I have a 2000 Monte Carlo SS with the 3.8L V6 engine. The engine has always been very smooth and quiet, but in the last few months, it’s developed what I would call an intermittent random misfire.
This can happen at any time, at any speed, under any conditions. Just backing out of the driveway or 15 miles down the road. Driving down the highway at a constant 60 mph, or idling at a traffic light. Wet or dry. Makes no difference.
It’s as if the ignition key had been switched off momentarily and then back on again. Before and after each event, the engine runs as smooth as ever.
The local Chevy dealership is guessing bad coil, ignition wiring, spark plugs or fuel injector. They want $75. up front just to try and diagnose the problem and I wouldn’t put it past them to just start replacing parts until they hit on the problem and then present me with a bill for $1000. and tell me that all the replaced parts were contributing to the problem and all needed to be replaced. It really doesn’t feel like any of those, since the engine runs and idles just fine before and after each momentary hiccup.
A trusted independent shop has tested the coils and put the engine on their analyzer. They tell me that they can see it happening, but can’t pin it down to any particular source and the car isn’t storing any faults in the computer. The shop owner says he thought he had heard of something similar on a GM car that turned out to be a bad ignition switch. However, he said that was just an educated guess and warned me that it would cost me $250. to replace the switch just to find out if he’s right.
I’m inclined to agree with the independent shop on the bad ignition switch diagnosis because:
1. The car isn’t storing any faults in the computer. If it’s a case of the whole ignition system shutting down for a fraction of a second and then back on, maybe the computer hasn’t been programmed to recognize “ignition off – ignition on” as a fault.
2. That’s exactly what it feels like – as if the key had been turned off and on again.
Are these ignition switches so sophisticated nowadays that they could possibly cause an intermittent problem like I’ve described?
Has anyone out there heard of anything involving a bad ignition switch in GM cars causing a problem like this?
Help!

 

I got the same problem . I already replaced the S-Plugs! 100% accurate gap.
* changed my S-Plug wires.
* replaced my downstream o2 sensor !
* even replaced one of my ignition coils
but still the car wont pass smog! $#&* the Chinese guy who sold it to me
- so today its a rainy day here in Cali and i found this stuff pretty useful , you might give it a try . here is the LINK - http://www.youtube.com/watch?v=OyvdWeyDHf4
ima try it now .

 

Cat could be getting clogged, fuel filter, spark plugs/wires, MAF going bad, ICM going bad, crank sensor going bad, the list goes on and on

 

It's not uncommon. There are several threads on this board describing somewhat similar issues. If your shop is able to replicate the issue, then they should be able to test the signal from the ignition switch without blindly throwing a $250 part at it. Just sayin.


If you're setting a P0300 code, then your issue is completely different than what the OP is describing. What's causing the smog test to fail?

 

Agreed!

For $75.00 I would let the dealer put it on the analyzer. You could have the independent shop change out the switch, but if it still does it your out $250.00. Mine was cutting out before I took it in, but when I drove it to the dealership the next morning everything was A-OK.

I wrote a list of items they replaced in an earlier thread and the Monte seems to be fine now.

https://montecarloforum.com/forum/sh...ad.php?t=26170

Good Luck!

 

this happened to me, and it ended up being a bad ground wire.

 

Turned out to be the Mass Air Flow Sensor. GM dealer wanted $430.+ to replace it. Local independent shop wanted $250.+ for the same job. After a little online research, I bought a brand-new unused part on eBay for $75. and installed it myself. Monte now runs like a top.

If that's all I was going to do, it's actually easier than checking the air in the tires, probably the easiest repair on the whole car. But I also elected to put in a new throttle body screen, spray some throttle body cleaner inside the TB, wipe it out and put in a new air filter.

A few words of caution here, though. The MAF Sensor is held in with "Tamper-Proof" Torx screws. You'd best have some tamper-proof Torx bits handy beforehand and avoid a trip to the hardware store in the middle of the job. If you're going to remove and/or replace the TB air flow screen, be prepared with a pair of internal snap ring pliers. The TB screen is a tin-foil honeycomb and is extremely delicate and difficult, if not impossible, to remove and replace without damaging it. As this screen is designed to smooth out the air flow to the MAF Sensor, you don't want to deform or crush it in any way. If you're going to remove the screen to clean the TB, you might as well have a new one ready. I once saw an after-market "performance" TB screen made out of plastic that was much sturdier that he OEM item. If I could find it again, I'd probably buy it.

Can anyone give us a lead on a sturdier plastic after-market TB screen?

 

Generally, all of the thing people are listed will return a code. I had a 98 doing the same thing. Started out with a slight misfire under load and got worse over time. Did get a random misfire code on Cylinder 6.
Long story short, it was the upper intake plenum burn through syndrome and was filling that cylinder with water. VERY common issue on the 3.8...

We didn't catch it soon enough and spun a bearing on the crank... Had to do a total rebuild..

 

Actually, I did have the codes read at four different places. AutoZone, Advance Auto, GM dealer and independent shop. Only the people at Advance Auto and the independent shop read it correctly. As soon as two of the four agreed on the correct diagnosis, I went ahead and did the repair and they were right!