1990 GMC runs rough

Tiny
JASON.BLAKE1
  • MEMBER
  • 1990 GMC S15
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 123,000 MILES
I have a 1990 gmc s15 4.3l tbi 4x4 runs rough at stop have replaced plugs wires cap rotor and distributor is loosing spark intermittently to #1 cylinder put the timing light on it and it doesn't fire all the time also when I unplug the vacuum line going to the air cleaner it runs a little bit smoother with that line plugged in it dies at stop lights with it unplugged it does not any ideas thanks
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Tuesday, May 17th, 2011 AT 4:37 PM

20 Replies

Tiny
WRENCHTECH
  • EXPERT
Is your check engine light coming on at all?
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Tuesday, May 17th, 2011 AT 5:24 PM
Tiny
JASON.BLAKE1
  • MEMBER
Cel comes on some time usually after driving for about 10 to 15 miles but shuts off with vehicle
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Tuesday, May 17th, 2011 AT 6:15 PM
Tiny
WRENCHTECH
  • EXPERT
The "check engine" light is an indicator for a system that monitors many electronic functions in the system, also called the "malfunction indicator lamp" (MIL). It can come on for any of hundreds of different causes from any of the systems that the computer monitors. Some are very important and can lead to further component or engine damage and some are emissions related not as serious but still a problem and need to be repaired.

Your first step is to have the computer scanned to retrieve the trouble codes that were set when the check engine light came on. Those codes will give you specific information about what the computer saw and will get you pointed in the right direction to find your problem. With a 1996 or newer and some 95 cars and you have an AutoZone or Advanced auto parts in your area, they will read them for free. Once you have these code numbers, we can be a lot more specific about what your problem may be.
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Tuesday, May 17th, 2011 AT 6:24 PM
Tiny
JASON.BLAKE1
  • MEMBER
Also I jumped the terminals on the obd1 port and all I got is code 12 and 13
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Tuesday, May 17th, 2011 AT 6:32 PM
Tiny
WRENCHTECH
  • EXPERT
Code 12 is an indication of a problem with the ECU.
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Tuesday, May 17th, 2011 AT 6:35 PM
Tiny
WRENCHTECH
  • EXPERT
Actually, 13 is also.
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Tuesday, May 17th, 2011 AT 6:35 PM
Tiny
JASON.BLAKE1
  • MEMBER
I suspect it may be vacuum related but cant find a diagram anywhere
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Tuesday, May 17th, 2011 AT 6:53 PM
Tiny
WRENCHTECH
  • EXPERT
You have 2 codes pointing to a faulty ECU and you think it's a vacuum leak?
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Tuesday, May 17th, 2011 AT 6:56 PM
Tiny
JASON.BLAKE1
  • MEMBER
I thought code 12 was the no fault code and 13 o2 sensor circuit open
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Tuesday, May 17th, 2011 AT 6:56 PM
Tiny
WRENCHTECH
  • EXPERT
No, they are both ECU error codes as I already stated.
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Tuesday, May 17th, 2011 AT 6:58 PM
Tiny
JASON.BLAKE1
  • MEMBER
Yeah
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Tuesday, May 17th, 2011 AT 7:00 PM
Tiny
JASON.BLAKE1
  • MEMBER
GM Trouble Code Info
Accessing Trouble Codes

Turn ignition switch to OFF position
Locate Data Link Connector (DLC), see image below.
Jumper the A&B terminals(a paper clip or a jumper wire work ok)
Turn Ignition switch to ON position.
Count the flashes on the "CHECK ENGINE" or "SERVICE ENGINE" light.
FLASH, pause, FLASH, FLASH = code 12
NOTE: Some 94 & 95 models do not have the B terminal. In which case a scanner is required.
NOTE: Some 94 & 95 models that DO have the A & B terminals still require a scanner.
All vehicles after 96 are OBDII, and require a scanner to access them.

12 Pin DLC
A - Ground F - TCC
B - Test Terminal G - Fuel Pump
C - Air Injection H - Brake Sense Speed Input
E - Serial Data M - Serial Data

Clearing Trouble Codes
Diagnostic trouble codes may be cleared by disconnecting the battery ground cable for at least 20 seconds. Reconnect negative battery cable and recheck codes to confirm the repair.

