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Chevy: computer keeps going wacko..Silverado..v6 4.3 liter engine…

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I have posted this question earlier today, but the computer keeps going wacko. I have a Chevy 1990 Silverado pickup, V6 4.3 liter engine, and I cannot get any fuel from the tank to the TBI. It quit a week ago, all the symptoms of out of gas. I added gas, no start. Replaced fuel pump, filter, relay, No start. Fuse is OK, relay tested fine. Pump works only when hotwired. Is there another fuel cutoff switch? The manual does not specify any. Paypal have already paid my deposit.
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Answered in 9 minutes by:
6/28/2010
cartech
cartech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,332
Experience: 25 years ase mastertech. shop owner and tech
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if you spray some starting fluid does it start and die
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Customer reply replied 8 years ago
No. Starting fluid produces no action.
does the truck have spark at the plugs
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Customer reply replied 8 years ago
I have managed to get fuel to the TBI by hooking up a direct line from batt. pos. to the grey wire terminal at the underhood fuel pump fuse. Pump etc. seems to be working OK but there's nothing from the ign. switch to the fuse. Still no action on start. I have hooked up an inline spark checker but cannot get a reading.
ok i will do some research this will take me until am as for im finishing up for this evening if this is not ok i will send your question to another expert
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Customer reply replied 8 years ago
Thanks! Truck is still dead in the water so your time and research is welcome. I'm starting to think that maybe the ignition switch is bad, but everything else electrical appears to work fine, except now the brake lights won't come on and I have just installed a new switch, because they refused to go out!
Customer reply replied 8 years ago
According to the wiring diagrams I have, the brake lights/fuel pump fuse etc. appear to route through the ignition circuit. Could this problem be the ecm or the tcc relay? I still cannot get any action from the brake lights or the fuel pump fuse through the ignition switch.
you need to check the ecm ign fuse in the fuse box this fuse runs the stop light switch and the computer so it won't turn the fuel pump on
cartech
cartech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,332
Experience: 25 years ase mastertech. shop owner and tech
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Customer reply replied 8 years ago
ECM/ign fuse is OK.
with the key on do you have power at it
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Customer reply replied 8 years ago
I do get a volt/ohm meter reading with the key on and the fuse removed.
check to see if you have power at the brake lamp switch with the fuse in
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Customer reply replied 8 years ago
Yes I get a reading at the brake light switch.
do you have power at the fuel pump fuse
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Customer reply replied 8 years ago
No power at the fuel pump fuse
do you have single fuel tank or dual tank
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Customer reply replied 8 years ago
It's a single fuel tank
check for voltage on the orange wire of the oil pressure sending unit
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Customer reply replied 8 years ago
The oil pressure sending unit has a blue wire. I get a reading of .8 volts on it.
orange wire on fuel pump relay voltage or not
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Customer reply replied 8 years ago
Yes, 12.19 volts with ign. key on.
dark green and white on the relay do you have power when you turn the key on
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Customer reply replied 8 years ago
No power at the green and white
sorry to say this is the wire from the computer so i will need to dig into that area unfortunately i will not be able to until tomorrow i will be unavailable due to a wedding
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Customer reply replied 8 years ago
I really appreciate your help. Thank you for going the extra mile. If this is your wedding, congratulations! Tomorrow or Monday is fine.
you may need to open the question back up it is getting ready to time out it is my best friends and we thank you
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Customer reply replied 8 years ago
OK I'll reopen question when I figure out how. Have a great time at the wedding!
Customer reply replied 8 years ago
I have traced the green/white wire and it does enter the ecm. I guess replacing the ecm will be the next step, unless there's another test? I don't see any point in having another expert repeat the same steps you have already taken.
i will continue to help i need to get a diagram for the ecm before we make that decision
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Customer reply replied 8 years ago
Thanks! I need to place another deposit so we can treat this as a new issue.
Customer reply replied 8 years ago
The ecm serv.# XXXXX XXXXX 86ATKP K300580414 if this info. is helpful.
on each computer plug there is a orange wire see if there is power to those
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Customer reply replied 8 years ago
No power at either plug
this is the problem there is a burnt fuse link on the power there should be a terminal block with the wires bolted to it pull on each one a little way from the terminal and see if it breaks or stretches
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Customer reply replied 8 years ago
Can't get any break or stretch on these wires. Each one has a black plastic connector fitted to it, may be trouble lies in there. Maybe hooking up a direct lead to each terminal from battery will reveal the troubled wire?

