Shifting Issues (Automatic)

btwilson86 · 11-01-2007, 06:10 AM

I have an 87 7MGE with an Auto Trans.
CEL codes say TPS, Knock Sensor, and Neutral Start Switch.

I had the transmission rebuilt about 2 miles before I blew my old engine about 2 years ago. The car had sat since then for about a year and a half, until I dropped in a used Jasper motor. I have since been troubleshooting all problems, and have now faced a transmission issue I'm not sure how to fix.

Transmission Parts replaced: Torque converter (at time of rebuild on tranny), kickdown cable (cable from throttle assembly to transmission), Neutral Start Switch (a couple days ago- fixes NSS CEL), transmission fluid, transmission filter. Fixed bypassed Neutral Start Switch wiring to stock set-up. Switch has been tested to good, working condition.

The problem pretty much lies between Neutral to first gear, and first to second gear. When in Drive, if I step on the gas from a dead to near-dead stop, the engine revs without hardly moving the car (like someone letting off of the clutch WAY to slow on a MT). Ones everything locks up correctly, the car will drive fine until it is near time to shift to 2nd. At this gear change, the tranny will upshift, then downshift, then upshift, then downshift, and so on and so forth. Note that this happens with absolutely NO fluctuation in the throttle position. After it's in second gear, the car will shift to third with no problem. However, with O/D on, the car will not go into Overdrive after 3rd.

Another issue is that when in gear, if I punch the accelerator pedal to the floor, sometimes it will downshift and accelerate, and sometimes it will stay in the gear it was in and attempt to power through it (just run at WOT in the gear).

I notice no shift changes when in Economy vs. Power setting, as well as O/D on or off.

I have also noticed that if I floor it from the dead stop, most of the time it will take off right away, but sometimes still rev a little first. If I move the gear selector manually while driving (i.e. L to start, move to 2 to shift, then D to shift to third), everything operates exactly as it should; no revving, no sporatice shifting, nothing strange at all. This leads me to believe that there is no issue with the gearing in the transmission.

I'm wondering if the computer control for the tranny relies on a signal from the TPS (among other sensors) to determine shift points, and if this sounds like an electrical or mechanical issue.

Any help that can be provided is much appreciated, and I will respond as quickly as possible.

Thank You for your help in advance

mrnickleye · 11-01-2007, 02:05 PM

It sounds electrical. The computer and related shift solenoids need to be tested by a professional.

btwilson86 · 11-01-2007, 04:09 PM

Okay. By professional, do you refer to a reputable transmission shop?

jfunez · 11-03-2007, 06:48 AM

i would start by fixing the TPS code...then and only the continue with tha tranny problems....

btwilson86 · 11-03-2007, 07:05 AM

I was thinking that... Doesn't the computer for the transmission receive the signal from the TPS as well as other sensors to determine shift points for that particular moment?

For that matter, does anyone know what signals the Automatic Transmission on a MKIII receives to determine when to shift?

I want to do whatever I can before I take mrnickleye's advice.

11-01-2007, 06:10 AM	#1
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Shifting Issues (Automatic) I have an 87 7MGE with an Auto Trans. CEL codes say TPS, Knock Sensor, and Neutral Start Switch. I had the transmission rebuilt about 2 miles before I blew my old engine about 2 years ago. The car had sat since then for about a year and a half, until I dropped in a used Jasper motor. I have since been troubleshooting all problems, and have now faced a transmission issue I'm not sure how to fix. Transmission Parts replaced: Torque converter (at time of rebuild on tranny), kickdown cable (cable from throttle assembly to transmission), Neutral Start Switch (a couple days ago- fixes NSS CEL), transmission fluid, transmission filter. Fixed bypassed Neutral Start Switch wiring to stock set-up. Switch has been tested to good, working condition. The problem pretty much lies between Neutral to first gear, and first to second gear. When in Drive, if I step on the gas from a dead to near-dead stop, the engine revs without hardly moving the car (like someone letting off of the clutch WAY to slow on a MT). Ones everything locks up correctly, the car will drive fine until it is near time to shift to 2nd. At this gear change, the tranny will upshift, then downshift, then upshift, then downshift, and so on and so forth. Note that this happens with absolutely NO fluctuation in the throttle position. After it's in second gear, the car will shift to third with no problem. However, with O/D on, the car will not go into Overdrive after 3rd. Another issue is that when in gear, if I punch the accelerator pedal to the floor, sometimes it will downshift and accelerate, and sometimes it will stay in the gear it was in and attempt to power through it (just run at WOT in the gear). I notice no shift changes when in Economy vs. Power setting, as well as O/D on or off. I have also noticed that if I floor it from the dead stop, most of the time it will take off right away, but sometimes still rev a little first. If I move the gear selector manually while driving (i.e. L to start, move to 2 to shift, then D to shift to third), everything operates exactly as it should; no revving, no sporatice shifting, nothing strange at all. This leads me to believe that there is no issue with the gearing in the transmission. I'm wondering if the computer control for the tranny relies on a signal from the TPS (among other sensors) to determine shift points, and if this sounds like an electrical or mechanical issue. Any help that can be provided is much appreciated, and I will respond as quickly as possible. Thank You for your help in advance __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

11-01-2007, 02:05 PM	#2
mrnickleye 1000whp postwhore Join Date: Jun 2005 Location: Mojave Desert, Calif. Posts: 1,705	It sounds electrical. The computer and related shift solenoids need to be tested by a professional. __________________ Had a Red 1989 N/A. Automatic. Sports Pkg. w/wing. TEMS, and some nice MODS. Sold to a friend 10/08/08.

11-01-2007, 04:09 PM	#3
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Okay. By professional, do you refer to a reputable transmission shop? __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

11-03-2007, 07:05 AM	#5
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	I was thinking that... Doesn't the computer for the transmission receive the signal from the TPS as well as other sensors to determine shift points for that particular moment? For that matter, does anyone know what signals the Automatic Transmission on a MKIII receives to determine when to shift? I want to do whatever I can before I take mrnickleye's advice. __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

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11-03-2007, 06:48 AM	#4
jfunez 12psi boost Join Date: Oct 2005 Location: georgia,usa Posts: 338	i would start by fixing the TPS code...then and only the continue with tha tranny problems....