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Discussion Starter · #1 ·
Last year I had my engine rebuilt bored and stroked. Of course shortly thereafteri lost 3rd gear and had to have transmission rebuilt. I took this opertunity to upgrade to handle the power. Used a hughs performance kit, transgo shift kit (stage2) and 1800 stall converter. Now in 4th gear between1200-1800rpm 40-55mph the torque converter locks and unlocks resultin in a rough ride. Anyone got a good fix for this
 

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Discussion Starter · #3 ·
No I didn't. Sadly I live in lower delaware there isn't anyone around that does that. I've heard really good things about pcm for less but between the engine and transmition I've kind of blown my budget for the near future...that said car ran awesome with stock transmition (until third gear clutches burned up) is pcm tune only way to change lock up
Honestly if anyone knows a dyno tuner in the delmarva peninsula that will tune it I'd love to get phone number to schedule
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Failure to tune probably contributed to tranny failure.

What are the detailed mods for you engine? What cam, what heads, what size injectors, etc? Fuel that engine wrong and you can wash down the cylinder walls, destroy the rings, dilute the oil, leading to disaster.

Torque converter sounds way too small... not much different than stock.
 

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']['exXxas']['itan
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Yeah I thought it was stock speeds as well. I dont consider anything under 2800 to be a stall converter.
 

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I would make sure the brake light switch is not adjusted wrong or bad causing the brake light circuit to cut in and out. I would check the Throttle position sensor voltage when at low throttle angle because the TCC solenoid is released under min and max throttle. The TCC solenoid itself may be going bad or the + or - wires going to it are loose somewhere in the path (the PCM makes the coil in the TCC hot by completing the ground path). The O-ring at the top of the TCC could be going bad and not holding full pressure. I think the Transgo kit comes with a replacement converter regulator valve line up that "fixes" this busy valve bore that wears out over time by making it into an ON/OFF set up instead of the stock gradual apply design, so this should take care of dreaded P1870 converter slip code. Speaking of codes are there any codes pointing to transmission issues? Have you hooked a pressure gauge to the port just above where the gear selector shaft goes into the trans case to check line pressure? I would try to eliminate any possible electrical connection issues with the TCC ground and + wire paths all the way back to the PCM. If need be, pull the pan and check the TCC valve itself and the connections.
 

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Discussion Starter · #7 ·
Factory stall is 1200. Engine bored .040 over 0 deck afr 190cc heads comp xfi cam can't remember specs 11.5:1 compression. Issues not with the engine set up. Tyranny burned up from running 500 hp through 120k mile stock first generation 4l60e. 1800 stall isnot much but it's not a track car it's a glorified grocery getter
Joe peek the shop that rebuilt the tyranny clait's he used all the parts that came in the transgo kit. So based on that it sounds highly probable that something didn't get installed right
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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No one claimed there was anything wrong with the engine build. I was just trying to understand how badly the combo mismatched a stock tune. You didn't answer the question about injector size. You can't make 500 HP on stock injectors.

But you seem to feel you have found your problem with the shift kit install, so I'll stop annoying you with my ignorance.

Good luck
 

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Discussion Starter · #9 ·
It wasn't an annoyance bud. I just wanted to see if the problem would be something I could repair myself caused by changing the stall speed or if it sounded more like my builder (who I'm sorry I have dealt with already) may not have done something right. It is still on factory injectors which I believe barely calculate as sufficient to support the estimated 500 hp. Car is still a work in progress b I was hoping to use tax refund on 30 lb injectors and Pcm for less
When I mentioned to my builder he said we would have to interrupt the signal but I don't want to pay him to do something he should have done in the first place
Also after the engine was built it ran 4 tanks of gas very smooth very fast and very awesome with the t tops out :)
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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To make 500 flywheel HP (normally aspirated) on the stock 24 #/HR injectors (programmed as 24.896 #/HR) you would have to have a brake specific fuel consumption (BSFC) of less than 0.40 #/HR/HP and the injectors would have to be at 100% duty cycle, neither of which is very likely.

Online injector sizing programs recommend that you use 0.50 #/HR BSFC and 80% duty cycle. At 500 HP that would require a 39.1 #/HR injector. That is extremely conservative, considering modern EFI capabilities and modern injector design. My recommendation is to multiply flywheel HP x 0.07 to get the correct minimum injector size. That assumes a BSFC of 0.476 and a max DC of 85%. Example 500 x 0.07 = 35 #/HR (note sea dog is pretty much at the same number).

Efficient combustion chamber design and extensive dyno tuning can improve BSFC. My setup achieved 0.44 #/HR/HP. Any duty cycle above 85-90% can cause the injectors to become unstable with regard to both spray pattern and flow capacity.

