C5 auto LS1 238x246 cam, magnacharger

I am getting a surging in RPM when I try to maintain cruise speed. If I speed up or let go of the throttle it is fine. It only seems to be at about 5% throttle. I have EFI Live and am about to try and figure this out. Any suggestions where to start? It only started when I had a local tuner tune my car on the dyno. It also doesn't do it when I am not moving (i.e. in park holding the pedal down). It does it at any speed > 0, in any gear, while maintaining a speed.

Thanks

 

Take it back to him, it is a tunning problem.

 

correct !

and dont beat him up over it because you have a big boy cam in there.

Make sure your VE table and MAF was tuned. That will help alot

 

I have been back 3 times, he says there is nothing more he can do about it. That the 98 computer is too slow to make the car run right. I am pretty much fed up because it is a long drive to bring it to him. He says he spent 14 hours on it. I just need it running like it was before, without the surging, so I bought the EFI Live V2 and am going to try and figure it out. Either that or I need to fly some one in to fix it. I have spent a few years tuning my other cars with the AEM, but am new to the EFI. It almost seems like it is switching between something, because when it surges the rpms drop instantly, then come back up again. Taking it back to the tuner is not an option at this point.

 

One thing to note is that before I went there last, when the idle rpm was at 800, it use to only surge on a warm restart. When I would start from cold then drive it and let it warm up it would run fine and not surge. But then if I would stop the engine and restart it, then it would surge until I would stop the engine, let it completely cool down and restart it cold. Last time I went back I had him bring the idle up to 900rpm, because at 800 it would stall if I let go of the gas to quickly. Now at 900rpm it surges whether it be a cold or a warm start.

Maybe it has something to do with the idle relearn? Because maintaining speed, throttle is only open 5% above idle. Any more and it is good.

 

what year car is it ?

 

first make sure ur ve table is not choppy, and also check ur timing i not too large gaps between cells. those 2 there cause lot of surging when cruising at low speeds. Some times big cams like to run a lil rich when they are down low.

 

Your profile is pretty much useless if someone wants to help.

If you are in Winnipeg, there is a very knowledgeable tuner in Regina that may have a contact or know someone that maybe able to help you.

 

I have updated my profile. Basically it's a 98 couple, LS1, magnacharger, headers, 238x246 comp cam, FLP A4 trans.

 

I will check those, thanks!

 

So your first post suggests your car ran good prior to the dyno tune?

What did they change in the part throttle area to bring on the surge?

Hunt down Russ Kemp in Regina, I'm not sure of his company name. I have it somewhere if you cannot find him. He is a very good tuner & he may have a contact in "Winter peg".

As mentioned above sometimes big cams like to be a tad richer in the surge area. I've found that the idle timing table & main spark need to match or be very close so that does not set surging off should you be driving in that transition stage. Idle air, Base Running Airflow....those have to be right.

What I just figure out recently, I use HPT, is how actually get that idle door open @ idle so the motor can breath @ low speed, that really helped.

Also I don't think there is one magic pill with every combination, such as maybe your O2's are in a differnet location. Or what your 02's really see compared to another. Lots of trail & error till you find your silver bullet.

 

Maybe you should send a pm to Arun@CCP explaining what your car is doing. He is a tuner located in the Toronto area. Nothing but good reviews on the forum about his work. good luck

 

Hi----Did you put the maggy components together yourself OR did you buy a complete kit from Maggy ??
I am not a fan of handheld programmers however when maggy sells a kit they always include a baseline tune on a superchips handheld for you--AND they always work !!!! You thn can fine tune them after that---If you put the kit together yourself---You can call Maggy and tell them all your mods and they will sell you a baseline tune---Even if you bought a kit--Did you get the handheld baseline tune with it ??

I even think maggy has EFILIVE and all you would have to do is buy the tune from them and download it----
Sounds to me it SC related--maybe the vacuum relief isn't set rite and you're getting too much boost at cruising speeds and it throws the fueling haywire---
rather than chaisng your tail and spendng hours thrying to sort it out with advice from several people--just spend the $$ and go to maggy and I'm sure they can get you going---

 

95% of the time surging is from too much timing-attack it only after you verified that the AFR is perfect in that area. you might find that actually need to command a richer AFR in that cell where the surging arises. Put the car in O/L and confirm.

