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Slow Start...sometimes

B

Bowtie70SS

New member
I have a 99 GTP and it starts slow sometimes. Randomly sometimes when hot sometimes when cold. I changed the cam and crank sensors and it seemed to help a little. I have a parts car available to test parts. Would a control module do this too? Only other thing I can think of is fuel pump/cracked line.
 


The FPR looks new as were the cranks sensor and cam sensor although I think they were cheapos like Autozone or something. I could change it easy enough but the randomness has me puzzled.
 


Negative numbers means your PCM is cutting fuel I think.
So I think you would be lean.
Don't hold me to that thought.
 
-3 to -5 is normal. Not even a brand new car off the lot will just sit at 0. Some older cars will get up in the 8% range and still are ok.

I believe you are correct that negative numbers mean the PM is cutting fuel but that would not mean he is lean that would mean he is running rich so the PCM takes away fuel to get to (stoichiometric ratio) 14.7:1
 
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Negative means it is pulling fuel, you want to err on the rich side. I did not mess with factory tune. Those are short term fuel trims. Onve I get the pulley on I am going to have it dyno tuned on a load bearing dyno. I have not checked fuel trims since my K and N drop in and high flow down pipe and resonator delete. I don't believe a dirty throttle blade has anything to do with it. Case relearn makes sense and iim gonna swap out control modules as I have a spare along with lots of stuff for test parts.
 


I know you said the FPR looks new, but prime the pump and then pull the vacuum line off it, if fuel comes out you know its bad.

Wouldnt hurt to check anyway, to rule it out.
 


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