You can increase injector flow capacity by raising the fuel pressure, but the stock GM Multec injectors don't like high pressures.
 

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And install a flux capacitor...holy moly the tech speak has my head spinning!
 

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Discussion Starter · #13 ·
Lol were off topic. Engine runs smooth Pcm for less is in the plan along with larger injectors. Question was about whether there was a tune issue or more likely a rebuild issue in regards to trans unlocking at low rpm load in 4th gear
 

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Discussion Starter · #14 ·
500 hp was estimated based on the build in chevy high performance magazine head competition whichas is the build I modeled except I'm running a higher compression ration. But again the question was with transmission tune causing unlocking because of higher stall speed or did my mechanic screw something up
 

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You don't seem to understand.... the degree to which the 4L60E strategy needs to be changed in the PCM is to some extent dependent on the degree by which the current build differs from the (in this case) STOCK tune. When you provide unrealistic info, like being able to produce 500 HP with stock injectors, and blaming trans failure on handling that 500 HP, your problem becomes very difficult to comprehend.

See if this helps:

1-What controls the shifts in a 4L60E 4L80E and can I replace the PCM with a vacuum modulator.

The answer is the PCM is in complete control of every aspect of when and how the 4L60E shifts, Line Pressure and Lockup. If the command is given barring any mechanical failure clutches, Band ETC the transmission must make the shift or slip and burn itself up trying. Alternately It cannot shift before its commanded.
Lockup again is strictly a function of the PCM turning on the lockup solenoid and pulsing the PWM solenoid.

I hear a lot of people say my converter locks up sometimes and other not what wrong with it. Well If your converter locks up properly anytime, then its more than likely a tuning issue and not a TRANSMISSION/CONVERTER issue.
With the chance of offending you for taking your thread off topic, is your 4L60E the original trans from your 95? If not, was it replaced with a trans from a 95? This is important, because installing any other year trans in a 95 will result in problems, and potential trans failure. A good reference:

http://ltxtech.com/forums/showthread.php?23419-4L60E-year-differences-and-interchanges

Are you running the stock rear axle ratio, or has it been changed? Torque converter lockup is in part dependent on MPH (e.g. MPH vs throttle position). If the PCM has not been corrected to match the new gear ratio, it doesn't know the correct MPH.
 

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While shift firmness can be effected by increasing the line pressure electronically (force motor), and the shift solenoids time gear to gear shift points, and these things can be changed with tuning changes, there are still many mechanical things that also effect the "personality" of the 4L60-E. Accumulator springs can be replaced with stiffer springs or be broken, servo area changes, separator plate hole sizes, broken valve body springs, and how well the valves seal and don't stick, or have leaking end plugs. Clutch packs, and how good the apply pistons lip seals hold line pressure, pump condition,O-rings in many places, stuck checkballs.......... the list goes on. Just thought I would throw this out there because while a transmission that has no other issues, that has been assembled correctly, and is in overall good running condition, then yes...the torque converter lock up depends on the signals the TCC and PWM solenoids receive . But there are mechanical things that predictable converter lock up depends on too, and if they fail, even if the TCC, PWM, PCM, connections, and tune are perfect, the converter will not perform as expected.
 

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Joe:

I'm not arguing that it can't be an internal trans issue. But if the program is not adjusted to the current engine configuration, what is the point? It needs to be done. Not just for the trans, but for the sake of the entire engine.

Get a full tune done, see if anything changes, and if the problem persists, then you will KNOW it's a mechanical problem. Personally I think it could be as simple as the RPM lockup lower limit being set too low for the irregularities the more aggressive cam imparts to the locked converter. And the more aggressive the cam is the more important the tune is to eliminating the rough operation at low RPM. But then we know no more about the cam than we know about the rest of the engine.

I'm really done with this thread. It's simply going around in circles. I should have known to stop at post #8.
 

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Discussion Starter · #18 ·
Update: engine specs:eagle 383 stroker kit, bores .040 over, afr 195cc competition series heads 55cc combustion chamber, 11.5:1 static compression, comp 268xfi hr13 cam, mid length headers, MagnaFlow cat back, 58mm throttle body, stock maf with ported ends
Trans:1800 stall torque converter, 5 pinion front and rear planetaries, beast sun shell, Hugh's performance rebuild kit, transgo stage 2 shift kit.
Relieved flashed pcm from Pcm for less waiting on injectors (42lb delphi) hopefully they'll arrive with some sunshine and warm weather so I can knock it out and see what happens
If i drive with my left foot about 1/4" down on the brake it drives good
 
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