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GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
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1988 GMC: correct firing order..changing..distributor cap..spark plugs

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How do I find the correct firing order for my 1988 GMC Sierra 2500? My wires got crossed up while changing the distributor cap. The wires to the spark plugs are correct. Is this the correct firing order 1-8-4-3-6-5-7-2? The wires are connected to the distributor cap in this order. Number one being in the 6 o'clock position.

I can't get it started. is there a secret to getting them aligned correctly.

And yes, I scolded my son for screwing this up, but it wasn't his fault. I did it and I know better!
Welcome. The firing order is indeed 18436572, but the #1 is at the 4 oclock position if the water pump is at the 6 oclock position and the rotation is clock wise.
GM Tech (Cam) and 4 other GM Specialists are ready to help you
Customer: replied 8 years ago.
I will get back to shortly. Thank you for your quick reply. I hope you're not laughing at me to hard.

Don't worry, we all make mistakes, that is what makes us human!!!

Customer: replied 8 years ago.
If I understand you correctly, #1 is at the o'clock position. Should #8 be at the 6 o'clock position?
Basically yes. In teh picture I posted, the solid white dot on the distributor is #1. Also I should have said more like 5 oclock and #8 just past 6.
Customer: replied 8 years ago.
It's still not starting. The gas is getting there, but it's kin of coughing.
Is it flooded now from trying the other way? Try holding your foot to the floor when cranking.
Customer: replied 8 years ago.
O.K., flames just shot up from the carborator. It still won't start. I really appreciate your knowledge.
Ok, your wires are still off. Take the #1 plug out then turn the engine with a wrench until to feel compression in that hole. Move the crank even more until the timing XXXXX XXXXXnes up with the mark on the front cover. Then take the distributor cap off and see the exact terminal the rotor is pointing to. That is #1. Put the wire from there to #1 and work your way around again checking each and every wire.
Customer: replied 8 years ago.
Please explain a little more. (Take the #1 plug out then turn the engine with a wrench until to feel compression in that hole. Move the crank even more until the timing XXXXX XXXXXnes up with the mark on the front cover. Then take the distributor cap off and see the exact terminal the rotor is pointing to.)

The rest I understand.

WE need to verify the exact position of the rotor in the distributor when the engine is at #1 cylinder top dead center. Turning the engine with a wrench with the #1 plug out and feeling for compression with your finger as you turn the engine with the wrench will help you find the compression stroke on the #1 cylinder rather than the Exhaust stroke.

There is a notch in the timing cover and a line on the harmonic balancer that lines up with the notch for the timing marks.

Customer: replied 8 years ago.
I understand now, but how do I turn the enging with a wrench? can you send a diagram?
There is a bolt in the center of the harmonic balancer. Find a socket that size and use a ratchet. I should have said ratchet, not wrench, sorry.
Customer: replied 8 years ago.
Hello again, I apologize, I didn't follow the instructions you gave me. I have no idea where to find the harmonic balancer on my vehicle.

Could I some how replaced my rotor incorrectly? The vehicle started with no pronlem prior to me changing it. I lined-up the groves in the new rotor to the groves on the post. Did i do this wrong?

If I knew where the harmonic balancer was, I would give it a shot.


It is very likely something is installed wrong and the rotor is one, but if you lines it up properly and the rotor went into place, then I doubt it.

The harmonic balancer is the large round pulley at the bottom of the engine that the belt runs on.

Customer: replied 8 years ago.
I will get on it now. Thanks
You are welcome.
Customer: replied 8 years ago.
I have tried what you have suggested. I got under the truck to access the harmonic balancer with a ratchet, but this pulley won't budge. I can't get a pipe on the ratchet to assist me. (terrible mechanic)
It should not take much to turn this pulley. YOu may try a ratchet on the alternator. It usually slips in one direction but should turn in the other.
Customer: replied 8 years ago.
I have turned the the alternator and placed my finger in the #1 spark pug hole. I felt the pressure blow on my finger. I stopped turning and removed the rotor cap. The rotor was pointing to the #7 position at approx. 1 o'clock.

I didn't move anything yet. I am a little confused about the spark plug gap. I set them to 00.35. My confusion is in my Chilton truck book it says 00.45 for my model. Is this correct?

My VIN #2GTFC29K8J1559917

If this does not work, I'm going to shoot it.
OK, when it shot your finger out, did you continue to turn until the mark on the balancer lined up with the mark on the front cover?
Customer: replied 8 years ago.
Nope! doing it now.
OK, you are close, I would guess 1/4 turn or less.
Customer: replied 8 years ago.
There is a mark on the harmonic balancer and I aligned it with the most prominant indicator on the dial. The rotor lined up with #1. I had to turn it serveral time with the ratchet to get it there.
OK, so the crank only turned about 1/4 to 1/2 turns. So we now know where #1 is. Make sure the wire goes to #1 and check the wires working clockwise.
Customer: replied 8 years ago.
I did. All of the wires are in the correct positon. There was a old mechanic here today and just looked at the wiring. He said that the wiring was correct. That's as far as it got with him, he was here for another porpose. I just double checked again, they're correct.
OK, then there should be no reason this does not start. You have the wires to the proper positions, and you have the wire from the coil to the center of the distributor so it should work. What brand of cap did you buy?
Customer: replied 8 years ago.
OK, I would try putting the old cap back on and see if it starts. This may be a bad cap.
Customer: replied 8 years ago.
O.K. I will do it now.
OK, I look forward tot he results.
Customer: replied 8 years ago.
No go. I have rechecked everything over and over. I don't know what else to do. I want to say thank you for helping me I really appreciate what you do. Thanks.
YOu are welcome. At the moment I must say that I am sorry we have not got your engine running. I suspect there has to be something simple we have missed. Is your mechanic friend able to come over and have a peak at it? Second set of eye so to speak?
Customer: replied 8 years ago.
He was not a friend, he was the water meter reader. I will see if I can reach him.