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Larry
Larry, ASE Certified Technician
Category: Chevy
Satisfied Customers: 145
Experience:  29 yrs in repair and transmission overhaul and an ASE Master tech I have owned my shop for 23 yrs
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My 96 Astro Van (2wd) starts and idles fine, but when trying

Customer Question

My 96 Astro Van (2wd) starts and idles fine, but when trying to accelerate or climb a hill it bogs down. On several occaissions it will get to the top of the hill then the rpm just drops off and giving gas slows it and backing off (feathering the throttle) will let it top the hill. I have had the codes read and get Ö2 sensor heating circuit bad" and "Multiple engine misfires". I have replaced the cap & rotor, plugs, wires, Ignition module, MAF, MAP, and the problem remains the same...maybe worse.
Submitted: 5 years ago.
Category: Chevy
Expert:  Larry replied 5 years ago.

Hi Im Larry Crow,

The 4.3 engine in this vehicle has a high fuel pump pressure requirement of about 60-65 psi. I suspect that its to low and or the fuel filter is restricted. This is a common problem and I think you will find your self replacing the fuel pump and filter. Run a fuel pressure gauge on here and if its below 60 psi replace the pump and always replace the filter when replacing the pump or you will not get a warranty on the pump.

The lean condition of low fuel pressure will cause the random misfire code but the o2 sensor code will be a hard fault in the sensor and will need to be replaced also. The O2 sensor will not cause your power problem, but it will affect your gas mileage. This should get you down the road to a solve for your symptom. If you need more help please ask me and I will be glad to help you. Thanks again for using justanswer.com

P.S. after hitting the accept button please leave positive feedback if I have been helpful to you. Thank You!

 

Customer: replied 5 years ago.
I put a pressure gage on it this morning and drove up the road and up one of the hills that I've had this problem on. The fuel pressure was 54 at idle and would go up to 58 on acceleration. The usual stumble/bog never happened, I drove up and down over and over but could not get the symptom to appear. When I shut off the engine, the pressure slowly crept up to 62 in about a minute.
Expert:  Larry replied 5 years ago.
The pressure is below spec and has been a known source of symptoms like yours. After shutting engine off heat will cause the fuel to expand and that causes fuel pressure increase. That tells us the the fuel system is not leaking down through an injector or regulator. On my fuel pressure tester it has a valve so I can purge fuel off into a container that can be measured this is volume. sometimes when testing volume on vehicles like yours, when the pressure is that low it will die during the volume test because the fuel pump can not keep up. The last test that I would perform before replaceing the pump and filter would be to place a lab scope on the electric feed to the pump so I could see the wave form of the pump motor to see if the brushes were bad or armiture.
Larry, ASE Certified Technician
Category: Chevy
Satisfied Customers: 145
Experience: 29 yrs in repair and transmission overhaul and an ASE Master tech I have owned my shop for 23 yrs
Larry and other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
I just changed the fuel filter and took the van out for a drive. The pressure at idle has gone p to about 56 and a shakey 60-61 at a steady 55mph. Not sure if thats from air in the line from the new filter, but it is certainly running better with no bog/stumple when accelerating. I'll drive it in to work tonight. The drive home has a 2 mile 30% grade that has been the main location for the problem. That will also use up some of the 25 gallons of gas I put in yesterday. Dang, I hate dropping that tank!

Thanks Larry. You've been a great help!
Expert:  Larry replied 5 years ago.

I know its a pain to drop. You have increased your fuel pressure though and may not have to do a pump. keep your fingers crossed and let me know how it works for you.

FYI It always seems that when we have to do a fuel pump the tank is always full.

One more note , the manufactures that make these pumps claim that they will last a lot longer if you keep the fuel filter changed every 10,000 miles and always keep the tank above 1/4 tank. Good luck and let me know how it goes.

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