Idle issues - Advice on tracking the problem down (1 Viewer)

[Tecnos]

I have a 1980 FJ40 with 2f. Most of the vacuum lines have been removed. There is one running from the distributor to the carb. The vacuum on that carb. port reads 12 psi.

I was looking through one of the desomgging treads to make sure everything was correctly connected, but much of the system is removed. (Vac switches are gone) So there really isn't much to check. I replaced the vac hoses that were present.

The truck starts very easily, and it is drivable, but it takes work to keep it running. It has run well in the state that it is in since I bought it last May until probably September with regular driving. The only issue I had with it at that time was a slight backfire (pop, pop, pop) when decelerating.

If I half choke the truck, it will run but the idle is too high, and it seems to rev higher at times. It may do better on a flat surface, but I can't be sure of that. When the choke is all the way in, the truck will usually die, but occasionally it will run for a moment before it sputters to a stop. There is a little bit of sputtering at low RPM's when accelerating. It seems to run fine at higher mid to higher RPMs.

One thing that was odd about driving it last summer is it ran like this once when the truck got a little hot. I replaced the plugs and wires and it seemed to run good again.

I am considering a DUI distributor and possibly a Holley Sniper, but I would like to try to see if I can get it running at least as well as it ran last summer if possible.

Regarding the DUI distributor, how does this system affect the vacuum system?

Any advice on where to start would be appreciated.

 

[rkymtnflyfisher]

Checked the timing and valves lately?

 

[Skeet]

The backfire on decel and choke needed to idle would have me looking at the manifold for leaks

 

[Chestcutter]

I had the same problems on my '78 40. Stalling after decelleration may have been the brake booster, which had a significant vacuum leak, but the idle solenoid was also bad and so the carb idle circuit wasn't reliable.

I believe the 1980 has a 2 wire idle solenoid. Easy to remove from the carb and test with a 9V battery. If the solenoid tests good out of the carb you may still have a ground issue. The 2 wire solenoid ground is via the emissions computer. If you bypass that and connect the ground side to a chassis ground it will keep the idle circuit on whenever the ignition is on.

Search here for "green wire mod"

For me new brake booster and fixing the idle solenoid problem leads to good idle at 650 RPM although the vacuum is low at 14 probably due to manifold vac leak. Make sure you are measuring vac directly from the manifold. The distributor connection should be ported vacuum.

I'm sure the experts here will have better advice, just weighing in since I've been working through the same issues myself

 

[Tecnos]

Thank you - I will start with the items you guys listed and report back

 

[Tecnos]

I had the same problems on my '78 40. Stalling after decelleration may have been the brake booster, which had a significant vacuum leak, but the idle solenoid was also bad and so the carb idle circuit wasn't reliable.

I believe the 1980 has a 2 wire idle solenoid. Easy to remove from the carb and test with a 9V battery. If the solenoid tests good out of the carb you may still have a ground issue. The 2 wire solenoid ground is via the emissions computer. If you bypass that and connect the ground side to a chassis ground it will keep the idle circuit on whenever the ignition is on.

Search here for "green wire mod"

For me new brake booster and fixing the idle solenoid problem leads to good idle at 650 RPM although the vacuum is low at 14 probably due to manifold vac leak. Make sure you are measuring vac directly from the manifold. The distributor connection should be ported vacuum.

I'm sure the experts here will have better advice, just weighing in since I've been working through the same issues myself

I am working through the suggestions.

I tried the green wire mod and that did not work. The solenoid tested operational.

On the brake booster. Is it normally the booster itself that is the problem or the lines? How do you determine the source of the leak? Just vacuum test the fitting coming out of the brake booster, then the line going into the engine?

Thanks for your patience. I am an amateur at this.

 

[Chestcutter]

Definitely an amateur as well. I used a handheld vacuum pump. disconnect the brake booster hose at the manifold and connect to the pump. the hose and booster should hold vacuum. If not could be the hose or booster. I replaced the hose and the booster clearly leaked.

 

[Tecnos]

Ok. So the truck is running quite a bit better. Re-gapped the plugs, put some carb cleaner in the carb, looked for vacuum leaks, but have yet to find one. Adjusted the idle on the carb, which helped, but it was running better before the adjustment, just wouldn't hold idle. I am not certain what has helped the most.

I was checking the timing with a friend yesterday and found that it is timed a TDC. We were going to adjust the distributor, but when I loosen the bolt to the right of the distributer, we can't get it to move. There is a small clamp under the distributer as well. I loosened that, but it still wouldn't move. Any advice on getting it to move?