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Discussion Starter · #1 ·
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
 

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Did you use a synchronometer to balance the throttle bodies?
 

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Discussion Starter · #5 ·
Did you use a synchronometer to balance the throttle bodies?
Yep, but is it perfect, no. Most are really close to the same, one is significantly different. When the idle was lower, they are all pretty close, with it higher it starts diverging. But good thought to take some more time getting it closer.
 

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Bruce,
More details on the other forum. Close only counts in horseshoes and hand grenades. All eight must match exactly at idle and also at higher rpm. Until they do, you'll be chasing your tail.

Do you have one or two O2 sensors? Just one is asking for trouble. Two sensors, are you sure they are reporting to the ECU correctly as to which side.

Take it out of closed-loop until you get the throttle bodies adjusted properly. O2 sensor senses too rich, dials out the fuel for that side, RPM changes accordingly and then the other side senses too lean so it pumps in fuel. Surges. Make sure both sides are set the same and reporting properly

Paul
 

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Yep, but is it perfect, no. Most are really close to the same, one is significantly different. When the idle was lower, they are all pretty close, with it higher it starts diverging. But good thought to take some more time getting it closer.
This is the problem. At idle, they all need to be exactly the same. The most common cause of a surging idle is a lean mixture. In an ITB system, one cylinder can be lean, and the rest slightly rich. The O2 sensor will tell you it's perfect. But with one lean cylinder you'll get surging.

And, there might be another problem. If they are all pretty close, but then diverge, that tells you the linkage is not correct.

set the primary throttle body so the blade is open exactly 1/8". Use a drill bit to measure.

Check the rest to make sure they are also at 1/8".

Then open the throttle bodies about 1/2-3/4, and then measure all of them to see if they're the same. If not, there's a problem with the linkage.

I messed around with my linkage (No, not that) for a while, and never could get it right. I eventually threw it out, and fabricated everything new. After that, tuning was much easier.
 

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Discussion Starter · #8 ·
This is the problem. At idle, they all need to be exactly the same. The most common cause of a surging idle is a lean mixture. In an ITB system, one cylinder can be lean, and the rest slightly rich. The O2 sensor will tell you it's perfect. But with one lean cylinder you'll get surging.

And, there might be another problem. If they are all pretty close, but then diverge, that tells you the linkage is not correct.

set the primary throttle body so the blade is open exactly 1/8". Use a drill bit to measure.

Check the rest to make sure they are also at 1/8".

Then open the throttle bodies about 1/2-3/4, and then measure all of them to see if they're the same. If not, there's a problem with the linkage.

I messed around with my linkage (No, not that) for a while, and never could get it right. I eventually threw it out, and fabricated everything new. After that, tuning was much easier.
I spent Sunday cleaning and checking everything. I got it used and a basic clean and check, but this time broke it all down. Dirty, but clean now and reset all the blades. One coupling was missing a set screw. May not have hurt, but didn't help. Waiting on replacement, then check it all again and go through you process and go from there.

Thx
 

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Discussion Starter · #11 ·
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.
 

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Did you check the balance at 2500 rpm?
 

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Discussion Starter · #13 ·
Couldn't. Should have been more clear, rich/lean over 2000, also caused the RPM to bounce wildly. Wouldn't/Couldn't stabilize at any above 2000. Had the idle as low as ~900 and around 1100 when checking the balance. Everything stayed consistent. As RPM when up, so did the synchro readings, but looked predicable uptick.
 

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Maybe should have asked this early on. Are you trying to run them in Speed-Density mode (RPM & MAP)? ITB's need to operate in Alpha-N (RPM & TPS%). If your trying to use Speed-Density, you're wasting your time.

Paul
 

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Discussion Starter · #17 ·
Maybe should have asked this early on. Are you trying to run them in Speed-Density mode (RPM & MAP)? ITB's need to operate in Alpha-N (RPM & TPS%). If your trying to use Speed-Density, you're wasting your time.

Paul
TEC_GT has an option to balance the MAP readings using TPS% - think it is similar to your Alpha-N description. It did help, but once I balanced the ITBs, I didn't have to use the balancing. However was thinking, and your post got me thinking some more, the TEC_GT guidance has been to use the TPS% balancing at lower RPMs because of MAP fluctuation and low RPM. Maybe there's a tip over point where at 2000RPM it skews the sensors and jacks things up. Was thinking using the TPS% at higher RPM to get over the surging. Trying that this weekend. Thx
 

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Discussion Starter · #18 ·
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.
 
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