Why does my 79 chevy pu withe a manual trans. jump out of 3 rd gear

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Question answer by Jeff Armer, our Automotive Electronics Tech.

Jeff Armer Mar 30, 2024
Under the hood in the engine compartment .And it's called a PCM - powertrain control module.
Powertrain Control Module (PCM)
At the left front side of the engine compartment
--------------------------------------------------------------------------------

Powertrain Control Module Connector End Views
Connector 1: Powertrain Control Module (PCM) C1
Connector 2: Powertrain Control Module (PCM) C2

Powertrain Control Module (PCM) C1



Connector Part Information
OEM: 12191110
Service: 12167308
Description: 80-Way F Micro-Pack 100W Sealed (BU)

Terminal Part Information
Pins: 1- 7, 11, 12, 14, 15, 19-21, 23-30, 33, 36, 37, 39, 40, 43-, 48, 51, 54, 57, 58, 61, 63-70, 73-77, 80
Terminal/Tray: See Terminal Repair Kit
Core/Insulation Crimp: See Terminal Repair Kit
Release Tool/Test Probe: See Terminal Repair Kit

Powertrain Control Module (PCM) C1 Pin
Wire Color
Circuit No.
Function

1
BK/WH
451
Ground

2
L-GN
1867
12-Volt Reference

3
PK/BK
1746
Fuel Injector 3 Control

4
L-GN/BK
1745
Fuel Injector 2 Control

5-6
--
--
Not Used

7
GY
2705
5-Volt Reference

8-10
--
--
Not Used

11
L-BU
1876
KS 2 Signal

12
D-BU/WH
1869
CKP Sensor Signal

13
--
--
Not Used

14
OG/BK
1061
UART Serial Data

15
D-BU/WH
774
UART Serial Data

16-18
--
--
Not Used

19
PK
439
Ignition 1 Voltage

20
OG
440
Battery Positive Voltage

21
YE/BK
1868
Low Reference

22
--
--
Not Used

23
BK
470
Low Reference

24
BK/WH
451
Ground (NC1/NC8)

25
TN
1671
HO2S Low Signal Bank 2 Sensor 2 (NC1/NC8)

26
TN
1667
HO2S Low Signal Bank 2 Sensor 1

27
BK/WH
451
Ground (NC1/NC8)

28
TN/WH
1669
HO2S Low Signal Bank 1 Sensor 2 (NC1/NC8)

29
TN
1664
HO2S Low Signal Bank 1 Sensor 1

30
L-GN
1478
Coolant Level Switch Signal

31-32
--
--
Not Used

33
PU
420
TCC Brake Switch/Cruise Control Release Signal

34-35
--
--
Not Used

36
BK
1744
Fuel Injector 1 Control

37
YE/BK
846
Fuel Injector 6 Control

38
--
--
Not Used

39
YE/BK
625
Starter Enable Relay Control

40
BK/WH
451
Ground

41-42
--
--
Not Used

43
RD/BK
877
Fuel Injector 7 Control

44
L-BU/BK
844
Fuel Injector 4 Control

45
GY
2700
5-Volt Reference

46
GY
474
5-Volt Reference

47
--
--
Not Used

48
GY
597
5-Volt Reference

49-50
--
--
Not Used

51
D-BU
496
KS 1 Signal

52-53
--
--
Not Used

54
OG/BK
469
Low Reference

55-56
--
--
Not Used

57
OG
440
Battery Positive Voltage

58
D-GN
1049
Class 2 Serial Data

59-60
--
--
Not Used

61
PK/BK
632
Low Reference

62
--
--
Not Used

63
BK
2755
Low Reference

64
BK/WH
451
Ground

65
PU
1670
HO2S High Signal Bank 2 Sensor 2 (NC1/NC8)

66
PU
1666
HO2S High Signal Bank 2 Sensor 1

67
BK/WH
451
Ground

68
PU/WH
1668
HO2S High Signal Bank 1 Sensor 2 (NC1/NC8)

69
PU/WH
1665
HO2S High Signal Bank 1 Sensor 1

70
BN
1174
Oil Level Switch Signal

71-72
--
--
Not Used

73
BN/WH
633
CMP Sensor Signal

74
YE
410
ECT Sensor Signal

75
PK
1020
Ignition 0 Voltage

76
BK/WH
845
Fuel Injector 5 Control

77
D-BU/WH
878
Fuel Injector 8 Control

78-79
--
--
Not Used

80
BK
407
Low Reference


Powertrain Control Module (PCM) C2



Connector Part Information
OEM: 12191110
Service: 12167308
Description: 80-Way F Micro-Pack 100W Sealed (GN)

