1979 Wagoneer 360 - Engine stumbles/backfires/dies when given any kind of throttle.... completely lost

[iancbf32]

As the subject implies, it seems my engine is entirely unhappy right now. It's a 1979 360 with the Motorcraft 2150 carburetor. When I picked up the jeep, it wasn't super great with off-idle throttle response. It would mostly respond ok, but it would also die sometimes. It was good enough to drive around, but I could tell there was an issue. I rebuilt the carb last weekend and the same problem has persisted/gotten worse. Sometimes it's good enough to drive, other times it won't make it past about 5% throttle input without sputtering and dying. I pulled one of the plugs and noticed it was yellowish-white; indicating a lean condition - so I know I have a fuel delivery problem. Here's where I'm lost.

It's got a new fuel pump on it, new fuel filter (clear, so I can see that fuel is flowing ok), and new carb gasket. I've checked for leaks around the carb base by spraying carb cleaner generously, but not change in engine speed. I've plugged any open vacuum lines, and can't seem to find any bad vacuum leaks (spraying more carb cleaner around any vacuum ports). Lastly, I've installed .058 jets in the carb, which seem to be the biggest available. Also confirmed that idle mixture screws are set at 2.5 turns out. There still seems to be a fuel delivery issue, as either dribbling some fuel into the carb from a squirt bottle or lightly spraying starting fluid GREATLY improves idle quality and engine speed.

Anyone have any ideas? Should I just pony up the $200 for a new carburetor from National Carb?

The only "off" thing I've noticed is that I need to have the distributor rotated counter-clockwise to the point of the vacuum port hitting the power steering pump bracket to have the best idle performance (as adjusted with timing). So, I'm guessing the previous owner installed the distributor 1 tooth off.

[Stuka]

You have a vacuum leak, everything you describe suggests as much. Could be some other vacuum line going to the dash, or the transfercase, or the brake booster. Need to check all of these, could even be the booster itself, or the vacuum ball on the fire wall.

I would start by disconnecting these from the engine to rule out an entire system first. Several things run off the vacuum ball on the fire wall, so disconnect that first. I think both the dash systems and transfercase go off the vacuum ball.

Oh and yeah, 1 tooth off on the distributer most likely. Not an issue so long as you can still get it timed.

[iancbf32]

You have a vacuum leak, everything you describe suggests as much. Could be some other vacuum line going to the dash, or the transfercase, or the brake booster. Need to check all of these, could even be the booster itself, or the vacuum ball on the fire wall.

I would start by disconnecting these from the engine to rule out an entire system first. Several things run off the vacuum ball on the fire wall, so disconnect that first. I think both the dash systems and transfercase go off the vacuum ball.

Oh and yeah, 1 tooth off on the distributer most likely. Not an issue so long as you can still get it timed.

Thanks for the reply,

What do the vacuum lines through the firewall, into the dash actually go to/operate? My Chilton's manual is worthless for vacuum routing. It actually completely skips over 1979 entirely. The vehicle also has AC, if that matters.

[tgreese]

Yes, the Chiltons is worthless on many topics. Not totally worthless ... makes a good door stop, or to hold up the corner of your bed.

There is a complete 1979 TSM at oljeep.com ... http://oljeep.com/edge_parts_man.html ... I suggest you download it and page through the whole thing to see what's there. Lots of year and model specific info.

The heater is operated by vacuum motors. They all have this. You also may have transfer case controls (the emergency switch, or "e-switch") that is powered by vacuum, if your Jeep is equipped with the Quadratrac full-time transfer case. The vacuum ball is a reservoir that buffers the vacuum supply to the dash devices.

[iancbf32]

Looks like I'll have a bit of reading waiting for me when I get home tonight. I think my plan for the weekend is to go through and just replace all of the vacuum lines. Between the smog stuff and the vacuum lines, the engine bay is a bit daunting (even though it's 99% unmolested).

I did see 3 vacuum lines going through the firewall that all look a bit rotted. I'm guessing those are for the heater and t-case? I do have that emergency switch in the glovebox. Two of the lines seem to originate from some sort of block behind the passenger side valve cover that has relatively long metal tubes sticking up from it.

For the lines going into the dash, on a scale of 1 to 10, how terrible are they to completely pull/replace?

[tgreese]

Depends on your skill level. To get to the heater controls, you loosen the steering column from the bottom of the dash and pull the dash cluster out. The e-switch is in the glove box. The transfer case lines may be steel for part ot their run, considering they go under the car.

