1988 chevy TBI - The 1947 - Present Chevrolet & GMC Truck Message Board Network

heirless · 09-11-2004, 05:54 PM

My truck has developed a run problem, it will not idle, it just dies, like it runs out of gas, i have replaced the fuel filter, replaced distributor, rotor, and distributor cap, the only way to get it to run at all, is to flutter the gas pedal, but this will only run rough, if you floor it, the motor will die, the motor is a 350 5.7 Liter with a TBI injection system, if any one knows how to fix this problem, PLAESE LET ME KNOW ! !

ChevyTech · 09-11-2004, 07:56 PM

It sounds like it may be starving for fuel. Look at the injector spray pattern with a trouble light when it's running. It should be a nice even wide spray pattern. If the fuel is dribbling out or has a narrow pattern the fuel pressure is most likely very low. It may be time for a fuel pump. Sounds like it runs so bad you will need someones help to do this.

The best thing to do is tee in a fuel pressure gauge at the fuel filter to test you fuel system pressure. TBI trucks do not have a pressure port like port fuel injected vehicles.

Another posibility is the EGR valve has a piece of carbon holding it part of the way open.

Did the check engine light come on with is running? If it did the computer will store a trouble code. If you need to know how to retrieve the codes here is a site that tells how.

http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

Good luck and let me know what you find.
ChevyTech

heirless · 09-11-2004, 08:18 PM

no the check engine light did not come on, my brother has been helping me with this, and he says that the injectors are spraying a cone shaped spay, he says it looks like it is a lot of gas, have not checked the EGR valve, will have to check that, thanks for your input.

heirless · 09-12-2004, 07:10 PM

well just to update, i now have replaced the EGR valve, fuel pump, map sensor,if i unhook the hose to the map sensor it will idle for a while then die, if i push throttle down just a little it will run for a short while then i have to flutter the throttle, the only thing i have not done is to replace the injectors,back when i bought the truck i put a overhaul kit in the TBI, but did not replace the injectors at that time either....i am at a loss what to do now...........

ChevyTech · 09-12-2004, 07:31 PM

If I was working on it, I would tee in a fuel pressure gauge. Then I would know if the fuel pump and fuel pressure regulator were running within spec.

Here is a link thats shows the least expensive tool, I know of, to tee in on a TBI system. You will also need a fuel presure gauge.

http://www.sjdiscounttools.com/ta37650.html

heirless · 09-12-2004, 09:11 PM

i will have try that, thanks for the info.

**kwmech** · 09-13-2004, 09:13 PM

The TBIs have a habit of blowing the base gasket in the right rear under the IAC motor which will crate fits.

heirless · 09-13-2004, 11:30 PM

Quote:

Originally Posted by ChevyTech

If I was working on it, I would tee in a fuel pressure gauge. Then I would know if the fuel pump and fuel pressure regulator were running within spec.

Here is a link thats shows the least expensive tool, I know of, to tee in on a TBI system. You will also need a fuel presure gauge.

http://www.sjdiscounttools.com/ta37650.html

just to let you know i have finally teed in a pressure guage, when i turn on the ignition switch i hear the pump in tank run for about two to three secounds, the pressure guage does not even move, the guage starts at 10 lbs. i am curious is there any relay that can be telling the pump not to run, is there any way i can test the pump out of the tank to see if it alone is pumping enough gas, also i have been told by a friend that after market pumps don't work very well, i purchased the pump from advance auto parts.i have also got the truck to run for a little while, even then the guage does not show anything.

ChevyTech · 09-14-2004, 11:24 AM

There is no relay the tells the fuel pump not to run.

The fuel pump relay applies to prime the system when you first turn the key on - which you hear it run, it's just not building pressure. The relay is also applied when the engine is cranking and the ECM recieves a distributor referance pulse.

One more test you should do to make sure the pump is not good and the fuel pressure regulator is bad and dumpping all the fuel back in the return line to the tank as fast as the pump can pump it. Carefully pinch off the fuel return line. There is rubber line that can be pinched by the trans bellhousing. Be carefull not to damage the return hose. If you have good pressure only when this return is blocked you have a regulator failure.

TBI fuel systems should have 9-13 psi. I have seen them limp along running on much less. You will like the power it has with a new pump.