Terminal Part Information
Terminal/Tray: See Terminal Repair Kit
Core/Insulation Crimp: See Terminal Repair Kit
Release Tool/Test Probe: See Terminal Repair Kit

Powertrain Control Module (PCM) C2 Pin
Wire Color
Circuit No.
Function

1
BK/WH
451
Ground

2
--
--
Not Used

3
TN
1465
Fuel Pump Relay Control - Secondary

4-8
--
--
Not Used

9
D-GN/WH
465
Fuel Pump Relay Control

10
WH
121
Engine Speed Signal

11-13
--
--
Not Used

14
RD/BK
380
A/C Refrigerant Pressure Sensor Signal

15
BN
25
Charge Indicator Control

16
GY/BK
1694
4WD Low Signal

17-19
--
--
Not Used

20
L-GN/BK
822
VSS Low Signal

21
PU/WH
821
VSS High Signal

22-24
--
--
Not Used

25
TN
472
IAT Sensor Signal

26
PU
2121
IC 1 Control

27
RD
2127
IC 7 Control

28
L-BU/WH
2126
IC 6 Control

29
D-GN/WH
2124
IC 4 Control

30
--
--
Not Used

31
YE
492
MAF Sensor Signal

32
L-GN
432
MAP Sensor Signal

33
--
--
Not Used

34
D-GN/WH
428
EVAP Canister Purge Solenoid Control

35-38
--
--
Not Used

39
RD
631
12-Volt Reference

40
BK/WH
451
Ground

41-42
--
--
Not Used

43
D-GN/WH
459
A/C Compressor Clutch Relay Control

44
--
--
Not Used

45
WH
1310
EVAP Canister Vent Solenoid Control

46
BN/WH
419
MIL Control

47-48
--
--
Not Used

49
YE/BK
1827
Vehicle Speed Signal

50
D-GN/WH
817
Vehicle Speed Signal

51
--
--
Not Used

52
BN
2391
HO2S Heater Low Control Bank 1 Sensor 2 (NC1/NC8)

53
RD/WH
3223
HO2S Heater Low Control Bank 2 Sensor 2 (NC1/NC8)

54
PU
1589
Fuel Level Sensor Signal - Primary

55-56
--
--
Not Used

57
BK
552
Low Reference

58
TN/WH
332
Oil Pressure Sensor Signal

59
PU
806
Crank Voltage

60
BN
2129
Low Reference

61
BN/WH
2130
Low Reference

62-63
--
--
Not Used

64
D-GN
890
Fuel Tank Pressure Sensor Signal

65
--
--
Not Used

66
PU/WH
2128
IC 8 Control

67
RD/WH
2122
IC 2 Control

68
D-GN
2125
IC 5 Control

69
L-BU
2123
IC 3 Control

70-71
--
--
Not Used

72
BK/WH
3113
HO2S Heater Low Control Bank 1 Sensor 2 (NC1/NC8)

73
D-BU
1936
Fuel Level Sensor Signal - Secondary

74
L-GN
3212
HO2S Heater Low Control Bank 2 Sensor 1

75
GY
23
Generator Field Duty Cycle Signal

76-79
--
--
Not Used

80
BK
2751
Low Reference

Internal transmission problems, syncros or gears worn out, damaged,,,,,,,,, take to trans shop or swap out transmission for a good one.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/michael_2496c4f07ad24453

5speed manual transmission.
jumps to neutral? moving fast, slow, hills ,turns, down hill, where>?
my guess. is:
1: bad engine/tranny mounts
2: bad shift linkage.
3: bad trans.

WELL YES YOU CAN PUT THEM ON BUT NEED TO REPLACE THEM WITH WIREING HARNESS AND COMPUTERS AND EXUST SISTEM THATS THE ONLY WAY THEN YOU WILL HAVE PROBLEM GETING IT TO SMOG UNLESS YOU TAKE TO STATE SMOG REFERY

Do you mean start the car in drive? if so that problem is inhibitor switch. Other shift problems can be caused by TPS (throttle posistion sensor) if applicable

governor or throttle valves are stuck

check your trans fluid it could be low. it could be that one of your gears in your trans is going out or a trans mount

I'm not sure what trans you have but if you have a standard trans you have either a broken shifting fork or a bad synchronizer i would not suggest trying to replace them your self unless you are familiar with transmissions, I've seen a lot of people do more harm than good because they didn't know what they were doing. If you are mechanically apt you can get manuals on overhauling them.

Please ensure that this has gear oil because some of these actually ran regular dexron tranny fluid. If it is gear oil a standard 80w-90 is a good all grade gear oil to run in it.

pull the shifter out and check for bent and worn parts, most likely the shaift rails are worn out and it is stuck between gears.