FAQ: Hesitation, Stutter(Studder), Shudder, Stumbling, on Acceleration/Load

ibmoses wrote:

Are you sure its not the transmission slipping?
Does the problem occur as the vehicle approaches the shift from 1-2 and the shift from 2-3 ?
Watch the Tach when the "sputter" or "hesitation" is happening and report back with your findings.

Bert

Oh no, it's not the transmission. The car shifts firmly and it's not always right around the shift, it's just most noticable then. It did make a sloppy shift the other day but on average it shifts firm. Moderate acceleration still gives me firm solid shifts.

Time to put a scanner on it. You can get excessive KR due to very cold temps.

I had the same problem. What it turned out to be was a bad spark plug boot on #6 allowing arcing at higher acceleration. Was fine under light load. Got worse over time. Replace wire(s) back to WOT :-)

Sorry for the delay but I was out of town an I forgot my password to log in so I had to wait till I got back to answer. The plugs and wires are only a few months old. There was a vacuum line disconnected but it only helped, it didn't fix the problem entirely. I noticed that the little outlet PSI regulator thingy for the supercharger has broken. I'm gonna replace that as soon as i get a min. to get to a junkyard. I started the car again about 2 or 3 days ago to take a little more in depth look at the problem an upon discovering the broken PSI regulator (or whatever its called) I noticed that there is a slightly audible sound comming from inside the supercharger housing that resembled a vacuum sucking up pennies. Is it possible I trashed the coupler too? Thanks for the advice!

The coupler is just plastic (nylon or delrin or some such) and wears over time. It's not so much that YOU trashed it, it's just that it has so much wear after so much use. There are other threads on this board telling how to replace it.

Dealers can get you the outlet PSI regulator thingy for the blower; it is not freakishly expensive.

As for the plugs, if you have not checked yet you might want to go wire by wire and make sure that the wire terminals are on properly. To do this disconnect each end one at a time and push the boot back off the crime end of the terminal, see that the conductor is under the crimp. Once and only once I had a new plug wire on which the crimp had damaged the carbon fiber conductor, store gave me a replacement. When you put the terminals back on you can (a) put a little tune up grease (polysiloxane) on the ends so they don't tack themselves together (b) connect the terminal then slide the boot over the connection and burp out the air if any. Don't use much tune up grease, a thin film will do just fine.

You also could just have had one of the coils die. THat is, a bad wire will mess up a coil.

Here is a scenario. You look under the hood - find a bad plug wire. So you replace plugs and wires - problem does not really go away. If you remember where the bad wire was it might not be a waste of time to replace that coil.

You can get a few coils from your local 'pick and pull,' test the windings with a meter, OR just get one good one from AutoZone or some such. Then swap a coil out for the new one and start up, see if the problem is solved. If not, move to the next coil. In the almost 200,000 miles on my RIv I have had one coil quit, and it died becuase of a bad plug wire. The OE ignition on the Riv has good coils and wires and is strong - but does not last forever...

What are you going to do next?

Albertj

It was a few months since I last changed the spark plugs and she hasnt skiped a beat until this. My original thought from just off the top of my head before I took a good look was a coil quit on me. But they all are firing. I'm gonna replace that psi regulator and see what happens, cause I drove it after I found the disconnected vacuum hose and it stoped feeling like a missfire and more of a jerk as if it was being choked. From what I understand of the way the supercharger works if the regulator was to break the butterfly at the bottom of the supercharger wont open an psi built up by the supercharger wont be able to enter the L.I.M.. If thats true then i would venture to guess that, that could cause her to choke, and the backed up psi could cause excess wear on the coupler. So hopefully replacing those 2 parts should fix it.

thanks - yeah the regulator bleeds off the boost when you probably don't want it - as far as the coupler goes you have a nice guess, there might have been excess coupler wear but no kidding the OE couplers just wear out, whether or not you are having regulator issues. Although the later couplers (I think the blown Series II 3800) were somewhat more durable I was told.

Every well designed mechanical system has a fuse of some sort. A solid drive shaft will have shear pins at the couplers. Accessories on an engine are most often driven by belts rather than directly with gears. And the blower on the Riv is belt driven, and has that plastic coupler to boot.

