2002 LM7 Swap - No Start - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ole Greenie · 07-31-2015, 02:03 PM

Guys, I'm hoping to gain a bit of help for a no-start condition I have on a swap I am doing in my 70 CST. Fuel pump is fine. I get plenty of gas to the rails. I have removed and replaced the injectors as the original ones were clogged. Next, I poured a bit of gas into the intake...not even a sputter. Then, I removed a spark plug...no spark. I'm inclined to think that the ECU isn't sending a signal. All wiring from custom harness is connected to the correct sensor/bank. No spark.

Any info is much appreciated!

cableguy0 · 07-31-2015, 07:30 PM

Was the computer reprogrammed? Are the injectors firing? Sounds like vats wasn't disabled.

Also Im going to move this to the LS section for you to get some more responses.

**truckdude239** · 07-31-2015, 08:06 PM

Try running a ground wire to the ecm case and see what it does.

ls1nova71 · 07-31-2015, 10:28 PM

Check your grounds in the harness and make sure they are clean and tight. If VATS isn't disabled it should start and die. In an original harness there are two grounds at the rear of both heads, and one up front down low behind the power steering pump, this is the one that controls the coils.

Ole Greenie · 08-02-2015, 06:05 PM

Okay, I did a bit more checking...
1) I checked all the grounds...GTG
2) I checked the power lead to PCM and the accessory wire too. I found that the PCM requires a continual 12V for ACC wire through the cranking cycle. There is no where on the OEM fuse block that can supply 12V from ACC to Cranking and then back.

I managed to connect a switch to 12V. Essentially, I'll flip it on when I want to start the engine.

Is there a wire location and color, that is original to the truck that I can tap into that would provide this signal?

BTW, This thing runs awesome. New cam, DT headers, no cats...you know the deal.

**dayj1** · 08-02-2015, 09:33 PM

Quote:

Originally Posted by Ole Greenie

Is there a wire location and color, that is original to the truck that I can tap into that would provide this signal?

I always use the wire that originally powered the distributor. It is hot when the switch is in the "Crank" position.

EDIT: I should mention that if the wire mentioned above was powering a points type distributor before the engine swap, it is probably a resistance wire and should be changed for a "regular" wire to get the full 12V that you need.

ls1nova71 · 08-03-2015, 03:21 PM

Quote:

Originally Posted by dayj1

I always use the wire that originally powered the distributor. It is hot when the switch is in the "Crank" position.

EDIT: I should mention that if the wire mentioned above was powering a points type distributor before the engine swap, it is probably a resistance wire and should be changed for a "regular" wire to get the full 12V that you need.

I use this wire also, to power the LS harness ignition wires, but the two orange constant hots cant be put on a toggle switch that you flip to start the truck, they are what keep the memory in the PCM. Just hook them up to either the battery or the junction block (with a fuse of course) that is hot all the time.

Ole Greenie · 08-03-2015, 07:24 PM

Thanks Folks!

07-31-2015, 02:03 PM	#1
Ole Greenie Registered User Join Date: Apr 2010 Location: Hagerstown, MD Posts: 246	2002 LM7 Swap - No Start Guys, I'm hoping to gain a bit of help for a no-start condition I have on a swap I am doing in my 70 CST. Fuel pump is fine. I get plenty of gas to the rails. I have removed and replaced the injectors as the original ones were clogged. Next, I poured a bit of gas into the intake...not even a sputter. Then, I removed a spark plug...no spark. I'm inclined to think that the ECU isn't sending a signal. All wiring from custom harness is connected to the correct sensor/bank. No spark. Any info is much appreciated! __________________ John Paap Ole Greenie Hagerstown, MD My Mistress 70 CST Short/Step LS 5.3/4L65E New motor install Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=667773

07-31-2015, 07:30 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: 2002 LM7 Swap - No Start Was the computer reprogrammed? Are the injectors firing? Sounds like vats wasn't disabled. Also Im going to move this to the LS section for you to get some more responses. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

07-31-2015, 08:06 PM	#3
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,238	Re: 2002 LM7 Swap - No Start Try running a ground wire to the ecm case and see what it does. __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

07-31-2015, 10:28 PM	#4
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: 2002 LM7 Swap - No Start Check your grounds in the harness and make sure they are clean and tight. If VATS isn't disabled it should start and die. In an original harness there are two grounds at the rear of both heads, and one up front down low behind the power steering pump, this is the one that controls the coils. __________________ 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

08-02-2015, 06:05 PM	#5
Ole Greenie Registered User Join Date: Apr 2010 Location: Hagerstown, MD Posts: 246	Re: 2002 LM7 Swap - No Start Okay, I did a bit more checking... 1) I checked all the grounds...GTG 2) I checked the power lead to PCM and the accessory wire too. I found that the PCM requires a continual 12V for ACC wire through the cranking cycle. There is no where on the OEM fuse block that can supply 12V from ACC to Cranking and then back. I managed to connect a switch to 12V. Essentially, I'll flip it on when I want to start the engine. Is there a wire location and color, that is original to the truck that I can tap into that would provide this signal? BTW, This thing runs awesome. New cam, DT headers, no cats...you know the deal. __________________ John Paap Ole Greenie Hagerstown, MD My Mistress 70 CST Short/Step LS 5.3/4L65E New motor install Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=667773

08-03-2015, 07:24 PM	#8
Ole Greenie Registered User Join Date: Apr 2010 Location: Hagerstown, MD Posts: 246	Re: 2002 LM7 Swap - No Start Thanks Folks! __________________ John Paap Ole Greenie Hagerstown, MD My Mistress 70 CST Short/Step LS 5.3/4L65E New motor install Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=667773



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