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91 burb runs! updated 11/12

AKbigsub

AKbigsub

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A friend has a 91 V2500 with a 5.7L gasser and a 4L80E trans. It was running great until their daughter went into the ditch at 55mph. After recovering it from the ditch, they drove it home but it ran rough and was burning rich. Here is the list if parts the shop replace (but it still runs the same):
Fuel pump (fuel pressure is 20 but the mechanic says it should 9-13).
Plugs, cap, rotor, and wires
Ignition module
MAP sensor
EGR valve
ECM
Throttle body (not sure if the injectors are new)
The fuel lines have been blown out and inspected for kinks.

Help!!??
 
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Well, 20 is a lot of fuel pressure for TBI. There is a spring in the back of the TBI covered by a small plate...best I remember that controls pressure. Does it have adjustable pressure regulator or factory?

Not sure if it would make a difference but might try putting a new pressure spring in it. They are a bit aggravating to take out but cheap.

Maybe someone else will know more than me and get you some help.
 
any body looking at comp live data? O2 sensor helps the computer set fuel ratio. long term and short term fuel trim is help full as well. put a vac gauge on it and check timing maybe chain slipped when went in ditch.
 
I haven't been able to think of anything else yet. Looking through your parts list and what Wes Harden said maybe that's it. Good luck with it and keep us updated.
 
Fuel pressure is definitely off if its 20. I somewhat find that hard to believe as I dealt with two of the TBI fuel pumps and neither, brand new, could push more than 14PSI. You can use a higher pressure pump, but the regulator should still keep it in spec.

Did anyone check the o2 sensor? Going into a ditch, maybe something ripped the wire out, or somehow damaged the sensor. Pretty common for them to run rich without o2 input, but it would be the same with 20psi. No way the system would be able to choke the injectors down enough to control fueling under idle and light load conditions. As mentioned, if the o2 works, and you look at the data stream, youd see the BLMs maxed out. I want to say 110 would be what youd see even during light throttle cruise, if the system was so rich the ECM couldnt reduce fueling enough, AND the o2 sensor was working.
 
I am skeptical on that fuel pressure reading. Since it is a PITA to test TBI fuel pressure, I am betting they dead headed the pump for the test. I normally put my pass through gauge in place of the fuel filter when I am changing the filter.
 
Wes Harden said:
I am skeptical on that fuel pressure reading. Since it is a PITA to test TBI fuel pressure, I am betting they dead headed the pump for the test. I normally put my pass through gauge in place of the fuel filter when I am changing the filter.
Click to expand...

Yep. Autozone has a fuel pressure tester they will loan you that works for TBI (if all the parts are there) I just put the adapter between the fuel line and filter.
 
AKbigsub said:
A friend has a 91 V2500 with a 5.7L gasser and a 4L80E trans. It was running great until their daughter went into the ditch at 55mph. After recovering it from the ditch, they drove it home but it ran rough and was burning rich. Here is the list if parts the shop replace (but it still runs the same):
Fuel pump (fuel pressure is 20 but the mechanic says it should 9-13).
Plugs, cap, rotor, and wires
Ignition module
MAP sensor
EGR valve
ECM
Throttle body (not sure if the injectors are new)
The fuel lines have been blown out and inspected for kinks.

Help!!??
Click to expand...
I agree on the questionable fuel pressure data, how about crushed/restricted exhaust? Catalytic converters plugged from the event or rich running condition?
 
bradshawtech said:
I agree on the questionable fuel pressure data, how about crushed/restricted exhaust? Catalytic converters plugged from the event or rich running condition?
Click to expand...

I second checking the exhaust. Rare collapsed exhaust in my y-pipe had my 89 burb not running for years before I discovered. Easy to disconnect at the collectors and try. I also discovered going thru my tbi a bunch of times when it wouldn't run that too they also will not run with too much fuel. The temp sensor or pig tail can make them flood out.
 
Update. Here is a very poorly written statement from the mechanic working on this burb. I copied and pasted it:
There's going to be a lot of people that are going to say computer or ignition module fact of the matter is is that somewhere somehow your fuel injector is getting grounded with the key on it's spraying Full Tilt with the key turned on just like your fuel pump runs with the key on so does your fuel injector it should only run when the computer grounds it and it should just be pulsing it well it's cranking not with the key on Is fuel pump should only run when you turn the key on for 3 seconds and it's running the whole time that keys on So somewhere we got a short to ground I'm going to sit down look at some wiring diagrams tonight and see if the fuel pump in the driver for the fuel pump share anyting it might be smashed part of the harness are some wires that got pulled Going to try to make time to get out there in the next few days we got two problems with your truck the fuel pump runs all the time with key on it should only run for a few seconds when you turn the key on. Then after you start it oil pressure switch provides power to the fuel pump. I need to see why it's running all the time maybe somebody hot-wired it key on. So that's the first problem the second problem is that after running for a few the fuel injector at least one of them I'm not sure maybe both are losing their ground from the computer to fire If I try to start the truck after it dies it won't start at all because there's no driver signal to the injectors but if I turn the key off then back on starts every time Almost like it's tripping a circuit breaker in the computer or elsewhere now it'll run for a few and die again every time because it's losing its drivers signal to the injectors but if I turn the key back off and try to start it the Driver signal comes back every time. So I'm thinking that the fuel injectors or injector it's on too many amps and tripping some kind of circuit breaker somewhere unlikely that it it shorted or a wire is bad because of how it comes back every time when you turn the key off. So that's what we're dealing with they try to gather some more information before I head out there I'll let you know when I'm on my way Yeah. She's wordy.
 
AKbigsub said:
A friend has a 91 V2500 with a 5.7L gasser and a 4L80E trans. It was running great until their daughter went into the ditch at 55mph. After recovering it from the ditch, they drove it home but it ran rough and was burning rich. Here is the list if parts the shop replace (but it still runs the same):
Fuel pump (fuel pressure is 20 but the mechanic says it should 9-13).
Plugs, cap, rotor, and wires
Ignition module
MAP sensor
EGR valve
ECM
Throttle body (not sure if the injectors are new)
The fuel lines have been blown out and inspected for kinks.

Help!!??
Click to expand...
It is fixed! Fuel pump relay and oil pressure switch. He says it runs
 
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