Top 10 1990 GMC Sierra Questions & Answers

Is it getting fuel?
is it getting spark?


as for the code.........here is the code list for gm vehicles



Code: Meaning:
12
No Distributor pulses
13
Oxygen sensor
14
Coolant Temp sensor circuit
15
Coolant Temp sensor circuit
21
Throttle Position Sensor
22
Throttle Position Sensor
23
Manifold Air temperature sensor
24
VSS (Vehicle Speed sensor)
25
Manifold Air temperature sensor
32
EGR system
33
MAP sensor or MAF sensor depending on engine
34
MAP sensor or MAF sensor depending on engine
35
Idle Air Control Valve
36
MAF Burn-off circuit
41
No Distributor pulses, cylinder select error
42
Electronic Spark Timing or Bypass fault
43
Electronic Spark Control fault
44
Lean exhaust
45
Rich exhaust
46
VATS system fault
51
PROM fault
52
CALPAK fault
53
System over-voltage
54
Fuel pump circuit
55
ECM fault
61
Oxygen sensor fault (degraded sensor)

Call a tire dealership....Discount Tires, Costco, Firestone. It is free info and free is ALWAYS good! They are the professionals.

for the most part its the sending unit checkout all of you fuses and and if you can see if all the wires are in good shape on the top of the fuel tank i would also like to give you this information they sell only GM-parts its Schram auto & truck parts 1-800-292-1032 and they website is www.schramauto.com and i hope i have been some help to you Michigan Man

1-8-4-3-6-5-7-2 Distributor turns clockwise Number one should be in the 5 oclock position. You should be able to draw an imaginary straight line between the coil tower and number one tower on the cap and the number one spark plug.

This can be a simple loose connection or your fuel sending unit is bad which is located in the tank. the coolant temperature sender is usually located on the cylinder head or by the thermostat.

May want to look at replacing the wiper circuit board.It is located on the firewall adjacent to the wiper motor and has a some what square black cover with 3 torx screws and wireing harness pluged into the side.We had a truck that every time you washed it the wipers would stay on until it dryed out.You can try removing it and spaying it down with contact cleaner just watch the brease on the two contact tips.Well hope this helps.

Here is the firing order diagram for that vehicle and engine.

Generally these controls go bad and nothing works. They are an imported item GM uses of course. The electronics short circuit and go completely dead. Best to find a used one that works for new ones are expensive

Visit the on-line store, know as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem.
Best Manuals

Best Manuals

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To review, you have two temp sensors, one for the gauge on the dash and one for the computer. If you unplug the sensor for the computer the reading will be minus 30 degrees or over 300 which will make it very hard to start. Unplugging the sensor for the gauge would have no effect on the computer.
According to the wiring diagram, the wire for the temp gauge is green, and the wires for the temp sensor for the computer are yellow and black.