CT5-V engine surge / "porpoising"

[jkg]

hello - i have only had my car for a few days, but i have found on two separate occasions that the engine will surge, with the engine moving up and down in rpm, so that the car surges back and forth while driving. both times it happened while cruising - i am used to this with high performance carbureted race engines, where if you try to "lug" the engine, it will surge like this and the car will rock forward and back. the usual cure in those cars is to put the clutch in, and get the rpms up.
this morning, i was in third gear going up a hill, so i downshifted to second, but it kept doing it in second gear. then i shifted back to third and then fourth, and it did it in all these gears. eventually i got up the hill and it stopped, but not before giving everyone around me quite a show. i wonder if this is just the way it is going to be, or perhaps because i have the engine is sport mode not tour mode, or something is wrong with my car?

 

[WONT TAP]

Do you have a Check Engine light?

 

[jkg]

no check engine light
car doesnt seem to notice it.
a quick search of the C7 forums for corvettes shows some complaints about surging perhaps related to active fuel management. not sure

 

[frankfast97]

U run out of gas up the hill?

 

[jkg]

no, gas was half full
i made sure all the spark plug wires were secure later the same day, cant say any were loose, but it has not done this again since that day. but it has only been 200 miles since then so we will see

 

[jkg]

well, it did it again - second time 8 days after the first. both times, was running up a moderate incline in 3rd gear at around 1500-2000 rpm. the engine starts surging - up and down about 200 rpms continuously. if i downshft to second, it continues. if i upshift to 4th, it continues. if i try to give gas and power through it, it continues. after 10-15 seconds, it just stops. maybe because i put in neutral and let it return to idle? not sure. i wish i had some way to see a log of what the computer is doing. i guess we will see how it goes.

 

[jkg]

i hooked it up to hptuner software and no engine codes. it thinks it is happy. will have to wait and try to figure things out if it keeps happening, frustrating.

 

[1Evil55]

Has it happened on an incline both times? Is it possible your tank is low enough to hit a spot in the tank away from the fuel pump? I don't have my car yet to see or know where all these pieces sit exactly.

 

[jkg]

No gas tank mostly full both times. Very frustrating

 

[1Evil55]

Do our BW's have the anti roll brake like you see in trucks? That is definitely not the correct name for the function. Basically when you let off the brake from dead stop, the car remains in its place without concern of rolling forward or back. If it is equiped, could the sensors/program be acting up?

 

[jkg]

yes, the cars have "hill hold" feature. im not sure if i like it or not. i like to keep things simple and real
in this case, it is engine rpm surging. when i put in clutch, it is not there. interesting thought though
engine surging is something that seems common with computer controlled cars over the years. i have found links to it related to supercharger coolant air in the system, bad tunes ( but i dont have a tune), ignition misses (bad plug or wire or coil). not sure where this is going to go. appreciate the thoughts and suggestions.

 

[1Evil55]

I guess I'm just stuck on the thought it keeps happening while you are on an incline. I too am not a big fan of the hill hold. I'm even less a fan of the cars that automatically hit your brakes for you if you're coming in too hot on a car in front of you. First time it happened to me in boss lady's Denali I about shit myself. I quickly learned how to disable it.

 

[jkg]

@Mirza Grebovic
Any chance you could connect me with an engineer/tech person at cadillac/GM who might be able to help me with this engine issue? I'm not taking it to the dealer at this point, because there are no engine codes and the problem is very sporadic. i dont want to leave it there for them to drive for a few days trying to reproduce it

 

[jkg]

If i can learn how to reproduce the problem, i can use hptuners scan software to log the event. i hope it doesnt happen again, but i expect it will

 

[Tall Steve]

@Mirza Grebovic
Any chance you could connect me with an engineer/tech person at cadillac/GM who might be able to help me with this engine issue? I'm not taking it to the dealer at this point, because there are no engine codes and the problem is very sporadic. i dont want to leave it there for them to drive for a few days trying to reproduce it

If you are a Cadillac V-Club member you can post this over there and get a very quick response..

 

[Mirza Grebovic]

@Mirza Grebovic
Any chance you could connect me with an engineer/tech person at cadillac/GM who might be able to help me with this engine issue? I'm not taking it to the dealer at this point, because there are no engine codes and the problem is very sporadic. i dont want to leave it there for them to drive for a few days trying to reproduce it

Are you in cruise control and what RPM? I apologize but what car CT5 or 4 and what mode are you in, throttle progression is different in diff modes but I see you said going up hill, hence RPM info would help.

 

[jkg]

Thanks @Mirza Grebovic
has happened in my mode - custom mode - steering at touring setting, brake at sport, engine sound at highest track setting.
i tried to change mode to tour mode while it was happening, but the engine surge continued even when i changed it for a few more seconds
CT5.

 

[Mirza Grebovic]

Any chance you have PDR and can record it? I can forward to team. Does it feel like a manual bog at low RPM where you dont have enough throttle or is it happening at higher RPMs?

 

[jkg]

i do not have PDR. i do have hptuners software scan tool, so if i can consistently reproduce it, i can record the event. It does feel like a manual bog - like when i try to drive my vintage mustang with a race engine - but when it happens on the CT5 BW, i downshifted from 3rd to 2nd gear to raise the rpms and it continued to do this surging for several more seconds. if it was a bog from "lugging" the engine, then it should have gone away with the downshift? also, i wasnt bogging it that badly at all. it has happened 3 times in the first 500 miles.
During the last "event," i first downshifted to 2nd, but it continued surging, then i upshifted to 4th, and it continued surging. then i put it in neutral and coasted for a few seconds, then it was gone. basically it happened on an on ramp to the GW bridge here in NY (which is 1 mile long), and it resolved by the middle of the bridge. i was traveling 15-25 mph i would estimate during the event.
I am a very experienced driver/tuner/mechanic (have restored many old cars; track both vintage and modern corvettes/mustang; have done a bit of tuning on previous CTS-Vs) - this was far out of the range of normal operation, is quite concerning for safety, and seems like it is coming from the electronics somehow. fuel tank was not near empty.

 

[Mirza Grebovic]

I know you said you dont want to take it to the dealer but opening a case with them and asking for a field service engineer would be appropriate. If you do get a recording send it over. The vehicle does have anti stall so at those low speeds and on ramps it might be bogging to where its trying to add torque. If you try to start out in 1st without throttle you will notice anti stall kick in too.