slickfx3

car is tune nicely, no knocks, timing at 14 degrees at idle

16k on the build, it dieseled way back hen it was new, but more lately, I use 91 octane, the best I can get..

comment?

do i need to spray water in it?
if so how?

paulo57509

What is your idle speed?

slickfx3

700-800 rpm

i just tried seafoam, and I think my gas vapor recirculation valve is broken, lately the gas tank builds pressure too fast....

dimented24x7

iTrader: (2)

Sounds like you have leaking injectors or something else thats giving the engine fuel after shutdown. Id be willing to bet that a lot of the EFI builds would diesel if the injectors where allowed to continue to deliver fuel after shutdown due to the advance most people run. Fixing the dieseling will just be fixing the effect, and not the root cause of teh problem, which is that fuel is still available to the engine after shutdown when it should not.

slickfx3

My advance is 14 deg at idle, not what you call aggressive....

I thought about that, can the vacuum pull fuel out of an otherwise good injector?

how about fuel from the purge canister is this not a possible source? albeit upstream and into directly into the intake port instead of from the injectors

what could that something else be? can some of the gas mixture not be fully ignited allowing for the second or third bang? is this where that term volumetric efficiently VE comes in?

I bought the bosch III's from FIC, they had been inspected and flowed, but used they were.

I car dieseled, rarely at 4k miles, now 16k on the build, I smell no gas in the oil ever.

how to check for sure?

mlynch001

What is your base idle speed set at? Not your ECM controlled idle, the speed you set with the idle stop screw. Should be about 450 rpm.

mlynch001

If the idle speed is high and there is enough vapor from the purge canister that might. Cause the issue. Maybe the canister purge valve is stuck open? Canister purge is ported behind the throttle plates so if the purge was always open this could cause your problem.

slickfx3

no I checked the solenoid, stays closed near idle and the vacuum valve atop the can works fine and shuts down with no vacuum

yes base idle is low as per procedure,

how do you check for leaking injectors?

dimented24x7

iTrader: (2)

You can check the fuel pressure. If it sharply drops after shutdown, the injectors may be leaking fuel. If theyre leaking, closing the throttle down for getting the proper min air will actually make the problem worse as it makes it easier for the engine to build vacuum and continue to draw the fuel out while its dieseling. Its not uncommon for the old multecs to leak.

slickfx3

bosch III rebuilt and flowed by jon at fic the engine dieseled at 2k miles,albeit slight and seemed to go away with my jiggling the tune

i now have 16k on the engine build and that's what on the injectors 30lbs, they are

dimented24x7

iTrader: (2)

Have you tried temporarily disconnecting the CCP and plugging the vacuum port? That would at least eliminate that as the cause. The only other cause then is the injectors.

slickfx3

I will try that, thanks


Jon at FIC whom I bought the Bosch III's from suggests this:

the cam is big and the overlap allows fuel to be in the cylinders at shut off.

since the TPI system is batch fire separate by banks, not sequential. and the duration of the fire is not adjustable because of the old ecm.

so the injectors with squirt fuel for a given period regardless and independent of the cam timing, this with the combination of carbon build up from a rich condition and a higher idle required for bigger cams will cause dieseling.

if the injector or injectors leaked the car would be hard starting, smoke after starting from a stopping and generally run poorly, which my car does not.

I seafoamed the car last week, I went colder plugs the week before that, lets see....

DENN_SHAH

iTrader: (1)

from your other post, it sounds like the return and purge lines may be swapped at the tank.
the canister should never see liquid fuel.
if the canister has had very much liquid fuel fuel in it, its bad. when they go bad, the motor will pull charcoal out of the canister.
if your getting any fuel thru the purge system, it can cause the motor to diesel.
it would be impossible to get a good tune if the purge system is hooked up but isn't working right.

at the shop i used to work at, we had a cobra that had a completely dead fuel pump. there wasn't a drop of fuel coming out of the pressure line at the injector rail.
but it would still start and run because the purge valve was stuck open. it didn't run very good, but good enough we were able to drive the car into the shop from the parking lot. with the gas cap off, it would actually idle.
he had been driving the car for a while with a good number of run problems, engine light on, bad fuel mileage, stalling, and dieseling.
the bad purge valve was probably part of the reason the fuel pump went out.

slickfx3

i took a closer look with a flashlight and glasses, the teenie bit of fuel in the line is just a few drops and a few inches long bouncing around until stops as it bends upwards towards the canister, it never reaches the canister since the solenoid is not allowing a vacuum in the can to suck the fuel from the line and can, to the throttle body cavity. so that part is cool.

wow interesting story.. the can was not filled with gasoline, nor is it puking charcoal when i had it out for inspection,... I'll check again, when I took the line off there was some dripping, would it not be both lines exit on top of the tank and none at the bottom, so basically swapping these line( which I doubt ever happen, I know the car's history) would not affect anything...

DENN_SHAH

iTrader: (1)

its not uncommon for the return and purge hoses to get swapped at the tank when the fuel pump gets replaced.
the return line goes into the sending unit and runs pretty far down, almost to the bottom of the tank.
the puge line ends just inside the sending unit and normally has a check valve on the end of it.

the canister could still be full of liquid fuel and not leak. the charcoal in it will hold a lot of gas.
once you've held a known good canister, you know if one has been flooded with fuel. a good canister is pretty light, 2~3 pounds tops i would guess.

slickfx3

well i guess it felt empty of liquid, heck if full it should weight more than a 1pt water bottle, it did not, I am 51% sure it only had fumes.

well with one of the line reaching so far down the tank and the tank being higher than the line, etc, when full;my best guess is, if inadvertently swapped would Force gas streaming out of control forward towards the evap and when opened would empty the tank, given enough time, which it has not and did not.

I suppose the check ball you are talking about is a diode preventing fumes from re-entering the tank after it makes it's way into the purge line. then how does the tank equalize pressures?, if the cap suppose to close the system, albeit with a bleed valve at high pressures. there is no other way for positive or negative atmosphere to equalize.

all this said, I am surprised that a canister of 22 year old charcoal is expected to lower hydrocarbons, don't they have a expire date, or become smelly after a while, or is the deployment of such a mundane substance as burnt wood chips some gift from a higher authority?

DENN_SHAH

iTrader: (1)

i forgot that we are talking about a vette. i've haven't worked on many vettes so i don't know how the sending unit is set up on them.

the check valve on the purge line helps to prevent liquid fuel from entering the line. but the fumes can still pass in either direction. if the tank is overfilled, raw fuel can get into the purge line.

the ideal of the purge system is to collect the fuel vapors in the charcoal inside the canister and then burn those vapors.
i've seen canisters last a very long time if the purge system works right. the factory canister on my 83 Monte Carlo is still good.
i've seen some that were regularly flooded with gas for 1 reason or another that were bad before they were a year old.

have you had a chance to plug off the hose going to the canister from the motor to see if it makes a difference?

slickfx3

i have not circumvented the purge system, my dieseling was very minor, when it did or when it wanted or on the verge of dieseling...

after seafoam, i can hear it stop and the crank not try to rotate via some left behind fuel.

my solenoid closes the system at idle and that is when it needs to close, and when last checked it did just that.

so for now it's not dieseling i may go another round of seafoam for good measure the car ran rich for a while and with the compression, i think it was fertile.