Pumps fail a lot. I agree with your friend, I would not use a aftermarket pump. It's to much work to change it, and many aftermarket pumps fail within there warranty period or just after it expires. Also some aftermarket pump do not have check valve in them. No check valve can create a no start when the pump only primes for 2 seconds.

The pumps are such a common failure item, I have never tried to test one out of the tank. If you do, PLEASE use water, not gas, to test it.

People that change a lot of pumps prefer to take the box off the truck and change the pump with the tank in the truck. If you have several people to help lift the box and move it back, you may consider this method.

heirless · 09-14-2004, 10:04 PM

i will have to try that,putting the pump in water to test the pressure, i am in the process of dropping the tank, but you know as well as i do the daily7 to 5 job takes priority over the shade tree mechanic,
I want to thank you for all the help you have given to me on this matter,

heirless · 09-15-2004, 03:42 PM

Is the fuel pressure regulator adjustable inside the TBI unit?? I put an ovehaul kit in the TBI after I bought the truck. I'm not sure I got the pressure regulator back together correctly. The truck has been running OK for 3 months until this problem started.

ChevyTech · 09-15-2004, 04:15 PM

If it ran ok for three months I would think you got it put together right. Alterations can be made to them to make them adjustable, but the way they come out of the factory they are not adjustable.

If you tee in a gauge and have low fuel pressure, and then pinch off the fuel return to the tank, and get high pressure - it's time to look at the regulator.

If you have low/no fuel pressure and you pinch off the return and still have low/no fuel pressure- it's not the regulator causing it.

ChevyTech

heirless · 09-15-2004, 09:54 PM

The problem is fixed with the motor running now. Found hole in hose between fuel pump and fuel line in tank. Thanks for all the help and info.

Need to replace the bottom half of the TBI injector bottom - what years are interchangeable and can you use one off a 4.3? When putting top back on broke bottom piece.

ChevyTech · 09-16-2004, 10:54 AM

Your welcome and good to here you are making progress.

Interchangeability is good on TBI housings. The Injectors them fit into the TBI housings are different sizes for different engines. Big block TBI housings are different, but you should be ok with one from a 4.3

Good luck

Chevytech

heirless · 09-16-2004, 09:31 PM

well good news the project is done, my truck is running alright, i went to a junk yard called u-wrench-it,this junk yard is a self serve, I purchased the injector body and top for only $11.14. brought it home soaked it in can of carberator cleaner for about fifteen minutes, put all together and it is fine. once again thanks very much chevy tech, I would not have been able to do it with out your help, also thanks to the people that created this bulletin board.......

09-11-2004, 05:54 PM	#1
heirless Registered User Join Date: Mar 2004 Posts: 15	1988 chevy TBI My truck has developed a run problem, it will not idle, it just dies, like it runs out of gas, i have replaced the fuel filter, replaced distributor, rotor, and distributor cap, the only way to get it to run at all, is to flutter the gas pedal, but this will only run rough, if you floor it, the motor will die, the motor is a 350 5.7 Liter with a TBI injection system, if any one knows how to fix this problem, PLAESE LET ME KNOW ! !

09-11-2004, 07:56 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	It sounds like it may be starving for fuel. Look at the injector spray pattern with a trouble light when it's running. It should be a nice even wide spray pattern. If the fuel is dribbling out or has a narrow pattern the fuel pressure is most likely very low. It may be time for a fuel pump. Sounds like it runs so bad you will need someones help to do this. The best thing to do is tee in a fuel pressure gauge at the fuel filter to test you fuel system pressure. TBI trucks do not have a pressure port like port fuel injected vehicles. Another posibility is the EGR valve has a piece of carbon holding it part of the way open. Did the check engine light come on with is running? If it did the computer will store a trouble code. If you need to know how to retrieve the codes here is a site that tells how. http://www.cfm-tech.com/gm_tbi_trouble_codes.htm Good luck and let me know what you find. ChevyTech

09-11-2004, 08:18 PM	#3
heirless Registered User Join Date: Mar 2004 Posts: 15	no the check engine light did not come on, my brother has been helping me with this, and he says that the injectors are spraying a cone shaped spay, he says it looks like it is a lot of gas, have not checked the EGR valve, will have to check that, thanks for your input.

09-12-2004, 07:10 PM	#4
heirless Registered User Join Date: Mar 2004 Posts: 15	well just to update, i now have replaced the EGR valve, fuel pump, map sensor,if i unhook the hose to the map sensor it will idle for a while then die, if i push throttle down just a little it will run for a short while then i have to flutter the throttle, the only thing i have not done is to replace the injectors,back when i bought the truck i put a overhaul kit in the TBI, but did not replace the injectors at that time either....i am at a loss what to do now...........

