Ignition problem 98 Yukon SOLVED!

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redwing4900

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It looks like there are a few ignition issues popping up around the forum, here is mine. 98 Yukon 5.7L new spider injection, rebuilt engine with 32k miles on it, 210k total. It had new plugs wires and cap and rotor after the rebuild. I overheated the engine about a month ago because of a radiator leak. I replaced the radiator and it seemed to be ok until I noticed a hesitation especially in 4th gear at low rpm. It wouldn’t start one day later and I found the cap and rotor were VERY corroded. Replaced them both then it ran fine for a week. The hesitation came back, this time it was giving me a code for the module in the distributor I can’t recall the code or the part name (maybe cam position sensor). I went to change this sensor, and one of the bolts broke off so I had to remove the distributor completely to get at it. After I replaced the module, finding a part of the old rotor up I there, I was pretty sure that when I reinstalled the distributor, the alignment was correct, since it fell right in and I had lined it up the way it was (I thought), but when I went to start it the codes started flying and it wouldn’t run. It was about a month ago, I had a cylinder 5 misfire which I never had before, but I figured it was because of the extreme corrosion on the cap and rotor. Since I don’t want to go out and work on it in the blind, I figured I would bounce this latest issue off of the forum.
Do you think it could be the ignition module or engine ground Or something else? That’s where I figured I would start clean up the engine contacts, double check the timing make sure it’s correct. I was wondering if the overheat could have caused the wires to go bad, and figured I could change them and the plugs. Is 30,000 miles an appropriate time for changing wires and plugs? I thought they would last a little longer but maybe it’s time since the corroded cap may have caused some overload to them.
Sorry for the ramble, but I’m trying to include all that happened here. So what do you think? I will re test tomorrow and have some codes and pass along what I find.
Thanks
 

east302

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I’d start with getting the codes and going one by one on them.

You’ll need the CMP Retard set on the distributor. That usually trips the P1345 code and has to be reset when the distributor is removed. You’ll need a good scanner (GM Tech2, Snap-on, etc.) or a Bluetooth OBD adapter and an app (DashCommand or CarGaugePro) to read it. Spec is zero degrees (+/- 2) at 1,000 rpm.

To get it close, twist the distributor until the driver side screw tab is hitting the upper intake.

I’ve never had much luck with aftermarket caps, Delco is usually the way to go on them.

Swap the plug from 5 with another cylinder and see if the misfire moves. Repeat with the wire from #6, it’s probably the same length.

Also see what the #5 plug looks like.
 

Eman85

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Besides just dropping in did you mark the rotor position and distributor body position before removing? As stated you'll need a scan tool to set the CMP of the distributor.
For testing a suspected miss in the ignition the cheap fast fun and easy way is with a spray bottle of water. Have someone power brake the truck lightly to laod the engine and mist water around the plug wires. If you have a bad wire it will begin to miss. Also look at the plug porcelin, look for any carbon tracks or cracks. Look in the end of the wire in the spark plug boot, if it's black it's bad.
 
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redwing4900

redwing4900

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Great responses which I have come to expect From this forum, Thank you. I did mark distributor position which makes me suspect that may not be the problem. I will give the spray bottle a shot if I can get her running.
 

exp500

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If you are using a bluetooth OGD scanner, you need the "advanced options or GM Advanced PIDS" depending on which App you are using, some apps are paid $ for advanced.
 
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redwing4900

redwing4900

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I finally had some time today to look things over and found the pictures fuse blown that was in the ENG-I slot 20amp. I checked the timing and it appears correct now as it turns over without sputtering and coughing. Still no start. I have rechecked the previously blown fuse and it’s not blowing now. I’m going to check for spark now. Maybe the coil is bad? I don’t have a clear procedure for checking the coil for resistance. is there a way to check the cap? Maybe the new cap got overloaded? for resistance. Does anyone have that? The reason I ask about the cap check is because after I cleaned the corrosion off of the old one it wouldn’t work so I replaced it fired right up. Thank you
 

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exp500

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Put a spark tester in Coil and Dist Cap. test both for full hot spark.
These trucks hate cheap dist caps. burn holes in them. Use GM/Delco/ Delphi or United DCR-820x only.
Also in parts Use Only GM/Delco/Delphi - CPS, ICM, Coil. GM/Delco/ Ignition wires or better. NGK/Delco plugs.
Glad it's running!
 
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redwing4900

redwing4900

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Thank you for the response. I had an off brand cap before but this time it’s a Delco. It’s not running yet. Still working it out
 

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