[Stuka]

I have been able to change the heater lines without dropping the steering column. Loosen the screws, pull just the side back some, and you can get to them. You will most likely find them cracked on the ends.

But for testing purposes, I would disconnect those lines in the engine bay and block off the ports, and give it a test.

[iancbf32]

Thanks for the suggestions. I'll update tomorrow after I've blown everything apart and put it all back in place. I'll already be replacing the evap canister, so may as well not stop there.

[iancbf32]

Sooo... I think I found the source of my vacuum leak:

Looks relatively normal, right?
http://imgur.com/a/tduIn

HA! just kidding
http://imgur.com/a/tWAUq

Yep, someone put a completely empty evap canister back in the vehicle and hooked up the vacuum hoses like normal.

After replacing the evap canister with a GM model (CP1004), I'm now pulling down 18-20 pounds of vacuum. Does that number sound normal? The engine still falls flat on it's face when you go past 5 or 10% throttle input. Any ideas?

[iancbf32]

Additionally, went through and put on a new dist cap, rotor, and plugs. I made sure the vacuum advance works by applying vacuum from a handheld vacuum pump.

Problem still exists. I don't know what direction to go from here.

[tgreese]

Have you traced all the vacuum lines through from the diagram in the TSM?

The 2150 carburetor has a power valve for low vacuum enrichment, and an accelerator pump. Either of those circuits could be involved. Or you could have an additional vacuum leak.

[iancbf32]

I've traced the vacuum lines and ensured that they all terminate where they are supposed to and/or the ports are sealed with a vacuum cap. I disconnected the dash vacuum lines and firewall vacuum ball and capped the ports that led to them.

The engine still doesn't pick up speed at all. You can't really drive it faster than about 15 mph or so because it won't accelerate. Bad fuel pump? Maybe a blown power valve from one of the backfires?

Should I go pick up a $40 electric fuel pump in the morning?

[memo43]

If you do and all works out, then you have isolated your fuel pump, maybe a bad diaphram,
Also try and run it without a fuel filter.
I recall picking up a new one that was capped from the manufacture, sometime a new parts don't always work out
You also mentioned blown power valves from a backfire.
Have you taken your carb apart to verify the power valve are still intack
Not being able to accelerate
Fuel delivery?
Spark how do you have your ignition wired

Memo

[iancbf32]

Ignition is stock. Verified all the plug wires are going to the correct cylinders and in the correct spot on the dist cap.

My general feeling leans towards a fuel delivery issue still; as squirting fuel directly into the carb throat cures the sputtering and hesitation when i give it throttle.

I have not taken the carb back apart since the last backfire to verify the condition of the power valve. I guess I can do that tomorrow. It's a new PV since I rebuilt the carb last weekend,

[tgreese]

You don't need a fuel pump. You can run the engine from a can of gas sitting on the cowl, and connected by siphon to the carburetor.

The power valve is held closed by vacuum, so if it has no vacuum or there is a hole in the diaphragm it's open all the time. This results in a very rich mixture, and excess fuel consumption, but not poor drivability.

More likely is the accelerator pump. If it has a hole in it, it no longer gives a squirt of gas. However, with a hole in the accelerator pump diaphragm, you should be able to slowly open the throttle to high speed. All is well as long as you don't open the throttle fast enough so that vacuum drops.

[babywag]

Check float level?

[iancbf32]

tgreese, I was initially inclined to also believe the accelerator pump was bad, but I just installed a new diaphragm, spring, and check valve when I rebuilt the carb. Additionally, the engine will hesitate/die even when I roll onto the throttle slowly. I'll try to take a video of this after I change my oil/replace my oil pressure sending unit.

[iancbf32]

Here's a video demonstrating the hesitation I'm seeing. This isn't the best example, but it should get the point across. This is amplified about 5x when the vehicle is in gear. Nearly any throttle input will cause the engine to just fall flat.

[iancbf32]

I think I fixed it. Swapped back in the original power valve and it's a night and day difference. It still bogs a little bit when you really peg the throttle, but I think that might actually be too rich. Thanks for all the help and suggestions, everyone

[memo43]

Was there any visible signs of damage to the new power valve versus the old one.
Since you have it running better I would
Go over timing, idle speed, air fuel mixture again and try to re establish a base line