If it's any consolation, the amount of time we are spening talking about it is approaching about equal the amount of time it will take you to change it. You can get a reman blower, or get a replacement coupler, unbolt the blower nose from the blower body on the car (warning - the oil STINKS) and pop a new coupler on. I don't remember whether you can replace the bearings too (with the body still on the engine) or if you need to pull the blower body and use an arbor press.

Albertj

I just graduated school a min ago an when I was in shop procedures I changed the coupler on my hommies GTP. We didn't need a press or nothin but yeah the oil does stink bad. I was readin the write up about it an it said that on my year i got to take the supercharger off. It's cold as hell here in Philly. I got to wait till a nice day to do it.

I'd sort out your boost bypass solenoid (thats that PSI thingy) before doing the coupler in the SC. I had a similar problem, this was before I had a boost gauge, the boost bypass solenoid was toast, but i had no clue, it was only giving me 2 PSI of boost at WOT, fixed it for 50 bucks(CAD) and suddenly i was into the stock 7psi. Big difference....

however, i'd like to hear more about this "the supercharger housing that resembled a vacuum sucking up pennies", a vacuum it should sound like, pennies going through said vacuum it should not. Dead coupler shouldn't sound like pennies in a vacuum....

What kind of wires did you buy? Are they meant specifically for the 3800 supercharged engine?

You don't need a press for the coupler, I was referring to the bearings.

Because if Karma is right you have some bearings to replace.

Some of the Pep Boys stores let you rent garage space by the day. Is that true in your area (Philly)?

Albertj

hey first post back on this board for a long time... i had the same exact problem with my riviera and was advised to change everything from plugs, wires, coils, fuel filter, and supercharger coupling. After doing all that and still not figuring it out i found low compression in three cylinders. It's in the shop now having a new engine put in after sitting for over a year. Maybe you should just check compression before you go too far with it?

Mrph, still haven't figured this out. It's bad enough that when in first and given hard gas the car doesn't squeal the tires like it used to. It accelerates right but it's rough and harsh. At higher speeds (i.e. 60 mph) if I floor it it's not so bad and seems to accelerate quickly and smoothly. It's only when I do it at lower speeds that it likes to do this.

It's almost like a pulsing thing. The motor is going, then it kind of shudders, then goes more, then shudders, then goes more, shudders, until it shifts. Definitely need to get this fixed, it could mess things up when I need the power to get into another lane. Does any of this help towards a further idea of the problem?

Not exactly pocket change, I'm trying to make sure I make no unnecessary purchases to fix this problem. Might I ask what it is that makes you believe this is the problem?

I explained a free method to diagnose the problem. If you're not willing to slip off the SC belt to rule out some possibilities, I'd suggest a new set of wires. It's a maintenance item, like tires, brake pads, etc.

What makes me believe it's the problem? The symptom is exactly that of a bad ignition source. Plugs are the cheapest, then wires, then coils. In my experience, coils are unlikely.

What have you tried so far out of the suggestions given?

Derek, I have checked the wires to make sure they're not rubbing pretty much. I don't have time with school and all this damn cold to go out there, take the plugs out, and look at them all (Plus I just put these in a few thousand miles ago, probably 2 or 3k ago tops).

Btw AA, the wires from the GTP were OEM. That process sounds like a pain and I don't want to risk tearing up the belt I had to pay to get put on since it was such a pain.

So I'm looking at some wires here from ZZP

OEM wires - $37.99 (Are these for NA or does it matter?)

But part of me wonders if while I'm doing this since I'm sick of replacing freakin' spark plug wires if I buy some nicer aftermarket ones if they'll stop crapping out (Yes I know the GM fail rate, but hey it's an opportunity upgrade). My question - what (if any) difference do these make over the OEM style?

ZZP 10.3mm wires - $100

Will I see any sort of gain from these wires? Are they a good supporting mod given a possible upgrade somewhere else that would make them impotant (like coils or something else)? I really don't mind paying $100 for nice wires if they'll make any difference over the OEMs (Plus I'm a sucker for the red, not that that should matter I guess).

