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sprinkles08, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 22827
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I have a 1997 Pontiac Bonneville SSEi with the supercharged

Customer Question

I have a 1997 Pontiac Bonneville SSEi with the supercharged 3.8. 262000 miles. On cold startup will run rough when accelerating. Hesitating/bogging.Will mostly go away when car warms up, But will occasionally pop up. No check engine lights. No pending CEL. Spark plugs are brand new and gapped correctly. Fuel pressure is good. I can't seem to grasp what's causing it and since it comes and goes it's hard to poke around and figure it out.
Submitted: 1 year ago.
Category: Pontiac
Customer: replied 1 year ago.
I should also add it will only die if I keep trying accelerate while it's hesitating for a while. If I let off the hesitating will go away until I accelerate again. This issue started after replacing the fuel filter, Valve cover gaskets, transmission fluid and filter, and PCV valve.Let me know if there are any more details that can help.
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to Justanswer!

It sounds as if you may have a failing upstream oxygen sensor. If the internal heater in the upstream sensor is weak then it will cause the oxygen sensor signal voltage to be abnormally high during warmup and the transition to closed loop operation, and it can also happen at low speeds or idle in some cases. If the voltage is too high because of a weak heater the engine controller will think the engine is running rich so it takes fuel away.

Try unplugging the upstream sensor, disconnect the battery to clear the adaptives, and then drive it to see if the problem is gone. If so then replace the sensor.

Customer: replied 1 year ago.
I should add when the car is in open loop the car will run rough. When it warms up and switched to closed loop it runs fine. I also notice it switches back to open loop and it will run rough again while cruising and again running fine after switching to closed loop.Wouldn't the voltage trigger a Check Engine Light though? Also how can I check the voltage with the car running and what voltage is too much/little?If it turns out not be the o2 sensor what should I try next?
Customer: replied 1 year ago.
When it does run rough for a bit I do notice a rich smell sometimes. Hope this helps.
Expert:  sprinkles08 replied 1 year ago.

You're able to monitor data?

Customer: replied 1 year ago.
I Have a Scangauge2 device. it can monitor a few things, But nowhere near a real scan tool.
Expert:  sprinkles08 replied 1 year ago.

Can you see coolant temperature?

Customer: replied 1 year ago.
Expert:  sprinkles08 replied 1 year ago.

After it hasn't been driven for eight hours or more do coolant, ambient and intake temperature agree?

Does coolant temperature go lower or higher when the problem happens?

Customer: replied 1 year ago.
The coolant temp rises and lowers normally. Coolant, ambient, and intake temps are about the same on cold startup. I haven't seen more than a 4 degree difference.
Expert:  sprinkles08 replied 1 year ago.

Does it show long and short term adaptives?

Customer: replied 1 year ago.
I cannot access that data.
Expert:  sprinkles08 replied 1 year ago.

Have you tried unplugging the upstream sensor and disconnecting the battery yet?

Customer: replied 1 year ago.
Sorry for the wait. Yes I did try that and there was no difference in how it ran.
Expert:  sprinkles08 replied 1 year ago.

What was your fuel pressure while the problem was happening?

Customer: replied 1 year ago.
I'll have to try that in the morning.On another note I had it in the shop yesterday and they found a p1571 code.P1571Description
TRACTION CONTROL SYSTEM DESIRED TORQUE CIRCUITTraction Control System (TCS) uses Anti-lock Brake System
(ABS) in conjunction with PCM fuel and ignition controls to limit
drive wheel slippage during acceleration.Any chance this can cause the issue I'm having?It also passed a compression test. I'll try and get a proper fuel pressure reading asap.
Expert:  sprinkles08 replied 1 year ago.

That code is most likely setting because of the loss of power.