Klotz

The car is a 2000 WS6. I got it dyno tuned about a week ago where they leaned out the air fuel mixture and then the other day I accidentally ran through a big puddle during the rainstorm we had over here in NY. After that, the car started to stumble at idle + - 50~75RPM. Then the car hesitated at low RPMs at WOT and bucked at partial throttle. At partial throttle it felt like I wasn't on the gas and all of a sudden jumped on it. Felt like the throttle was stuck closed and then broke open fast. Now when going WOT from low RPMs, it stumbled like before but then it bounced like I was hitting a rev limiter right around 3000 to 3500 and wouldn't go past that. The only way to get into upper RPMs is to give it barely any gas until around 4000 and then I can go WOT fine, but it feels like it's still down on power. So far I cleaned up the MAF and changed the o2 sensors. The car isn't giving me any SES light. I ordered NGK tr55 plugs, MSD wires and a new fuel filter waiting to install them when they come in to see if the problem persists. Any other ideas? I can't help but think it's electrical because it didn't happen until I hit the puddle... but could the problem lie in the tune? The first time I drove the car since the tune was right before I hit the puddle and couldn't tell if it was running right because it was wet out.

1 FMF

iTrader: (1)

the computer reprogram is bad.... sounds like a classic case of lean condition.... if u ever had a carbureted motor and know how to adjust carbs the problem and solution is more easy to see and troubleshoot. with efi and engine computer YOU are at a disadvantage and the shop will always blame any problem on something else.

when you snap the throttle open there is a sudden drop in manifold vacuum and causes a lean condition in any motor carb or efi. it needs a temorary rich fuel condition to get thru this scenario until airfllow into the motor picks up... then under a more steady state wot condition you can begin to lean out the af ratio to make max power over 4500 rpm. without seeing exactly what was changed in the computer and observing how knowledgable or dishonest whoever did the reprogram my guess is they incorrectly leaned things out across the board... or what they thought they were changing would ONLY happen at wot is not happening. and using an inertia dyno to tune is a bad idea for a street car because that is not how you drive the car and it does not replicate varying loads the engine sees under regular driving.

with the reprogram they can turn off much if not all the dtc's and you wont get an ses light, they need to show you what changes they did in the computer. did the car ever run great more than a day after the tune? i would say the tune is main problem the puddle is a coincidence... maybe put a new maf sensor in if you think water made its way all the way into the maf housing cause you have a crazy airlid setup thats exposed. ive never had luck with cleaner and over the years maf replacement is what actually fixed the problem when it was specifically a maf problem

Klotz

I changed the MAF, TPS, plugs and wires and one of the o2 sensors with no help. I sent the car back to the people who tuned it and they logged what was happening while driving the car. They're saying when going full throttle around 2500-3500rpm the computer says it is actually running full rich at that time when it's stumbling. The shop I brought it to says it's probably either a vacuum leak somewhere or a plugged cat. Would a vacuum leak do this? I'm thinking it's not a plugged cat because it still can rev high, it only stumbles and bucks around the mid range. It's very frustrating now that it's winter and it makes it a lot harder to work on the car and get everything sorted out.

1 FMF

iTrader: (1)

did the 2000 model year come with egr?
if so, is egr still installed on yours and functional?

TheZ346

I had this exact same issue right after I had the lts and street tune on my car done and I never figured out what the problem was but since I got a dyno tune I've had 0 issues.

TheZ346

Come to think of it this problem started after a heavy rain as well. I had an o2 sensor extension that a shop had tried to make themselves and was crimped in 3 places to make it long enough. Those voltage drops and exposed wiring may have been an issue aswell. Just some more food for thought.

Klotz

The 2000 had egr but it's gone because of the ls6 manifold. It's also tuned out of the computer.

Klotz

I had a bank 1 front o2 sensor ses light come on a while ago... I replaced the sensor but they tuned all those codes out of the computer. could that potentially faulty wiring of the o2 sensor cause all this?

TheZ346

Good buddy's car kept having o2 issues and it turned out that further up in the harness, the wire had actually melted and grounded out on the block. Maybe something else to look into.

TheZ346

Definitely sounds like an o2 issue, without a doubt.