Thread: Grand Prix Power Loss/Engine Bogging Help

Originally Posted by nickolaughagus

Hello everyone,

I have been having issues with my 04 GTP for a while now. I have recently gotten to the point where I can't stand it any more. I can't figure out how to fix the first issue, so I was hoping I could get some input on what to test from you guys!!!

My Grand Prix GTP Problems:

1. The biggest issue is that I have had lack of engine power in RPM's below 2500, noticeable in all gears. Once I hit 2500, it seems like the engine just effortlessly accelerates, with a lot more torque. Anything below that feels boggy. Especially when sportily accelerating in first gear from a stop. When doing that, it seems to just chug fuel and air while not moving fast for the first half second.

2. I have a small noticeable misfire when running in low RPM's especially under heavy load (up hills). I actually have to downshift on highways to get up hills sometimes.

4. I am running moderately rich on average. And it's super rich under WOT.

5. Rough Idle occasionally.

6. When accelerating from a stop, engine occasionally will accelerate in steps, choppily getting up to speed.

I have used the scan gauge.

It shows up with a knock sensor 1 no voltage, o2 sensor heater and o2 sensor heater circuit code for both sensor 1 and 2.
So I have to fix my knock sensor and rewire my O2 sensors wiring.

What I have done with most recent actions first:
1. Replace plugs with 104 iridium xps gapped at .056"
2. new wires
3. 3.6 pulley
4. new upstream o2 sensor
5. catless downpipe with defouler on Rear o2 to trick CEL.
6. Hot air intake
7. Cleaned MAF sensor multiple times


I plan on getting a tranny cooler, flushing tranny fluid and also installing a shift kit for firmer shifts, but...

What can I do about the weird 2500rpm come-to-life?

I really can't find any resources on this issue online.

Please help!

Thanks,
Nick

Bump

Originally Posted by Fivefingerdeathpunch

Did you fix the knock sensor problem?

How do you know it's running rich, do you have a wideband?

3.6 pulley on a GEN V with only a downpipe doesn't sound like enough flow mods to me, might have alot of knock retard going on.

What are fuel trims like? Those could point to a vacuum leak and the stumble. I prefer copper plugs to iridiums when modding.

I know its been running rich at WOT because the O2 sensor reads a very high voltage at those times. I have the torque app and it shows those readings.

I did have the knock sensor plugged in when I first ran the car with the 3.6, and it seemed fine. I think I was getting about 2-3 degrees of KR.

I finally found the reason why I am feeling these large, noticeable shifts in power today. I coordinated my Timing Advance readings with the RPM readings, and leading up to 2500RPM at times, the engine would provide 0 Timing Advance. Then when I felt the power kick in, it was snapping up the timing. So its pulling timing at random points in the Rev Range. I will work on the knock sensor this weekend. Do you think that is was could be causing the Weird timing issues?

I included a link to my Google Drive folder below, which contains screenshots of the timing, RPMS, and at the top, Throttle Position.

https://drive.google.com/folderview?...TV3WHNrbkZadlE

Thanks for the response,
Nick

Originally Posted by Fivefingerdeathpunch

High o2 readings doesn't mean it's running rich, they are not an accurate way of reading true AFR.

Some car could read 900mv and be pulling 11.0 afr and another car could see 940mv and be pulling the same 11.0 afr. o2 sensors are only accurate when they are trying to achive stoich, they swing lean or rich of stoich to try and reach 14.7 air fuel ratio while cruising. That is also where you could see what the fuel trims are doing and how lean or rich it's running at stoich.

There was another thread on here about that timing issue, I don't recall what he has done to fix it. It was the same things were timing would just drop out and come back at a certain rpm. I forget his name but he's from texas I think.

This is the thread youre referencing?

http://www.grandprixforums.net/threa...!Found-problem!

