Just_Dirty

My 955 CTT has been on a roll in terms of problems recently. Now I'm having an issue where at WOT there is very rough choppy acceleration and the boost gauge will reach about .6-.7 bar and then be pegged at .3-.4 bar after. The rough acceleration also occurs during part throttle high load. The car is an absolute dog at WOT now.

The car has had new coils and plugs replaced about 2k miles ago. Any ideas on what to check next?

deilenberger

What year is your CTT - that does make a difference, and they're not all identical to whatever yours is.

Just_Dirty

It's a 2004 955

Just_Dirty

Bump

nodoors

How old are the pumps and filter?

First thing I would do is watch the fuel pressure when you are experiencing those symptoms.

GDA

Initial guess would be a big vacuum leak....

Vacuum hoses to diverter valves
Diverter valve(s) failure
Failed o ring seal / loose turbo pipe driver side


+1 on potential weak fuel pumps as well

nodoors

A large vacuum leak would make it idle like crap. Boost leaks generally don't manifest as rough surging like he is describing - the car usually just feels down on power.

It would be more likely to be a boost leak in one of the charge pipes than a vacuum leak if it only expresses symptoms at WOT or high load which will build boost. With all that said what he is describing would be most likely to be a fuel flow or spark issue, but the ignition issue is less likely with the new plugs and coils.

After checking the fuel delivery and being sure everything is up to snuff, I would then revisit the new plugs and coils before checking for intake/vacuum issues if it is idling well. There could be a bad new coil or a loose connection from the install and reading the plugs would instantly show that.

Scan the computer as well and see if you have any pending codes that have not fired an SES light. That could provide a helpful tip.

Just_Dirty

Figured out the problem guys

One or more of the coil packs had gone bad. After I made some videos to document my problem the car started to misfire and buck very badly. Luckily RockAuto provides a warranty for their parts and I was able to swap all 8 coil packs out yesterday. She runs smooth as butter and pulls hard again.

nodoors

Thanks for following up. Bummer when new parts don't hold up! Where there any pending codes on the computer to help tip you off?

Glad to hear rockauto supports their parts that well. I am surprised they let you swap them all!