Heads and Intake Swap Problems :/

5-oh-MUSTANG

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I just swapped on some gt40p heads that had some work done to them and have been converted to stud mounted 1.6 roller rockers and along with a gt40 intake manifold onto my 95 mustang gt. I used hardened stock length push rods as the heads had guide plates. I have the valve lash set to about 1/4 turn after there was no up and down play between the rocker and lifter. I could have gone half turn but the polynut was already pretty tight. Anyways, after buttoning up everything i decided to see if everything is okay and runs. Well it fires up and runs, but the at idle it shakes wayyy to much for having a stock cam. Never like i had before i swapped the heads or intake. Im at a lost. Im not sure if maybe a lower manifold gasket slipped causing a vacuum leak or maybe i have the incorrect valve adjustment? The mid pipe is not hooked up but that shouldn't affect cold start idle (open loop o2 sensors)? I had primed the oil pump before i even set the lash as well just to make sure the lifters were pumped up. The car revs and sounds fine at higher rpms, just at idle the engine is shaking too much. Idle rpm is steady smooth at about 1000 rpm. What do you guys think this could be?
 

96blak54

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Ill be the one that says it

You gonna have to go backwards....disassemble untill you figure out what the problem is. Id start with the pushrods just cause its the easiest. Make absolutely sure your process was correct.
 

evilcw311

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Did you measure for pushrod length?? Anytime you change heads, cam, and or rockers it’s time to measure.


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96blak54

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This is true! Decked heads or decked block can scew pushrod lengths. Also hydraulic lifters that are bled down can cause problems.
 
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5-oh-MUSTANG

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any codes?
no codes or check engine light.
Did you measure for pushrod length?? Anytime you change heads, cam, and or rockers it’s time to measure.


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previous owner of the gt40p heads ran stock length with an e303 cam so id assume with stock cam it wouldnt be a problem? The geometry of the rockers look fine though.
 
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5-oh-MUSTANG

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This is true! Decked heads or decked block can scew pushrod lengths. Also hydraulic lifters that are bled down can cause problems.
Yes i thought this too, but i primed the motor as i set the lash to circulate the oil throughout the motor.
 

07GtS197

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Sounds like a vacuum leak to me, though a mechanical fault cant be ruled out. Do you hear any hissing when its running?


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01yellercobra

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How close are the O2 sensors to the end of the collectors? Years ago I was told not to run the O2's close to fresh air because it could cause issues with the readings. That's why an exhaust leak can cause driveability issues.
 

07GtS197

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O2 sensor issues usually cause problems in all but wide open throttle whereas a vacuum leak only gives issues at idle and low throttle input. The op said it only acts up at idle which makes me think vacuum leak.


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5-oh-MUSTANG

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How close are the O2 sensors to the end of the collectors? Years ago I was told not to run the O2's close to fresh air because it could cause issues with the readings. That's why an exhaust leak can cause driveability issues.
O2 sensor issues usually cause problems in all but wide open throttle whereas a vacuum leak only gives issues at idle and low throttle input. The op said it only acts up at idle which makes me think vacuum leak.


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I was told cold start the o2 sensors are in open loop so they dont take any readings from them as they need to be heated up to produce a real reading..
 

01yellercobra

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Cold start is just a few seconds. It doesn't take long for them to heat up.
 

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Is the harmonic balancer matched for the 351W? I believe it calls for a 28 oz up through 1996 but am not 100% sure. Seems like a vacuum leak would make it run rough. The op says it just shakes but "Idle rpm is steady smooth at about 1000 rpm".
 
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5-oh-MUSTANG

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Ok well I did the test where you block the pcv valve and check for any vacuum at the oil filler and didnt have any, so the lower intake gasket should in theory be fine. I do not want to take off the lower intake manifold again if I do not have to. So this probably means my valves are miss adjusted which i had a feeling of because when I crank over the motor it doesnt sound right either. Anyways, I just unbolted the driver side valve cover and roller rockers. Let the lifters sit for couple minutes. If i push down on my pushrods through the guideplates i cannot seem to compress the lifter spring? Is there not supposed to be spring tension on the lifter as i push down on it, hence when setting the preload it goes down? I just tried to adjust them again by turning the engine over by hand until cylinder 5 exhaust valve was opening, i adjusted that cylinders intake valve. Then when intake opened and started to close I adjusted that cylinders exhaust valve. I moved the pushrod up and down till they stopped jiggling/no up down movement and then gave the nut a half turn from that point. I repeated this for cylinders 5-8 and by the time i was done and turned the motor over by hand a few times again all the pushrods I had just adjusted had a bit of slack in them again and were a bit loose? So are my lifters a problem or is this side of the motor safe to say is set or did I do this all wrong again??!!
 

Road_Runna

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All rubber hoses and lines on the passenger side still in good shape? I remember this one time disconnecting and forgetting to re connect my o2 sensors my engine would shake. best of luck, im going to be doing the same gt40p swap pretty soon.
 

01yellercobra

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If you're running hydraulic lifters they'll pump up and not have any slack. You shouldn't be able to push them after they're pumped up. When you say you can move the push rods up and down do you mean they don't contact the lifter?

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Randall Garner

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I just swapped on some gt40p heads that had some work done to them and have been converted to stud mounted 1.6 roller rockers and along with a gt40 intake manifold onto my 95 mustang gt. I used hardened stock length push rods as the heads had guide plates. I have the valve lash set to about 1/4 turn after there was no up and down play between the rocker and lifter. I could have gone half turn but the polynut was already pretty tight. Anyways, after buttoning up everything i decided to see if everything is okay and runs. Well it fires up and runs, but the at idle it shakes wayyy to much for having a stock cam. Never like i had before i swapped the heads or intake. Im at a lost. Im not sure if maybe a lower manifold gasket slipped causing a vacuum leak or maybe i have the incorrect valve adjustment? The mid pipe is not hooked up but that shouldn't affect cold start idle (open loop o2 sensors)? I had primed the oil pump before i even set the lash as well just to make sure the lifters were pumped up. The car revs and sounds fine at higher rpms, just at idle the engine is shaking too much. Idle rpm is steady smooth at about 1000 rpm. What do you guys think this could be?




Have you verified vacuum. Reading with a gauge. And once you start a engine it is best to reset the lash once good steady oil pressure is established. When running an adjustable rocker system. 2 ways to do it. One is a bit messy but. Gives good results. 1. Loosen set screws and start engine let it warm up enough to run on its own, then going fire order or bank to bank. Loosen each rocker until you hear slight ticking. Then reset to .030-.060 preload. Depending on which stud you have. Will determine. The amount in addition after going quite. 3/8-16. Means 16 threads per inch. You have to do the math to get the correct amount of turn. For which ever studs you have. Other is after engine warm stop go through fire order and be able to ensure you on base circle of cam when setting. Lash and preload. But the same amount applies. With engine running a vacuum gauge also helps to ensure your not holding a valve open. When adjusting
 
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5-oh-MUSTANG

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If you're running hydraulic lifters they'll pump up and not have any slack. You shouldn't be able to push them after they're pumped up. When you say you can move the push rods up and down do you mean they don't contact the lifter?

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Yes i believe that is what the problem is. The lifters are full of oil and are not bleeding down due to the cold and old oil. There is contact between the lifter and rocker cup but the spring in the lifter is not allowing me to properly set the preload. I do not want to remove the lower intake to remove the lifters and remove the oil out of them so im not sure what options I have.
 

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