Intense has the $60 wires you spoke of AA, but would those $38 ones from ZZP be the same ones?

two things, Shintsu

1) do you know how to detect arcing of the plug wires?

2) how's the puppy?

Albertj

1) No. My dad might, but I certainly don't.

2) Good. Climbing steps on his own now and going outside without someone carrying him. On to the serious house training now...I'm tired of cleaning up his messes!

Actually, spotting arcing is easy. First, you have to do it in a very dark garage, or at night in a dark area. Open hood, take off the plastic engine cover, start the car, get out and look at the engine. If your wires are compromised you'll see flashes of blue along them. Those are often called "coronas" and they are the electrical energy leaking out the wires due to insulation breakdown or other electrical problems. Good wires don't have coronas. Wires that look perfectly good but are marginal will have coronas. I think you might get a corona from a wire that's good connected to a plug that's bad - spark has to go somewhere - and that can fry a wire and you'd never 'see' it except at night. Eventually the coil will blow from trying to fire the bad circuit. Then you'd have two cylinders that won't fire, like #1 and #4, because they come off the same coil. Once the coil blows, you won't get a corona anymore (no energy in the wire).

The OEM wires for the RIviera are quite good - they have to be since the OE ignition is high energy to begin with. That said, only wires I know of that are provably better than OEMs are Magnecors. http://www.magnecor.com - if nothing else there is a lot of useful informaiton on that site, with reasonably clear technical explanations. THe ZZP wires won't fit into the wire looms on the engine. There is one channel under the valve covers and various clips around the top. What you do is up to you but truthfully I would not bother.

Bottom line is that even though it is cold out, there is an easy check you can do to quickly get an idea of wire condition. Although it has to be at night or someplace *very* dark. Coronas are not very bright.

As for the puppy, put newspaper over the entire floor and as the pupy soils it, take up all the soiled paper but put a piece the puppy dampened near the door you want him to go to when he has to go. Keep doing that for a week or so, you're done when the puppy goes only by the door - take the paper away when he's not around, he'll ask to go out when he goes to the door and can't find the paper.

Albertj

It's pretty easy to crack the insulation of a plug while installing it, even a hairline crack is enough to make it stop working later. You should check your plugs.

Quote :

Actually, spotting arcing is easy. First, you have to do it in a very dark garage, or at night in a dark area. Open hood, take off the plastic engine cover, start the car, get out and look at the engine. If your wires are compromised you'll see flashes of blue along them. Those are often called "coronas" and they are the electrical energy leaking out the wires due to insulation breakdown or other electrical problems. Good wires don't have coronas.

Normally, this works, but on our supercharged engines, it's not that simple. My wires worked fine at idle and with most light to medium acceleration - engine ran perfect. But when you get into boost, the PCM uses a hotter set of spark tables to fire the plugs. This extra voltage will cause arcing through cracked or worn insulation, whereas the normal spark might not,

This is why taking the SC belt off is a way to diagnose the problem. The engine never goes into boost, so the hotter spark isn't delivered, and the sputter doesn't occur. Easy way to diagnose bad wires after ruling out plugs. It could be a coil, but those are more expensive to replace.

How old are these wires from the GTP? How many times were they removed from the plugs? Were they removed properly (you can destroy the boots easily with just a few swaps)? Did you swap all the wires, or just some? They should be replaced as a set. How do you know the old ones on your car are still good?

N/A wires will not work for our SC engines. Are you certain the GTP had the correct wires?

I knew some of the wires were bad on the Riv because one of the the boot came seperate from the wire and another one the wire broke inside the boot. The plugs for the GTP were the right ones, the box for them is around somewhere.

We took them off once and put them on once. My dad told me all about how easy wires can tear and why you must pull from the boot so we removed them properly (some just tore due to age I gather). We only swapped what looked bad.

Derek, where will this crack appear on the plug? It's something I could look at while taking the wires off.

Would still like to know if the 10.3 mm plugs make any difference over OEM also.

Maybe take the other wires off the GTP and move over to the Riv, replacing even the wires you thought were good.

10.3 mm would be overkill. 8 mm are big enough. 10.3 mm should work fine though, but no performance advantage from paying extra.