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Old 12-21-2012, 12:49 PM
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87 gm tbi will not start

Ok so I have swapped a 400 sbc into a tractor with a 350 tbi topend. When I go to start it I have spark and fuel but it will not run. I have checked valve lash and compression. Both were fine. I played around with the timing of the distributor and spark plug wires. It will backfire and shoot flames but it won't start. I have checked the iac and it works fine. Like I said it has fuel and spark and I have spun the darn distributor right around but it will not fire. I'm not sure what's going on. Any help or advice would be great.

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Old 12-21-2012, 12:53 PM
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I'm not an electrical genius kinda guy but are you sure that you don't have the distributor out 180 degrees...kinda sounds like it.

Ray
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Old 12-21-2012, 05:04 PM
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X 2 with timing. You need to reset the static timing and go from there.
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Old 12-21-2012, 05:11 PM
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Matty8,

Check the gasket under the tbi. These seem to dry out and get sucked in and then you have a big vacuum leak.

Scholman
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Old 12-22-2012, 04:52 AM
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I have tried spinning the distributor around 180 a couple times. And when I was checking the valve lash I had the valve covers off, so I have it in the on the correct stroke.

I think the gasket will get changed and see what happens. The gasket is old and when it cranked and puffed, smoke came out of the top, sides and bottom of the tbi
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Old 12-25-2012, 06:36 PM
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is there a sensor that would effect the amount of fuel being sprayed during start up? I crank it over continuously for such long amounts of time and the plugs don't even get wet. Maybe it's not getting enough fuel?
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Old 12-25-2012, 07:06 PM
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Coolant sensor. If it goes open circuit (-40 F) it will pour the fuel in .
If it shorts internally it could go to 265 F and not spray fuel.
Thought the injectors were spraying. Wasnt it belching fire? Belching fire would indicate to me the fuel is being delivered.
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Old 12-25-2012, 07:13 PM
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Quote:
Originally Posted by Matty8 View Post
It will backfire and shoot flames but it won't start. I have checked the iac and it works fine.
Like I said it has fuel and spark and I have spun the darn distributor right around but it will not fire.
???????
N eed to start with the basics. Sounds to me like you are guessing.
Unplug the coil power lead, (so you dont burn off your eyebrows) crank it over and look down the throttle bore. See if the injectors are spraying a cone shape pattern.
Maybe you have the wrong balancer and the TDC mark is in the wrong place, or it slipped, resulting in an innacurate static timing setting.
Verify TDC #1 by the piston stop method,slowly crank engine with a socket wrench, while feeling inside the #1 hole for the piston to rise to the top, then compare topDead center to the balancer marks, to see if it is correct.
Post back after you are done.
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Old 12-28-2012, 11:42 AM
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I checked the balancer marks and they are correct. I've had the valve covers removed to verify that the engine is on the correct stroke and the distributor is not out 180 degrees. When I crank the engine I can see fuel squirting from the injectors. This is why I'm confused. Everything seems to be working but it will not start. That's why I'm wondering if a sensor is out of wack and throwing the mixture way off.
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Old 12-28-2012, 05:24 PM
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Be sure your engine is grounded well.Check all the grounds.
It could be a bad Ignition coil or module, firing when it isnt supposed to. An open winding in a coil primary can fire at the wrong time due to vibration across the broken wire. Also a module, which controls the coil primary, can have similar issues and cause a crossfire or incorrect firing time as it can open the circuit to the coil primary at the wrong time causing a ealry/late/crossfire.
Also a cracked dizzy cap can cause a crossfire/misfire.
Look around for carbon tracking. look at the cap and rotor.
Maybe replace the coil, if that doesnt do it, try a module.
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Old 12-28-2012, 07:49 PM
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The cap and rotor are both new, no cracks. Is there any way to test if it is misfiring?
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Old 12-28-2012, 07:51 PM
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And I have all my grounds bolted on the same spot at the front of the head. I have cleaned them up and made sure there is a proper ground
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Old 12-29-2012, 08:34 AM
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Try swapping out the coil, if that doesnt work, try a module.
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