TBI Set-up
12-19-2004, 01:26 AM
#1
Guest
Posts: n/a
TBI Set-up
Hey all,
I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
system and I am trying to find out how to properly set it up. I am
having a lot of problems with hesitation. The engine runs great when it
is cold but after it warms up it develops a bad hesitation from idle or
in the low rpm range. I am a pretty good mechanic but I dont know much
about setting up a TBI system. Thanks in advance for any help.
I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
system and I am trying to find out how to properly set it up. I am
having a lot of problems with hesitation. The engine runs great when it
is cold but after it warms up it develops a bad hesitation from idle or
in the low rpm range. I am a pretty good mechanic but I dont know much
about setting up a TBI system. Thanks in advance for any help.
12-19-2004, 01:56 AM
#2
Guest
Posts: n/a
Re: TBI Set-up
A hesitation on a carburetor, would indicate a lean mixture, caused
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
12-19-2004, 01:56 AM
#3
Guest
Posts: n/a
Re: TBI Set-up
A hesitation on a carburetor, would indicate a lean mixture, caused
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
12-19-2004, 01:56 AM
#4
Guest
Posts: n/a
Re: TBI Set-up
A hesitation on a carburetor, would indicate a lean mixture, caused
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
by a weak accelerator pump. Test your line pressure to be at least forty
pounds. Pinch the return line and look for ninety. A little trick is to
remove the plug cover hiding the adjustable screw in the center of the
pressure regulator sitting atop your throttle body venturi, that looks
like this: http://www.jetchip.com/fuel/fpr.cfm Otherwise, it'll be a
learning experience reprograming your computer.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/
chopper5jrt@comcast.net wrote:
>
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
12-20-2004, 01:11 AM
#8
Guest
Posts: n/a
Re: TBI Set-up
Is it a Howell, CustomEFIS, Holley or homebrew system?
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
12-20-2004, 01:11 AM
#9
Guest
Posts: n/a
Re: TBI Set-up
Is it a Howell, CustomEFIS, Holley or homebrew system?
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
12-20-2004, 01:11 AM
#10
Guest
Posts: n/a
Re: TBI Set-up
Is it a Howell, CustomEFIS, Holley or homebrew system?
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
When the engine is warm it goes "closed loop" and tries to use the data from
the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip
could cause your problem, as well as faulty sensors.
When cold it runs in "open loop" mode, using a fixed fuel mixture table.
One way of keeping it open loop after warming up is to unplug the o2 sensor.
Yes, it will set a trouble code and turn on the check engine light, but at
least it will give you a starting point to where the problem might lie.
The fact that it "runs great when it is cold" leads me to believe it's
sensor problems. If he mounted the o2 sensor too far downstream and it is a
one-wire unit, it may not be getting hot enough. Fix: replace with a
three-wire heated unit. Although, there are many more people running TBI on
360's than 304's, meaning the chip might not be optimized for the smaller
motor. If it's a homebrew system he might still be running a stock chevy
chip. Open up the little door on the ECM and see if the chip looks tampered,
aftermarket or stock GM.
BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line
pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs
fine cold I wouldn't worry about the pressure. Don't go cranking it up
unless you have some spare injectors and a very good fire extinguisher.
<chopper5jrt@comcast.net> wrote in message
news:1103437589.096382.46040@f14g2000cwb.googlegro ups.com...
> Hey all,
>
> I own a 1978 CJ-7 with a 304. The previous owner installed a new TBI
> system and I am trying to find out how to properly set it up. I am
> having a lot of problems with hesitation. The engine runs great when it
> is cold but after it warms up it develops a bad hesitation from idle or
> in the low rpm range. I am a pretty good mechanic but I dont know much
> about setting up a TBI system. Thanks in advance for any help.
>
