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Discussion Starter #1
I have a 91 efi stock 460 with an exhaust and headers.
When it’s cold it runs great! Once it warms up to normal operating temperature it falls flat and has no power. It does have a random miss at idle Compression is good (lowest was 125 with no more then 10% difference between cylinders) and no codes are present. I have done the normal tuneup and it didn't help at all.

I was thinking either EGR or O2 sensor. Is there any way to check these?

Thanks for the help

Chris
 

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Discussion Starter #3
Thanks 2slow.
I will check the plugs

Is the testing, if there is resistance its good and open means bad? Is there different ways to test the o2 opposed to the temp sensor?

chris
 

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Check to see if 02 wires are melted against exhaust. Being as how it runs good in open loop, could be any number of things, MAP sensor, TPS. Most of the sensores can be far enough out of range to make it run like *** without setting a code on an OBD 1 computer system. Need the use of a scan tool to watch the data-stream and compare sensor range performance to known values for each particular sensor.
 

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Check to see if 02 wires are melted against exhaust. Being as how it runs good in open loop, could be any number of things, MAP sensor, TPS. Most of the sensores can be far enough out of range to make it run like *** without setting a code on an OBD 1 computer system. Need the use of a scan tool to watch the data-stream and compare sensor range performance to known values for each particular sensor.
91 truck doen't have a direct live read out from a scanner. need a break out box . tps & map would be the same cold as hot but map hose could have a small vacuum leak
 

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Discussion Starter #8
Do most shops have a break out box?
MAP is hose is fine...
thanks
[


QUOTE=2slow;921547]91 truck doen't have a direct live read out from a scanner. need a break out box . tps & map would be the same cold as hot but map hose could have a small vacuum leak[/QUOTE]
 

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Discussion Starter #10
So they hooked it up to the break out box. They want the truck back on Monday so they can have more time (keep in mind they had it for 4 freaken hrs 2day)
What they came up with so far is
*TPS error, position out of range
*Erratic distributor reading
*low fuel pressure on start up.

Im hoping for the TPS, seems like the cheapest..

Any thoughts?

Thanks

Chris
 

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I'm pretty sure the TPS sensor isn't adjustable. Replace that first. Usually when they go bad the engine will run too rich, sometimes to the point they won't even start when cold. Of course the rich condition is even more out of whack when the engine is warmed up. You can put a volt meter on it and open the throttle to see if it goes through an even voltage swing, something like 1-4 volts, I can't remember for sure. If not, replace. Erratic dizzy reading is pretty vague. If it doesn't die and/or stutter really bad when it warms up, it's probably not a problem with the dizzy module (a somewhat common failure) and may just mean it needs a new cap and rotor. Low fuel pressure on start-up? I wouldn't worry about it. Prob just low voltage from the battery while the starter is cranking the engine. If it starts fine, no problems with that.
 

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Discussion Starter #12
But wouldn't the TPS make it run like a POS all the time, not only when the engine is warmed up??

THanks Scott
 

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Yeah, it'd be an issue at all times, but when the engine is cold, the overly rich condition isn't as much of a problem, like when you have the choke on.
 

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Discussion Starter #15
Changed the TPS and no difference.
Pulled the plugs and they all look nice and slightly tan..

Running out of ideas..

chris
 

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Discussion Starter #16
So now the Engine light flash's. Got to love OB1. I get home and throw the reader on it and all is good. It registers no problems. I think ill tape over that damn light...
 

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Discussion Starter #17
Any other ideas? The break out box is showing no errors 2day and I can never get the reader n it when the light comes on and it ony flashes on and off.
How do you guys feel about the block off plate for the egr just so I can take that out of the pob?
 
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