Immediate help needed TBI nightmare!!!!!!!

[opfor2]

This morning I wanted to change the throttle position sensor on the throttle body of my 90 K-5 w/5.7L eng. As I was removing the two screws they both snapped off inside of the throttle body. One snapped off right at the opening while the other snapped off well inside of the TBI. The TPS is being held on by just one of the screws and the truck seems to run ok for now. What I need to know is who sells the TBI aluminum body so I can replace it? This really sucks, something that should have been a 10 minute job has turned into a nightmare. This is my daily driver and I need to get the TBI replaces ASAP. HELP!!!!

Thanks

Dan..

 

[camok5]

You can get one through turbo city or cfm-tech.

 

[southernspeed]

I've seen lots on ebay!

 

[Ryan B.]

junkyard time.

 

[shane74]

Ok, here is what you need to do to save yourself some $$. Pull the TBI unit off the truck. The screws that snapped off are 5mm screws. Go get the correct size drill and a 6mm tap. Drill the screws out and re-tap it for 6mm screws. Next, drill out the holes on the TPS sensor (use the same drill you use for the 6mm tap). There is plenty of material in the TBI body to do this. Start with a small drill bit (1/16" or 1/8") to drill through the snapped off bolts. Then upsize to the drill for the 6mm screws. Go slow and drill as straight as possible, and you will be fine.

I have had to do this on 3 or 4 of my TBI units. It's not a big deal. Just be patient and take your time to do it right. The reason the screws snapped off is because they are a different material than the aluminum TBI unit. Electrolysis "welds" them into place. Snapping them is a common occurance when replacing the TPS sensor.

Actually, I'm really suprised the TPS sensor went bad at all. Why did you have to replace it? Did you re-set it for the correct voltage?

 

[opfor2]

Well I’m having a hesitation problem with my blazer. When I’m at a stop light the idle sometimes bounces around a little bit and when I depress the gas pedal to take off the truck seems to stumble. This only happens when I lightly press the gas pedal. I’ve checked for vacuum leaks, rebuilt the TBI unit, replaced all gaskets on the unit, replaces all vacuum hoses, and now I’m replacing sensors. I was thinking that the TPS might have gone bad because the vehicle only hesitated when I press the gas pedal lightly…

 

[shane74]

Well I’m having a hesitation problem with my blazer. When I’m at a stop light the idle sometimes bounces around a little bit and when I depress the gas pedal to take off the truck seems to stumble. This only happens when I lightly press the gas pedal. I’ve checked for vacuum leaks, rebuilt the TBI unit, replaced all gaskets on the unit, replaces all vacuum hoses, and now I’m replacing sensors. I was thinking that the TPS might have gone bad because the vehicle only hesitated when I press the gas pedal lightly…

$100 says it's your EGR valve. They are not controlled by the ECM, but they influence it big time. There is a vac. line that runs from the EGR to the MAP sensor. IF the EGR goes bad, it will throw all kinds of codes. None of which are your problem. If it is your EGR, replace it with an OEM. DO NOT waste your money on a cheap aftermarket unit. They break quickly and are generally a POS. I just went through this with my '87 TBI 350. I'd bet $100 right now that it's your EGR and none of other sensors. You do have a vacuum leak..it's the EGR not functioning correctly.

 

[dyeager535]

And you can typically disconnect the EGR and prove to yourself whether it is the cause or not.

Throwing parts at this stuff is expensive, TPS is easily tested.

 

[mtrdrms]

I have a TBI from an 87 350. If you want it I will sell it to you for cheap. Email me at [email protected]

 

[shane74]

And you can typically disconnect the EGR and prove to yourself whether it is the cause or not.

Nope, not on the 86-87's you can't. The way to prove if it's the EGR or not is to stick your finger under it and push on the diaphram. If you can't move it, it's shot. If you can and nothing changes, it's shot. If you can move it and it does change the way the eng runs, it might be working intermittently. Mine did that, The shaft that controls the diaphram cracked in the middle. Sometimes it would work, other times it wouldn't.

The EGR is a complete PITA in the early TBI rigs.

 

[dyeager535]

That's right, we went over this before didn't we?

However, if you remove the vacuum source, couldn't that potentially make the problem either 100% consistent, or eliminate the problem?

Just thinking aloud here...if it's getting vacuum when it shouldn't (again, you are more familiar with this than I) or is sticking open after it DOES get vacuum, it's possible disconnecting vac line can still give an indication, right? I just don't know how that vacuum is "switched" for EGR operaton. No EGR solenoid as I recall, you say MAP has a line running to it, guessing MAP sensor is what "switches" EGR in truck app's?

I can see if the problem is 100%, that the valve just can't/won't seat because of failure, or simply carbon buildup.

 

[shane74]

That's right, we went over this before didn't we?

However, if you remove the vacuum source, couldn't that potentially make the problem either 100% consistent, or eliminate the problem?

Just thinking aloud here...if it's getting vacuum when it shouldn't (again, you are more familiar with this than I) or is sticking open after it DOES get vacuum, it's possible disconnecting vac line can still give an indication, right? I just don't know how that vacuum is "switched" for EGR operaton. No EGR solenoid as I recall, you say MAP has a line running to it, guessing MAP sensor is what "switches" EGR in truck app's?

I can see if the problem is 100%, that the valve just can't/won't seat because of failure, or simply carbon buildup.

Unfortunately, the EGR is just a plain b*tch to work with. Yes, you would think that disconnecting it would either improve or at least create a constant condition. What I found was that the carbon build up inside the intake manifold was also messing with me. Once I cleaned it all out, then you could get a constant condition by plugging off the egr and MAP sensor. Till then, it was a bear to diagnose. Heck, eventhe dealer couldn't find it!

 

[dyeager535]

Heck, eventhe dealer couldn't find it!

Come on now, you think fixing a problem the dealer couldn't is an accomplishment?

(lemme rephrase: you are surprised you are more accomplished/intelligent than certified technicians that GM charges you $75/hour for?)

Seriously though, pulling an EGR that has tons of miles on it to clean the passages and inspect everything is certainly not harmful. Especially when it's a "common" problem.

 

[shane74]

Come on now, you think fixing a problem the dealer couldn't is an accomplishment?

(lemme rephrase: you are surprised you are more accomplished/intelligent than certified technicians that GM charges you $75/hour for?)

Seriously though, pulling an EGR that has tons of miles on it to clean the passages and inspect everything is certainly not harmful. Especially when it's a "common" problem.

Smartass!

Yeah, the EGR is so often the culprit and it is almost always over looked because it's not controlled by the ECM and throws no codes. It's another of those "what you'd really like to slap a GM engineer" things. If I don't sell my burb, I am going to see if I can get away with ripping all that crap off and blocking off the EGR. I'll have to find another vacuum source for the MAP sensor, but in comparison, it shouldn't be that hard.