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Finished a head gasket replacement, and now the truck idles rough and shuts off. Thinking it’s just a vacuum issue since I have a vacuum line that I can’t figure out where to put it. Anyone knows that this goes to? Pictures below, it’s the longest line coming off the upper intake. Line in question More of that line Shorter section goes a fuel something Where the line originates
Might go to the VRES, vacuum reservoir, passenger side front of engine bay, down low
See if your Vents in the cab work, i.e. panel and floor air direction, if its stuck in Defrost only air flow then thats where it goes
Reservoir is busted prior to the gasket replacement, so that’s a possibility, and I just didn’t notice it was already disconnected when I took it all apart. That’s worrying though, since it would mean the rough idle/dying is from something different.
Progress is being made I think...The wires were correct for the coils/sequencing, pretty sure it’s just a vacuum leak. I got the vacuum lines mapped out and connected, and now I’m looking at the upper intake, so two questions...
1) Is there a larger gasket that goes between the fuel rail and upper intake in addition to the little odd-shaped gaskets that sit inside the upper intake? I see some diagrams that have one, but mine did not.
2) Is anything supposed to connect to the hole/port on the fuel rail/lower intake in the picture below?
No dice...Replaced upper intake gaskets, got new vacuum hoses for the rough looking ones and redid that. Runs exactly the same as before doing that. Super rough, sometimes stalls, sometimes revs up before dropping back to rough and then stalling.
On Cold start the computer should set Choke Mod, rich fuel mix and high idle, 1,100rpms at least, then as engine/coolant warms up the computer will lower the idle down bit by bit top warm idle target, 750 for automatic and 650 for manual trans
Computer uses the 2 wire ECT(engine coolant temp) sensor for this, no connection to temp gauge on dash, this is a 5volt sensor only used by the computer
There is also a 12volt temp SENDER used for dash temp gauge, just FYI
The computer uses the IAC(idle air control) Valve to set the high idle, it on upper intake near the throttle, looks like a can, 2 wires
If Cold start doesn't get you a high idle then I would replace ECT sensor just on speculation, sensor will have a grey/red wire, the sender will have a red/white wire, these will be next to each other by thermostat housing on lower intake
How long has the vehicle been sitting?
Gasoline can't mix with water and water settles to the bottom of the gas tank when a vehicle sits, so water/gas gets sucked in by fuel pump and engine runs like crap, lol
You can chase your tail with "bad gas" in the tank, ask me how I know, lol
1996 with have a Fuel Pressure regulator(FPR) on the engine, on the 4.0l is on lower intake at the front, behind alternator
It will have the Fuel Return hose attached, AND a vacuum hose, pull off that vacuum hose and check it for gasoline, if FPR should fail/leak, then raw fuel gets sucked into the engine via that vacuum line, causing rough running and stalling, floods engine
When I start the engine, it quickly and briefly idles high and smoothly, but that lasts less than two seconds.
It's been in my shop for about two weeks since I started tearing down to replace the heads. Drove it for probably 20 miles to get it home after I bought it. Ran relatively fine, nothing like what it's doing now, but then I realized it needed head gaskets...
Haven't noticed fuel on the vacuum line from the FPR. I've had it off a few times during the troubleshooting, but I didn't actively check it for fuel in the line. Will do that when I get back.
So does it does REV high at start up, should do that every time it starts, warm or cold, just FYI, but then doesn't stay at high idle?
Can you keep it running until it warms up a bit, say 3 or 4 minutes?
That would take it out of needing to be choked
If it starts running smoother the warmer it gets then its is a choke issue, well no choke so there is an issue, lol
Does rev high at start every time. Applied throttle to keep it running for a few minutes to get the temp up, but it still shakes and runs like crap then stalls after I let off the gas. Seems to be smooth at high RPM. Pic below is leaking from the exhaust when I get it to run like that. Just unburned fuel? Wasn’t expecting the black stuff.
04-11-2021
