What tells the computer when to fire on a TBI w/no crankshaft sensor

10

Asked by Feb 20, 2014 at 10:54 AM about the GMC Sierra 1500

Question type: Maintenance & Repair

Distributor has no points. Timing light shows the firing is all over the place,It looks like a
two inch band from about zero to 8 deg. plus BTDC. It's a 1994. It's the model before you
could use the hand held diagnostic computer.

3 Answers

11,615

K here is the rundown. In the distributor there is a pick-up coil under the plate on the shaft that has two wires and is plugged into the ICM (Ignition Control Module). The ICM is plugged into the coil and back to the ECM. The pick-up coil detects the engine rotation. The ICM takes this signal and uses it to control the spark -> it also sends signal back to the ECM as the RPM input. The computer uses the data for fueling. The ECM sends the spark advance/retard signal back to the ICM for proper spark under the current engine condition. On a side note the ECM will note spray fuel untill it sees ~400 rpm!

1 people found this helpful.
11,615

You can scan codes and live sensor data from this truck and most other GM OBD1 vehicles with the right equipment. Of course shops and GM scanners can but with a 70 dollar cable and free software anybody can with a laptop. Look-up ALDL cable.

1 people found this helpful.
11,615

I would change the ICM first. #5 on my '92. Make sure you use the supplied heat sink compound between the module and the baseplate or get some to use. Or it will cook quickly, yes one of the 5.

2 people found this helpful.

Your Answer:

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 60,847 nationwide Sierra 1500 listings starting at $1,395.

ZIP:

GMC Sierra 1500 Experts

  • #1
    dragonflyoffshore
    Reputation
    5,600
  • #2
    John Saffrahn
    Reputation
    3,890
  • #3
    Glenn Clingenpeel
    Reputation
    3,720
View All

Related Models For Sale

Used Chevrolet Silverado 1500
1,755 Great Deals out of 153,126 listings starting at $1,000
Used Ford F-150
2,231 Great Deals out of 209,289 listings starting at $1,300
Used GMC Sierra 2500HD
143 Great Deals out of 17,369 listings starting at $2,999
Used Toyota Tundra
455 Great Deals out of 39,340 listings starting at $2,700
Used Ram 1500
901 Great Deals out of 121,353 listings starting at $3,900
Used Chevrolet Silverado 2500HD
378 Great Deals out of 30,129 listings starting at $2,750
Used Dodge Ram 1500
320 Great Deals out of 9,389 listings starting at $1,500
Used Toyota Tacoma
405 Great Deals out of 47,516 listings starting at $2,994
Used Chevrolet Tahoe
525 Great Deals out of 37,767 listings starting at $1,250
Used GMC Yukon
324 Great Deals out of 21,404 listings starting at $2,450
Used Ford F-250 Super Duty
487 Great Deals out of 40,366 listings starting at $2,800
Used GMC Canyon
86 Great Deals out of 15,093 listings starting at $2,750
Used Chevrolet Colorado
261 Great Deals out of 40,191 listings starting at $1,999
Used Chevrolet Camaro
229 Great Deals out of 27,307 listings starting at $2,800
Used Nissan Titan
251 Great Deals out of 22,452 listings starting at $1,995

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.