Hello fellow 996 turbo/gt2 owners,

I've been having a rather strange problem with my car, and am now turning to the community to see if anyone has any ideas.

My car is a 2003 gt2, which I recently upgraded (did the work in my garage with a buddy) to the following:

Tial gt2871r's
80lb Injectors
Walbro 450l/h conversion
Protomotive mafless tune

Upon the first drive, I noticed the car was very jerky out of the driveway. Once on the road, the car drove as if it had half the engine missfiring. I circled the block and came back home.

The next day I broke out the durametric and started the car while it idled. Sure enough, cylinders 4, 5 and 6 were missfiring over and over. So much so that they counted up 0 to 15 within a few seconds, while 1, 2 and 3 didn't have a single missfire. I lifted the car up, and checked all of the coilpack connections on the right side (passenger side) of the car, as well as the electrical connections around them ( I think they are called the cam timing solenoid?). There is one near the fuel rail, and one inbetween coilpack 4 and 5.

Not having found the problem, I noticed the idle was suddenly smooth. I read the missfires on the durametric and they had gone away. I figured that I had bumped some electrical connection that fixed the problem. I put the intercoolers, heatshielding, ypipe and piping back on.

The whole day the car ran perfectly, pulling extremely hard and scaring my girlfriend. Except for one small issue of the car having a small "bump" or "jerk" are partial throttle, and slow acceleration. The bump/jerk would occur on a rhythm, about once every second.

Today was a different story... The bad missfiring is now back. I spent the day looking for vacuum leaks and found a couple small ones, but this didn't change anything. I have now ruled out that something that makes the car drive so horribly, can be a mere vacuum leak.


I'm asking for suggestions now, because I'm completely lost...


tl;dr - Upgraded my gt2 to new stuff, the tune is now mafless. It ran rough at idle but I figured it was the mafless. First drive was terrible and super jerky and rough. Durametric said missfires on cylinders 4, 5, and 6. The next day the car ran smoothly out of the blue, boosting and pulling perfectly (except for a small jerking every second at partial throttle). But today Its all back. The same misfiring.

Thanks for the help to anyone who has advice!

 

Happened to me you need the 997 coils and FR6 Bosch Plugs.......

 

My coils are the 997 bosch coilpacks. My plugs are the denso iridium ik22. I replaced them about 3k miles ago... I would be suprised if they failed already. Do you think thats possible?

Why would they fail perfectly on just one side of the engine?

 

Call Todd..............

 

Did you remove the engine to do the injectors or did u just lower the motor to install?Did you remove the coil packs at all?Is the engine ground on the passenger frame rail tight?Did you remove the o2 sensors from the exhaust?

 

Todd is extremely busy and I can hardly get him to reply to an email. Though I have sent him a couple.

I lowered the engine on the mounts only. I left the coilpacks in-tact, but removed the plugs from them. I made sure they were tight when I undid the intercoolers after I first got the missfire.

What do you mean engine ground? The rails however are rock solid. I have tried disabling each injector one by one, and they are deffinely spraying fuel fine.

I only unpluged the o2's but I made sure they are plugged back in.

Can the o2 sensors effect this?? My o2s are pretty old.

 

yes the o2 can cause a problem but sounds more like an electrical issue like a bad ground(there is a ground strap on the passenger frame rail right above pass turbo)or a bumped connector.Also if the o2's are in the wrong position or installed in the wrong holes before or after cat but you should be getting codes and cel.What cel codes are you getting other than misfires?

 

The only codes I get are cylinder missfire. Todd has my cat cel turned off (my exhaust is catless) and I have a secondary air delete.

It also sounds like an electrical problem to me too. Like the cam position sensor isnt getting a signal or something...

Im curious about this rail ground... Is this a problem that shows up often? I didn't notice a ground spot that was undone.

 

Sounds like your cam sensor bracket broke it happens alot. 10.00 part.

4,5,6 cylinders yup sounds like it.

 

I checked the bracket, and it looks perfect. Nothing wrong with it at all. :/

 

I was going to use those plugs but was told there not good by my shop. Thats why i went with FR6 and never had a miss fire.

I think something is not right you have miss fires in 4,5,6 so theres something else going on. Any other codes showing up? Sometimes there hidden.

 

Yeah. If it was the plugs it would be on all cylinders. Or just one.

No other codes besides the missfire. I clear the missfire codes and they come back after 30 seconds of driving.

 

did you do a pressure test to lets say 20 psi from the lower boost hoses? maybe your injectors are leaking...

 

Not yet. It is something I plan on doing soon.

 

Not yet. It is something I plan on doing soon. There is no fuel smell though.