Diagnostic Codes
Select your Vehicle or look below for Generic codes.
Year Eng 8th digit of the VIN Number
82-83 2.5L All
82-83 3.0L All
86 1.8L Multi Port Fuel Injection, VIN J
86 1.8L Throttle Body Injection, VIN 0
86 2.0L Throttle Body Injection, VIN P
86 2.5L Throttle Body Injection, VIN 2
86 2.8L Carb, VIN X
86 3.8L Fuel Injection, VIN B
86-87 3.8L Carb, VIN A
86-87 4.1L 4.1L Fuel Injection, VIN 8
86-87 5.0L 5.0L Carburetor, VIN 9
86-88 2.5L Throttle Body Injection, VIN U
86-88 2.5L Throttle Body Injection, VIN R
86-88 2.8L Multi Port Fuel Injection, VIN 9
86-88 3.0L Multi Port Fuel Injection, VIN L
86-88 3.8L Fuel Injection, VIN 7
86-88 3.8L Fuel Injection, VIN 3
86-88 5.0L Carburetor, VIN H
86-88 5.0L Carburetor, VIN G
86-88 5.7L Fuel Injection, VIN 8
86-88 5.7L Carburetor, VIN 6
86-89 2.8L Multi Port Fuel Injection, VIN W
86-89 2.8L Multi Port Fuel Injection, VIN S
86-89 5.0L Fuel Injection, VIN F
86-90 4.3L Throttle Body Injection, VIN Z
87-88 2.0L Throttle Body Injection, VIN 1
87 2.8L Throttle Body Injection VIN R
87-88 4.1L Multi Port Fuel Injection, VIN 7
87-90 2.0L Multi Port Fuel Injection, VIN M
87-90 5.0L Carb, VIN Y
87-91 2.0L Throttle Body Injection, VIN K
88-89 2.3L Multi Port Fuel Injection, VIN D
88-89 3.1L Multi Port Fuel Injection, VIN T
88-89 4.5L VIN 5
88-90 3.8L VIN C
88-93 5.0L Throttle Body Injection, VIN E
89 2.0L Throttle Body Injection, VIN 1
89 2.3L Multi Port Fuel Injection, VIN A
89 3.1L Multi Port Fuel Injection, VIN V
89 5.7L VIN 8
89-90 5.7L Throttle Body Injection, VIN 7
89-95 5.7L VIN K
89-91 2.5L Throttle Body Injection, VIN R
89-91 3.3L Multi Port Fuel Injection, VIN N
90 2.3L Multi Port Fuel Injection, VIN D
90 2.3L Multi Port Fuel Injection, VIN A
90 3.8L VIN L
90 4.5L VIN 3
90 5.7L VIN J
90-91 2.2L Throttle Body Injection, VIN G
90-91 3.1L Multi Port Fuel Injection, VIN V
90-91 5.0L VIN F
90-91 5.7L VIN 8
91 2.3L Multi Port Fuel Injection, VIN D
91 2.3L Multi Port Fuel Injection, VIN A
91 3.8L VIN C
91 3.8L VIN L
91 4.9L VIN B
91 5.7L Throttle Body Injection, VIN 7
91 5.7L VIN J
91-92 1.9L Throttle Body Injection, VIN 9
91-92 1.9L Single Port Fuel Injection, VIN 7
91-92 3.4L Multi Port Fuel Injection, VIN X
92 2.0L Multi Port Fuel Injection, VIN H
92 2.2L VIN 4
92 2.3L Multi Port Fuel Injection, VIN D
92 2.3L Multi Port Fuel Injection, VIN A
92 2.3L Multi Port Fuel Injection, VIN 3
92 2.5L Throttle Body Injection, VIN R
92 5.0L VIN F
92 5.7L Throttle Body Injection, VIN 7
92 5.7L VIN J
92 5.7L VIN 8
92-93 3.3L Multi Port Fuel Injection, VIN N
92-93 3.8L general & Supercharged
92-93 4.3L Throttle Body Injection, VIN Z
92-93 4.9L VIN B
92-93 5.7L VIN P
92-95 3.8L VIN L
93 2.0L Multi Port Fuel Injection, VIN H
93 2.2L VIN 4
93 2.3L Multi Port Fuel Injection, VIN D
93 2.3L Multi Port Fuel Injection, VIN A
93 2.3L Multi Port Fuel Injection, VIN 3
93 2.5L VIN A
93 3.1L Fuel Injection, VIN T
93 5.7L Throttle Body Injection, VIN 7
93 5.7L VIN J
93-94 1.9L Throttle Body Injection, VIN 9
93-95 1.9L VIN 7
93-95 3.4L VIN X
93-95 3.4L VIN S
93-95 4.3L VIN W
93-95 4.6L VIN Y
93-95 4.6L VIN 9
94 2.0L Multi Port Fuel Injection, VIN H
94 2.2L VIN 4
94 2.3L Multi Port Fuel Injection, VIN D
94 2.3L Multi Port Fuel Injection, VIN A
94 2.3L Multi Port Fuel Injection, VIN 3
94 3.1L Multi Port Fuel Injection, VIN T
94 5.7L VIN P
94-95 3.1L VIN M
94-95 4.3L VIN Z
94-95 4.9L VIN B
94-95 5.7L VIN J
94-95 6.5L 6.5 Diesel
95 1.9L Throttle Body Injection, VIN 8
95 2.2L VIN 4
95 2.3L Multi Port Fuel Injection, VIN D
95 5.7L VIN P
96 5.7L VIN P OBDII
96 5.7L VIN 5 OBDII
96 6.5L 6.5L Diesel
97 6.5L 6.5L Diesel

