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Old 09-07-2011, 10:15 AM
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Rebuilt TBI 350 black smoking, running rough

Hello all, I have recently rebuilt a .030 overbore 350 engine and it is black smoking a little and seems to run rough in higher RPMs.
I'm not much of a Chevrolet mechanic, but I made a project truck out of one of the 1500s that I own.
The modifactions I have done are as follows:
A Comp cams camshaft kit which includes seals, springs, etc. I can't quite remember the camshaft duration, but it was very, very mild. And it it supposedly a camshaft designed for fuel injection engines.
I had the heads reworked, the crankshaft journals checked, and I reused and re-ringed the pistons that were in it.
For fuel upgrades, I put the Holley direct replacement upgrade TB on it (bought used from a friend). I had to rewire that and put the TPS sensor from my old TB onto the Holley TB.
I still have stock exhaust manifolds for the moment (I plan to run headers), and I have yet to purchase a ECM chip.
If you guys could offer any insight, let me know.
I don't know if the piston rings aren't seated, or if it's the throttle body, the TPS sensor, or even the O2 sensor. If you guys could help it'd be greatly appreciated. If you need any more info, feel free to ask.

Thanks!


(Also, if this is in the wrong forum subsection, feel free to move it!)

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Old 09-07-2011, 11:07 AM
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Might I add that I don't know if maybe me not running a programmed chip in the ECM could be the problem. If I put a scan tool on the truck is it going to give me false readings without said chip?
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Old 09-08-2011, 09:55 AM
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Well, at any rate I'm going to get new injectors for the TB and install a custom chip. Also going to install a new knock sensor. I will let you guys know if it works
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Old 09-08-2011, 10:34 AM
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Just saw your thread. Black smoke almost always is an indication of an overly rich air/fuel mixture. Have you checked the fuel pressure? Any codes set? Obviously if the injector(s) are leaking, this can cause an overly rich condition. And that in turn can make the engine run rough.

Any time a cam swap is done on a factory ECM-equipped vehicle, there is a possibility the cam won't play well w/the computer- even if all the sensors are in place and working. This can be due to the difference in vacuum between the OEM cam and the aftermarket cam.

I believe you are on the right track w/a chip change to tailor the ECM to the engine. TBI Chips, Jet or CFM Technologies do this type mods to the TBI chips. Just be sure there are no other issues before buying the chip.

Last edited by cobalt327; 09-08-2011 at 11:03 AM.
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Old 09-08-2011, 01:39 PM
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Quote:
Originally Posted by scarecr0w
Hello all, I have recently rebuilt a .030 overbore 350 engine and it is black smoking a little and seems to run rough in higher RPMs.
I'm not much of a Chevrolet mechanic, but I made a project truck out of one of the 1500s that I own.
The modifactions I have done are as follows:
A Comp cams camshaft kit which includes seals, springs, etc. I can't quite remember the camshaft duration, but it was very, very mild. And it it supposedly a camshaft designed for fuel injection engines.
I had the heads reworked, the crankshaft journals checked, and I reused and re-ringed the pistons that were in it.
For fuel upgrades, I put the Holley direct replacement upgrade TB on it (bought used from a friend). I had to rewire that and put the TPS sensor from my old TB onto the Holley TB.
I still have stock exhaust manifolds for the moment (I plan to run headers), and I have yet to purchase a ECM chip.
If you guys could offer any insight, let me know.
I don't know if the piston rings aren't seated, or if it's the throttle body, the TPS sensor, or even the O2 sensor. If you guys could help it'd be greatly appreciated. If you need any more info, feel free to ask.

Thanks!


(Also, if this is in the wrong forum subsection, feel free to move it!)

Tuning the chip to the cam is a big issue with TBI, especially the Holley system which is really made for competition engines and leaves a lot of tuning flexibility on the table that is needed by street engine's, it can be massaged but it takes time and understanding.

You really need to know about the cam and rockers; even though a cam may be listed as compatible with injection that doesn't mean that considerable tuning and possibly a custom chip isn't required. All the note of the cam being compatible with TBI means is that it can be tuned to work. Rocker ratio has a big effect which is why I included it as a remark. if you changed from 1.5s to 1.6s the tuning difficulty goes up.

Bogie
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Old 09-08-2011, 02:46 PM
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I have done some more research and I believe I have to have a custom chip with the camshaft I went with. And I'm sure my self aligning rockers will work just fine. My camshaft has more lift that what the factory ECM knows what to do with.
Also, I have heard that the Holley throttle bodies have a bad knack for having blinky injectors. And I bought mine used, so go figure. I've decided to try and service the TB injectors, run a HEI system, and replace my stock intake manifold with the Edelbrock TBI performer.
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Old 09-08-2011, 02:48 PM
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Quote:
Originally Posted by cobalt327
Just saw your thread. Black smoke almost always is an indication of an overly rich air/fuel mixture. Have you checked the fuel pressure? Any codes set? Obviously if the injector(s) are leaking, this can cause an overly rich condition. And that in turn can make the engine run rough.

Any time a cam swap is done on a factory ECM-equipped vehicle, there is a possibility the cam won't play well w/the computer- even if all the sensors are in place and working. This can be due to the difference in vacuum between the OEM cam and the aftermarket cam.

I believe you are on the right track w/a chip change to tailor the ECM to the engine. TBI Chips, Jet or CFM Technologies do this type mods to the TBI chips. Just be sure there are no other issues before buying the chip.
I plan on purchasing a chip from TBIchips. And I have been reading the site and have found lots of pointers for the problems I am having. I'm pretty sure my Holley TB is puking way more fuel than needed. I mean, it is dumping it! So I think a chip and rebuilt injectors would be the way to go.
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Old 09-08-2011, 02:51 PM
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Quote:
Originally Posted by oldbogie
Tuning the chip to the cam is a big issue with TBI, especially the Holley system which is really made for competition engines and leaves a lot of tuning flexibility on the table that is needed by street engine's, it can be massaged but it takes time and understanding.

You really need to know about the cam and rockers; even though a cam may be listed as compatible with injection that doesn't mean that considerable tuning and possibly a custom chip isn't required. All the note of the cam being compatible with TBI means is that it can be tuned to work. Rocker ratio has a big effect which is why I included it as a remark. if you changed from 1.5s to 1.6s the tuning difficulty goes up.

Bogie
I'm still running 1.5 rocker arms. I read that 1.6s would be better, but I don't think I really need them with what I have done to the engine.
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