09-12-2004, 07:31 PM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	If I was working on it, I would tee in a fuel pressure gauge. Then I would know if the fuel pump and fuel pressure regulator were running within spec. Here is a link thats shows the least expensive tool, I know of, to tee in on a TBI system. You will also need a fuel presure gauge. http://www.sjdiscounttools.com/ta37650.html

09-12-2004, 09:11 PM	#6
heirless Registered User Join Date: Mar 2004 Posts: 15	i will have try that, thanks for the info.

09-13-2004, 09:13 PM	#7
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,944	The TBIs have a habit of blowing the base gasket in the right rear under the IAC motor which will crate fits.

09-14-2004, 11:24 AM	#9
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	There is no relay the tells the fuel pump not to run. The fuel pump relay applies to prime the system when you first turn the key on - which you hear it run, it's just not building pressure. The relay is also applied when the engine is cranking and the ECM recieves a distributor referance pulse. One more test you should do to make sure the pump is not good and the fuel pressure regulator is bad and dumpping all the fuel back in the return line to the tank as fast as the pump can pump it. Carefully pinch off the fuel return line. There is rubber line that can be pinched by the trans bellhousing. Be carefull not to damage the return hose. If you have good pressure only when this return is blocked you have a regulator failure. TBI fuel systems should have 9-13 psi. I have seen them limp along running on much less. You will like the power it has with a new pump. Pumps fail a lot. I agree with your friend, I would not use a aftermarket pump. It's to much work to change it, and many aftermarket pumps fail within there warranty period or just after it expires. Also some aftermarket pump do not have check valve in them. No check valve can create a no start when the pump only primes for 2 seconds. The pumps are such a common failure item, I have never tried to test one out of the tank. If you do, PLEASE use water, not gas, to test it. People that change a lot of pumps prefer to take the box off the truck and change the pump with the tank in the truck. If you have several people to help lift the box and move it back, you may consider this method.

09-14-2004, 10:04 PM	#10
heirless Registered User Join Date: Mar 2004 Posts: 15	i will have to try that,putting the pump in water to test the pressure, i am in the process of dropping the tank, but you know as well as i do the daily7 to 5 job takes priority over the shade tree mechanic, I want to thank you for all the help you have given to me on this matter,

09-15-2004, 03:42 PM	#11
heirless Registered User Join Date: Mar 2004 Posts: 15	Is the fuel pressure regulator adjustable inside the TBI unit?? I put an ovehaul kit in the TBI after I bought the truck. I'm not sure I got the pressure regulator back together correctly. The truck has been running OK for 3 months until this problem started.

09-15-2004, 04:15 PM	#12
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	If it ran ok for three months I would think you got it put together right. Alterations can be made to them to make them adjustable, but the way they come out of the factory they are not adjustable. If you tee in a gauge and have low fuel pressure, and then pinch off the fuel return to the tank, and get high pressure - it's time to look at the regulator. If you have low/no fuel pressure and you pinch off the return and still have low/no fuel pressure- it's not the regulator causing it. ChevyTech



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09-15-2004, 09:54 PM	#13
heirless Registered User Join Date: Mar 2004 Posts: 15	The problem is fixed with the motor running now. Found hole in hose between fuel pump and fuel line in tank. Thanks for all the help and info. Need to replace the bottom half of the TBI injector bottom - what years are interchangeable and can you use one off a 4.3? When putting top back on broke bottom piece.

09-16-2004, 10:54 AM	#14
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Your welcome and good to here you are making progress. Interchangeability is good on TBI housings. The Injectors them fit into the TBI housings are different sizes for different engines. Big block TBI housings are different, but you should be ok with one from a 4.3 Good luck Chevytech

09-16-2004, 09:31 PM	#15
heirless Registered User Join Date: Mar 2004 Posts: 15	well good news the project is done, my truck is running alright, i went to a junk yard called u-wrench-it,this junk yard is a self serve, I purchased the injector body and top for only $11.14. brought it home soaked it in can of carberator cleaner for about fifteen minutes, put all together and it is fine. once again thanks very much chevy tech, I would not have been able to do it with out your help, also thanks to the people that created this bulletin board.......

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