LS2 402 swap - won't start
Thread Starter
Instructor
Joined: Mar 2009
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From: Mansfield Texas
LS2 402 swap - won't start
Hellp-
I'm doing a LS2 402 swap in my 98 A4 and finally finished it up tonight but it won't start. Here's what I checked so far:
- It sat for a bit so I pumped out old fuel and put in new fuel
- Fuel pressure at the rails shows 50 psi
- Spark is happening
- TB is opening fine
Cranking sounds a bit weird to me. It's not the typical loping sound but rather a smooth, consistent sound.
If I let it crank for a bit, I get maybe one mid-severe backfire.
I'm starting to wonder if I put the cam in wrong. I triple checked the cam when I installed it but maybe I missed something?
Been working on this for a while so I could use some guidance on this one. Definitely bummed out
Thanks folks for any help in advance.
Jake
I'm doing a LS2 402 swap in my 98 A4 and finally finished it up tonight but it won't start. Here's what I checked so far:
- It sat for a bit so I pumped out old fuel and put in new fuel
- Fuel pressure at the rails shows 50 psi
- Spark is happening
- TB is opening fine
Cranking sounds a bit weird to me. It's not the typical loping sound but rather a smooth, consistent sound.
If I let it crank for a bit, I get maybe one mid-severe backfire.
I'm starting to wonder if I put the cam in wrong. I triple checked the cam when I installed it but maybe I missed something?
Been working on this for a while so I could use some guidance on this one. Definitely bummed out
Thanks folks for any help in advance.Jake
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2020 Corvette of the Year Finalist (performance mods)
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did you do a cam swap only and it was running before or is it a new motor?... is it throwing any codes?... if not maybe try a compression test and see if you have any dead or low cylinders
Thread Starter
Instructor
Joined: Mar 2009
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From: Mansfield Texas
Brand new motor and cam. I need to check for codes again, when I checked it didn't show any codes but the DIC was showing low coolant, low brake fluid, service traction control, etc which I would figure would show some codes!
Compression test is a good idea, I will do that as well.
Compression test is a good idea, I will do that as well.
Thread Starter
Instructor
Joined: Mar 2009
Posts: 114
Likes: 2
From: Mansfield Texas
Thread Starter
Instructor
Joined: Mar 2009
Posts: 114
Likes: 2
From: Mansfield Texas
It's alive!!! Did some research and found some posts in another forum about valves being stuck open. So I opened the valve covers and loosened the rocket bolts a bit and got compression!! Did the same all the way around and got good compression on each cylinder. Bolted everything back up and it started right up! Thanks for the tip to check compression that's what led me in the right direction.
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Thread Starter
Instructor
Joined: Mar 2009
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From: Mansfield Texas
Hmm I hadn't thought about that possibilty. I know when I measured them using an adjustable one it seemed to measure out ok. The rockers seemed to be very tight so I am wondering if my torque wrench was off when I tightened then down.
Le Mans Master
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Do you have adjustable rockers? Stock rockers are non adjustable?? Crank to 22ft lbs and done
Uneducated autodidact
Joined: Feb 2001
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From: West of the Sabine, Texas
It's alive!!! Did some research and found some posts in another forum about valves being stuck open. So I opened the valve covers and loosened the rocket bolts a bit and got compression!! Did the same all the way around and got good compression on each cylinder. Bolted everything back up and it started right up! Thanks for the tip to check compression that's what led me in the right direction.
Thread Starter
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From: Mansfield Texas
Hmm, I will double check them for sure. I am also getting P0343 Camshaft Position Sensor A Circuit High, is this what you were getting to Deputy_Dangle when your pinout was wrong? How did you determine the write pin out? Not sure I want to be probing around while the car is running.
Uneducated autodidact
Joined: Feb 2001
Posts: 5,413
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From: West of the Sabine, Texas
What I'm saying is, if you backed off the rocker bolts and some valves closed there is an issue. LS rockers are non adjustable and supposed to fit flush, torqued down with no clearance under them. I wouldn't run the engine until you figure it out.
