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

He disappeared.....

You gotta give us some info though, like TS89 said.

Riviera's go from '65 to '99 around here, and have everything from a turbo six, to a super six, to a 455. And there's also 87, 89, and 93 fuel that you could be feeding this thing. If you tell us about the car and a more specific description of the problem, we can help you.

its 1996 seris 2 supercharged i dont know much about this car

If it has high miles it sounds like it's due for a cleanup and tuneup. If you're overdue for a tuneup, that's why you have this problem. If there's no power coming from the enigne, and there doesn't seem to be a transmission problem, then there's probably a lot of gunk inside too. Have your fuel filter checked and cleaned if it needs to be done, and start using something like Z-Max if it's a high mileage engine. When you go for a tuneup, just ask them to check everything that may be holding you back. How many miles are on it?

125000

Sounds right, do you know if it had a tune up since the 80,000 mile mark?

thats about when i bought havent done much to it since besides oil change

could the slow response be because the fuel im using

Fuel shouldn't have much to do with it, unless it's used to premium and you give it regular. The slow response means the engine's interior components are gunked up and there's a lot of resistance. Buy some Z-Max, take a drive, and that should clean it up.

k thanks

replace the ignition wires, then spark plugs if necessary. Good luck.

watch your octane (super super super!), basic tune-up, then we can go from there.

Any funny noises coming from the serpentine belts?

most likely a spark and/or fuel problem.
definitely start with plugs (cheap) and perhaps wires ( I still have my originals).
a fuel filter is cheap and probably due too. some sea-foam might help too.

My car started hesitating last week. Missing under load etc. It was idling well enough, starting fine. Under very light accel, it did ok. Once I got on the accel, it would hesitate. I remember an old Regal (81) that did this, and it was timing.
Anyhow, put the scanner on while driving. At idle, advance is around 23 degrees. While driving down the interstate, around 3k RPM, advance was at upper 30s. When I got on it, accelerating, advance dropped to between 9-15 degrees. That causes alarm. Would think that it would either stay, or go up when accelerating.
Anyhow, knock count goes thru the roof as well when under accel.
I am thinking my crank and/or cam sensor might be the culprit.
As far as other things go, plugs and wires are < 20k old. Considered gas before, but it started when I needed a fillup. Still doing it after. Put in heat to make sure no water etc. Car also stalls in cold weather. Just stops while driving. Leave it sit for a few minutes, and it starts right up. When it does stall, it cranks fine, just no hint of firing. Has yet to stall on me when above 50 degrees. (not completely sure, could be 40, or maybe 55)

What kind of scanner do you have? Do you have an SES light? Any trouble codes?

The accel problem sounds like a bad spark plug to me. Timing sounds normal, it's generally around 15 but with KR the computer is pulling timing. I suspect your KR could also be due to your bad plug (if that's the issue).

I'd like to see a scan of a number of parameters including MAF Hz as we start our troubleshooting...

What year is your car? It's very helpful to us for you to put info about your car into your signature.

-Derek

Forgot about the SES. No light, no codes. KR remains at 0 no matter what I do.
The car is a 95 Rivi, SC. about 145k miles. Also, no weak cylinders are reported. The scanner is an Auto Xray. I forget the model.

how old is the fuel filter? have you cleaned the maf recently? plugs look ok?
that is surprising that no code pops up.

What kind of ignition wires did you buy? How long since you changed the fuel filter?

How can knock count be through the roof when KR remains 0 no matter what you do?

AA wrote:

What kind of ignition wires did you buy? How long since you changed the fuel filter?

How can knock count be through the roof when KR remains 0 no matter what you do?

Well, I guess it happens like this. Scanner shows knock count increasing. It reaches 255 then starts over again. Switch to KR, and no matter how hard I get on it, it never changes from 0.

I have to check the plugs yet. The wires are stock, oem wires. The thing that moves me from plugs and wires is that the car had been stalling while driving, like it is now, since last winter. Stalls out, let it sit for a few minutes, starts right up again. I also have had codes for the cam/crank sensor. It does not specify which one, just that one or both have a problem. I do not have the specific code on me.

is this hesitation only once during a drive cycle or does it do it every time you get on the gas?

Mr.Riviera wrote:

is this hesitation only once during a drive cycle or does it do it every time you get on the gas?

Every time I get on the gas. It appears to get better as time goes by/car warms up, but it is still there.

Is cat converter okay? One way to test is to put car in neutral and rev the engine to the 3-4k range (when warm). According to GM:

"If the engine freely accelerates to higher RPM in Neutral, you can assume that the engine and the exhaust system are normal."

If there is any lag in getting into the upper RPMs, you might have a clogged cat.

AA wrote:

Is cat converter okay? One way to test is to put car in neutral and rev the engine to the 3-4k range (when warm). According to GM:

"If the engine freely accelerates to higher RPM in Neutral, you can assume that the engine and the exhaust system are normal."

If there is any lag in getting into the upper RPMs, you might have a clogged cat.

I don't get how that would work. That would only be like 5-10% throttle tops.

I think it's the speed (time) at which the revs are achieved. If it's delayed compared to normal (whatever that is), the cat is clogged. I copied that out of my GM shop manual.

Mr.Riviera wrote:

how old is the fuel filter? have you cleaned the maf recently? plugs look ok?
that is surprising that no code pops up.

You have replaced the fuel filter?

Bert

Did not realize that I was posting this in Series II, as mine is a 95. Anyhow, it sounds like a coil is going to pot, and the mechanic (Riv enthusiast) also said that the SC is going bad. He thinks that it is starting to impede air into the engine. I explained that before this happened, it was running great. Ran quick and hard. Not doubting that the unit could be going bad, but I doubt that it is my problem right now.
Anyhow, good place to get a cheap SC for my 95? Cheap because I am not looking to drop much more cash into this car. It is about to meet the crusher with all it as cost me.