NEW Problem

TGP Nick · October 21, 2007, 11:23:24 AM

Ok my TGP is having a strange problem, and it only happens while you are going a steady speed and not under boost. For example, yesterday I was driving the TGP down the highway with the cruise set at 70 MPH; it ran fine for the first 125 miles of my trip, but for the last 25 miles, the car would surge and jerk and it would shake the whole car when it did this. The RPM needle didn't move much when it did this, but the boost gauge needle was all over the place in the green "vacuum" part of the gauge. Heres a video I took yesterday on the freeway of the gauge freaking out-

What do you guys think this is? At first, I was thinking MAP sensor, since the boost gauge measures pressure and that would make sense if that went bad, but it happens when you are going a fairly steady speed or light acceleration while not under boost. Also, when you accelerate and do NOT boost, it will do it under that condition also, but lightly. If you accelerate hard under boost, it runs perfect, but once you are out of boost, it comes back. Also, it idles perfectly, doesn't surge or anything at idle... It won't always surge like this, either. The problem comes up at random... it ran fine this weekend during the road trip down to New Ulm (150 miles) and on the way back home it ran perfect for 125 miles and the last 25 miles I wasn't sure the car would make it home..

Any ideas?

pontiac6ksteawd · October 21, 2007, 12:59:48 PM

My TGP does this from time to time too. What I do to solve the problem is downshift into 3rd gear on the tranny, drive it that way for 10 miles or so, and shift it back into OD. Sometimes that fixes the problem, and sometimes it doesnt.

TGP Nick · October 21, 2007, 01:16:13 PM

Other than the bucking and jerking for the last 25 miles, it ran great for the whole trip- I averaged 31 MPG at an avg speed of 62 MPH during the trip.

sleeperred90tgp · October 21, 2007, 04:06:13 PM

That would be your TC clutch locking up and unlocking.When it unlocks you vacuum will go up because it's kind of free wheeling until it locks up again.

Fixes. Could be alot of things. Vacuum leak, exhaust leak like a cracked Xover contanimating the o2. Could even be a bad switch but I doubt that. It's on the front of the trans. Could even be an ignition glitch which lowers the vacuum when it misses and the ecm thinks it needs power.

Scares the hell out of your passengers doesn't it. :icon_frown:

Jud

TGP Nick · October 21, 2007, 04:17:56 PM

Transmission is new with 15,000 miles on it. I replaced the x-over this spring with a Jeff M. unit and everything is tight. I don't think I have any vacuum leaks, because I had the cruise on and the panel vents on during the whole trip... everything vacuum controlled worked fine... No check engine light, either, even while it is bucking like crazy, there is no check engine light... I find it strange that it only does it at random and often times it works perfectly... like the road trip for example
Any other ideas? :confused:

TGP Nick · October 21, 2007, 04:20:49 PM

Also, I don't think it is the TC clutch, because it keeps constant RPMs when it does this.. usually when my TC clutch locks and unlocks, the RPMs will go up/down by ~500 RPMs according to my gauges.

GutlessSupreme · October 21, 2007, 04:56:58 PM

for the hell of it, make sure your aux battery terminal nut is tightened down all the way.

flybynite · October 21, 2007, 05:14:13 PM

USUALLY when you have bucking it's a lean condition. MAYBE your cat is starting to get clogged and you have more backpressure than normal. That will make the o2 think it's overally rich and the ecm will try to lean things out a little. Just a guess...

TGP Nick · October 21, 2007, 05:21:52 PM

I think my cat has been gutted by the previous owner... I think this because it has a really shitty weld all the way around the perimeter of the cat.. it looks like a really thick amateur weld. I could be wrong, but I don't see any other reason why it would be welded like that.

On the other hand, I pulled my front 3 plugs to just check them about a month ago and they were all clean, but were WHITE. I don't know why it would be running lean though. It is completely stock with a Jeff M. crossover, airfilter is clean in stock airbox, has NEW C 302 injectors in it this summer, and I am running non-oxy, non-ethanol 92 octane gas in it.

TGPvsTIII · October 21, 2007, 05:42:14 PM

It does sound like a miss. The vacuum gauge would lean toward that too. Also the white plugs. What heat range plug are you running? stock? colder? When you looked at the plugs was there any build up on them? How many miles are on them. How old is the O2 sensor? Do you have a scanner to look at live data?
Tim

TGP Nick · October 21, 2007, 05:49:56 PM

I'm not sure what heat range the plugs are- I know they are regular AC Delcos and I suspect they are the original plugs. I believe the car has original plugs, wires, O2 sensor, and all sensors are stock. The plugs were clean with no buildup on them, but they were white. My neighbor has a scanner, but I'm not sure how in-depth it goes as far as taking sensor readings and such. I was hoping the car would run with the stock equipment until I put it away for the winter, as I was going to do a full tuneup this winter.
Again, I believe everything on the car is stock, other than the injectors (C302 yellow tops), crossover (Jeff M.), and Turbo oil return line (KAZ).
Also, the car has 120K miles on it with original equipment. When it doesn't have the bucking problem, the car runs flawlessly. Will smoke the tires.

flybynite · October 21, 2007, 06:44:36 PM

Quote from: TGP Nick on October 21, 2007, 05:49:56 PM

Also, the car has 120K miles on it with original equipment. When it doesn't have the bucking problem, the car runs flawlessly. Will smoke the tires.

The plugs need to be changed every 30-35,000 miles. If they are indeed the originals they will need to be changed regardless if it solves the problem or not. Could be that the plugs are so worn that the end gap is larger than the .035 GM recommends. That will create hotter cylinder temps and could cause a lean condition..

TGP Nick · October 21, 2007, 06:51:57 PM

What would cause the car to run like this all of a sudden?

flybynite · October 21, 2007, 07:05:48 PM

Quote from: TGP Nick on October 21, 2007, 06:51:57 PM
What would cause the car to run like this all of a sudden?

Who knows... Maybe it's just time for a tune up, or maybe the o2 is tired and ready for a replacement or both. Pull a plug and check the end gap...

flybynite · October 21, 2007, 07:36:37 PM

Could be a plug wire breaking down also... It gets pretty hot under the hood of a TGP ;)