Tip in hesitation

[Milktruck]

Hey folks,

I’ve got a hesitation at tip in (low rpm) that is stumping me. Hope I can get some ideas of where to look.

Description:

Stock 5.9
Automatic Transmission- rebuilt within last 20K, leaks pretty badly, but topped up
Electric Fuel Pump
Fuel pump pressure ~ 4psi constant

This fall I’ve started warming up the engine to operating temp before leaving the driveway b/c if not, the truck will stall at tip in from stop. Once warm, the truck seems to run fine. But in the last 100 miles, the warm up has gotten less smooth. Like the engine might be missing or stumbling. It felt like the engine was running on less than all eight cylinders just kinda ran rough. Once warm, the engine seemed smooth at idle, but when pulling away it would kinda puff and fart and seem weak.

I warmed it up really well today, and took it out on the highway to give it a full throttle “tune up”. Seemed to run well. In fact once I got past the low rpms it pulled great. Constant speed was fine on the highway, everything was smooth and strong until I exited. I stopped at the off ramp, and then when I pulled away, the damn thing stalled. Grr

Any thoughts where to start?

I’ve:

Checked the fuel pressure
Checked all the wires on the block and the distributor cap
Checked Oil/Auto Transmission fluid

All seem fine.

[fulsizjeep]

What is your timing set at? (degrees BTDC or on vacuum gauge)
When was last time the carb was cleaned and kitted?

[letank]

I would guess, lean off idle if the accelerator pump is non worky, can you see a shot of gas down the venturi when depressing throttle -engine off-

Check for the usual vacuum leaks. If EGR present make sure that it is plumb as specs.

As above, then what is your intake manifold reading at idle?

[candymancan]

bypass your egr by unplugging the vacuum lines and plugging them with a screw. this way you can eliminate the egr as the cause

[Milktruck]

I just replaced the power valve + accelerator pump diaphragm. There was a bit of fuel drip when I pulled the vac hose off of the power valve. New block and gaskets. The lower plastic block was cracked in the rear. Got it all together and it fired up like it has not done in a while. Now I have an exhaust leak from the heater tubes that run from the intake manifold. Anyone know what the gasket is for that? Mine is obviously shot.

Getting closer...

Thanks for the help!

[Milktruck]

Found it: Choke tube gasket. Lucky $1.99 but I've got to wait until tomorrow.

[candymancan]

My heater tubes are broken and i guess the previous owner used high temp silicone to hold em on. It works lol

[Milktruck]

All back together and the issue appears resolved. I need to drive it for some miles and make sure, but the low rpm hesitation did not appear on a 30 minute stop and go drive. Right now it pulls smoothly and it even started easy (like there was fuel in the carb) when I turned the key this afternoon.

[Milktruck]

All fixed. Reliability is back when moving away from a stop. Wish I could say that the gas mileage improved significantly - but I ain’t kidding myself.

[Milktruck]

Wanted to update regarding the Choke Tube Gasket. I burned through three of the $1.99 Fel-Pro variety and got mighty pissed off. Remember this sounds like rocker/pushrod ticking so it annoys the heck outta ya. I went a bit ape on the fix and ordered a sheet of the remtech gasket material that is super crushable. Cut my own gasket using that third excuse for a gasket I took off. No more problems. I’m sure the flanges on the cover are crap after all these years. Remtech gaskets fixed my exhaust manifold issues, and sure fixed the choke tube gasket issue too. Just wanted this documented.