lq4 swap ran but now no spark/start issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**cdub2010** · 05-20-2018, 03:35 PM

My 5.3 swap went fine, I have had it running and driving in the driveway. Did a little paint work on the rear frame and pulled it back in the shop. It stopped running, now it has a no start issue. No check engine light at start like it used to, it cranks but has no spark. I have fuel at the rail and sprayed starting fluid in the manifold still no start. Pulled plug confirmed no spark. Brand new PSI harness and computer were used. 12+ volts at the battery, drops to 10.5 voltage when cranking. Where else to look?

ls1nova71 · 05-21-2018, 02:20 AM

Check to make sure all your fuses are good and also check to make sure all your grounds are clean and tight. Sounds like wiring issue to me and these are the two main culprits.

davepl · 05-25-2018, 11:08 AM

Can you confirm you're seeing 10.5v or better at the pink IGN trigger line going to the ECM? The one that tells it the car is ON (as opposed to the main battery connection)?

**cdub2010** · 05-30-2018, 07:38 PM

Turns out the ground on the cylinder head was a tiny bit loose. I checked them all over and over but just a half turn on the bolt and she fired right up again. Crazy how finicky it is. Also found out my front headlight harness is crap as well. Gotta love these things.

Rich84 · 05-31-2018, 10:30 AM

The simplest things sometimes...Glad you got it sorted out.

05-20-2018, 03:35 PM	#1
cdub2010 Senior Member Join Date: Apr 2014 Location: detroit mi Posts: 209	5.3 swap ran but now no spark/start issue My 5.3 swap went fine, I have had it running and driving in the driveway. Did a little paint work on the rear frame and pulled it back in the shop. It stopped running, now it has a no start issue. No check engine light at start like it used to, it cranks but has no spark. I have fuel at the rail and sprayed starting fluid in the manifold still no start. Pulled plug confirmed no spark. Brand new PSI harness and computer were used. 12+ volts at the battery, drops to 10.5 voltage when cranking. Where else to look? Last edited by cdub2010; 05-20-2018 at 05:21 PM.

05-21-2018, 02:20 AM	#2
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: lq4 swap ran but now no spark/start issue Check to make sure all your fuses are good and also check to make sure all your grounds are clean and tight. Sounds like wiring issue to me and these are the two main culprits. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

05-25-2018, 11:08 AM	#3
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: lq4 swap ran but now no spark/start issue Can you confirm you're seeing 10.5v or better at the pink IGN trigger line going to the ECM? The one that tells it the car is ON (as opposed to the main battery connection)? __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

05-30-2018, 07:38 PM	#4
cdub2010 Senior Member Join Date: Apr 2014 Location: detroit mi Posts: 209	Re: lq4 swap ran but now no spark/start issue Turns out the ground on the cylinder head was a tiny bit loose. I checked them all over and over but just a half turn on the bolt and she fired right up again. Crazy how finicky it is. Also found out my front headlight harness is crap as well. Gotta love these things.

05-31-2018, 10:30 AM	#5
Rich84 Registered User Join Date: Mar 2012 Location: Woodbury, Ct. Posts: 1,693	Re: lq4 swap ran but now no spark/start issue The simplest things sometimes...Glad you got it sorted out.



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