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Diagnose This ('90 350 TBI) *UPDATE*

Bubba Ray Boudreaux

Bubba Ray Boudreaux

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Diagnose This (\'90 350 TBI) *UPDATE*

This ought to be a hoot so here we go.

Vehicle: '90 3/4 ton 4wd with 350 TBI, 4 SPD manual well abused farm truck.

Problem: It ain't running.

This is my brother's truck. He thought it was the fuel pump, so after replacement, it still ain't running.

Knock sensor was replaced in conjuction with the fuel pump because when he replaced the engine, he didn't know the knock sensor was a needed item. I hooked the new sensor up last night, is the plug suppose to be a bare, needle looking thing? My thought is that there used to be some sort of rubber cover over this.

So the truck wasn't running, narrowed down to there's no power to the fuel pump, since it's not running with the key on. Today, he said he is not even getting a check engine light.

One thing we found last night was a wire (orange with black stripe IIRC) going into the fuel pump relay had been wrecked, showing bare wire which occured because apparently the air filter housing turned around /forums/images/graemlins/confused.gif.

I'm at a lost, and I'm the one who's got the knowledge to get us this far, but don't have the truck running yet.

Thoughts, ideas????????????

5/21/04

I mentioned the bare wire up above. I had called my father in law Monday night, and he told me the fusible link was probably the problem.

Well last night, we went back down and a buddy that is good at this electrical stuff started chasing stuff and I show him the wire. With a disbeleiving audience gathered around (except myself), he showed the world that in fact this was the problem and in fact the fusible link had gotten killed by this bare wire. So in the end, my brother gets all kinds of grief for not listening to the more intelligent folks and I get a free spare fuel pump. /forums/images/graemlins/thumb.gif
 
Re: Diagnose This (\'90 350 TBI)

Is there a fuse for that fuel pump wire? Are you getting power in and out of the relay?
 
Re: Diagnose This (\'90 350 TBI)

Well, since y'all are in Okie Land, check to see if there's an engine under the hood.... /forums/images/graemlins/grin.gif /forums/images/graemlins/rotfl.gif
 
Re: Diagnose This (\'90 350 TBI)

check the fuse, if power there then checkthe relay, physically pull the square plastic cover off of it make sure itworks as advertised. if not replace itif yes then make surethat you get power fromfuse to the relay and make sure there is power coming from where ever it comes from to activate the relay. then check continuity between the relay and the pump. and check the ground for the pump also.if relay is not being activated find out why now that your this far, you will need a wireing diagram, I prefer alldata, its very indepth for things like this ???pm me, I'll get back to you as soon as I can /forums/images/graemlins/waytogo.gif
 
Re: Diagnose This (\'90 350 TBI)

[ QUOTE ]
Well, since y'all are in Okie Land, check to see if there's an engine under the hood.... /forums/images/graemlins/grin.gif /forums/images/graemlins/rotfl.gif

[/ QUOTE ]


/forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif
 
Re: Diagnose This (\'90 350 TBI)

[ QUOTE ]
Well, since y'all are in Okie Land, check to see if there's an engine under the hood.... /forums/images/graemlins/grin.gif /forums/images/graemlins/rotfl.gif

[/ QUOTE ]

Hey buttmunch, if I wanted your answer, I would have given it to you /forums/images/graemlins/waytogo.gif
/forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif

Forgot to add one piece of information, checked all fuses since this POS doesn't have a fuse labeled for the fuel pump. There was one that was not working, it was the SGL LGHT fuse. The book said that the fuel pump fuse should be 20 amp, checked all of those, all were good.
 
Re: Diagnose This (\'90 350 TBI)

[ QUOTE ]
[ QUOTE ]
Check for power in and out of the relay next.

[/ QUOTE ]

Nada coming out of the relay............

[/ QUOTE ]

Any power in with the key on? Should actually have 2 wires with power when the key is on and only 1 when the key is off.
 
Re: Diagnose This (\'90 350 TBI)

The wire you said was wrecked goes directly to the fuel pump. You can jump from the battery to that wire and see if the fuel pump is working properly. Have you checked any of the fuse links on the fire wall?
 
Re: Diagnose This (\'90 350 TBI)

Does the truck have any power? Sounds like it could be a bad ground.
 
Re: Diagnose This (\'90 350 TBI)

i recently had the same problem with my 90 blazer with the 350 and tbi. changed fuel pump, relay, and oil pressure sending unit. changed ignition module and has run fine since. module sends signal to emc to fire injectors. it would run for a few seconds whn gas was poured down the tbi. hope this helps.
 
Re: Diagnose This (\'90 350 TBI)

My 88 tbi would run good with a squirt of starting fluid. But if you shut it off you would have to squirt it again. Turned out to be the fuel sending relay. 14.00 at Motion Auto.
 
Re: Diagnose This (\'90 350 TBI)

[ QUOTE ]
Does the truck have any power? Sounds like it could be a bad ground.

[/ QUOTE ]

It's got power, but no power to the fuel pump.
 
Re: Diagnose This (\'90 350 TBI)

Check your ignition module like Mudbudd says. If it goes out, the ECM will cut power to the fuel pump/relay to keep the engine from flooding.
 
Re: Diagnose This (\'90 350 TBI)

You should have power with the key off to the orange wire at the relay. With the key on, there should be power on a green with black stripe wire. With the key on, check for power on both of these, if you have power on both of them, then check for power on the tan with white stripe wire, this should be the wire going to the fuel pump. If there is no power on it, then I would check to make sure the black wire going to the relay is grounded. If it is, then I would say the relay is bad.
 
Re: Diagnose This (\'90 350 TBI)

I also had the same problem. I had blown my ecm or ecmb fuse ( the one for the fuel pump). Replaced that fuse and all was good.
 
Re: Diagnose This (\'90 350 TBI)

Fix that broken wire. Make sure your oil pressure switch is connected. You can bypass the Fuel Pump Relay (factory bypass), jump power to that extra wire sticking out of the relay located on the firewall towards the passenger side. If you have access to a wiring diagram it would be very helpful....check that, you also have to know some electrical diagnosis. A knock sensor would not prevent the truck from running. So if the fuel pump does not work after that bypass, its probably a bad wire, like a ground rusted. Look back under the rear driverside wheel well and check for that ground on the frame. If it all possible, check the wiring harness at the tank for power to the pump. Once the pump starts working, crank the engine and watch the injectors for fuel spray. If it don't start then its ignition related. Good luck.
 
Re: Diagnose This (\'90 350 TBI)

[ QUOTE ]
Check your ignition module like Mudbudd says. If it goes out, the ECM will cut power to the fuel pump/relay to keep the engine from flooding.

[/ QUOTE ]

Are you sure? When I had an ignition module go out a few years ago, I didn't lose power to the pump. /forums/images/graemlins/confused.gif

[ QUOTE ]
Did you check all the fuses?

[/ QUOTE ]

Yup.
 
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