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peterpete190, GMC Mechanic
Category: GMC
Positive Feedback: 97.4 %
Satisfied Customers: 11219
Experience: GM training and dealer tech for 14+ years. Diagnostics
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GMC 1500 suburban: I have replaced the cam sensor, crank sensor,

Customer Question

I have replaced the cam sensor, crank sensor, rotor button , distributor cap, coil, ignition module. all one at a time and it runs perfectly after each fix for several hours, then when you cut it off it wont start for two days. No spark. I tested the leads going to coil when I replaced it. I thought the two out side wires were both hot. The module had one hot lead on the left end of connector. Now when I check the wires going into the coil only one is hot, and one on the module, this is with key in the run position. Are the two wires going into the coil suppose to be hot continously with key on? Module also ? Where does their power come from does it originate in the pcm on the fender well?

Submitted: 1 year ago.
Category: GMC
Expert:  peterpete190 replied 1 year ago.

Hello,I will be glad to try and assist you with this,Welcome to Just Answer.

Hi.

I just need a little more info to assist better.

Do you have a multi meter/voltmeter for testing voltage or are you using a test light to test these wires?

Let me know so we can continue,Thanks Pete!

Customer: replied 1 year ago.

I was using a test light to test the wires going to the coil and the module, but I do have a multimeter.I am not near the vehicle at this time I'm at work.

Expert:  peterpete190 replied 1 year ago.

O.k.

When you can get to your vehicle for some testing with the multi meter let me know and I will tell you what to test so we can locate the faulty component here.

Thanks Pete!

Customer: replied 1 year ago.

I just got home and its too dark out to work on the truck I tried clicking on the accept and it wouldn t click . i'll have to try you again tommorrow afternoon sorry. I wasnt able to get to it sooner thank you.

Expert:  peterpete190 replied 1 year ago.

Not a problem,come back when you are ready and I can assist more.

Thanks Pete!

peterpete190, GMC Mechanic
Category: GMC
Positive Feedback: 97.4 %
Satisfied Customers: 11219
Experience: GM training and dealer tech for 14+ years. Diagnostics
peterpete190 and 12 other GMC Specialists are ready to help you
Customer: replied 1 year ago.

are you there

Expert:  peterpete190 replied 1 year ago.

O.k.

Probe terminal C at the coil connector with the connector disconnected,this is the white wire with black stripe.Connect your test light to battery positive cable and the other lead to terminal C.

Crank over the engine and see if the test light flashes.

Let me know,Thanks Pete!

Customer: replied 1 year ago.

the truck is running i have found that only one wire would light up the test light going to the ignighter that is when the engine has no spark currently there is juice in both terminals and the engine is at temperature and cranks up everytime i try it

Expert:  peterpete190 replied 1 year ago.

O.k.

The wire posted above needs tested when it wont start.If there is no flashing test light when it wont start when cranking over the engine then this is most likely the module at fault,since it has been replaced already most likely it is o.k. and if you have no spark and with all of the components you have replaced here this can be caused by a faulty computer or wiring from the computer to the module or from the module or to the coil.

Customer: replied 1 year ago.

thats the reason im asking you are you suggesting replacing the computer

Expert:  peterpete190 replied 1 year ago.

It is possible it is the computer but the only way we can find out is to test these wires when it isnt starting.

Customer: replied 1 year ago.

a continuity test on the white and black wire from the igniter to where . the only other variable is that when i drive it i have the intake system on it with the mas air flow and the intake air temp sensor hooked up why do i have to drive it for two hours to get it to quit and why does it have to sit for two days before it will crank again

Expert:  peterpete190 replied 1 year ago.

Are you sure you are losing spark when it wont start or are you losing injector pulses or fuel pressure or have these been checked when it wont start?

Customer: replied 1 year ago.

it is definetly no spark also when it wouldnt crank the black and white wire going to the igniter module was dead now it is hot. where does that wire go from there does it go to the puter

Expert:  peterpete190 replied 1 year ago.

You should have two black and white wires at the module.

One is white with a black stripe this is a pulsed ground signal when the engine is cranked over and when running.This leads from the ignition module to the coil.

The other wire is a black wire with a white stripe.This should be a solid ground at all times,key on or off.

Customer: replied 1 year ago.

I have four wires going into the ignition module pink, black and white, white and black,what and one appears to be mostly black, three going to the coil pink , black and white, and white and black

 

 

Expert:  peterpete190 replied 1 year ago.

Pink is power from the ECM 1 fuse in the under hood fuse box,it should have power with the key on and engine running.

The white with black stripe is the pulsed ground signal that is fed from the module to the coil.

The black with white stripe is ground at all times,this wire supplies ground to the module.

The other wire is the white wire(it may be black) and is controlled by the computer to pulse the coil,so this wire is fed from the computer to the module.It will pulse when the computer sees correct crankshaft and camshaft signals,this looks to be a varying voltage signal when cranking and running.If this signal is missing then this may be the computer itself at fault.

These wires do need tested when the vehicle wont start.

Customer: replied 1 year ago.

I just cut it off and it wont start

Expert:  peterpete190 replied 1 year ago.

O.k.

Test the pink wire for power with the key on,the black wire with white stripe for ground at all times and see if you have a ground pulse with your test light connected to the battery positive and the other end connected to the white wire with black stripe,see if the test light flashes.If it doesn't we know the module is o.k. as it has been replaced so this means the computer itself has an internal fault and needs replaced.

Customer: replied 1 year ago.

and it spit out a 1351 code on the scanner

Expert:  peterpete190 replied 1 year ago.

O.k.

This fault code is for the ignition system at fault which we know as it has no spark,it can lead to a faulty ignition module,faulty coil,faulty crank sensor or a faulty computer.All of these have been replaced except for the computer.Most likely the fault is either in the computer itself and needs replaced or the wiring from the computer to the ignition module.Check the wiring at the computer and module and make sure it is o.k. as well as the connections at these two components.If the wiring is o.k. then the computer most likely needs replaced.

Customer: replied 1 year ago.

Im looking at the computer it has four terminal connections with multiple wires top bottom left right

Expert:  peterpete190 replied 1 year ago.

You will have to check all wires and connections at the computer.

Customer: replied 1 year ago.

i was hoping it would be one harness or another,can I test the module now with the multimeter and eliminate 99% it being the cause factory defect maybe

Expert:  peterpete190 replied 1 year ago.

You can test the wiring as posted above,if you have all signals to the module except the white wire with black stripe isn't giving you a ground pulse when cranking the engine then the module is faulty.

If you are missing the fluctuating voltage signal at the white wire to the module while cranking then most likely the computer is at fault.

Customer: replied 1 year ago.

im still at it give me a few more minutes

Customer: replied 1 year ago.

I would like to click accept

Expert:  peterpete190 replied 1 year ago.

You already have once and don't need to again,you can leave a bonus/tip if you want by locating the accept you clicked on above and clicking on it again to leave a bonus,this choice is up to you and isn't required.

Thanks Pete!

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