GM Generic Codes
Without Onboard Diagnostics (OBD-II)
12 Diagnostic mode 44 O2 sensor (lean exhaust)
13 O2 sensor or circuit 45 O2 sensor(exhaust rich)
14 coolant sensor/high temp 46 vehicle anti-theft system
15 coolant temp/low temp 47 air condition clutch and cruise circuit
16 system voltage high (3.8L) DIS circuit 51 PROM, MEM CAL or ECM problem (3.1L)
17 crank signal circuit
ECM fault crank position sensor circuit (3.8L)
52 CALPK or ECM problem (3.1L)
18 crank signal circuit
ECM fault injector circuit (vin P-5.7L)
53 system overvoltage
EGR system (carb models)
alternator out of range

19 fuel pump circuit(shorted)
crank position sensor(88-91)
54 fuel pump circuit
EGR fault (3.8L)

20 fuel pump circuit (open) 55 O2 sensor or ECM
21 TPS circuit 56 vacuum sensor Quad drvier B (3.8L)
22 TPS out of adjustment 58 Trans code-TTS temp high
21/22 grounded WOT circuit 59 Trans code-TTS temp low
23 MAT circuit
IAC sensor (95 models)
61 O2 sensor signal faulty
24 vehicle speed sensor 63 MAP sensor voltage high
25 MAT circuit 64 MAP sensor voltage low
RH side O2 sensor lean

26 Quad driver circuit
Throttle switch shorted
65 RH side O2 sensor rich
27 throttle switch open 66 3-2 Control solenoid circuit fault(4L60-E)
A/C pressure sensor circuit out of range

28 Transmission range pressure switch 67 TCC solenoid circuit (4L60-E)
31 park/neutral switch
cam sensor circuit
EGR circuit (88-90)
MAP sensor (shorted)
68 O/D ratio error (4L80-E)
32 BARO sensor circuit(carb models)
EGR circuit(injected models)
MAP sensor(open)
69 TCC stuck on (4L60-E &4L80-E)
A/C head pressure switch circuit

33 MAP sensor(low vacuum)
MAF sensor
MAP sensor(voltage high)
72 VSS circuit loss transmission output signal
34 MAP sensor(voltage low)
MAF sensor
73 trans pressure control solenoid
35 IAC valve or circuit
idle speed control circuit(shorted)
74 Trans input speed error (4L80-E)
36 MAF sensor
DIS system(quad 4)
transaxle shift control (3.8L)
75 system voltage low
37 MAT sensor temp high (3.8L)
brake switch(4L60-E trans)
79 Transmission fluid temp high
38 brake input circuit
MAT sensor temp low(84-86)
81 transmission 2-3 error
39 TCC knock sensor shorted(4.3L)
82 transmission 1-2 error
40 power steering pressure switch 83 TCC solenoid circuit fault
41 faulty ignition module cam sensor (3.8L) 85 undefined gear ratio
42 EST circuit 86 low gear ratio error
43 ESC circuit
knock sensor signal
87 high gear ratio error
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Tuesday, May 17th, 2011 AT 7:04 PM
Tiny
JASON.BLAKE1
  • MEMBER
So how do I check the ecu
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Tuesday, May 17th, 2011 AT 7:09 PM
Tiny
WRENCHTECH
  • EXPERT
There is no good way to get solid confirmation on an ECU. All you can do is confirm all the inputs and outputs to be problem free.
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Tuesday, May 17th, 2011 AT 7:16 PM
Tiny
JEFFJ
  • MEMBER
WOULD THE "TAP TEST" WRENCHTECH TO HELP THIS GENTLEMAN?
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Tuesday, May 17th, 2011 AT 8:02 PM
Tiny
WRENCHTECH
  • EXPERT
There's a small chance it might. Give it a try. With the engine running, tap on the ECM and see if it responds in any way.
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Tuesday, May 17th, 2011 AT 8:09 PM
Tiny
JASON.BLAKE1
  • MEMBER
Nope didnt work not realy wanting to throw 200 dollars at it in the dark
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Tuesday, May 17th, 2011 AT 9:00 PM
Tiny
WRENCHTECH
  • EXPERT
Nobody does. You can always pay a shop a couple hundred in diagnostic time and still not be any more sure than you are not.
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Tuesday, May 17th, 2011 AT 9:04 PM
Tiny
HMAC300
  • EXPERT
If this is a TBi unit spray choke cleaner around the base of the tbi. If the rpm changes or engeine smoothes out replacethe base gasket as they tend to burn out and cause rough running, etc. Also check the ose going to the map sensor as it gets soft and trys to konck out the map sensor.
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Monday, June 6th, 2011 AT 11:30 PM
Tiny
WRENCHTECH
  • EXPERT
Sure, those are common problems with that vehicle but nothing to do with the ECM failure codes stored.
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Monday, June 6th, 2011 AT 11:35 PM

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