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Running issues. I'm out of ideas


MGTS

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1983 California base model, manual, Z24, using stock carb. When I got it, it ran well enough to get it home. I started adjusting the things I'm familiar with. Adjusted valves. Found that the vacuum hoses were turned around and pulling too much advance at idle. I've replaced all vacuum hoses, rebuilt carb, float is good, accelerator pump is working, replaced intake manifold gasket, replaced temp sender in the intake for the computer. It idles great. Got it set to 700 rpm and pulling 20 inches vacuum. Timing set to 4 degrees. All plugs getting spark and all plugs are new within a year and look great. Adjusted gap. Choke plate is opening as it gets warmer. Thermostatic vacuum valve on the intake is working right.

 

I got everything set and was revving by hand and it would just constantly bog down and nearly die. Discovered that it was taking in a LOT of air from the canister. I plugged it and it seemed to help significantly. I also plugged the hose going to the EGR and to the ATC in the air box. The next day I went back and it's doing the same thing again. Idles great. Giving it any kind of throttle from idle and it falls on its face. Doesn't usually die, but it feels like it's going to. On the road, if I'm trying to accelerate at all, it feels really anemic. There is all this "wall" that it kind of hits. If I'm trying to accelerate, it just feels awful, but if I let of the gas slowly, it will "jump" back to normal. It kind of feels like lack of fuel. 

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Electric fuel pump on these and they like to clog filters. Disconnect fuel line to carb put in a glass jar and turn on ignition and check flow. Eliminate this one issue at a time. Seems like you have a good grasp of mechanics after what you have done so far.

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What? was taking too much air from the canister???? Only vacuum is applied to the canister to trigger a purge valve. It's sealed so other than the hose off or connected to the wrong fitting or a crack in the hose.... it can't get air. It uses vacuum advance vacuum so even if hose is off it won't affect running. Connect the ATC.

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All the ATC does is open and close the hot air intake. I just want something predictable while I run tests. I also need to check that it doesn't leak. The second hose going to the canister connects straight to manifold. When the top hose opens the diaphragm, I can hear the lower hose sucking in air. I will get some videos tomorrow

Tv7aSwz.jpg

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That is the image you sent me Mike from my other thread. The routing is the same on mine, but I don't have the vacuum control valve or a boost control valve

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Connect the ATC and run the engine. With a pair of pliers pinch the vacuum hose closed. If the idle changes there may be a leak. The ATC regulates the intake air to keep it closely controlled. Even in the winter the engine will think it's summer and run accordingly.    

 

I see that the canister purge signal in a ported vacuum source... they used to be on the same ported vacuum source as the vacuum advance. But in all cases this is not intake vacuum but a port above the closed throttle plate. Above idle the throttle plate lifts above the ports and intake vacuum is applied. Thus there is no vacuum advance or EGR or canister purge at idle. All three hoses could be off and the engine will be unaffected when idling or driving. (well other than the vacuum advance isn't working)

 

 

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Alright, video time

 

Cold start https://www.youtube.com/watch?v=0acV_zKtgIY

 

Driving (skip to 1:15) https://www.youtube.com/watch?v=_ZET7hrQVXc

 

Canister https://www.youtube.com/watch?v=_ZET7hrQVXc

 

Throttle blips https://www.youtube.com/watch?v=Z0VcSxefAic

 

More throttle blips https://www.youtube.com/watch?v=bc2eZ9d8mdY

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Engine off, top of air filter off. Look down the barrel and pump the gas. The accelerator pump should discharge a strong squirt of fuel.  Weak discharge will cause stumble above idle.

 

Inspect the inside and outside of the distributor cap for carbon tracking. This is where a spark has jumped and burned a small path making it easier to jump the next time. Look at the wires for damage or rubbing.

 

After dark (has to be very dark) start it up and rev it where it stumbles and look all over the distributor cap and along the wires for any signs of blue flashes or sparks. Don't forget both coils too. Sparks on coils jump to the negative terminals. 

 

 

The second video.... was that vibration shaking the camera??? was that the engine or the road???

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In the second video it's the truck. Road is pretty smooth. 

The pump was replaced with the rebuild. It seems to squirt ok. The intensity changes with how hard I bump the throttle 

And to answer bottomwatcher. The float bowl is at the right level. Bad fuel delivery would only make itself known at higher speeds right?

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34 minutes ago, MGTS said:

In the second video it's the truck. Road is pretty smooth. 

The pump was replaced with the rebuild. It seems to squirt ok. The intensity changes with how hard I bump the throttle 

And to answer bottomwatcher. The float bowl is at the right level. Bad fuel delivery would only make itself known at higher speeds right?

Usually you will notice a decrease of top end speed. This is really noticable on long trips you can max at 70, 65, 60 ect. If it is really plugged you may get similar symtoms to what you have. It only takes a couple of minutes to disconnect the fuel line from the carb and let it run into a container and observe the flow. I used to fill my coleman stove this way when camping.

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I guess ok for squirt. As long as the carburetor gas gas in  the float chamber it will run normally. If there is a fuel delivery problem such a partly plugged fuel filter or reduced output from the pump when you put a heavy load on the engine as in passing on the highway, climbing a long hill or accelerating onto a highway the carburetor will use more gas than can be provided. It will act like it's running out of gas but as soon as you let off it will act normally again.

 

Can you check the ignition wires and coil in the dark?

Can you do a compression check?

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First thing I did when I got it home was check compression. 180-185 in all cylinders. I will try to do a spark test later. Wouldn't that affect it running at idle? I did discover that my valve seals are leaking BAD, but I don't feel like that would affect the way its running this much

 

In general, does this seem like an air, or fuel delivery problem?

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Like I said if there is fuel in the carburetor it will run normally. The accelerator pump proves there is fuel.

 

 

Try something? With it warmed up and the top off the air filter hold the choke partly closed. Just enough to affect the idle... then rev it up and see if the idle still stumbles.

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When warmed up and if it runs better with the choke on slightly, this would indicate that it is running lean and the choke corrects this. 

 

This is the ECC carburetor with the 6 wire plug at the back? and O2 sensor? This would be the electronics telling the carburetor to be that way. Maybe one of the sensors is giving bad info to it? Just for example if the TPS is saying the carburetor is at full throttle or full closed at idle, the O2 sensor air fuel information is ignored.  

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I have replaced the temp sender and the O2 sensor, I confirmed via multi meter that the throttle switch i working. I guess I have to follow the book and check all connections going to the computer. I should have tested the fuel cut solenoid when I rebuilt the carb.

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So just to humor myself, I did a manual check of the mixture and fuel cut solenoid. Directly connecting them to battery power. Mixture clicks. Fuel cut doesn't. I pulled it off and did a bench test too

 

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I'd be careful of the mixture solenoid. It's meant to turn on and off rapidly and NOT to be on for any time as it might over heat.

 

The idle cut can run on for ever. If it doesn't click, you won't be able to set the idle.

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