.

3" catted downpipe installed 3 weeks ago.

TDC FWI installed 6 days ago.

PLOG installed yesterday (plug wires disconnected to allow for removal, and they were reseated after PLOG was in place).

Like I said, I didn't notice anything performing poorly until my first drive after the PLOG install.

Last item of note. I am still researching this as I simply don't know, but after we had the front 3 plug wires removed to get ready for the PLOG install, we changed our plans and started tackling my broken sway bar. At one point my dad, bless him for being here to help, started the car for about 2 full seconds with only 3 plug wires (the rears) connected so that he could use the power steering to turn the wheels for better access to things under the car. I hope that didn't screw anything up.

So any thoughts or ideas would be helpful. Again, there is nobody anywhere near me that is able to do a scan, which makes things tricky.

Thanks everyone.

The car seems to idle the same. The first start up was a little "gassy" smelling and rough for a few seconds, but I am guessing that was just the extra fuel in those 3 cylinders.

It is hard to tell if there is anything "louder" in the front with the FWI being so loud. I am not sure how to test for the vacuum leaks or exhaust leaks.

Could I be running "lean" and just hit some threshold with the PLOG (not one individual piece was causing it, but the PLOG, FWI, and Downpipe together did???)???

go back and check your wires. i changed my plugs on new years day and my car started studdering like you explained and it ended p being that i messed up one of the wires.

Originally Posted by carl06GT

go back and check your wires. i changed my plugs on new years day and my car started studdering like you explained and it ended p being that i messed up one of the wires.

I'll give them a good look over. I know that they went on in the right order (masking tape and a marker were my friends for that labeling job), but maybe something got messed up with I disconnected them.

I keep putting off new spark plugs (waiting until I can do a Seafoam job late at night to not create all of the smoke when my neighbors can see me doing it. I hear that seafoam will usually force you to replace the plugs within a couple of days.) Anyway, I could just make plans for a seafoam night and get the plugs replaced too, but from my searching, it doesn't sound like that would fix it. Who knows.

Other ideas? I want to get all of my options on the table and tackling the potential sources.

Oh, and since nobody is around me to ever run a scan, would it be worth the $$$ to get an AeroForce Interceptor to not only give me some scanning ability, but also real time data for down the road?

EDIT: I just saw the comment right above this about the Interceptor. LOL. Nothing like posting a question that is already being answered while I type. As for the plug boots, they actually came off pretty easy. I put some special "boot grease" stuff on them when I put them on. I did the normal "grand the boot, not the wire, twist a little and pull" without any issue, but I'll still check them out.

How were the wires when you pulled them off? They are usually pretty tuff to get off, you may off damaged one while removing them. It might idle fine but under load it sounds like you have a miss. There are vacuum lines in that area as well, check all of them. This is why the first mod for anyone should be an interceptor scan guage or something that scans.

go to orieley's and get your a new set of $30 wires and see if that fixes it. mine you couldnt see put i messed up one of the connector ends. and i bought a new set of wires and blame problem fixed

I just looked over the wires. They are "Autolite Professional Series Premium Spark PLug Wires - 7mm". I think that they cost me like $35 a year ago. They all look (I know looks can be very deceiving) fine. Here is something that I noticed though about the #3 plug (middle front plug) looks to be cracked. I didn't actually remove it, and at first I just thought that it was discolored or dirty, but I rubbed it with a thin cloth and while some of the dirt DID go away, I could feel a crack.

The following picture is not mine, but my crack was in about the same spot, only a little darker in color.
I know that this is bad, but does a cracked plug problem cause studdering only under boost (higher RPM)? Seems like it could. And would a cracked plug mess up my wires? Thanks again!

Its quite possible. You might have hit it either removing the front mani or installing the plog. The spark might be jumping across and grounding to the eng block at higher rpm's. Change them and see what happens.

Should (could) I drop to the Autolite 104's now? I was planning to when I got closer to my pulley drop later this year.

What is a good wire that I could pick up locally (so I can see about fixing this without waiting for shipping) without being crazy priced for someone looking to just get to a 3.4 or 3.5 pulley and not go much further than I am now?

OK. Thanks for the tips on the plugs and wires. Actually, the more I think about it, I think that I got my current plug wires from Advance Auto, and they show them as a Limited Lifetime Warranty item. Now, hopefully I still have the receipt.

I did think of one other thing that happened tonight when driving. It only happened once, but after starting the car (oddly enough, after returning loaner tools to Advance Auto), I pulled out into traffic a LITTLE aggressively, but not bad at all. When I let off the gas, I heard a subtle "pop-pop" backfire. How does THAT factor into this problem?