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2020 Corvette of the Year Finalist (performance mods)
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he never stated if he had stock or aftermarket rockers though... on the cam harness personally I would prefer to solder in a new pigtail with the correct plug if possible, I have seen too many issues with conversion harnesses... sometimes they are pinned incorrectly and sometimes the wires are not properly crimped so you end up with a bad connection... solder/heatshrink/loom and be done with it
Uneducated autodidact
Joined: Feb 2001
Posts: 5,413
Likes: 252
From: West of the Sabine, Texas
he never stated if he had stock or aftermarket rockers though... on the cam harness personally I would prefer to solder in a new pigtail with the correct plug if possible, I have seen too many issues with conversion harnesses... sometimes they are pinned incorrectly and sometimes the wires are not properly crimped so you end up with a bad connection... solder/heatshrink/loom and be done with it
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From: Mansfield Texas
Pro
Joined: Oct 2007
Posts: 607
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From: Tulsa Oklahoma
What are your cam specs/pushrod length? Stock or milled heads? Id venture to guess that you would strip the rocker bolt hole on the aluminum heads before you could bind the valves if your pushrods are the correct size. I would defintely check for correct length before firing it up. A quick check will give peace of mind and could save you a lot of trouble down the road. Whatever you find it is, let us know.
Thread Starter
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Joined: Mar 2009
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From: Mansfield Texas
Cam is 242/248 112
Pushrods are 7.550"
Heads are TFS 235cc 70cc, not milled
Lifters are Lunati street hydraulic
The Yella Terra rockers came with a shim and a pedestal for each rocker. I didn't use the shim because the rub pattern on the spring was dead center. I used an adjustable pushrod checker when the engine was out.
Happy to measure again, could use some guidance on the best way to do it when the engine is in the car. I can't get to the crank bolt but can use the starter with the fuel pump relay pulled.
Thanks for all the help I really appreciate it!
Mowpow
Pushrods are 7.550"
Heads are TFS 235cc 70cc, not milled
Lifters are Lunati street hydraulic
The Yella Terra rockers came with a shim and a pedestal for each rocker. I didn't use the shim because the rub pattern on the spring was dead center. I used an adjustable pushrod checker when the engine was out.
Happy to measure again, could use some guidance on the best way to do it when the engine is in the car. I can't get to the crank bolt but can use the starter with the fuel pump relay pulled.
Thanks for all the help I really appreciate it!
Mowpow
What are your cam specs/pushrod length? Stock or milled heads? Id venture to guess that you would strip the rocker bolt hole on the aluminum heads before you could bind the valves if your pushrods are the correct size. I would defintely check for correct length before firing it up. A quick check will give peace of mind and could save you a lot of trouble down the road. Whatever you find it is, let us know.
Pro
Joined: Oct 2007
Posts: 607
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From: Tulsa Oklahoma
I guess the other question I didnt ask is, how much lifter preload did you add? Im not going to pretend I know the spec for the lunati street lifter preload off the top of my head. Did you add something like .100 or .050, more or less?
I would recheck the pushrod length to be on the safe side. There's a whole host of tricks to spin the engine while in the car. From strap wrenchs to modified or pass through sockets or even spinning the alternator backwards. Removing the spark plugs will help you turn it over.
If all checks out and you're confident in you're measurement, you're good! But the not knowing part would drive me crazy. Something happened to cause the valves to stick open.
I would recheck the pushrod length to be on the safe side. There's a whole host of tricks to spin the engine while in the car. From strap wrenchs to modified or pass through sockets or even spinning the alternator backwards. Removing the spark plugs will help you turn it over.
If all checks out and you're confident in you're measurement, you're good! But the not knowing part would drive me crazy. Something happened to cause the valves to stick open.