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Old 01-28-2009, 01:19 PM
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TBI Idle issues

I`ll give a list of what I`m running since it`s not stock.
92 4.3 V6 Bored .030 Decked .010
Flat top 4 valve relief pistons 1.560 comp height
Quench distance .045 or so.
Swirl vane heads lightly bowl ported. Ferrea necked down valves with back cut. 1.94 In. 1.50 Ex.
Isky hydraulic roller cam. Comp. Compatible. Duration 206 In. 209 Ex.
Comp cams 1.6 roller rockers. Comp Cams push rods.
Crane roller tappets. Milodon true roller timing set.
Edelbrock performer TBI intake.
Ported throttle body. Fuel press. Regulator vacuum compensated.
Fuel pressure 13 psi.
Venom high flow fuel injectors.
MSD plug wires. MSD coil.
K&N air filter.
Dual exhaust.
The issue is at idle it`s rough, makes the whole truck shake.
Spark timing is set with ECM wire off to 6 degrees BTDC. I moved it up to 10 degrees and it idled smooth once I reconnected the wire but kind of on the high side so I moved it back down to 6. I removed and cleaned the idle control. Checked for vacuum leaks, found none. Checked all vacuum hoses, all good. The factory timing setting calls for 0 but I`ve always set it higher than the factory spec as the stock computer don`t give it much advance.
EGR valve is not in operation so I know thats not the issue.
Only clue I got left is the fuel pressure is too high. Anybody else got any other ideas of what I can check? Much Appreciate it.

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Old 01-28-2009, 03:47 PM
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Quote:
Originally Posted by DoubleVision
I`ll give a list of what I`m running since it`s not stock.
92 4.3 V6 Bored .030 Decked .010
Flat top 4 valve relief pistons 1.560 comp height
Quench distance .045 or so.
Swirl vane heads lightly bowl ported. Ferrea necked down valves with back cut. 1.94 In. 1.50 Ex.
Isky hydraulic roller cam. Comp. Compatible. Duration 206 In. 209 Ex.
Comp cams 1.6 roller rockers. Comp Cams push rods.
Crane roller tappets. Milodon true roller timing set.
Edelbrock performer TBI intake.
Ported throttle body. Fuel press. Regulator vacuum compensated.
Fuel pressure 13 psi.
Venom high flow fuel injectors.
MSD plug wires. MSD coil.
K&N air filter.
Dual exhaust.
The issue is at idle it`s rough, makes the whole truck shake.
Spark timing is set with ECM wire off to 6 degrees BTDC. I moved it up to 10 degrees and it idled smooth once I reconnected the wire but kind of on the high side so I moved it back down to 6. I removed and cleaned the idle control. Checked for vacuum leaks, found none. Checked all vacuum hoses, all good. The factory timing setting calls for 0 but I`ve always set it higher than the factory spec as the stock computer don`t give it much advance.
EGR valve is not in operation so I know thats not the issue.
Only clue I got left is the fuel pressure is too high. Anybody else got any other ideas of what I can check? Much Appreciate it.
Where's the new chip, the computer has no way of knowing about these changes, it doesn't adjust and contrary to advertised it doesn't learn, at least not much. You have made substantial changes which has affect the relationships of manifold vacuum (what the manufacturer call Manifold Absolute Pressure (MAP) to RPM and to throttle position. This has the sensor inputs to the computer out of coordination with the fuel and ignition maps. There is no way to get that coordination back except to return the vehicle and engine to stock or have a new PROM chip made, for which there are a considerable number of vendors doing this stuff see the URLs:

http://www.fastchip.com/

http://www.tbichips.com/

http://www.hypertech-inc.com/

http://www.superchips.com/

http://www.tpis.com/

and there are more.

Disconnected EGR screws lots of things up, again the computer doesn't understand this, it's looking for the EGR function by comparing an expected MAP value against the real time value and finding a disparity. Disconnecting EGR causes the mixture to fall lean, this is something the computer reprogramming has to take into account if that's how you're going to configure the engine. If the O2 sensor is in place and functional it will try to correct the mixture, but it doesn't have unlimited authority, it can only do what it can whether that's enough or not.

Changing the base timing by advancing the distributor with a computer isn the system doesn't alter anything, the computer figures this out (one of its real learn functions) and electronically reduces the running advance to compensate. Again this is something that can be changed with a reprogrammed PROM.

Changing the engine's operating temp below 180 degrees will also cause the computer to deliver incorrect commands to the injectors unless the PROM is reprogrammed.

So you can see that there's a lot of changes you have done that the computer has no way to resolve without a new chip.

Bogie
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Old 01-28-2009, 04:19 PM
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Does it run good everywhere else except idle?

Is this a new build your just starting up or has this combo been running well up until now?


Most of the time TBI problems or either fuel delivery or distributor related.


Old bogie is correct...anything other than stock does not agree too well with the stock tune.
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Old 01-28-2009, 04:56 PM
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Okay then my next move will be to get a chip for it. Surprisingly, it rarely gives me any codes. It only gives me the code of EGR failure and it only does so rarely. It runs real strong and revs fast as lightning. I built it last year, and never had any idle issues. some months ago, the crank bolt that holds the balancer on broke and took out the crank with it so I had to install a crank kit, after I reinstalled it, it`s not idled right since. Thanks for the great info Bogie. I don`t use the EGR as after I finished building it I had it connected and it ran like crap, had no power and was giving the same EGR failure code. I disconnected it and it`s ran okay since. It`s a new EGR valve, so I don`t know if they sold me a bum one or I didn`t put the right restrictor in. If there`s a formula for the restrictor size to use I`d like to know it, but if it takes try them all, that takes a while. I am guessing since I`ve made so many mods I`ll have to get a custom chip made? Thanks again for the info.

Last edited by DoubleVision; 01-28-2009 at 05:06 PM.
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Old 01-28-2009, 06:34 PM
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You need to take it to Hypertech or Jets and let then burn a chip in on their chassis Dyno.
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Old 01-28-2009, 08:32 PM
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timing

I have a 4.3 chevy and Base Timing does effect driveablity and idle, the computer only adjust timing based on maps for timing and fuel and only retards based on knock sensor. I have open up spark plug gap to .060 and set the timing at 7 btdc it smoothed out the idle and increased gas mileage with the egr hooked up. All this was on a TBI model 4.3
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Old 01-25-2011, 09:36 PM
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Doublevision;

Chebby even-fire V6 is different from a Buick odd-fire V6.

Make sure the crank matches the distributor.

These beasties also run the infamous oil pressure switch for powering the fuel pump. Thin oil in old engines lowers the idle oil pressure, and the fuel switch turns off. Believe me, this one ain't in the books anywhere! I've had several like this come in.

Hank W
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