[Chevy408]

Hey folks,
I have an 85 TPI IROC and I just reassembled the engine. It's running well, but the air/fuel ratio is unbeleivably rich. Is there a way to manually adjust the mixture? Thanks alot, you guys are great.

Ben

[sschevyfan]

No adjustment possible without changing chip.Get a scan tool and see what sensors are reading.Computer controls the mixture.To high a fuel pressure?Without knowing what the sensors are reading everything is just a guess.

[wplax26]

Actually, there is a way to manually adjust the mixture, however, i do agree that you should change the mixture through a computer controller instead.

[sschevyfan]

Not to sound like a smart ass but I'd like to hear how you 'manually'adjust the fuel mixture.You can raise fuel pressure by installing an adjustable regulator or make the engine run richer by putting a resistor in coolant sensor circuit but otherwise I don't see nothing else.You can 'manually'adjust minimum air by adjusting throttle plate opening but that's not adjusting mixture.Maybe you can educate me.Again this is NOT a smart ass reply.

[Chevy408]

Well aside from that question, it is basically a problem of way too rich of a mixture being burned. Could it be a stuck cold start injector? Any suggestions at all?

[davidpozzi]

A bad water or intake air temp sensor or sensor wire would make the computer think the engine is cold when it isn't.
That would keep the mixture rich.

If the engine is warm up enough to go into closed loop, any vaccum leak would put excess oxygen into the exhaust and the oxygen sensor would tell the computer to go rich.

A bad plug wire or plug would cause excess oxygen in the exhaust and do the same.

You might have a bad seal on the intake or a hose. Even a bad brake booster leak can do it.

You need a good scan tool which will tell you what the computer is seeing from the sensors, and what the computer is doing about it.

The only methods I know about of controling the mixture in a sort of manual method involved fooling with the sensors to make them lie to the computer to get a richer or leaner response, such as making the computer think the engine was colder than it really was or the throttle position or oxy sensor was a different computer input value.

Also manually adjustable fuel pressure regulators can change mixture.
I have heard of pressure regulators going bad and allowing fuel pressure to go too high at less than full throttle. There is a vaccum line from pressure valve to the plenum and if you pull it off, the regulator pressure will go up, thinking you are at full throttle.
David

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67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 02-04-2002).]

[18436572]

There are lots of possibilities.........most need a scantool or at least a fuel pressure guage to diagnose......one easy quick thing to check comes to mind, without the need for tools, is the fuel pressure regulator for a ruptured diaphram .......simply remove the vacuum hose and check for fuel in the hose....there should be none present....if the hose is wet the regulator is bad.....(Not uncommon)

[This message has been edited by 18436572 (edited 02-05-2002).]