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32dmadden, Auto Repair Shop Owner
Category: Chevy
Satisfied Customers: 1207
Experience:  A.S.E. Certified Master Technician, L-1 37 yrs. Auto Repair Experience
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1994 Chevy: c1500..Replaced fuel was under spec for pressure

Customer Question

1994 Chevy c1500 Replaced fuel pump because it was under spec for pressure. Spec is 12 to 15 I have 9.
Submitted: 8 years ago.
Category: Chevy
Expert:  32dmadden replied 8 years ago.
Sounds like it can be the pressure regulator not working correctly. It is the hat on the top of the throttle body. Try squeezing the return line. If the pressure goes up then the regulator is the problem. You do have the throttle body with the two injectors in the top don't you? The fuel pressure spec I have is 9 psi to 13 psi. That's from GM. Are you having any performance problems? I would say the fuel pressure is okay. Let me know if you need more help.
32dmadden and 4 other Chevy Specialists are ready to help you
Customer: replied 8 years ago.
the pressure goes up to 25 when I sqeeze the return line
Customer: replied 8 years ago.
before I replaced the pump it read 8 psi
Customer: replied 8 years ago.
I need to clarify something someone with your staff told me if you pinch the return line and the pressure goes up that the regulator is working properly
Expert:  32dmadden replied 8 years ago.
The pressure will go up when you pinch the return line. This is the same thing the regulator does to maintain its pressure. Now if you have low fuel pressure say 6 psi and you squeeze the return line and it goes up that means the regulator is not working correctly. If you were to squeeze the return line and the pressure does not go up then the pump is the problem. You say you have 9 psi for the pressure reading. That is with in the specs I have for that model. Everything looks good to me. Let me know if you need more help.
Customer: replied 8 years ago.
I wish I could have been told about the regulator yesterday. This vehicle has a problem getting fuel at high RPM so you think if I go buy a regulator that will fix the problem?
Expert:  32dmadden replied 8 years ago.
If the fuel pressure is low at higher RPMs then I would go for the regulator, if it stays at 9 psi the regulator is working. You can also watch the voltage on the O2 sensor to see if it is going lean at higher RPM. Use a volt meter and tap in to the purple wire going to the Os sensor. Leave it connected just tap in to it. It should go back and fourth across 0.45 volts. Anything below is lean and anything above is rich. Does the check engine light ever come on? If so the codes need to be pulled from the computer. I can send you a diagram on code accessing. I'll be hear if you need me.
Customer: replied 8 years ago.
Customer: replied 8 years ago.
Sorry The pressure does not drop at the fuel pressure gauge that I have installed behing the fuel filter. If it does not drop on aceleration does that mean the pressure is ok. I am trying to be clear because a regulator is 50 dollars I am not ready to through that kind of money at this Truck unless it is going to fix it. I am not trying to be difficult I am trying to make a well informed decision and I do appriciate your help
Expert:  32dmadden replied 8 years ago.
Yes no drop means every thing is okay. I would not get the regulator. What is the truck doing that you are trying to fix? I'm sure we can get to the bottom of things. I'll be here if you need me. I'm going to be on a break for a couple of hours so don't think I forgot you.
Customer: replied 8 years ago.
When you try to acelerate the truck wants to die it has a strange pusle about it, it looses all power. I have checked the ECM when you tap on it I get no change or at the connector of the ECM. I switched out coils temp nothing. I replaced cap and rotor they were burned. I checked the pickup coi in the distributor it reads 887 ohms this is good. So I have been through most of the ingnition and fuel what does that leave. Oh I dropped the exhaust to check for a plugged cat no help.
Customer: replied 8 years ago.
I have not received a reply to my Question yet
Customer: replied 8 years ago.
I pulled plug number 1 and it is black on the insulator like it is not firing at times which leads me to belive this is an ingntion problem
Customer: replied 8 years ago.
I found a very large vaccum leak in the intake mantifold gasket and there was also an oil leak there so I fixed that and the truck runs better but it still loses power when you step hard on the gas. It shuts off both of the fuel injectors when you step on the gas. I thought the governor was kicking in but my scanner read no governor. The fuel pressure does not drop when this happens. Im not sure which way to go with this now. Wonder if you have any suggestions.
Expert:  32dmadden replied 8 years ago.
I'm sorry it has taken so long to reply to your question. I don't know if it was my computer or the site but every time I tried to open your question I would get a no such address page. Finally got it to work today. The plug being black was caused by the vacuum leak. That air is not metered air so when all of it shows up on the O2 sensor the computer richens up the mixture. When you are cranking the engine and hold the gas pedal to the floor it will turn the injectors off. This is called clear flood mode. It does this by watching reference pulses from the distributor. Do you see an RPM reading on your scanner when the engine is running? If you haven't driven it for 20 miles after the gasket was installed the computer may need to relearn. Also the timing needs to be checked along with the MAP sensor and its vacuum supply. Check the vacuum port it is on, make sure carbon has not plugged or restricted it. The TPS needs to be checked for bad spots in the reaosat. Last make sure the EGR valve is not leaking. On your scanner in the data menu look for the block learn and the integrator. 128 is normal for both. Below 128 is lean fuel mixture and above is rich. Let me know the O2 reading too. I'll be waiting to hear from you.
Customer: replied 8 years ago.
Thank you for your information this is very useful I will be using it in the future I may reply to this message again later.
Expert:  32dmadden replied 8 years ago.
Have you had time to check anything? I'm here if you need me.

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