After a few seconds of a wide open throttle run, my car will suddenly buck the exact same way it does when you hit the factory speed limiter - except I'm nowhere near the speed limiter. What would cause this? Does over advanced ignition timing cause it? Because I may try retarding that a little bit first before anything else. Up until that point though the car pulls great.

The car did not start doing this until very recently, and I changed my distributor cap and rotor, spark plugs, and spark plug wires about 15k ago. Fuel filter less than 2k ago. The car has a GM Blaster coil on it, but I don't know about its age because it was on when I got the car over a year ago. Maybe my injectors suddenly went bad? I have new Bosch 3s to install anyways. I just hope it's not my fuel pump.

 

What rpm and mph does it occur? Its not converter locking up right?

It hits a wall and does not pull anymore like a fuel/rev cut limiter?

 

It doesn't feel like the converter locking up, it feels EXACTLY like the fuel cut out limiter the factory put on these cars. It happens at probably around 80-90 mph at around 4800-5000 rpm in third gear only. I'm heading out of town for the weekend, but when I come back I'm gonna inspect my coil for cracks and pull my plugs and check them all out. Also gonna check the contacts on the distributor cap.

 

Some chip tunes force lockup at exactly 80 mph or so, so just pointing that out.

And i'm not sure if it will shift into overdrive at that rpm at wot unless trans was modified. Not 100% sure on that

Could also be valvefloat

 

Would the converter locking up make the car jerk and stop accelerating like that? At wot even? And my car does not shift into overdrive at wot. Also I've never experience valve float before, what does that feel like? I always figured it would just feel like the car stopped pulling as hard as it was. This feels like the engine just completely quits making ANY power to the wheels and jerks back and forth. It's does over and over again until I let off the gas too. It will buck on and off just like it does if you hit the factory speed limiter and the ecm cuts fuel to the injectors. That's why my theory is that it's either cutting the fuel or for some reason it stops getting spark. Either way it feels like it makes all cylinders stop firing for the car to slow down a little bit and then fire again back and forth until I lift.

 

Well lockin converter will feel like a light bog but go away. Wont buck and limit the car

Valvefloat can be lack of power/pull after a certain rpm, and if very bad, could act like a limiter.

Your issue sounds like a limiter type effect so check ignition. Also check fuel pressure and what do the spark plugs look like? Goin extemely lean real quick can also make motor buck/jerk or feel like it shut off sometimes.

 

Yeah, that's what I figured. I plan to check fuel pressure and pull plugs as soon as I can. Do you think that maybe my plugs need regapped already? I do drive the car hard, and from what I'm reading spark blowout feels exactly like what I'm experiencing.

 

What plug gap? What ignition?

I havent seen streetable all motor combos blow out spark tho. Stock hei ignition is pretty good. Gap around .035-.040 should do it

 

I have stock HEI and the plug gap I'm actually not certain of since they were just AC Delco performance header plugs and I didn't inspect the gap when I put them in They worked fine though for the last year. I'm thinking that I have either a bad ignition coil, pickup coil, or something is causing electric noise to interfere with my VSS wire that is activating it before I'm actually at the speed limiter.

I just started the car to move it since I'm leaving for the weekend and this time it took a lot longer than normal to crank, idled at about 1500, and misfired noticeably while I was moving it. It hasn't done that before. It was a cold morning though if that has anything to do with it. Whenever the bucking happens though it is like the motor is bouncing up and down in RPM. It revs and then it stops revving and the cycle keeps repeating until I lift.

 

might sound dumb, but try pulling the fuel filter out and see if its plugged up some. i know you said you just changed it, but ive seen some that had to be a changed a few times.

 

Thanks for the tip, I think I'm gonna try inspecting/changing my ignition coil first since it's the only ignition part besides the distributor and HEI that I didn't change upon buying the car, and everything else was in very rough shape. Distributor cap contacts had corrosion all on them, spark plug wire boots had that same stuff in them, and the plugs definitely weren't brand new. So I think I'm gonna go for the coil first, especially since it had a hard time starting ONLY in cold weather, and then it idled very rough with multiple misfires. And prior to that it began breaking down under heavy load, so I think it may be about dead now. But if that is not the case and doesn't fix the problem I'll change my injectors and put my fuel pressure gauge on it, which should show me if my filter is clogged.

So, what coil do you guys recommend? I have the stock HEI ignition and a GM blaster coil right now that worked great until recently. Maybe an MSD coil?

 

Well guys, thank you all for your help, I solved the problem. Today I replaced my coil which did nothing, so that got me thinking that the problem didn't start until I removed my hypertech chip and just ran the stock chip. So I put the hypertech chip back in, and boom, works great again. No more hitting the wall like that. Also it happened at about 68 mph, not 80-90 as I originally said that I thought it was. I don't know why or how it went wrong like that with the stock chip, but it literally kicked my speed limiter on at 68 mph. Hypertech chip that I had in the car before (I had the chip for a long time, just kinda got it cheap) did not have that issue at all. I do still plan to start working on tuning the car myself though in the near future.

 

Is your speedo/vss accurate?

 

No, it is not corrected for the 4.10 gears so at 65 mph my speedometer reads 100 mph. But either way before the gears it would cut out at 110 mph with either chip in it.