Need help with a 93 silverado 454 map sensor/idle problem

[Shibby50]

Buddy of mine had the check engine light come on on his 454 tbi. When I unplug the MAP it runs fine. With it plugged in, it won't idle at all. I think he messed with the idle control screw, not sure. He wants to get rid of the CEL and it's not really my area of expertise. Any idea's what's wrong? The MAP sensor itself?

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[LSx S10]

Buddy of mine had the check engine light come on on his 454 tbi. When I unplug the MAP it runs fine. With it plugged in, it won't idle at all. I think he messed with the idle control screw, not sure. He wants to get rid of the CEL and it's not really my area of expertise. Any idea's what's wrong? The MAP sensor itself?

My TBI 4.3 did the exact same thing and it was a bad fuel pump. Could only accelerate under 1/4 throttle or less, but unplugging the map would make it run a lot better. The pump sounded strong but it ended up being bad. It's really hard to check fuel pressure on tbi's. The best way i found was to pull the fuel filter out and hook up a fuel pressure gauge right to the fuel line.

If it is the fuel pump, that CEL will be for a lean condition. You need a Tech 1 or Tech 2 to pull those codes. You could do the paper clip trick too.

 

[Turbocharged400sbc]

paper clip, short terminals a and b together and read the flashes of the ses
youl get 1 space 2 three times for the 12 start code and then youll get you codes listed in order then a 55 for end codes

it wil flash each code three times before moving to the next, dont blink too much lol

 

[Shibby50]

paper clip, short terminals a and b together and read the flashes of the ses
youl get 1 space 2 three times for the 12 start code and then youll get you codes listed in order then a 55 for end codes

it wil flash each code three times before moving to the next, dont blink too much lol

It only gets a ses when the MAP is unplugged. Which is when it runs. When the MAP is plugged in and the car wont run it has no ses.

 

[Turbocharged400sbc]

gonna have to scan it with an obd1 scanner/snapon red brick or start checkign the basics like fuel pressure/timing, maybe swap for a known good map and retest

 

[LSx S10]

Buddy of mine had the check engine light come on on his 454 tbi. When I unplug the MAP it runs fine. With it plugged in, it won't idle at all.

It only gets a ses when the MAP is unplugged. Which is when it runs. When the MAP is plugged in and the car wont run it has no ses.

Which is it?

If you guys weren't so far away I would let you use my tech 1. I think your next step should be to pull the codes with a paper clip, and if you get a lean code, check the fuel pressure.

If it ends up being the fuel pump, don't try to drop the tank. Just get a couple buddies and pull the bed off, sounds crazy but it is sooo much easier. Especially because the fuel lines on the top of the tank are going to be really rusty, and with the bed out of the way you don't have to unhook them. The whole assembly will come out with the lines still attached. What you can even do instead of pulling the bed completely off, is set something up behind the truck that is about the height of the rear bumper and just slide the bed back. That way just you and your buddy could do it yourselves.