Another area to address could be the idle airflow tables-you ahve too much airflow as well.

 

http://forums.corvetteforum.com/memb...73-russ-k.html

Russ is a good tuner/builder, hasen't been on the Forum for a while though, I have a pretty good set of heads done up by him BTW....G/L getting your car fixed, Arun down here is the local supercharger/tuning guru....maybe he can help...

 

I also have a 98 Corvette and I am in Winnipeg Arun flew in to tune my car,we made just over 900rwhp,and are working on making more,if interested we are planning on going back to the dyno soon to make some adjustments,I no of a few tuners in town that may be able to help you also.

 

Thanks for the props guys. First off that size of camshaft will have a light throttle, light load surge/fish bite at low RPM. I have a LG G5X3 (234/242/114) camshaft, and also have a slight surge/fish bite. This is due to the EGR effect of the valve overlap. No tuning will eliminate this. What LSA is your camshaft?

Now if your tuner changed the gear ratio to 3.42, the stock shift points will be lowered to shift into OD at 22 mph, and the TCC will lock at 36 mph. I would be raising the shift points & TCC lock up speeds which will help. If you had Hp Tuners, I could set up your shift points for you.

Keep in mind that the magnacharger tune is for a stock camshaft & exhaust. Just tuned a 1997 with a 416 iron block/5psi Procharger. This car was very lean after 4000 rpm due to the fuel pressure dropping to 20 psi by 6000 rpm. The fuel filter was replaced, then installed a new GM pump. This improved the fuel pressure to 30. After installing a Caspers fuel pump hot wire kit, the pressure was still under 40 at 6000 rpm. Finally after swapping a LPE fuel pump for the stock pump, the fuel pressure stays at 58 right to 6000 rpm. I really don't believe that a stock pump with the magnavolt module will have sufficient fuel pressure with your camshaft and the increased rpm potential.

Russ Kemp

dankhts, I sold my LPE heads to Sami. I didn't modify them.

 

and those heads are working good Russ, making good power with my combo

 

OK... I have solved all of the issues with the tuning software. I will list all of my changes below (Some of them don't make a lot of sense)

The surge on start up. When I would start the car it would surge between 600-800 rpm for about 20 seconds until it would finally go to the desired idle of 950rpm. To fix this I went to Idle/Learning/Parameters and first changed (B4511) Startup Engine Underspeed Time Limit from 2.0 seconds to 1.0 seconds. This then caused it to only surge for 10 seconds. I tried then to change it to 0.3 seconds and it surged for 3 seconds. Now putting it to 0.0 seconds, as soon as I start it, it goes to the desired RPM with no BS.

The surge when I wuld put it into gear from park. I went to Fuel/CrankStart/ Park to Drive Enrichment. Stock it had 0.2 in all of the fields. If I put this value to 0.3 it would surge even more. The rpm would go from 500-800rpm. Like it was running rich. I would have to hold the brake for 10 seconds for it to finally find itself. Therefore I changed all of these values to 0.0000. Now when I put it into gear it drops maybe 50rpm then goes instantly back up to the desired idle.

Now the big one, the surge when I was driving at constant speed. I went to Idle/General/Parameters and changed (B4614) RPM set point adjust timer. This was set to 0.5 seconds. I changed this to 1.0 seconds and it caused the surging to decrease and over/undershoot a little less. At 2.0 seconds it was almost unnoticable, and at 3.0 seconds it is gone. I am figuring that this setting is the same as an Integral time, meaning that the higher this value the more the PID loop will ease into the desired rpm and not over shoot. With a low integral time of 0.5 seconds the PID will be adding to much error to the output causing the output to increase too rapidly, which in turn causes too much of an overshoot in rpm, giving me the surging. Parameter B4612 would be the proportional value. This is at 2 rpm.

Output = Gain (Error + 1/Integral Time ∫ Error)

Output is what causes the increase in rpm
Gain is going to be B4612 or 2rpm
Error is going to be my current rpm - desired rpm
Integral Time is going to be now my 3 seconds B4614

I have tried putting any one of these paramters back and the issue sure enough comes back. The car has run mint for the past 3 days since making these changes.

Any comments?