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Wiring question
04-09-2016, 04:49 PM
Post: #1
Wiring question
Hello, I just finished rebuilding the heads off a 1991 chevy G20 5.7 and I have hit a wall. I cannot get it to start. She turns over, gets fuel and spark but wont actually fire up. TDC set, distrubutor rotor reset, all wire harnesses accounted for save for a white lead off the ignition coil that shortly ends in a harness. Research tells me its either useless or goes to the tac. What concerns me is that in the main wire harness there is a pair of wires still homeless(black with white stripe and a solid tan). What are they and are they the source of my problem? Did I forget something in the rebuild process? Do I need to score my ignition system with a wire tester?
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04-09-2016, 11:54 PM
Post: #2
RE: Wiring question
Don't recall all of the wire colors but the most common mistakes are forgetting to plug in the ignition module next to the coil. (each has it's own plug) The next item that comes to mind is the ground wire that goes on the T-stat housing bolt. (ground for the fuel pump relay?) The last is that you don't have the distributor in correctly at TDC.

I only mention the distributor because there are two timing marks on the front pulley. One lines up with the conventional spot on the timing cover between 1-2 o'clock (almost impossible to see on a van) and the other lines up with a casting mark on the cover between 4-5 o'clock, which is very east to spot with a drop light.

The last, and biggest pain, is there's a slight possibility the engine may have jumped time on the cam chain. You didn't say how many miles are on this thing but it's common enough to happen during big jobs and no way to really predict it in advance.
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04-10-2016, 08:38 AM (This post was last modified: 04-10-2016 08:42 AM by 1991G20.)
Post: #3
RE: Wiring question
She's got 200K something. I can't see any other wires on the engine that aren't hooked up though. It's definetly an hei distrubutor with a remote coil and I'm concerned something isn't grounded right. I already burned up 1 coil Smile My ignition module is on the distibutor, both harnesses back on. Should I grab a tester and just scoure my entire ignition system?

Thanks for the feedback!
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04-10-2016, 10:23 AM
Post: #4
RE: Wiring question
You said that it has spark, right? You checked for this at the plugs? If it has spark at the plugs I would guess that the ignition wiring isn't the problem. Either the timing is 180 degrees out, the fuel pressure is too low, or; as Rupe mentioned, the cam timing is out. I would check for 180 out and proper firing order first. They are the easiest to check and the most common mishap. I have been doing mechanic work for over 30 years and I have still made both of those mistakes. I don't even waste time telling myself that it's correct, I just double check it. 9 times out of 10 when someone else calls me to figure out a similar problem I find that they have a problem with the firing order. You have to know which way the distributor turns, where number one is, and what the correct firing order is. 180 out is also an easy mistake. You reach TDC twice in a single cycle of the engine. You have to be on #1 on the compression stroke, not the exhaust stroke. You may have to lift the distributor and turn it 180 degrees?

I don't know your skill level or understanding of how things work so I don't know how "in depth" to go on explaining? If you need more details, just ask. Also, if you figure it out, please let us know what you found as it could help others.

Thanks for using the forum,
Garner

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04-10-2016, 10:28 AM (This post was last modified: 04-10-2016 10:34 AM by 1991G20.)
Post: #5
RE: Wiring question
Yeah, I checked TDC compression and distributor a dozen times. Firing order 18436572 clockwise. I tried firing it up with and without the EST harness hooked up. The motor has backfired too.

I took the valve covers back off and was going to tune my valve and do final timing adjustments at the same time. Took out plugs to see if i could turn the crank by hand, which i could not. Did a few quick cranks with ignition disabled and was rewarded with my timing mark right at my timing plate.

Tomorrow after work I'll pull my cap off the DST and spin the rotor 180 just to be sure. What if it's a fuel problem? She has been parked since Dec.
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04-10-2016, 10:40 AM
Post: #6
RE: Wiring question
OK, if the motor backfired that would still indicate that it's not a wiring problem. You must have spark for it to backfire. If it were me doing the job, I'd probably just turn the distributor 180 to check it since it's so easy to do. Possibly give it a shot of starting fluid just to see if there is a fuel issue? Proper fuel pressure needs to be checked with a gauge. Just a couple of pounds low can cause the engine not to start.

Please keep us posted on your findings.

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Garner

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04-10-2016, 10:43 AM
Post: #7
RE: Wiring question
Oops, didn't see that you modified your post. Looks like you're already on the right track.

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Garner

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04-10-2016, 10:44 AM (This post was last modified: 04-10-2016 10:46 AM by 1991G20.)
Post: #8
RE: Wiring question
I will. The snow has returned unfortunatly, but when I get out of work tomorrow (3rd shift) i'll spin the Dst and pick up a can of starting fluid. Question though; if I so that and its not right either it's not going to explode in my face or anything will it? Smile

I will also take off my fuel lines at the carb and make sure they're clean, it's also RIGHT THERE and only take a minute. Got olent of carb clean laying around.
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04-10-2016, 10:52 AM
Post: #9
RE: Wiring question
You want to just give it a little shot of starting fluid, enough to see if it will just fire up for a second or two. If you are in the car turning the ignition, you should be safe. If you have a helper turning the ignition, give it a shot before the key is turned and back up. If it backfires you can just keep cranking and suck the flames back down the intake. Or keep a large, damp towel handy to smother the flames. It's usually not an issue but you are very wise to use caution and common sense.

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Garner

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04-10-2016, 10:54 AM
Post: #10
RE: Wiring question
Carb? I thought that engine was fuel injection?

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Garner

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