Hard shut off on 4.1l engine

[kcabbie]

I got this pickup a couple months back and it's been a great truck. It has some small oil leaks which will be fixed soon, hopefully. But lately it's having trouble shutting off. If feels like a diesel engine when you try to kill it. Sometime's it takes up to like 10 seconds to full cut off.
I thought it was the timming, so i took it to a shop(did not have a light) and they said it was spot on. Any other ideas? Has to be with the ignition correct? Gasoline won't combust under just pressure like diesel correct(atleast what little compression my little six banger has)?
Thanks for all help guys.

[tucsonjwt]

I would check for high idle. Partially stuck choke or throttle bracket/linkage - disconnect choke and fast idle solenoid for a quick check.

[geezer#99]

Try swapping your vacuum advance over to a full time or manifold vacuum source. Your engine will speed up of coarse. Then turn your idle down which closes off the throttle plate in the carb. The throttle plate being too far open at idle causes the deseiling effect.

[kcabbie]

Originally Posted by geezer#99

Try swapping your vacuum advance over to a full time or manifold vacuum source. Your engine will speed up of coarse. Then turn your idle down which closes off the throttle plate in the carb. The throttle plate being too far open at idle causes the deseiling effect.

Thanks for the reply. What does it use as an advance now? and i took it to the shop yesterday to get the timming checked, and they turned the idle down WAY to low. I think they just wanted a reason to get my money "it should help your gas mileage" Does that make sense? Lower idle = more mpg?

Anyways, i'll definatly take your advice. Just tell me how. I recently replaced all the vacuum lines(all were put in original places, and the problem started before this)

[geezer#99]

Got a camera. Take a pic of your motor for us. Prefer one with air cleaner off so we can see your vacuum hose routing.

[1LowToy]

Proper tuning will increase fuel mileage of course. The carburator more than likely has an idle solinoid which when is in the run position (key on) is your curb idle position. Key off the solinoid retracts to a very low idle position, usually 75 to 100 rpms less than the curb idle. This it what stops the dieseling after shut down provided the carburator is not running too rich at idle. If you turn the key on and ever so gently touch the throttle you can feel it engauge. After proper tuning and the idle solinoid is adjusted properly the dieseling should stop. If not you have carbon buildup on tops of the pistons and combustion chambers. The carbon is glowing and igniting the fuel coming in from the carburator.

[kcabbie]

Okay guys, i'll go snap one in a second and post up. Thanks for all the help.
Also, do i need to rebuild the carb as well? Would that be where i should start?

[Toxic Redline]

Check timing also, my retaining bolt loosend up once and my distibuter moved and it dieseled out when i shut it off

[kcabbie]

Timming was first thing checked. It was spot on.

[1LowToy]

You dieseling symtems are caused by a few simple things. Too fast of an idle, too rich at idle and carbon build up on the pistons and combustion chambers. If your running too rich and it won't lean out then you need to rebuild it.

[kcabbie]

How do i lean it out? The plugs were black when i changed them.

[1LowToy]

There is an idle mixture screw on the base plate. It may have a tamper resistent cover over it. If it's still covered you may wanna rebulild it, as it is over 25 years old. Turn the screw in until idle speed drops by about 50 to 75 rpm. You may need a special socket to fit it as it was designed not to be messed with.

What year model is your truck?

[kcabbie]

Okay, they used a special hex shaped tool at the shop. It's an '84 with a 2bbl if that means anything.
So just by lowering the idle speed it will make it more lean? They decreased the idle by i'd say atleast 75 rpm.

[1LowToy]

1984 you should have an O2 sensor on the exhaust and a computer behind the glove box. The carburator is wheat they call a feed back carburator. The oxegen sensor(O2 swnsor) is contently checking the exhaust gasses and feeding the info back to the computer. The computer is sending a signal to the mixture control solinoid in the carburator. It may be running rich due to a bad O2 sensor. See if you can pick up a good carb book of that erra. That carb is fairly expensive to get a rebuilt one but they are really not that complicated to rebuild. There is a voltage test that can be done to test the duty cycle of the mixture solinoid to see if it is within range. Does the truck have a check engine light on the dash?

[kcabbie]

I had always seen the sensor on the the exhuast manifold and just never clicked. I guess because i didn't think of something with a carb having an 02 sensor.
But i will definatly pick a new one up.. Would that cause bad mpg?
Also, i was quoted 75 bucks for arebuild if i furnish the carb kit.

Which of these would be the best?
http://www.autozone.com/autozone/par.../N-ik2xdZ9gslx

[1LowToy]

The O2 sensor produces a small amount of voltage which varies to tell the computer, to tell the carburator to richen up or lean out depending on the voltage. Sorry I can remember which way is richer or leaner. As I remember there are two wires going into the carb and you checked the voltage, or dwell reading there for the duty cycle. I happen to have an 80 I6 but it's not a feedback carb.

[kcabbie]

Okay, well i just ordered a new o2 sensor! Hopefully that will fix it up. It was rated 25 hw mpg. It's only getting about fifteen. Even if it's not going to get the whole 25,, which i understand,, it should get ALOT better than it does.
So did i make a good call on getting the new sensor?
Thanks again for all the help.

[1LowToy]

As I recall the O2 sensor detects oxygen in the exhaust and creates voltage. The higher the voltage output of the sensor the lower the duty cycle will be to the carb to richen the mixture. The other thing is a water temerature sensor to tell the computer that the engine is warm enough to start functioning or go into what they call closed loop (Closed loop computer taking charge of the engine fuel management).

See if Autozone has a diagnostic for the O2 sensor.

25 MPG is a high estimate, and may include wind at your back. What transmission do you have? Rear axle ratio? (that may be listed on the equipment list on you glovebox door.

[kcabbie]

Okay, well i'll look in the glove box for the rear end. But i have a muncie 3 on the tree.
I'll stop by autozone today.

[kcabbie]

Where will the sensor be at? On the exhuast manifold? There is a plug type thing that has one wire(green) going into the dashboard area. Would this be it? Also, the plug on the wire going to the selonoid on the carb is broke. Where can i get another that i can use to replace it?
Thanks guys

[1LowToy]

The wire for the carb idle solinoid is broken? If it is it needs to be repaird to idle in the run position. There is another idle screw on the linkage that needs to be lower (adjusted 75 t0 150 rpms lower with the solinoid unplugged). That lowers the idle when you shut it of to stop the dieseling. The O2 senser cold be on the exhaust mainifold or header pipe I'm nit sure.

What's the axle ratio? I'd love to shoot for 20 + mpgs

[kcabbie]

It's not broken to the point that it's not functional. The plastic is broke, so it's possible the contact goes in and out. It's kind of loose.
And i checked the glove compartment, all that the tag has is info on a camper for the bed. The door only has info on tires. How tall are 165's? I have smaller tires(i fear by alot) and i'm not sure how much shorter they are.

[kcabbie]

Any idea on where i can get replacement plugs for these wires? I'm worried there is others in the same condition that should be replaced. I can't find anything.
Thanks

[kcabbie]

Hey guys, I just got the plug in the mail and I spent about thirty minutes looking for the o2 sensor. I cannot find it anywhere. I looked all up and down the exhuast. From the manifold to the muffler, and nothing. Am I missing something? I would think that when auto zone says they have this part for my truck, it's really FOR MY TRUCK. It does have one, for sure. Right?
Thanks

[1LowToy]

Look to see if your carbyrator has two wires or a two wire plug going into the top it. No two wire plug, no computer management, no O2 sensor. This would be to the metering solinoid that meters fuel for the main jet. Autozone should be able to print out a location for it. I would think an 84 model would have one.