Got a question from a friend

phat46 · October 12, 2005, 06:06:41 PM

A friend of mine is building a truck for his sons first vehicle. He has a 4X4 S-10 that had a 4.3 in it. He put a 350 in it and is using the throttle body injection from the 4.3 on the 350, he was told it will work. The problem comes when he tries to start it. It has fuel to the throttle body, but it won't inject it into the throttle body. It has about 8 pounds of fuel pressure, and power to the throttle body. Any ideas? BTW he is using the 4.3 computer and wiring.

enjenjo · October 12, 2005, 06:22:18 PM

He will probably have tp change the prom. What is he using for a distributor?

phat46 · October 12, 2005, 06:42:47 PM

Quote from: "enjenjo"What is he using for a distributor?

Dunno, I'll ask tomorrow if he doesn't get it figgered out tonight

SKR8PN · October 12, 2005, 08:42:41 PM

Quote from: "phat46"A friend of mine is building a truck for his sons first vehicle. He has a 4X4 S-10 that had a 4.3 in it. He put a 350 in it and is using the throttle body injection from the 4.3 on the 350, he was told it will work. The problem comes when he tries to start it. It has fuel to the throttle body, but it won't inject it into the throttle body. It has about 8 pounds of fuel pressure, and power to the throttle body. Any ideas? BTW he is using the 4.3 computer and wiring.

I don't think 8 lbs is near enough fuel pressure............Should be up around 45-50lbs??

Stakebed · October 12, 2005, 08:46:48 PM

I'm no expert on fuel injection, but a cavalier I used to own wouldn't run at times. The fuel pressure if I remember right was about 40 psi and was supposed to be about 45 psi. It was throttle body. I don't know if the systems vary that much but 8 psi sounds low from my limited knowledge.

tomslik · October 12, 2005, 08:52:44 PM

Quote from: "SKR8PN"
Quote from: "phat46"A friend of mine is building a truck for his sons first vehicle. He has a 4X4 S-10 that had a 4.3 in it. He put a 350 in it and is using the throttle body injection from the 4.3 on the 350, he was told it will work. The problem comes when he tries to start it. It has fuel to the throttle body, but it won't inject it into the throttle body. It has about 8 pounds of fuel pressure, and power to the throttle body. Any ideas? BTW he is using the 4.3 computer and wiring.

I don't think 8 lbs is near enough fuel pressure............Should be up around 45-50lbs??

nope 9-13 on tbi units...

do you have injector pulse?
spark?

phat46 · October 12, 2005, 09:09:08 PM

Quote from: "tomslik"
Quote from: "SKR8PN"
Quote from: "phat46"A friend of mine is building a truck for his sons first vehicle. He has a 4X4 S-10 that had a 4.3 in it. He put a 350 in it and is using the throttle body injection from the 4.3 on the 350, he was told it will work. The problem comes when he tries to start it. It has fuel to the throttle body, but it won't inject it into the throttle body. It has about 8 pounds of fuel pressure, and power to the throttle body. Any ideas? BTW he is using the 4.3 computer and wiring.

I don't think 8 lbs is near enough fuel pressure............Should be up around 45-50lbs??

nope 9-13 on tbi units...

He tells me that he was told it would need 5-8 lbs. I don't know about pulse, but I wouldn't think so, is there any way to check that?
It must have spark, he said it will fire with gas dumped in the T.B.

do you have injector pulse?
spark?

1FATGMC · October 12, 2005, 09:31:50 PM

Quote from: "phat46"A friend of mine is building a truck for his sons first vehicle. He has a 4X4 S-10 that had a 4.3 in it. He put a 350 in it and is using the throttle body injection from the 4.3 on the 350, he was told it will work. The problem comes when he tries to start it. It has fuel to the throttle body, but it won't inject it into the throttle body. It has about 8 pounds of fuel pressure, and power to the throttle body. Any ideas? BTW he is using the 4.3 computer and wiring.

Is he using the computer off of the 4.3? I would think that it should start if all the sensors are hooked up, etc., but there is no way that I think the injectors would be big enough and the fuel curve right to work with the 350 if the computer and everything else came off of the 4.3. I'm guessing that something is not hooked up right to the computer and it won't fire the injectors as it sees something is out of bounds.

From what I've read even the stock 5.0 V-8 stuff is not really right to run stock on a 5.7.

c ya, Sum

Crosley.In.AZ · October 12, 2005, 10:10:18 PM

Quote from: "1FATGMC"
From what I've read even the stock 5.0 V-8 stuff is not really right to run stock on a 5.7.

c ya, Sum

that is correct , been there.

I changed the prom in the ecm and the truck ran well with a Hypertech chip in a 1989 TBI setup from a 305 motor onto a stock crate 350 motor

phat46 · October 12, 2005, 10:18:25 PM

Is he using the computer off of the 4.3? I would think that it should start if all the sensors are hooked up, etc., but there is no way that I think the injectors would be big enough and the fuel curve right to work with the 350 if the computer and everything else came off of the 4.3. I'm guessing that something is not hooked up right to the computer and it won't fire the injectors as it sees something is out of bounds.

From what I've read even the stock 5.0 V-8 stuff is not really right to run stock on a 5.7.

c ya, Sum[/quote]
...that's kinda what i thought, but I don't know much about F.I. but had heard the same thing....my friend was told that it would work....

rooster · October 12, 2005, 10:38:47 PM

Just a guess! If the donor 4.3 and computer had Vac adv Dizzy , I would think it should work, If the 350 has vac advance also. Intresting post!

jaybee · October 12, 2005, 10:41:28 PM

"I don't know about pulse, but I wouldn't think so, is there any way to check that?"

Just had to answer that very question on one of my own. Unhook the injector plug and probe it with a grounded test light. Crank the engine. The light should flash. Either bright or dark but constant is a failure. It could show a dim light if it's pulsing too fast to see as a pulse. That wasn't an issue with the multiport system I'm dealing with but might be with some others. As cross check you could also hook your test light to the positive battery terminal and repeat. Some units signal the injector by grounding it so you have to provide power instead of ground in order to test. I think all GM units signal the injector by powering it. Mechanics have lights that plug into the injector harness to perform this test.

enjenjo · October 12, 2005, 10:51:18 PM

The computer itself is the same, but the prom is different. The injector can be changed for one from a 5.7 if it's a problem, but it hasn't got that far yet. The engine gives the computer a check pulse once a revolution to restart the sequence, GM does it different ways on different engines. If the new engine is not supplying the check pulse, it won't start. That's why I asked about the distributor. I think the 4.3 supplied the pulse from a crank trigger, and a 5.7 usually comes from the distributor.

junkyardjeff · October 12, 2005, 11:01:48 PM

A friend installed a 350 in a 89 astro van,he had to change the prom and had to go to a 350 throttle body. It would run with the 4.3 throttle body but would surge,if I can remember correctly the 4.3 and 350s used the same sensors so it should fire up if the prom is changed. Jeff

rooster · October 12, 2005, 11:51:43 PM

What year is the s10?

update:
My Delco book only gos to 92 !

S10s used the D1990 module and the D1987 pickup coil 1987-92 4.3L!

Chevy trucks used that exact set up only in 1991-87 ! 5.0L,5.7L,7.4L!

In the Chevy cars I can find no exact match!

But that is as far as my book goes'.