lets try to narrow down the location of power lose check the following for power

this is a bit confusing since there are a couple diagrams for this model so we may have some different results do the best you can

 

 

with the relay for the fuel pump removed from the harness you have voltage to the orange wire this is correct right



Edited by cartech on 7/6/2010 at 10:48 AM EST
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Customer reply replied 8 years ago
Correct. There is 7.5 volts reading at the orange wire. I also checked the readings along the terminal block, each terminal reads 7.5/6 volts.
how much voltage is at the battery itself
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Customer reply replied 8 years ago
Battery reads 8.7 volts.
first thing we need to charge that battery and then test those wires again there isn't enough voltage to be accurate
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Customer reply replied 8 years ago
OK I have installed a fully charged batterywhich reads over 12 volts at the battery and the orange wire on the fuel pump relay and across the terminal posts.
ok what has happened their is a area where the wire branches off on that orange that has failed it feeds those 2 orange on the computer you may want to follow the wire from the relay back and see if you can locate it or just run another wire from the relay orange to the orange on the computer
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Customer reply replied 8 years ago
I have found the branch. There appears to be three orange wires feeding to two. I'll try powering up the computer with new wires and let you know.
sounds good
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Customer reply replied 8 years ago
I now have 12 volts from the orange wire on the larger computer connector and the outer orange wire on the shorter connector. I get no reading from the second orange wire on the short connector, either with or without the ignition on.
let me get my laptop it has the diagram on it did you run one wire or one to each
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what pin is the other orange wire on that plug the power wire should be on terminal 1 at the end
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Customer reply replied 8 years ago
The end orange wires on both plugs have a 12.5 reading. The 'dead' wire on the short plug is about 5 pins in, next to a white/black wire.
that wire should not be hot so now when you turn the key on the green and white next to the orange does it get power the computer must be plugged in
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Customer reply replied 8 years ago
With computer plugged in, the green & white reads .05 with key on, .02 with key off.
and you still have the power to the orange wires
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Customer reply replied 8 years ago
Yes the orange wires read 12 volts
the computer still is not turning the fuel pump on not sure why
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Customer reply replied 8 years ago
Nope. I have double-checked all connections still no action. The grey wire from the pump fuse operates the pump when direct wired to the battery +, but there's no action from the ignition switch. Maybe the ecu is bad after all?
let me take a look and see if there are any other options maybe something chewed the harness and there are more bad wires
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Customer reply replied 8 years ago
OK thanks.
im out of ideas might want to try a new computer
cartech
cartech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,332
Experience: 25 years ase mastertech. shop owner and tech
Verified
cartech and 87 other Chevy Specialists are ready to help you
Ask your own question now
Customer reply replied 8 years ago
Thanks for all your help. I'm going to double-check all the ground connections, and have the ecu checked as well. Previous owner informed me last night that he had problems with one of the ground connections. I posted another deposit which you are fully entitled to, wish I could make it more. I'll let you know if anything works!
thanks i really appreciate it
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Customer reply replied 8 years ago
I have now replaced the ecu, with no result. Still nothing from ignition switch to fuel pump, no spark at coil. No start. So far, I have replaced the fuel pump, filter, relay, fuse, ecm, O2 sensor.
Customer reply replied 8 years ago
If this issue can be revitalised, I have now replaced the distributor (old one was broken at the top) and the ignition coil, engine will start and run briefly when I prime it by hot wiring the fuel pump fuse, but still no fuel pump action from the ignition.
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