Yellow Bullet Forums banner
1 - 2 of 2 Posts

239 Posts
Discussion Starter · #1 · (Edited)
I will attempt to keep this long story short as possible while including all pertinent info.

TLDR: Old lower power motor would spool converter on TB no problem in 2020. Come 2021 would no longer spool, converter out of nowhere seems much much tighter than before. New motor in 2022, makes more torque but has same problem stalling the converter.

Back in 2020 I swapped the 5 speed manual out for a th400 with a brake and a UCC converter from lenny. Car was a twin turbo 4.6 mod motor in a 3200lb mustang. The converter was a little tight, but was manageable for the time being.

All of 2020 I worked the bugs out of it and was able to get it running pretty good. The converter would go to 3200 rpm on the TB wot, and over about 4 seconds, build rpm and boost to my 4500 rpm 2 step and 5-7psi boost setting on the line.

Has zero problems spooling all of 2020. Come 2021 and first pass down the track for the year, I had an injector driver in my ecu short on, which hung an injector open mid pass. (I only had my 2step set to 3k rpm on this run) << info for later

I was lucky or so I thought, and didn't think it did any hard part damage. Took it home, pulled plugs, got the fuel out of that cylinder, did a leak down and compression test. The one cylinder that has the injector problem was a little lower than the others, but not enough to condemn it so to speak.

Over the rest of 2021, I saved up and bought a Holley efi to replace the failed megasquirt ms3x I had. Installed the Holley and went to test the TB. Found motor would go right up to 3200 like usual, but would slowly fall down to 3000rpm over a couple seconds, and only build like 2psi boost.

No matter what I did with fuel or timing ect, it just wouldn't get over that hump and build rpm.

So I figured maybe the motor is hurt worse then I think, so I pull the motor out and find one of the rods slightly bent from the stuck injector hydrolocking it.

Figured that was causing my lack of rpm on the TB issue, but inspected the stator tube to see if it spun (grabbed with big pliers and couldn't turn it myself, and verified the mechanical diode in the converter turns/ratchets in one direction, and locks in the other with a long screw driver. Figure it's gotta be the wounded motor causing it.

So over the winter I decided to build a nicer bullet and put together a 302 inch 4v stroker mod motor. 12 to 1 on methanol, same twin turbos, same camshafts for now, same heads/intake , same everything except the shortblock basically.

Kept the same ucc converter thinking i'd get some data and make any adjustments to it once I had that data to do so.

Got the new motor fired up and the tune roughed in. Go to put it on the break and it goes to 3400 rpm at first stab of wot, builds to 3900-4000 (4500rpm 2step) over 5-6 seconds and then kinds falls off 200-300 rpm before I let off at the 7 second mark.

I keep messing with the tuneup trying different things. Only 1 time have I been able to get it to actually hit the 2step rpm (4000rpm that time) and this was after trying 2 separate times on the TB within like 15 seconds of each other.

I come out the next day, warm it up and try again, and it's right back to the same 3800-3900 wall then dropping back to 3500 rpm thing 3.5psi boost.

What are the chances something in the converter or the transmission is causing this low stall issue on 2 different motors. Like I said, in 2020 with the old lower power motor, it would jump right up to 3200 rpm and build to 4500rpm no problem every time over 4-5 seconds. I even took it as high as 5k on the TB before, and it wasn't an issue.

Something changed over winter 2020-2021 and I don't know what. The only pass I made in 2021, I had my 2step set real low (3000 rpm) to work on getting off the line, so I'm not sure if it was acting proper then or not, but the injector stuck mid pass and that was it for 2021 passes.

I'll include a picture of 2 datalogs overlaid, the solid line is the old motor on holley, and the dotted is new motor on holley. You can see the new motor is making more torque down low, but the problem still persists. You can see it gets stuck at a wall and then drops a little rpm at the end before I let off the throttle. I've tired richer/leaner, more timing/less timing ect.

Trans line pressure is 210 and converter charge sits between 80-100psi on the brake.

Green= TPS / Light red in middle= RPM / darker red towards bottom is boost

Colorfulness Product Rectangle Slope Font

here is an example of the old engine on megasquirt. I spun on the hit but it goes to 3200 on wot and builds to 4500 and 6psi no problem.
white=rpm / red boost

Electricity Sky Midnight Darkness Event

another where i lost the tire but stabbed it and ran it out. dropped about 1300 rpm on the shift, but was still on low power.

Rectangle Slope Organism Font Plot

Here is a pic of the log where I did 2 basically back to back Trans Brake test, 1st attempt it did the usual, the 2nd time it got up to 4200 rpm (4200 rpm 2step) and 5psi boost, then rpm falls back 300-400 before letting off.
green=tps light red= rpm dark red=boost

Rectangle Font Slope Parallel Terrestrial plant

Super Moderator
20,194 Posts
If tuning has maxxed out, the only thing left to do is converter changes or cooler line exhaust solenoid to help slightly. If things were broken (converter diode or stator tube problem), stall would be stuck around 1800 and just sit there.

1 - 2 of 2 Posts