water in the gas?

[chessman21]

my 91 4.0 wont idle now hardly at all now but starts up fine and seems to run well down the road This was after i put in 3 gal out of a can that i think may of had about a cup of rain water at most, then let i let the truck run completely out of gas.. Then i added 5oz of seafoam to 5 gallons of fresh gas and half way through it now i still have the idle issue.

And Now i hear a massive vacuum leak coming from from vacuum T boot from what i"think" [cant see it] goes to pressure reg via plastic line down behind engine...

The boot seems to fit snug, its almost like either theres to much vacuum or the line is blocked..

ac is blocked off
cruise work fine.
brakes fine

Its possible there wasnt any water in the gas to start with and because i just noticed or heard the vacuum,, i dont know.

I havent disconnected battery,, could it be an ecm problem with system trying to figure water in on the mix?

What yall think?

 

[RonD]

Octane Boost or HEET will absorb any water in the tank, methanol/ethanol bonds with water, gasoline does not

Clean spark plug ends and inspect each for that cylinders condition

After engine is warm, let it idle and unplug IAC Valve's 2 wire connector

If idle doesn't drop or engine stall then you do have a vacuum leak

All gasoline has water in it, "bad gas" just has more water.
Since gasoline and water can't mix, and water is Heavier than gasoline, the water will settle to the bottom of the gas tank, or gas can just FYI.
Fuel pump pick up is at the bottom of the gas tank, so...................after sitting over night the water will settle to the bottom and you get a high percentage of water on start up, this will clear itself out fairly fast, unless there is alot of water but then I doubt engine would even start.

 

[chessman21]

If idle doesn't drop or engine stall then you do have a vacuum leak

I know i have a vacuum leak, i can hear it with the hood shut. Its coming from the boot on vacuum Junction T that goes to what i thinks called a pressure regulator. The boot fits snug and tight like it should be. Could that line be clogged up, From the boots good condition seems logical the only way it could be leaking like that is if what ever was plugged into it it wasnt letting any air thru it..?

 

[RonD]

If it is a vacuum line, no air should move thru it.
Any vacuum line should be "blocked" or it is a "leak"

At start up negative pressure(vacuum) is established, and then no air movement

PCV system is the only one that "uses up" vacuum, controlled vacuum leak
Power brake booster can but check valve is mainly to keep 17-20" vacuum pressure all the time
Cruise Control can "release" vacuum, thru brake pedal valve.

But all other vacuum systems should be "air tight", blocked at the device end

If you can hear air being sucked in then hose or device has a leak

Pull off any vacuum hose from the intake manifold(except PCV hose, lol) and suck on it, it should hold negative pressure, no air movement after initial "suck"

 

[RonD]

Could be IAC Valve issue, it should react when you stop a vacuum leak by raising air flow(opening a bit) to compensate for a drop in the RPM, sputtering

Computer has "target" engine RPM values for all engine temps(from ECT sensor)
And computer is very fast to react to any changes in RPM and opens/closes IAC Valve to keep RPMs within 25rpm of that "target"

You should be able to block ALL vacuum ports on the intake, except PCV system port, and it should have no effect what so ever with engine idle

FPR vacuum is just to maintain medium pressure, 30-40psi pre-1998, when vacuum is high/demand low, no vacuum at FPR shouldn't effect engine, in fact it goes to 0 vacuum every time you accelerate.
Leaking diaphragm IN the FPR will cause fuel to be sucked into intake, which will cause rough running and a big drop in MPG

 

[chessman21]

empty port.

@ RonD: I deleted last post before i realized you answered it because i found a open port on backside of T and didnt want to waist your time with stupid.....But now i wonder what it went to..I got ::

ac blocked off
cruise hooked
brake hooked
tranny hooked
and i think fpr hooked.

and a now unknown small size pvc type open ?

 

[RonD]

Vacuum reservoir(cab vents) or EVAP system are left

1991 4.0l shouldn't have EGR system

 

[chessman21]

Vacuum reservoir(cab vents) or EVAP system are left

1991 4.0l shouldn't have EGR system

AC has never worked got fan and heat/defroster works, but i allways get air through the vents blowing when im rolling.

Not sure what effect not having a evap hooked but i plugged the port and engine runs well now.

Thank you for your help! I think you've helped me b4 good looking out.. I dont have allot of money, im disabled and retired IT. If you have and issue with windows 95/10 i can fix it via remote and u aint gotta suck nothin. chessman2121 at gmail

iv got some none urgent questions about this engine. Should i poste them here or start another thread?