Surging idle - stack injection Tec-GT

[MVRight]

I've learned a lot building, like to learn and do on my own. The forum's been great, and I'm on the last thing before I can register and on the road. I'm checking with the collective wisdom to get me over the finish line.

Have a 331, 8 stack injection system using Electromotive Tec-GT computer. It starts and idles ~800RPM when cold, but once warm idles up to 1000 and surges to 2000s then back down. Doesn't stop. MAT is in the intake manifold and will register 161 degrees which could be heat sink. I'm trying to get it idling and half decent running to register and get it dyno tuned. I'm stuck and looking to see if anyone had ideas to get me over this hump. I know it is a unique setup, but any fuel injection tuning ideas are welcome.

thx,

Bruce

[PaulProe]

Two possible things to look at

1) The settings on your Idle Air Control are incorrect and it is not operating as it should. Most systems have settings change as the engine warms up - may explain why it is ok at startup but then begins to act up as it heats up. Without knowledge of the system and the settings, can't tell you any more than that. If your system allows it, try turning off the IAC until you get the tune closer.

2) The throttle linkage is not 100%. Stack injection is VERY sensitive to linkage and the left side and right side opening and closing together. If the center pylon isn't positioned properly, one side may close and the other side remains slightly open. You can't spend enough time on the linkage making it right. It needs to be exact or you'll have issues.

Paul

[bobl]

You need to determine what is causing the surge. Look at your data when it’s surging. Are the IAC counts changing? Timing advancing and retarding or maybe the A/F is going rich and lean. Do you have a wide band 02 controller installed? Does this system run in closed loop? Try unplugging the IAC and adjust idle with screws to see if you can stabilize it. Once you can get a somewhat stabile idle, as Paul said you need to sync the throttle bodies with a tool. The TEC-Gt seems to have a lot of idle control capability, you just have to get a solid baseline to work with. If you could post some info that is going on we can probably help you get it sorted out. Lots of tuning knowledge on here.
Bob

[MVRight]

Thanks, the system doesn't have IAC, unless I'm really missing something. Bob had similar comment in the other forum on linkage and balancing. I got them close, except for one, but guess need to get back in and get better than close.

[MVRight]

Thanks, do have a wide band O2 installed and is running in closed loop. No IAC in system and it is turned off in the TEC-GT. Based on everyone's input, really need to work on the linkage and sync the throttle bodies. Thanks for everyone's input, back to confirm I got the basics correct.

[PaulProe]

. . . I got them close, except for one, but guess need to get back in and get better than close.

Bruce,
When I set mine up, it took a fair amount of back and forth till I got them all to match. I recommend using an SK meter to check airflow.



If the throttle bodies have air adjustment screws, make sure they are all screwed in (seated)
check your cross linkage that both sides are the exact same distance from rod end to rod end. When they are identical length, lock the nuts so they don't change, yet.
Your first one is the drivers side, inboard where the throttle linkage first connects. check it with the meter while idling to determine the base number.
2nd one is the other throttle body on the same side. Adjust the interlink to get the air meter reading the the same amount as the first.
Now switch to the other side and adjust the one that has the cross linkage. Adjust the cross linkage to get the same reading - 1/2 adjust on the drivers side link 1/2 adjustment on the pass side link. I mark them with a Sharpie so you can reference the turns. Be ware, 1/6 turn (one flat) on each link is a lot of change, they are really sensitive.
When the third one is close, then adjust the fourth using the interbody link on that side.
Now you can start with the air bleed screws to get the individual bodies to match. Go back to the first one and get the reading, then check the barrel on the same throttle body. If it is lower, you can crack open the air bleed screw which will bring the air flow up. If that barrel is higher than the first, you crack the bleed on the first one, but that will cause you to start thru the entire process all over.
Repeat this around the circle, following the same path. It takes about five times around the circuit to get them all to match. I match the line on the gauge to the line on the scale, you can get pretty precise doing it that way and closer is better. There really isn't room for any tolerance


Now that you have this done at idle speed, you then need to check it at about 2000-2500 rpm. Figure out a way to depress and hold your gas pedal very steady so the car is running at this higher rpm. It MUST stay constant during the setting. Now check the reading from side to side. Again, it must match exactly. If it doesn't match, adjust the two crosslinks (1/2 the amount on each, they must stay the same length) to get it to match.

Put it back to idle and check it again. It takes multiple times to get it right. And the closer it is, the better your car will run

Paul

[MVRight]

Thanks for the detail. Those following here, cleaned and rechecked everything. Missing a set screw on one coupling. May not have hurt, but didn't help. Waiting on a replacement then go through the process. Thx

[MVRight]

Progress? Synchronization better - perfect no, but consistent, yes. Idles better, AFR 13.0-13.5 at idle. Process to get to 2500 and continue to tweaking the AFR is the problem. I can ease up to 2000RPM and once it goes above, it bounces from rich to lean. All the linkages look good and everything looks to open consistently. It would seem I'm still missing something basic. Ran a couple of data logs and will be digging into it some more, as well as rechecking the mechanicals.

[Robodent]

I kinda had the same issue with my build but with a fi tech and I had a intake leak I’m no mechanic but just a thought from my experience. Rob

[PaulProe]

Progress? Synchronization better - perfect no, but consistent, yes. Idles better, AFR 13.0-13.5 at idle. Process to get to 2500 and continue to tweaking the AFR is the problem. I can ease up to 2000RPM and once it goes above, it bounces from rich to lean. All the linkages look good and everything looks to open consistently. It would seem I'm still missing something basic. Ran a couple of data logs and will be digging into it some more, as well as rechecking the mechanicals.

If the airflow matches side to side, then it becomes a fuel table issue. Are you running single or dual O2 sensors. One of the biggest issues with better quality Fuel Injection systems are they are infinitely adjustable. Carburetion makes a lot of compromises but admittedly, is simpler.

[BRRT]

Is it possible you have an exhaust leak that is pulling air in, causing issues with your A/F ratio readings?

Jeff

[MVRight]

Catching up - running single O2 wideband. TEC_GT has a lot of flexibility, but don't want to go in messing with it until I get it reasonably tuned, unless I really have to. For exhaust leak, yeah checked that and they were loose after a couple of heat cycles. They were tight, but good thing to check again. Once I retightened, idled better, but still the issue above 2000. Got some more time this weekend to run through the above and work on it some more. Thx

[acmikee]

How you sync all of your throttle bodies

[MVRight]

Progress. There's a setting called ACE0 - Throttle Position Rate of Change Sensitivity, the threshold for activating the TPS based accel enrichment. Looking at the logs, as I was slowing pressing on the accelerator, the injectors stopped firing, went lean, RPM went up, dropped and continued the cycle. If I stabbed the throttle, didn't happen, but tough to land at 2500RPM. Increasing the sensitivity of ACE0 allowed me to clear up the injectors not firing. Can now hold at 2500RPM and work through the tuning. Too much going on today, to complete, but progress.

[MVRight]

I have a synchrometer that measures the air flow of each ITB. The intake is an old DC&O Racing setup and has limited adjustability. I can balance them in pairs, but individually is not possible without some extensive deconstruction of the intake. Balanced pretty well now, and not that I figured out the tip-in issue, I can fine tune them some more.