trax

My GM847 car has been driving great with the new ported intake manifold and 58mm TB. However, a strange issue popped up tonight and I'm trying to find out where to track it down.

Basically, if I'm going about 30-35 mph in 4th gear, that's just about 2K RPM. As traffic changes I'll let off the throttle and let the car idle down or give it more gas to accelerate. Well, as soon as I push the gas down, the car "bucks" considerably. It's like I can't gently press the gas to make the car accelerate. This just started happening today, and I'm wondering if it's either the PCM having trouble learning the cam or if it's some other issue.

The car has a Speed Inc tune for my OLD cam (xe 224/230).

High RPM / WOT still feels fine. Any idea what this could be?

Thanks!

OBE1 95Z28

Check to make sure you have the intake seated properly on the TB. A vacuum leak after the MAF will causing bucking.

zachs94camaro

1. Cut a hole in a box
2. Put your junk in that box
3. Make her open the box


I dunno, you've taken that car apart so many times there is no telling what you've done to it now lol. Good luck Pete.
-Zach (HarvDrivesGM)

Dave1980

I noticed I used to have some buck , but it seemed that after I fixed MAF that things got better.

ashakeandfrys

check your plug wires. a technician diagnosed the (read this if you have the problem above, as I do and have yet to change them yet..) car to have faulty wiring causing the ICM to have data errors the link is here

bloodsmith

(I'm new here) I have a 94 Z-28 with the 6spd tranny. In upper gears, 4,5 & 6 if I am below 2k rpms, the car stumbles under hard acceleration, above 2k it smooths out. Initially, it was determined to be dirty injectors, had 'em cleaned and it cleared up for a week or two. Recently, replaced injectors, FPR and O2 sensors. Still stumbles. I plan on hitting the plugs and wires next. A buddy of mine thinks I have a blown head gasket. Any ideas anyone? I really don't want the blown HG. Also checking for vacuum leaks soon. I mention the injectors in order to help fix Dave1980's problem.

sandman2100

Had the same problem a few weeks ago and the car finally just gave up on me. I t lasted for about 4 hours after noticing it was just not taking off right. Gradually it go worse and then on my comute home. pop.


Still sitting at a friends shop waiting for time on the lift. We traced it to either a bad cap/rotor OR the dreaded opti. Sad part is that the cap and rotor are almost the same price as a whole new distributor.

CrazyLT1

I was just gonna ask why nobody has suggested that his optispark could be starting to fail

bloodsmith

I didn't know how notorious the opti-spark set up was but it seems the more threads I read, the worse it seems. When the opti goes, will a code show on the OBD1 system? Being my Z stumbles at low rpms, I thought it might be an ignition problem. The optispark would cover that as far as I can read. When I plug in the code reader I get nothing, not even a code 12 to say all is well, total silence. Any suggestions? And what labor, time and cost is involved in replacing the opti-spark stuff?

CrazyLT1

Usually I would think that a bad opti would at least throw some type of misfire code.

Replacing the opti is not that bad at all. Anyone with basic mecanical abilities should be able to do the whole job in 5-6 hours at most

innocentz28

relax it is normal for a standard tranny to do that, because when you upgrade your cam the car is going to want more rpm's. I have a cc306 which is a very similiar cam to the gm847 and at low rpms the car will jerk and buck real hard, but when the rpm's get higher the cam becomes less aggressive. My car did not buck at stock, when i put a lt4 hot cam in it my car started doing it, and now i have a cc306 and it does it even more since its a bigger cam. Dont worry about it, its normal, even my dads car does it and we have done 2 cam swaps in his. Its just all apart of having a bigger cam in a standard transmission, however you might be able to tune the bucking out with computer tuning, but i am not for shure, talk to brian an PCMFORLESS.com

innocentz28

oh yea by the way get your computer tuned for that cam because your car will be running to lean if you have not tuned it for that cam, one of my header tubes was glowing cherry red because i didn't have a tune, also it will ruin your motor if you just keep drivig it without a tune.

trax

The XE 224/230 tune seems to be holding up fine for street driving. According to the scan tool, long-term fuel trim is bumped up by about 12% on each bank on the stock injectors. I'll definitely have Speed Inc update the tune before I hit the track though.

Schultz454

this happened to me once or twice after i replaced my intake, felt like the car was dying. never got it checked out, figured it would pass

no longer happens...

FeelTheSpeed

I agree with above post...I have a 23X 23X with .614 lift and it does not like to stay around the 2k range lol. Its just another thing you give up when going from stock to more performance oriented.