vicki711

Got a 95 z28 withe the lt4 hot cam kit.repaced all ignition parts as well as fuel.when the engine was rebuilt. I had a check engine lite on with a code 48 maf circuit failure.found a broken wire at the connector fixed checked for 4_6 v ref and 12 b+ all was good.cleared the code drove awhile the lite never comes back on but yet the car still bucks at normal driving speeds.fuel pressure also checks good .I'm losing my mind with this car

94Z28LS1toLT1

Is it bucking at high rpms like when u take off? Or just bucking as u accelerate slowly?

Injuneer

Is this basically a continuation of the same problem ("bucking") in this thread?

https://www.camaroz28.com/forums/lt1...ucking-878304/

vicki711

Yes thought once I got my lite off I was good to go but it runs slightly better but still buck at cruising and in tow speeds with no see lite

vicki711

Would it take awhile for my computer to relearn now that I fixed the maf wire?

94Z28LS1toLT1

No not at all it should be good after u fixed it,I'm wondering if on ur distributor if the rotor screws came out n causing the bucking bcuz mine did that

vicki711

I have checked everything I don't know what else to do

Injuneer

What about the tune? Did you ask Sinister Performance about the problem? Sounds like cam surge, which shouldn't happen with an LT4 HOT cam.

Next step would be a data log of the PCM, while operating it with the problem happening. Try Scan9495.

https://www.camaroz28.com/forums/com...95-lt1-874306/

vicki711

I'm waiting for a cable to arrive so I can do a data log just confuses me the way it's running there's no ses lite

vicki711

I also dbl checked my fuel press and have weird readings..koeo it has 37. Koer goes to ,40. Add pressure to the regulator no change in psi.. all the numbers seem low to me not sure if my new pump is junk or the reg

Injuneer

Idle you want 43.5 PSI with the vacuum line off the regulator. GM accepts anything in the range of 41-47 PSI as within spec. Reattach the vacuum line to the regulator, and pressure should drop proportional to intake manifold vacuum. With the HOT cam would probably drop about 6 PSI. Example: (no vacuum at the rail 43.5 PSI) - (6 PSI vacuum) = 37.5 PSI at the rail.

When the pump primes without the engine running, and shuts off, should be at least 40 PSI. When the pump shuts off, how fast does the pressure drop?

How did you "add pressure" to the regulator? Do you have an adjustable fuel pressure regulator? If so, what brand is it?

There are codes that don't turn on the SES light, although most of them prevent the engine from running. But you don't do a data log just to pull codes. You do it to see how all the sensors are working, and what parameters the PCM is using to run the engine.

vicki711

I added vacuum to the regulator 12-15 lbs and the pressure never changed. I was also told to keep the reg vac line plugged in while doing the tests is that wrong

Injuneer

How did you "add" 15 lbs of vacuum to the regulator? 14.7 psi vacuum is a full vacuum and not possible with a typical vacuum pump. Or did you apply 14"Hg? In any case applying vacuum to the regulator should reduce the pressure.

The method I gave for measuring the pressure, both with and without the vacuum line connected is 100% correct.

vicki711

Your right I was measuring in hg back to square one again