Anyone with Chevy TBI experience?

[SuperCab]

So I got the 400sbc up and running this week, but I'm having a pretty big problem with it.

It runs WAY too rich. It literally puffs black smoke out... It's like it never goes out of 'full choke' mode. The idle is a little high too.

Havn't really done anything to it yet, just looking for suggestions if anyone has any.

I'm thinking maybe the temp sensor for the ecm is bad and reading cold all the time, which would explain the rich running and the high idle...

Thanks for any help you guys can give.

 

[CowboyBilly9Mile]

I would pull codes since it's so easy to do; this will tell you if the temp sensor is at fault. If no codes show up, I'd focus on the TBI unit itself, as I recall they look like a contac capsule standing on end. I've been told that they weren't all that hard to rebuild either. These TBI units were not famous for reliability.

*I'm not sure what year your rig is, but the O2 sensor used on early GM CCCS's were a 24,000 mile replacement item. I can tell you from experience they don't seem to last (reliably) much past 35K; you'll start to experience the intermittent CEL.

 

[Fellro]

Look for a vacuum leak. Fuel injection is no different than carbs on this aspect. If you get a vacuum leak, it makes the computer think you are stomping on the pedal due to the low vacuum. Make sure that the injectors are pusing as well. Otherwise, it can be a control issue or short somewhere. I haven't had much for issues with the throttle body it self, usually something else, just a matter of understanding the system.

 

[polarbear]

A 400 with TBI? Any 400 I've been around had a quadrajet sitting on top of it.

 

[Fellro]

The TBI manifolds will bolt to the older motors. It's the Vortec intakes that need a little work to fit.

 

[SuperCab]

I pulled the codes, it said a bad cts and o2 sensor, so not bad.


I put the 400 into this formerly 5.7tbi equipped rig and kept the tbi. Not real hard to do. just change the middle 4 bolt holes on the tbi manifold a little an it'll bolt right up.

I like it so far - very powerful.

Thanks for the responses guys! At the chevy forum I got 0 replies. yup ZERO. bunch of losers...

 

[5.0]

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Did it say coolant temp out of range? Did you pull the codes with a warm engine?

Just curious, which Chevy forum were you asking on?

.

 

[Fellro]

Good chance the CTS read way cold, and the gauge reads off a different sender. I have watched a CTS go from normal operating temp to reading -54 before on a Pontiac Sunbird. At the same time, it would drop the TCC and go into open loop..

 

[CowboyBilly9Mile]

Sounds like an easy fix, let us know what happens.

 

[SuperCab]

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Just curious, which Chevy forum were you asking on?

.

73-87chevytrucks.com and I'm not real happy with it. any other good chev forums out there?

Good chance the CTS read way cold, and the gauge reads off a different sender. I have watched a CTS go from normal operating temp to reading -54 before on a Pontiac Sunbird. At the same time, it would drop the TCC and go into open loop..

Yeah, I think that's what happened, and the o2 sensor apparently was reading lean too, wich just made the problem worse.

I think I've got it now though.

 

[5.0]

any other good chev forums out there?

For my Chevy trucks I go to:

http://www.fullsizechevy.com/forums/
or
http://coloradok5.com/forums/index.php

Fullsize Chevy has a lot of younger guys on it and the tech is fairly good, although don't take anything as the truth just because it's posted over there.

CK5 has a more mature audience and the tech is right on. They are geared toward off roading the 73-87(91) trucks and blazers, but they know quite a bit about the TBI system.

.

 

[SuperCab]

Thanks for that 5.0!

I'm driving the 87 today. right now I'm sitting in the mall hogging the free wifi looking out the window at it. I told Brandon to leave his cell turned on in case I need a tow or something

It runs rough at low throttle, but when you get on it it really runs great. I didn't put new plug wires on it though, so that could have alot to do with it...

Also, what kinda muffler did these things have on em from the factory? I like the way it sounds, but I don't know if it's aftermarket or what...

 

[Fellro]

Should have a 3" into a dual 2" outlet if factory. I put a dynamax on mine when the muffler went bad when I had my 90, then had the pipe straight out the back, that sounded pretty good...