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Old 08-23-2004, 08:49 PM   #1
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Default '87 TBI 305 help....

How does this thing work?

We've got an '87 GMC vandura with the vin H LO3 305 engine.
It'* a conversion van and the ECM is under the drivers' seat..

I've found the 02, TPS, IAC, MAP and coolant temp sensor...

It cranks like it'* right on the edge of starting, but is either flooded or lean...

So far I've rebuilt the TB, Replaced the fuel filter and put new gas in it. It was parked one day two years ago when it wasn't needed anymore, but now it'* needed....

If it'll give you guys any insight, It would barely idle, but die when under even light load and rev slowly in neutral. So I rebuilt the TB today, New FPR diaphram, new gaskets, new injector seals and filters. Now it doesn't start. I removed probably 1/8" to 1/4" of gunk from every surface... When trying to start it almost fires, but as soon as you think about touching the gas it dies.

Does anyone know of a place I can find how to test the various sensors?
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Old 08-23-2004, 09:02 PM   #2
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There'* no codes, Plugs wires rotor cap were done about a month before it was parked. I can watch both injectors spray too. (that'* kinda cool)

So far I've found this site www.chevythunder.com that gave me the basic idea of how it works, and that it uses ECM 1227747... And 67-72chevytrucks.com basically told me they had nfc, and to check www.chevythunder.com....


(I edited the first post to be more complete)
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Old 08-23-2004, 09:23 PM   #3
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The 92 parts van I bought and gutted had a 350tbi also, same symptom. However this once was caused by mice and rats that ate the fuel pump harness and lines. Once those were repaired, it started right up, and yeah watching those injectors rain down gently is cool

I'm thinking spark or maladjusted timing, timing is computer controlled on those engines, but if the distributer got moved at all, then it needs to be reset, I think 0 degrees before TDC. I can look in this Haynes manual to be sure.

HTH
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Old 08-23-2004, 09:28 PM   #4
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is it also possible that the fuel pump is tired and not developing enough pressure? I think the TBI needs 6psi to function properly. Its a bear to drop this tank, especially if there is a reciever hitch installed. (mine did and I just about kilt myself getting it down) I will recheck the pressure spec and let you know if it isnt right. How does it run if you just pour a smidgen of fuel onto the throttle plates? Careful of backfires there.
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Old 08-23-2004, 09:50 PM   #5
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I know there'* more than enough fuel pressure... Dad and brother were sitting in the van reading the stuff I printed out from chevythunder, brother turned on key to listen to radio while I was changing fuel filter. There'* fuel pressure.

I just pulled out my trusty Actron CP7504 (inductive timing light), threw it on #1 and cranked... Everytime the van tries to start the light would light, when it just cranks, no light. Measuring ohms of spark plug wires now.

If this just comes down to wires I'd be soooooo happy, Ive learned so much about the van in the process.
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Old 08-23-2004, 09:58 PM   #6
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be sure to inspect the wires dude.. really well, because just a small crack can prove to be the problem


-justin
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Old 08-23-2004, 10:10 PM   #7
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Gee, can you guys guess what I'm telling dad to buy next?

1 - 13.78 Ohm
2 - 24.00 Ohm
3 - 11.80 Ohm
4 - 10.75 Ohm
5 - 11.29 Ohm
6 - 8.16 Ohm
7 - 6.78 Ohm
8 - 9.10 Ohm
Coil - .484

And I get nice even light from the coil wire too...
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Old 08-23-2004, 10:54 PM   #8
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Man, sorry you had to find out the hard way that there was fuel pressure, hope it didnt get in your eyes.

I hope wires fixes it, a good HEI should still push something thru em LOL. Is this a high mileage engine?
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Old 08-23-2004, 11:17 PM   #9
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The ODO says 52K, I'd bet 252K, we bought it in 95 with right around 100K.
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Old 08-24-2004, 12:45 AM   #10
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Well, I think we got this about whooped. We noticed the IAC motor was getting hot, Pulled it out, compared the pintle length to the hole depth by eye, it was open like 3/8". Tried to activate it both directions with 12v off the battery, it didn't move. Since we looked it up and it only costs dad $30 to replace, we broke it. It'* a bar with a partially threaded shaft, and a internally threaded rotor of the electric motor. And it was rusted solid. Now I know how those work. Dad'll get one in the morning, And we'll see how that works.
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