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

10,455

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 of 1 people found this helpful.
10,455

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 of 1 people found this helpful.
10,455

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 of 2 people found this helpful.

Your Answer

Add photo

Related Questions

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 68,232 nationwide Sierra 1500 listings starting at $1,800.

ZIP:

Search GMC Sierra 1500 Questions

GMC Sierra 1500 Experts

#1 dragonflyoffshore
dragonflyoffshore
Reputation 5,270
#2 John Saffrahn
John Saffrahn
Reputation 3,640
#3 Glenn Clingenpeel
Glenn Clingenpeel
Reputation 3,330
View All

Related Models For Sale

Used Chevrolet Silverado 1500
1,933 Great Deals out of 182,800 listings starting at $999
Used Ford F-150
2,090 Great Deals out of 191,495 listings starting at $290
Used GMC Sierra 2500HD
128 Great Deals out of 12,723 listings starting at $2,185
Used Toyota Tundra
449 Great Deals out of 34,299 listings starting at $1,950
Used Dodge Ram 1500
405 Great Deals out of 10,893 listings starting at $1,000
Used Ram 1500
925 Great Deals out of 112,963 listings starting at $5,386
Used Toyota Tacoma
562 Great Deals out of 42,402 listings starting at $1,995
Used GMC Yukon
439 Great Deals out of 20,487 listings starting at $1,495
Used Chevrolet Silverado 2500HD
301 Great Deals out of 28,747 listings starting at $2,995
Used Chevrolet Tahoe
598 Great Deals out of 33,202 listings starting at $1,375
Used Ford F-250 Super Duty
326 Great Deals out of 43,870 listings starting at $1,450
Used GMC Canyon
98 Great Deals out of 11,941 listings starting at $3,500
Used Chevrolet Camaro
377 Great Deals out of 31,277 listings starting at $2,500
Used Chevrolet Colorado
246 Great Deals out of 27,748 listings starting at $1,000
Used Nissan Titan
174 Great Deals out of 18,907 listings starting at $3,995

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.