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New owner of red '01 Grand Prix GTP coupe

W

wmorrison65

New member
Hi, all.

Just picked up a 2001 Pontiac Grand Prix GTP Special Edition coupe.

It seems... "sluggish" compared to what I would have expected. Runs fine, no hesitation or rough idling, goes into boost when you step on it, but I've driven a Chrysler Town & Country with a NA 3.8L (215 hp) that feels a bit peppier, at least under normal driving conditions (haven't gone WOT on the minivan.)

I've read I should look into clogged cats and badly adjusted bypass valves. Any other ideas, or comments on those?

Still not sure this isn't just my perception of the car based on one day of driving. I'll be hooking up my OBD adapter soon and logging some data while driving.
 


im probably wrong but ive noticed these motors (the 3800) run lower rpm than any other car I have owned, not sure if this could contribute to your sluggishness.
 
After work I put in the OBD adapter, started up Torque on my android, and set it to log sensor readings, then took a drive on the highway, and opened it up a little bit. There are some problems...

When I get into boost the engine "shudders." It doesn't even have to be full boost, low to mid does it too.

One time during the drive, while accelerating, there was a very short loss of power, less than half a second. Another time with a little more throttle there was quite a lot of power loss for a second or two. (Worse than the shuddering.)

Got off the highway and drove easy another mile or two home. When I parked and let it idle a bit, the revs kept dropping down to maybe 500-600 and jumping back up to 900-100 (a guess, wasn't looking at the tach,) repeated several times, then it smoothed out and idled steady when I was looking under the hood.

Looking at the data, I haven't been able to pinpoint the exact times of the power loss or shuddering, but I do see fuel trim making MAJOR jumps up and staying there from a few to several seconds, then jumping back down. Generally fuel trim was +-5, but the highest logged was 16.41 long term and 17.97 short term, cruising about 65mph at 11% throttle.

So for "shuddering" it seems like checking plugs, wires, and/or coil packs is the first place to start. What about clogged/failing injectors, or fuel filter? Fuel pump? I've also read some people say it could be torque converter... I sure hope not.

I can upload the CSV files if anybody cares to take a look at the data.
 
mikejohnlewis said:
im probably wrong but ive noticed these motors (the 3800) run lower rpm than any other car I have owned, not sure if this could contribute to your sluggishness.
Click to expand...

Actually, it revs higher than I would have expected for normal driving conditions. I'm trying to find the transmission gear ratios to figure out what I should be expecting. (And yes, I know how a torque converter works. ;) )
 


wmorrison65 said:
Actually, it revs higher than I would have expected for normal driving conditions. I'm trying to find the transmission gear ratios to figure out what I should be expecting. (And yes, I know how a torque converter works. ;) )
Click to expand...

I only have an srt4 to compare it to, and that things rpm gauge was distracting, it was a stock turbo but at 234,000 it blew and it becam the first N/A srt4 I know of.
 
do a tune up, and check for vac leaks, the t under the snout breaks, the fat hose of the TB to evap breaks. spray the lines with carb cleaner if the idle jumps you found the leak area.

if you have not checked to see if the lim gaskets are up graded yet, plan on that job too. look where the lim meets the head, if you see a black gasket you need to do a lim job. silver gasket and its been done already and your good to go.
 
I would start with these things.
Check for vacuum leaks.
Spark Plugs - AC Delco 41-101
Wires - Lifetime warranty parts store brand
Fuel Filter
 
I've put about 75K miles behind me in 3800 GPs and almost every performance issue has been a vaccum / boost leak somewhere. But you get the big loss of power when on the gas. When it shudders and tries hard sometimes and doesn't set a code immediately like a plug or wire will, its probably a coil pack. Cheap enoough to buy a new one and swap it around to see if the symptom changes.
 
The SES light flashes red for several seconds sometimes when the shuddering/power loss happens, not always, and it doesn't stay on afterward.

Is the SES (SERVICE ENGINE SOON) the equivalent of the "check engine light" icon on other cars? That comes on and stays on when there is an engine code to be read?
 


Clogged cat. I think you can tap it with a hammer, if it rattles its clogged. I remember reading something like that on here.
 
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