4.9 with 4t60e shifting issues (Page 1/1)
KissMySSFiero FEB 23, 11:33 AM
I need help on a 4t60e with a 4.9 swap that is shifting weird.
Under full throttle it shifts great. Firm shifts at the right RPM.
with no load it doesn't want to up shift. And when I'm cruising, it hunts between gears.
The only way to get it to shift up consistently is mash the pedal.
I don't know the history of the drive-train. It came in a car unfinished. I just recently got the engine in my formula and driving. It has the Ed Parks/Fiero Factory engine harness.
Any help is appreciated.

Edit to add. All 4 shift solenoids and Vacuum modulator have been replaced. Vehicle speed sensor works and is accurate compared to GPS.


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SSFiero@Aol.com

[This message has been edited by KissMySSFiero (edited 02-23-2020).]

Dennis LaGrua FEB 23, 07:40 PM

quote
Originally posted by KissMySSFiero:

I need help on a 4t60e with a 4.9 swap that is shifting weird.
Under full throttle it shifts great. Firm shifts at the right RPM.
with no load it doesn't want to up shift. And when I'm cruising, it hunts between gears.
The only way to get it to shift up consistently is mash the pedal.
I don't know the history of the drive-train. It came in a car unfinished. I just recently got the engine in my formula and driving. It has the Ed Parks/Fiero Factory engine harness.
Any help is appreciated.

Edit to add. All 4 shift solenoids and Vacuum modulator have been replaced. Vehicle speed sensor works and is accurate compared to GPS.




Make sure that the vacuum line is on the vacuum modulator In other words check that you have vacuum at the vacuum modulator. The transmission vacuum modulator determines how much load the engine is seeing so the transmission can shift properly. Defects will cause the problem that you describe. That part can be replaced with an adjustable unit so that shift points and firmness can be changed.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

KissMySSFiero FEB 23, 08:34 PM
Thanks. I just verified I have vacuum at the modulator.
I can feel it and the idle goes up when disconnected.
My next step might be to grab another vac mod from the junkyard.
I keep reading how the aftermarket adjustable ones aren’t that great.
OldsFiero FEB 24, 07:16 AM
Modulator only controls line pressure on a 4T60-E. The ECM determines when it shifts. I would look at TPS voltage for starters.
Marc
olejoedad FEB 24, 07:21 AM
Olds Fiero is correct.
Check the TPS.

Haven't had any trouble with the aftermarket adjustable modulators. Its a good idea to put one on it, the factory ones are set for the car and may not give you what you want in a Fiero application.

Edit to ask...

What RPM do you turn at 70 MPH?
What size tires on the rear of your car?

GM only used two ratios behind the 4.9, - we might be able to determine which one you have.

[This message has been edited by olejoedad (edited 02-24-2020).]

Dennis LaGrua FEB 24, 09:21 AM

quote
Originally posted by OldsFiero:

Modulator only controls line pressure on a 4T60-E. The ECM determines when it shifts. I would look at TPS voltage for starters.
Marc



That is true but you need proper line pressure for the shift to happen at the right points. A defective modulator will cause early or late shifting.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

KissMySSFiero FEB 26, 08:31 AM
TPS measured good......until it didn’t.
The ground going into the sensor let go due to a bad crimp.
I soldered the pins and got to go for a drive.
Thanks a ton for the lead.

Now a few questions.
Is there a way to see real-time data on an OBD-1 ecm?
If this had been OBD-2, I could have plugged in a scanner and found this on my phone.

Now I’m confident the drivetrain won’t have to come out again.

Next is getting the ac to work.

[This message has been edited by KissMySSFiero (edited 02-26-2020).]

OldsFiero FEB 27, 09:48 PM

quote
Originally posted by Dennis LaGrua:


That is true but you need proper line pressure for the shift to happen at the right points. A defective modulator will cause early or late shifting.



True for TH350, TH400, Ford C4, C5, C6, FMX, and many BW units back in the day. Not true for Powerglide, 4T60, 4T60-E, and most Mercedes hydraulic units that I have seen.
4T60-E exceptions; line pressure so low(worn pump or gross leak), that the shift valve won't move because the pressure can't overcome the spring weight on the valve, or leaking solenoid. If pressure is that low, you have bigger problems than shift timing problems. High pressure can cause late or missing shifts if the shift solenoid is restricted due to warp or contaminates.