After doing a lot of heavy reading it seems that the unplugged knock sensor could be pushing the PCM fully into the 'Low Octane' tables, where it reduces the timing possibly to 0. I couldn't find a Low Octane Timing MAP for the L32 specifically, but one that I saw on google depicted the timing being around 0 with heavier loads under 2500 rpm.

The screenshot of this table is in my Google Drive folder. I need to get that sensor plugged in before I can get anywhere else on this issue.

https://drive.google.com/folderview?...TV3WHNrbkZadlE

Hey guys,

I was able to fix this issue about a week ago. There were 2 main issues that contributed to the timing problem - my knock sensor was unplugged, and my IAT readings were thru the roof. Read on for more details.

I learned that your intake air temperature (IAT) influences timing. The PCM accounts for hot intake air by retarding timing 6 degrees or more when you have an IAT over 130. There are tables online, but basically it starts pulling timing at 90dF and increases the retard WRT temp. (It also advances timing in cooler Temps too!) My intake temp was great in the morning, but as I got closer to work, and during city driving, it would reach up to around 50dF over ambient!!! Average highway temp was about 20-30dF over ambient. So I started fixing my issue by dumping my Hot air intake, and buying flex tubing to run to the fender. Now, I have a fender well intake, and my readings are only about 10 degrees over ambient. I don't have it sealed off from the engine or anything, so there's a lot of room to optimize the intake, which I'll do next week. This improved my timing a bit, and I noticed that my car wasn't driving like **** anymore by the end of my commute.

I still had the weird RPM related timing issue though. After plugging the knock sensor back in, this issue was gone. My car now runs great.

Key takeaways? If a knock sensor becomes unplugged, fix it quick, they're super important. Also, it blows my mind that so many people don't care at all about using a hot air intake vs a real cold air intake. 6+ degrees of timing is a lot, people! Also, I've come to learn that there are many things that influence an IAT that aren't accounted for in many of the tests people run on youtube and what not.

And if you're still reading,
I have a new issue. When my supercharger kicks in, it seems to almost be screaming. It is probably 2X louder than normal. It started happening about 5 days after I put on the CAI. I tested the CAI by removing it, but the sound persists. any ideas? It sounds bad.

Sent from my SM-G935T using Tapatalk

I am having an issue with my car that I feel may or may not be related to this thread (need guidance).

I have a 2006 Grand Prix 3.8 NA with 171,000 miles on it. I have replaced the spark plugs and wires within the last 8,000 miles or so. I have recently cleaned the MAF and Throttle Body within the last 500 miles.

I drove to work this morning just fine (~3 miles away) while the temperature outside was ~75 degrees out. The car was sitting out in the parking lot all day and the temp. outside had reached 100 deg. by the time I was leaving work (I should also note that I drive a black car). As I was driving home, I got about 3/4 of the way home and my Engine Light came on and started blinking. As I rolled to a red stoplight and the engine RPMs were below 1000 the engine started to sputter and lose power like it was going to cut out. I was able to get it back up to speed ~30-35 MPH and limp home only having to stop and start once more.

Other things: The engine operating temp. never got to halfway on the gauge and Voltage was consistently ~14.8-15.0 V per the onboard driver info center on the dash.

I have no idea what is going on with it right now. I plan to take it to Autozone/Advance tomorrow (if possible) to see if they can check the OBD for any codes. My thoughts initially were that the extreme heat may have something to do with all of this affecting sensors and what not, but not entirely sure. I have also seen my MPGs drop off slightly over the past 9-12 months or so which made me think that perhaps the catalytic converter/O2 sensors have something to do with this?

Any and all help is greatly appreciated, thanks!

I had the car in the shop today and turns out my issue was that the Ignition Control Module had gone bad. The engine was misfiring on #1 and #4 cylinders. Ignition coils were fine and catalytic converter checked out (although I am doubtful about how long IT will last).

It cost about $350 for the repair with ~100$ in labor and $234 for the part (which seems high, but what are ya gonna do?).