Car jerks after boost?

[lxsv8]

Definitley has a return line!

 

[stevechumo]

I don't know about the AFM seeing boost and trigger the fuel cut because none of the forced inductions on the SC or LS has this problem, alhtough it's possible. That's why I'm still thinking it's the fuel pressure or flow capacity. If the ECU causes this, then all other cars should have the same problem because that's the setting from the factory.

The torque converter isn't related in this case.

 

[morris]

Sounds like fuel to me as well, I still dont see how fuel pressure can go above the factory intank regulators setting.

I would hook up a fuel pressure guage and check to make sure that the psi is not dropping. That would at least rule it out or confirm the issues.

 

[stevechumo]

Sounds like fuel to me as well, I still dont see how fuel pressure can go above the factory intank regulators setting.

I would hook up a fuel pressure guage and check to make sure that the psi is not dropping. That would at least rule it out or confirm the issues.

Yep, test out the fuel pressure and see if it's good.

 

[lxsv8]

Thank for all the replies. I have some good avenues to follow now. I will post results for future reference after I spend some time (and money) with another tuner. I will show him these posts and thankyou Erol for your time on the phone. I believe you may have nailed the problem with your suggestions.

 

[Toysrme]

on an unrelated discussion. why don't yall blow through the afm. i like that better.

 

[jibbby]

I had a simular problem while running the Nitrous system on my SC4..This only occured in second gear under full throttle and at launch....ECU signals combined with the auto tranny was one of the problems, also the way the exhaust was setup after the header install was the other.. ECU and sensor reads...

 

[kc95sc400]

Guys,

Old thread I know.

I'm having a similar problem and am wondering if an answer was ever found.

At higher road speeds, if I coast and then very lightly push the acc pedal, it bucks and goes lean, off the wideband gauge. Kinda flucuates from lean to rich very quickly. Goes away as soon as I push the pedal a little more.

Also, from a stop, if I hit the throttle fast, it bucks and jerks and goes lean off the gauge.

I figure its the TPS adjustment, and I tried adjusting it. Seemed to make a difference but I can't really say it's better or worse. I set it at .55 volts (was at .62volts) with the engine cold and off.

I will likely stop by work tomorrow so I can look up the specs, can't seem to find any posts with actual numbers.

Any other ideas?

Some notes. The EGR is blocked, has been for a while. I bypassed the fuel pump ECU, the problem started a couple of days later, so I am going to try un bypassing it. I don't believe that I am having a "running out of fuel problem", with 8-9 psi I'm around 12.5 to 1. It is quite possible I have a vac / boost leak somewhere, I haven't been able to find anything though.

KC

 

[stevechumo]

Guys,

Old thread I know.

I'm having a similar problem and am wondering if an answer was ever found.

At higher road speeds, if I coast and then very lightly push the acc pedal, it bucks and goes lean, off the wideband gauge. Kinda flucuates from lean to rich very quickly. Goes away as soon as I push the pedal a little more.

My car happens similarly. Cruising is very lean. However, as long as I press the gas in, it goes richer and richer. After letting go of the gas after boosting, it goes way too lean. Even if I was cruising and letting go the gas immediately, it also goes lean. Sometimes was over 18:1 ratio.

Also, from a stop, if I hit the throttle fast, it bucks and jerks and goes lean off the gauge.

I don't have this problem.

 

[kc95sc400]

My high speed (60mph+) light pedal problem has been going on for a couple of weeks, but it's recently gotten worse. The jerking from a stop problem is new. I assumes the two are related. Both problems go away when I press into the pedal more. And, otherwise it runs fine.
I'm going to check the TPS specs at work a little later, and I will also unbypass the fuel pump ecu and see if anything changes.

It wouldn't surprise me at all if I have a vac / boost leak somewhere.

KC

 

[stevechumo]

My high speed (60mph+) light pedal problem has been going on for a couple of weeks, but it's recently gotten worse. The jerking from a stop problem is new. I assumes the two are related. Both problems go away when I press into the pedal more. And, otherwise it runs fine.
I'm going to check the TPS specs at work a little later, and I will also unbypass the fuel pump ecu and see if anything changes.

It wouldn't surprise me at all if I have a vac / boost leak somewhere.

KC

I don't know if it's related to the TPS or not. And maybe the vac is leaked somewhere. I think that you may just install the high flow/high pressure fuel pump so you don't have to worry about bypassing the fuel pump. I know your supercharger is a little harder to change the boost, but if you can, go down to 6 psi and troubleshoot it. With less pressure on the engine and the engine can actually cope with 6 psi, it's easier to troubleshoot the issue.

 

[kc95sc400]

I don't know if it's related to the TPS or not. And maybe the vac is leaked somewhere. I think that you may just install the high flow/high pressure fuel pump so you don't have to worry about bypassing the fuel pump. I know your supercharger is a little harder to change the boost, but if you can, go down to 6 psi and troubleshoot it. With less pressure on the engine and the engine can actually cope with 6 psi, it's easier to troubleshoot the issue.

In case anyone needs to know, the specs for the TPS voltage are .3 to .8 with the throttle completly closed and with vacuum (from a hand pump with engine off) on the throttle opener.

I think I fixed it. It was the MAFTPro. Something wrong with it or with my settings. It shows frequency in and frequency out to / from the MAF. Well, from a stop I noticed the frequency in was fine but the frequency out was going crazy while it was jerking. I reset the unit and changed the settings around a bit and now it's fine.

I did unbypass the FPECU as well. I like it much better wired as intended. I have thought about upgrading the fuel pump, but don't have the funds right now. With full boost (8-9 psi) I haven't ever seen the AFR go above 13 to 1.

There is a likely possibility that I have a leak. I have some new piping on the way so I can un half ass the piping / IC install. Interestingly, when I had the non IC setup straight to the throttle body, I had the boost limiter valve installed right after the SC and way before the MAF. It kept popping out on me, and the car would run like crap with it missing. Again, before the MAF. So apparently, a leak before the MAF can potentialy cause problems.

KC

 

[kc95sc400]

Couple more notes.

If you haven't checked you tps, you should, it could be the problem and it's easy to check.

With all the different piping setups I've tried, the car acted a little differently with each one. I think the MAF is very sensitive to the way air enters and exits it. I also think that surge messes with the signal regardless of whether or not a BOV is installed. When I had the bypass valve installed, the car would stall rich with a quick open and close of the throttle. Even now, without a BOV or bypass, it goes way rich with a quick open and close.

When I kept having vac hoses popping off on me, I noticed a trend. If a hose was off or leaking after the throttle body, the engine would run lean with vacuum and run rich with boost. Unmetered air is getting into the engine under vac and metered air is escaping with boost.

KC