Correct intake for GT40 headswap
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New User
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Correct intake for GT40 headswap
I installed a pair of Gt40 heads and wanted to confirm that I can run original intake on my 351W?. I,have a very large vacum leak that is keeping truck from running. I suspect somthings going on at lower intake.
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New User
Joined: Dec 2010
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I can get truck to run/start by holding throttle to floor,and i have to give gas to contiue running. I have no vacum while cranking, or tryingtorun without a lotof throttle.
I used felpro 1250 intake gasket set.perhaps not correct choice.Or incorrrectly installed. I will have to dissaseble and inspect.
A few more clues,
Spark,timing,fuelpressure,pulse, compression, good.
97f250HD 351W gt40heads, stocklowerend,ported upperand lower intake,mustang off road headers, my custom exhaust. Egr is intact, eliminated allthe other emmissions crap.
I used felpro 1250 intake gasket set.perhaps not correct choice.Or incorrrectly installed. I will have to dissaseble and inspect.
A few more clues,
Spark,timing,fuelpressure,pulse, compression, good.
97f250HD 351W gt40heads, stocklowerend,ported upperand lower intake,mustang off road headers, my custom exhaust. Egr is intact, eliminated allthe other emmissions crap.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
With the throttle to the floor the TPS value should be at/near maximum output. The PCM will normally shut off the injectors when cranking the engine in this scenario. This is a built in feature to clear a flooded condition. You might want to check the TPS output signal.
Did you leave the MAP sensor hooked up? Assuming this truck is Speed Density....
Did you leave the MAP sensor hooked up? Assuming this truck is Speed Density....
Junior User
Joined: May 2003
Posts: 90
Likes: 0
From: AZ
I can get truck to run/start by holding throttle to floor,and i have to give gas to contiue running. I have no vacum while cranking, or tryingtorun without a lotof throttle.
I used felpro 1250 intake gasket set.perhaps not correct choice.Or incorrrectly installed. I will have to dissaseble and inspect.
A few more clues,
Spark,timing,fuelpressure,pulse, compression, good.
97f250HD 351W gt40heads, stocklowerend,ported upperand lower intake,mustang off road headers, my custom exhaust. Egr is intact, eliminated allthe other emmissions crap.
I used felpro 1250 intake gasket set.perhaps not correct choice.Or incorrrectly installed. I will have to dissaseble and inspect.
A few more clues,
Spark,timing,fuelpressure,pulse, compression, good.
97f250HD 351W gt40heads, stocklowerend,ported upperand lower intake,mustang off road headers, my custom exhaust. Egr is intact, eliminated allthe other emmissions crap.
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New User
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Yes injectors are correctly routed, i have tryed two sets of injectors. the originals that i installed new screens and o-rings, and a junkyard set to rule out bad injectors. fuel pressure's right on money, and I do have gas in it.
I've also had a Modis hooked up. No codes, and senor data is normal.
I have a occasional miss, but probably more related to the fact that i need to fine tune timing adjustment. I followed thread on site here about setting base timing to 10* before. But I need to get truck running and idleing correctly to set timing
Yes truck is still speed density,I have not sourced all the parts needed yet to do mass air flow conversion.
I know I'm missing somthing stupid. The truckran like atopbefore i swaped out heads and redid everything.
Also electical is good.I have 2/0 power and ground cables for battery. and numerous grounds dasiy chained together. 160 amp alternator,plus a lot of other goodies i swaped in.
I've also had a Modis hooked up. No codes, and senor data is normal.
I have a occasional miss, but probably more related to the fact that i need to fine tune timing adjustment. I followed thread on site here about setting base timing to 10* before. But I need to get truck running and idleing correctly to set timing
Yes truck is still speed density,I have not sourced all the parts needed yet to do mass air flow conversion.
I know I'm missing somthing stupid. The truckran like atopbefore i swaped out heads and redid everything.
Also electical is good.I have 2/0 power and ground cables for battery. and numerous grounds dasiy chained together. 160 amp alternator,plus a lot of other goodies i swaped in.
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Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
teh felpro 1250's are a great gasket,i uese those alot,when you hold the throttle to the floor and it starts that sounds like a fuel issue,if the injectors are spraying to much(stuck open ailttle)the will give you a hard time starting it,when you holt the throttle to the floor before you crank it,that will not spray the injectors till the motor fires.are you sure you have the injectors clips on the right injectors?when you get it started,does it sound like it misses when your keeping it running?
If the OP has to hold the throttle all the way open to "get it to run" something is wrong with the TPS circuit. A simple check with a $5 voltmeter will prove me right or wrong.
Junior User
Joined: May 2003
Posts: 90
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From: AZ
The engine will never fire under this condition. If you hold the throttle all the way down you can crank on that *****' until the battery dies. The PCM will not turn the injectors on.
If the OP has to hold the throttle all the way open to "get it to run" something is wrong with the TPS circuit. A simple check with a $5 voltmeter will prove me right or wrong.
If the OP has to hold the throttle all the way open to "get it to run" something is wrong with the TPS circuit. A simple check with a $5 voltmeter will prove me right or wrong.
Thread Starter
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New User
Joined: Dec 2010
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Well I looked at TPS circut. Been busy fixing other peoples crap boxes.
circut 351-VREF 5volts
355-tps input-0.912voltsclosed throttle, smooth progressive voltage rise to max 4.26volts at WOT.
359- sensor signal return.- Zero Ohms resistance. All grounds show no resistance. Sensor signal return circut good to PCM.
Also all PCM grounds good.
So I can run the truck intake,which i was pretty sure about. Andthe 1250 gaskets are okay to use.
Back to my original problem, lack of vacumn. I just smoke tested intake.nothing.If I have a lower intake gasket leak?. I cant see it and no smokes coming out.
I would like to thank all those who have responded.I need some good input from those who know these trucks. I'm dying to get this `truck`running. Its my first V8 ever.
circut 351-VREF 5volts
355-tps input-0.912voltsclosed throttle, smooth progressive voltage rise to max 4.26volts at WOT.
359- sensor signal return.- Zero Ohms resistance. All grounds show no resistance. Sensor signal return circut good to PCM.
Also all PCM grounds good.
So I can run the truck intake,which i was pretty sure about. Andthe 1250 gaskets are okay to use.
Back to my original problem, lack of vacumn. I just smoke tested intake.nothing.If I have a lower intake gasket leak?. I cant see it and no smokes coming out.
I would like to thank all those who have responded.I need some good input from those who know these trucks. I'm dying to get this `truck`running. Its my first V8 ever.
Senior User
Joined: Aug 2007
Posts: 104
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TPS looks ok, could bump it to .99 closed but nothing that would cause your problem. Do you have a vacuum gauge to test how much vacuum you're drawing? How does it run when you have the throttle down? Is it smooth or is it skipping or popping or anything?
As far as the heads go, are you running roller rockers with them, if so, how did you set the valve lash?
As far as the heads go, are you running roller rockers with them, if so, how did you set the valve lash?
Junior User
Joined: May 2003
Posts: 90
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From: AZ
are they the roller rockers?if so i would leave them,they are better than teh stamp steel ones
Senior User
Joined: Aug 2007
Posts: 104
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When you installed the heads, did you torque down the rocker arms to the right specs? The reason I say that is if you have them torqued too tight there could be too much pressure on the valves which could lead to problems. Also depending on how many miles on the motor the valve springs could be tired.