drperformance

iTrader: (5)

Ok so since I strocked my lt1 to a 12.5:1 compression 383 with direct port nitrous the engine surges at every speed about 100-200 rpm and 300 rpm at a stop? when I first start the car it seems to idle fine in park then when I start driving the car I can notice it start to surge the most while shifting gears and at stop lights, but it also surges at speed. Any ideas?

I already
replace opti with msd opti
new vss
new tps
cleaned iac
new o2s
new icm
checked the resistence on all plug wires (ok)
checked all plugs (tan)
checked resistence of coil (ok)
sprayed engine down with carbon choke cleaner and map gas for vacuum leaks and had no luck?


For some reson I keep thinking vacuum leak but am unsure, should I take the intake off and start over sealing everything?

What do you guys think?

drperformance

iTrader: (5)

I forgot to say that when I jump on it it has a slight stumble or miss then it screams, I only notice the surge at lower steady speeds or at idle. I have scanned the car multiple times and found no codes and all the readings look ok.

GMTech

Has this thing been tuned? The larger engine is going to need more fuel and the higher compression will need different spark tables. The cam will also effect it.

Is this Speed Density or MAF?

drperformance

iTrader: (5)

Yes, it was tuned by Bryan at pcmforless.

I have started to compression check the cylinders but could only get to three of them because of the headers, I will have to take them off. But the three were consistent.

J's T/A

iTrader: (2)

Was it dynotuned? I am guessing not..

I had a mail order tune with my head and cam swap and it ran like garbage, stalled, surged, you name it.. not pcmsforless but the closest competitor.

on the dyno it picked up 40 rwhp and the driveability improved dramatically..

Check for the obvious like vacuum leaks and then pony up the cash for the best tuner you can find, for me it was 450.00..

good luck.

Firebat

iTrader: (7)

What do you mean by tuner? Program or person or both?

J's T/A

iTrader: (2)

by tuner I mean person, not a hand held programmer..

I had my car tuned at Carolina Auto Masters (www.carolinaautomasters.com) , they have an excellent reputation and were able to make my LE2 cammed car extremely driveable, even with a stock displacement 234/244 duration on a 110 lsa.

Kennedys dynotune (www.kennedysdynotune.com) in NY is another shop that has a good rep for tuning extreme packages.. I am sure there are others.

I am still looking for a good place for my new combo here in the northwest now that I have moved.

Just my observation but the best tunes come from folks that run a shop with their own dyno in house.

LT1powered89

Im guessing its MAF since it is a 95 but is it an OBDI or ODBII? Have you checked to see if the car is going into closed loop mode?

drperformance

iTrader: (5)

yes the car is going into closed loop, but the problem is there befor and after it does so I do not think that it is a sensor. The car is an obd1, and I am getting no codes

Klortho

I would say replace the IAC with a known good one and try it, sometimes the little motor inside the IAC can do wierd things as it gets older.

drperformance

iTrader: (5)

Since I have the MSD opti now I have been playing around advancing the timing and the stumble when jumping on it seems so be taken care of but I can still feel surge.

I also have a holley throttle body, which they do not have that trough hole in the center of the throttle body, all the air at idle goes through the iac valve. So my iac values are high 70s to low 80s at idle and seem to be pretty steady not jumping around that much while driving it normal but there is some varience.

And I think that it is more noticable the more I drive it, but it hapens in closed and open loop?