Replaced Heads And Cam, Now Cylinders 5, 6, And 7 Aren't Firing

Austin90LX

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Jan 16, 2017
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So I pulled my motor out of my 90 5.0 and put on GT40X heads as well as an f cam, and now when it's at idle cylinders 5 6 and 7 aren't firing. I tested the compression, it's at around 120 on all cylinders. When I give it gas and rev to about 1500 the other cylinders seem to start firing. Checked TPS, it's at .96 volts. Unplugged the IAC and there was no change in idle. When I pull out the spark plugs after idling they are wet with gas. Also with the intake, upon startup the rpms will jump to about 1200 then immediately die, will only stay running with intake off. Ran perfect before I replaced heads and cam. Any help would be greatly appreciated guys
 
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I tried taking the three wires off that weren't firing and switching them around but it didn't do anything different. There might be coolant in the oil now too which I thought would be a blown headgasket but I checked compression and it was fine
 
Pull the valve cover off and make sure that the valves are opening and closing and that you don't have them tightened too much.
 
I did not check pushrod length, I tightened them all to 22ft-lbs and all of them would spin but not move up and down or side to side. I didn't use a manual since I only did heads and cam, I just looked up torque specs for everything. Intake was torqued from inside to outside at 18lbs, same with intake manifold except torqued to 25
 
Ok... so did you re-tighten the intake after a heat cycle?

What did you torque the head bolts to? What type did you use?
What lubricant did you use on the head bolts?
It hasn't been running long enough for a heat cycle it's ran for maybe five minutes cumulatively, and I used stock headbolts, was going to replace them once I put it together and made sure it was running
 
Ok... so did you re-tighten the intake after a heat cycle?

What did you torque the head bolts to? What type did you use?
What lubricant did you use on the head bolts?
Since you seem to have the best knowledge so far, I sprayed carb cleaner where the intake meets the head on the driver side, and idle picked up. This is indicative of an intake leak, correct?
 
We are all very knowledgeable. Each one of us could probably walk you through an entire engine teardown and rebuild.

We try not to give any advice unless we have a decisive answer.

You messed up on the intake.
-remove the intake
-Clean surfaces
Go buy 5/16 all-thread at the hardware store, cut them longer than the bolts for the intake.
-Install the gaskets with a smear of rtv around the water jackets, then screw the all thread into the bolt holes. (No need to do every one of them 4 will do)
Slide the intake over the all-thread this will ensure that everything lines up correctly.
-install the intake bolts then removing the all-thread and replace it with the correct bolts.
-re-torque intake and install plenum ect ect.




Good luck
 
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We are all very knowledgeable. Each one of us could probably walk you through an entire engine teardown and rebuild.

We try not to give any advice unless we have a decisive answer.

You messed up on the intake.
-remove the intake
-Clean surfaces
Go buy 5/16 all-thread at the hardware store, cut them longer than the bolts for the intake.
-Install the gaskets with a smear of rtv around the water jackets, then screw the all thread into the bolt holes. (No need to do every one of them 4 will do)
Slide the intake over the all-thread this will ensure that everything lines up correctly.
-install the intake bolts then removing the all-thread and replace it with the correct bolts.
-re-torque intake and install plenum ect ect.




Good luck
Could you describe what all-thread is? I've never heard of it before