HELP ! Bucking and jerking when trying to maintain speed!

[AllBlackZ28]

This seems to be a common problem. My 2000 Z28 auto with 105 thousand miles has been doing the same thing for about a year. First I changed the plugs, checked the fuel pressure (good at idle), changed PCV valve, and replaced the right hand cat with a walker cat. The car still has a mind of its own and inconsistent performance. I have not cleaned the mass air sensor, which has been recommended by many. I was sure the right cat was bad... but I was wrong....(230 dollars wrong). One of the salesmen at SLP said the right cat goes bad 98% of the time. The bog or non responsiveness seems to happen more when the car is dead cold. The car has never quit on me like some of the reports that I have heard from the bad fuel pump guys. I need help too, maybe 02's next???

[5abivt]

Is there a valve in the air system that prevents air being drawn into the header?

[0rion]

Is there a valve in the air system that prevents air being drawn into the header?

there are check valves on top of the manifolds.....

[0rion]

This seems to be a common problem. My 2000 Z28 auto with 105 thousand miles has been doing the same thing for about a year. First I changed the plugs, checked the fuel pressure (good at idle), changed PCV valve, and replaced the right hand cat with a walker cat. The car still has a mind of its own and inconsistent performance. I have not cleaned the mass air sensor, which has been recommended by many. I was sure the right cat was bad... but I was wrong....(230 dollars wrong). One of the salesmen at SLP said the right cat goes bad 98% of the time. The bog or non responsiveness seems to happen more when the car is dead cold. The car has never quit on me like some of the reports that I have heard from the bad fuel pump guys. I need help too, maybe 02's next???

if it's doing it when it's completely cold that would almost rule out O2's since they aren't functioning then anyhow. The O2's close the loop once the car comes up to temp. I would look more at cleaning your MAF and look for vacuum leaks. How's your idle?

[5abivt]

I have A new fuel filter but I'll do that when it's warmer maybe this weekend. I'm heading down now to check for any vacuum leaks on hosed etc and will put the air blockoff plates on if I can find them. Will report back soon!

[35th-ANV-SS]

My guess is vacuum leak since you're running lean on only the one bank.

[0rion]

My guess is vacuum leak since you're running lean on only the one bank.

vacuum leak should effect both banks really because it's letting the intake suck extra air but an exhaust leak will only effect 1.

[5abivt]

Put on the block off plates. I kept the metal piping off the plates so they still can blow air out and so I won't get codes. Here's plug #3 I just pulled to check.

[0rion]

you're gonna get codes either way......the pcm will look for changes in the O2 voltages and know that the air pump is not pumping into the exhaust stream. My guess is you'll get a check valve code as if the check valve was clogged up....that's a guess.

That plug looks like ass.

[5abivt]

Ya definitely rich for sure. There's less than 6k miles on them. Blockoff plates done and ya you're right I'll probably get a code. If things don't change I'll just rebook the air lines after I solve the problem. Checked all the hoses I could find all look to be in decent shape. Going out for a drive now... Going to clean the plugs out when she's hot the. Hit the highway and set the cruise control. Brb

[5abivt]

Been driving 5 mins or so almost fully hot .. No codes or light from air so far

[5abivt]

No luck got to 80 mph and settled down.. Felt slight hesitation in the pedal and knew it was coming.... Second later I get bucking and jerking I can hear the whole driveline clicking and clanking back and forth. Jetta vr6lol tries to race me.. Slaughter him and am now heading home.

I know the bank is rich so something is telling PCM to dump morefuel. Headers and cats/y look the same as always I'll spray for leaks when I get under it to change the rims. I'll ask local forum if anyone has an 02 I can plug in with fresh plugs for a drive to see what happens. I'll spray maf cleaner tomorrow if I can remember to buy some on the way home from work.

All I can think of for now.

[5abivt]

vacuum leak should effect both banks really because it's letting the intake suck extra air but an exhaust leak will only effect 1.

Good point. I'll check header bolts tomorrow too to make sure none have loosened. The first o2 was showing the code so I'd imagine it would have to be upstream of the sensor which is all header primaries and up :/

[AllBlackZ28]

if it's doing it when it's completely cold that would almost rule out O2's since they aren't functioning then anyhow. The O2's close the loop once the car comes up to temp. I would look more at cleaning your MAF and look for vacuum leaks. How's your idle?

The idle has been a little rough in the past, right now its ok. I also changed the fuel filter. My only mods are an SLP airbox and a predator tune.

[0rion]

The idle has been a little rough in the past, right now its ok. I also changed the fuel filter. My only mods are an SLP airbox and a predator tune.

start with your MAF sensor....you can buy MAF cleaner at any parts store. It's cheap and will only take a few minutes to do. I would recommend pulling that MAF completely off so you can spray from the front and the back. You'll see 3 little wires with resistors....soak those down really well with that cleaner but don't try to handle them or wipe them with anything because they're very fragile.

[0rion]

Good point. I'll check header bolts tomorrow too to make sure none have loosened. The first o2 was showing the code so I'd imagine it would have to be upstream of the sensor which is all header primaries and up :/

It almost has to be an exhaust leak or just a bad O2. Do you still have your rear O2's? If so you can move them up front. From the looks of that plug I'd bet your O2's are fouled also but it's hard to say if one led to the other. Check everything for leaks and then look at doing something about those O2's. Check a passenger side plug too and make sure it's only on 1 bank and not on both. I've just been going by the lean code that was bank 1 but bank 2 could have some issues also....wouldn't hurt to check a plug.

[AllBlackZ28]

start with your MAF sensor....you can buy MAF cleaner at any parts store. It's cheap and will only take a few minutes to do. I would recommend pulling that MAF completely off so you can spray from the front and the back. You'll see 3 little wires with resistors....soak those down really well with that cleaner but don't try to handle them or wipe them with anything because they're very fragile.

Thanks Orion, I'll give it a shot... of MAF cleaner.

[5abivt]

Allblack does your car do it all the time on the highway?

Update for me.. I'm on the way to work and late so I'm blasting every car through 3rd gear I figured I'd see if I could flex some muscle. My service engine light popped within 10 mins. On The highway now and no bucking or jerking at all so far :/

[5abivt]

At the very least I have a code i can recheck. Going to buy a code reader tonight and pull the code(s). WIll report back !

[35th-ANV-SS]

vacuum leak should effect both banks really because it's letting the intake suck extra air but an exhaust leak will only effect 1.

I agree with you. I was assuming it might be an exhaust leak since there was mention that the exhaust was hit on a speed bump.