Seriously bucking under full throttle

[Mad Cow]

I have the HEI and external coil mod, so it's not that. Also, I just drove it today and it's actually more around 2-3k RPM and goes away past 4k-ish. I have the timing set to where it idles highest, good enough for now I guess.

[projectzemx3]

yep, that PGT i mentioned earlier has a new disty as well so i know its not that. and its more around 2 - 3k just like you mad cow. im almost positive its oxygen sensor related now.

[Mad Cow]

Alright, thats reassuring, my TPS might be a bit bad too, I guess I'll grab one from a junkyard too next time I'm there.

[_-Night-Shade-_]

So I drove Mad Cow's MX-3 today and it's my first time driving a KLZE'ed car. Wow what a difference compared to the K8. And that's even without it being at its peak. I'm probably over-exaggerating lol, but the power increase is noticeable =P

[Mad Cow]

Now to get it running properly, what use is power if it goes on and off constantly?

[Mad Cow]

Ok so I replaced the O2 sensors and got a proper intake, bucking went away for a bit but it's been getting progressively worse. Now it's pretty down on power, especially below 4k rpm, and it's bucking again in 1st and 2nd at around the same RPM.

Could it be a clogged cat? I drove it daily for a good month with the O2's unplugged, I flooded it really, really badly a few times and it ran stupidly rich for a while. Could that clog the cat? And I don't know if I'm just imagining this, but the exhaust note seems to be getting more and more dull and flat. And the engine is running hotter than I'm comfortable with when it's sitting in traffic, but I have a feeling that the rad is clogged.

I really hope it's the just cat because I've been chasing this problem forever, and it would give me an excuse to beat out the catalyst and just gut the damn thing.

[_-Night-Shade-_]

Judging by the symptoms it does sound like a bad cat or fuel delivery problems, but both of those are pretty extreme cases. We gotta get together again I gotta drive it and see exactly what you mean.

[Whisper]

Get a high flow cat, and if that fixes it, then all is well. And if it doesn't, then at least you have a high flow cat.

[Mad Cow]

Judging by the symptoms it does sound like a bad cat or fuel delivery problems, but both of those are pretty extreme cases. We gotta get together again I gotta drive it and see exactly what you mean.

Since when did you know so much? You have learned well apprentice.

And I doubt it's a fuel delivery problem. If I wasn't getting enough fuel I would assume it would be lean, I got pretty good and estimating the AFR by the exhaust note from tuning my ATV, and the MX3 sounds more rich than anything, but the plugs weren't black last time I checked.

[Daninski]

Ok for starters the O2 sensors were never the problem IMO. Mine were broken right off and the car ran fine (failed the emissions horribly tho lol). If there's no difference between a rainy day and a dry day then we can rule out disty cap having a carbon line defect. I'm going to say change the fuel filter. I've had two cars that bucked like your talking about and in both instances it was a plugged filter. One last thing, if it seems to happen only under high fuel demand situations your fuel pump may be on it's way out.

[Daveb]

If its not a fuel problem (filter or pump) I would try another distributor, just for fun. Also check the resistance in your plug wires if they are not new.

Someone told me if you get caught without a cat its a $10,000.00 fine. Isnt the north already melting fast enough?

good luck

[Daninski]

Oh ya that reminds me, a friend who does Clean Air inspections said that ever car that's come in with a high flow cat has failed. Just thought I'd mention that.

[SuperK]

What do you mean the exhaust note is turning flat?

My ZE would buck like no other at few rpm's, then turned into bucking at all rpm's
then turned into on a stopped start, the exhaust note sounded like "bvvvvvvvvv," a flat note, car wouldn't go anywhere.

It got progressively worse until the point where it wouldn't even stay running.


It turned out to be the VAF. VAF didn't look bad, didn't seem bad, didn't test bad but was bad?

i did TPS, sparks, injectors, filters, fpr's, tested spark (strong spark!)
Just about everything.

I've also heard more people having VAF issues. Maybe they're getting to an age where they're failing, I dunno. But it's worth checking out.

[Daninski]

How about a "My VAF went bad at XXklms" post. Maybe there is a pattern just like the disty issue.

[_-Night-Shade-_]

Judging by the symptoms it does sound like a bad cat or fuel delivery problems, but both of those are pretty extreme cases. We gotta get together again I gotta drive it and see exactly what you mean.

Since when did you know so much? You have learned well apprentice.

And I doubt it's a fuel delivery problem. If I wasn't getting enough fuel I would assume it would be lean, I got pretty good and estimating the AFR by the exhaust note from tuning my ATV, and the MX3 sounds more rich than anything, but the plugs weren't black last time I checked.

Hahaha thanks man, I've been reading a lot! Anyways I think if your cat was bad you'd also have emission issues as well, and considering you already passed them with a bunch of components missing (like no oxygen sensors) I think the cat had to have been good. It's like what Dan said, could be fuel filter or pump.