TBI rebuild

[JPVortex]

Hello today I rebuilt the TBI unit on my 94 K1500 with the 350. The truck was running before but ran a bit rough cold.

I had to get a different throttle body to rebuild because I cross threaded a couple fittings on the old one working on fuel lines.

However after the rebuild today it does not want to run. I crank it and it pops off for a second then stalls. After toying with it for 15-20 minutes it finally starts up and runs. It runs great when it finally starts.

When cranking it and I give it gas sometimes it will stutter to life and rev like crap.

I took the IAC and TPS off my old throttle body and put them on my rebuild one, but still no luck at all.

I did notice when rebuilding the tbi that the fuel pressure regulator cap from my old one was a bit different from the one I rebuild off of and it had a piece inside that the other one didn’t. I couldn’t use the one that it was using though because it was bent so I took the one off the donor tbi with the spring from my old tbi unit. Could this be causing an issue? Should I rebuild it again with a totally new regulator and spring?

 

[Schurkey]

Use all the parts from one regulator...or all the parts from the other regulator. There's several styles. I don't know why GM didn't standardize one format and stick with it.

Verify fuel pressure during "prime" and when the engine is running.

Are you sure the poor starting is due to the throttle body, and not some other issue like a screwed-up coolant sensor, or the EGR stuck part-way open?

 

[JPVortex]

Use all the parts from one regulator...or all the parts from the other regulator. There's several styles. I don't know why GM didn't standardize one format and stick with it.

Verify fuel pressure during "prime" and when the engine is running.

Are you sure the poor starting is due to the throttle body, and not some other issue like a screwed-up coolant sensor, or the EGR stuck part-way open?

I will definitely try using the spring from the same regulator that I have the cap on, as I did mismatch those parts. I may end up ordering a new regulator with the cap, spring and everything.

I just don’t want to take it all apart again and damage the gaskets. Already had to pull parts of it apart today again because I didn’t install the regulator correctly and bent the cap for it(that’s why I swapped over to the other regulator cap with a mismatching spring) I wonder if there’s a slight difference in the springs retention “springiness” or length. I may need to get another gasket kit.

I don’t think anything else would cause it as it was starting fine before I did the tbi rebuild. I think the coolant temp sensor is fine, it was replaced a couple months back when I did intake gaskets, and the EGR diaphragm held pressure as of a couple months ago aswell.

 

[Scooterwrench]

Did you remove and reinstall the curb idle screw?

 

[JPVortex]

Did you remove and reinstall the curb idle screw?

No I did not

 

[JPVortex]

So for some reason the regulator cap on my old tbi regulator had this inner piece that I'm not seeing in a lot of them online(picture below circled, hard to see), but the one off




the tbi I am rebuilding doesn't have this at all. It just has the cap with the spring. I used that cap. However I did use that cap with the spring from the regulator off my old tbi unit that had that weird circle part in it. Could that be causing a problem with regulating fuel pressure? Should I pull the tbi apart again and either put that circle piece in there or use the spring that originally went with the cap that didn't have this circle piece in it?

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[JPVortex]

Here’s a good picture of the circle piece I’m talking about

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[tayto]

are the injectors from the original TBI? have you checked fuel pressure?

 

[Schurkey]

There has to be "something" for the spring to seat against. There's the stamped-sheetmetal spring seat like you've got pictured.

There's also a cast-zinc version. There may be other kinds as well.

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[Schurkey]

Are you sure the poor starting is due to the throttle body, and not some other issue like a screwed-up coolant sensor, or the EGR stuck part-way open?

I still think you need to connect a scan tool and verify all the sensors and computer outputs.

Wouldn't hurt to check the usual "tune-up" items--distributor cap, rotor, plug wire, plugs, initial timing, PCV system operation, fuel filter, fuel pressure, etc.