efi problems

[dirtwarrior17]

Me and my bro timed this beast it tonight and stll won't idle.
Crankshaft position sensor is not plugged in ... wires are too short. Also need to get an adapter for the holley throttle body for the foot pedal..... stock replacement my ass.

does crankshaft position sensor control idle?

does the throttle sit in different place with the linkcage hooked up?

also could be vacuum lines.

already adjusted idle screw.

 

[southernspeed]

Not sure of your set up but most systems use the crank position sensor to set the timing as the ecu won't know where to fire as it doesn't know where the crank is at. It's probebly running in a limp home mode.

Try connecting it up and set your timing again.

 

[dyeager535]

The point of limp mode is to get you home, that means that even if it won't go more than 25MPH, it WILL run, and should idle without problem.

Perhaps with no known "baseline" from initial start (taken from crank sensor) thats not possible but I personally have never dealt with these systems.

I say hook everything up that is supposed to be hooked up, and see if the problem disappears. No reason to try and fix other problems when a known issue is obvious.

 

[dirtwarrior17]

The motor is timed and runs real good when u give it a little gas....pisses whole neighbor hood off but sounds damn good . Im cuttin the wires as we speak bout to crimp em and extend em i will let u know wut happens.

Im not sure but i think the timing will be the same with or without the sensor because the computer can't control when the rotor hits its points.

It senses rpms ( i think) through the CPS then tells the injectors how much fuel too feed.... not sure.

 

[dyeager535]

Just assuming here, but crank position sensor in a very roundabout way probably influences fueling, but the whole point of it is to tell the ECM where each piston is as the engine runs, for timing events. The CPS can't determine demand on the engine. Demand is what determines fueling.

ECM doesn't control when the rotor makes contact, but it does control when it should fire from the *base* timing. In older systems limp mode would go back to a set timing value, I wouldn't be surprised if newer systems have some sort of "static" (doesn't change based on sensors as is optimal) advance for limp designed into them.

 

[dirtwarrior17]

Still don't understand how the ecm controls timing..

I started it up bout 10 min ago with the sensor and it was runnin real rough again and needs to be timed. how can the cps affect timing that much? I know it sets a base timing from the rpm and the piston position but what does the ecm do with the readings it gets and how does it change the timing?

Also found some milk on the end of my dipstick... not milk , oil and water and now im off to get 6 quarts of 10w 40 and a allen wobbly tool so i can tighten the bolt on the manifold all the way down<<<reason i got water in the oil. No worries though it only sat for 24 hours and was not runnin.

I've been doing all this with no exhaust, just headers and y pipe.... my moms boyfriend is sayin it'll warp the headers if i keep runnin it like this. Is he full of **** or am screwin up.

 

[dyeager535]

In the GM applications I deal with, you set base timing (typically 0-8* depending on application) with the ECM "feed" for timing disconnected. EST bypass in what its called for mine.

Without that hooked up, timing is handled by the ignition module in the distributor.

When it IS hooked up, over 400RPM, the ECM handles timing. It advances or retards spark based on numerous things...pre-set map based on throttle position, engine speed, pressure or airflow, if knock is detected, etc.

Basically, the less base timing you run, the easier the engine starts/turns over. With EFI, after the engine starts, the ECM will advance timing as far as it is programmed to do, which smooths out idle.

I don't fully understand CPS, so I can't really help much. But if it's there, it's something to do with ignition.

Initial engine break in should NOT be done with headers. Use manifolds for this. If the engine is used, then headers shouldn't be a big deal.

 

[southernspeed]

If you have a CPS system the ECU (ECM) uses the CPS to tell it where the crank is at. On HEI etc systems it's done via the distributor. With out the CPS the ECU is just guessing where it is. Time it up again and all should be well.

Then go and appolagize to your ECM for messing with it's head!

 

[dirtwarrior17]

the motor is a remanufactured 350 bored to a 355 with all the hot rod bells and whistles... moly rings, 10:1 flat tops, high volume oil pump, high pressure fuel pump, holley manifold, tbi, etc etc etc. It's been run on a stand but otherise has 0 miles on it. I put the headers on because the guy i bought it from said it'll make a huge difference on a high hp motor, in the throttle response and mid range power.


Y can't i use the headers to break it in?