Need help diagnosing engine problem...

[Rick '79 FJ40]

In the last few months, my truck has begun running rough at idle after it warms up. It cranks fine and runs fine when it's cold, but after it gets up to temperature, it doesn't want to idle and will cut off if I don't give it some gas at a red light. It seems to have plenty of power when its cold, but loses much of it after warm-up, too.

A week or so ago, I checked all of the vacuum lines and cut the worn out ends off of a couple of them to make sure the clamps hadn't cut into them and caused them to leak. I also tightened the clamps on all vacuum lines and on the fuel line. I also replaced the PCV valve which was stuck. This made it crank better than it ever had, so I figure I had at least 1 or 2 problems before in this area. It didn't fix the main problem though.

I originally suspected that I had a blown head gasket, but I haven't seen any evidence of water in the oil. I haven't done a leak-down test yet, because I don't have a tester. Could a blown head gasket cause these sort or symptoms?

Thanks for any help you guys can give me!

 

[Pin_Head]

Manifold vacuum leak?

 

[Full_Throttle]

Rick,
Can you give specs on your engine? Toyota or chevy, what type of fuel delievery, carb, efi...ect.
If it is a carb, have you checked around the base for leaks? I used to always spray a can of ether around the base of the carb and intake. If the engine surges, you have a vacuum leak wherever you sprayed the ether. It does sound like a vacuum leak to me. I guess it may be possible there is something wrong with your choke???? I would at least ckeck all the carb linkages and make sure it all looks good and move freely.

 

[Rick '79 FJ40]

Rick,
Can you give specs on your engine? Toyota or chevy, what type of fuel delievery, carb, efi...ect.
If it is a carb, have you checked around the base for leaks? I used to always spray a can of ether around the base of the carb and intake. If the engine surges, you have a vacuum leak wherever you sprayed the ether. It does sound like a vacuum leak to me. I guess it may be possible there is something wrong with your choke???? I would at least ckeck all the carb linkages and make sure it all looks good and move freely.

Sorry, I should have given you the details...

1979 2F with Weber 38 carb and headers. De-smogged. PO had used peices of hose with screws in the end to plug off some of the manifold vacuum ports. In conjunction with the vacuum hose checks I made a week or 2 ago, I replaced these with regular "store-bought" plugs. I didn't clamp them, so I am going to go back and put clamps on them to make sure they aren't leaking, but they seemed tight when I put them on.

Thanks!

 

[jus cruzin]

A blown head gasket doesn't always mean you will get water in the oil....oli pressure is usually greater than water pressure (10psi or so). Water can leak into cylinder and then exhaust. A cracked cylinder head will do this also. Check carby gaskets....maybe sucking in air between carby and manifold...................good luck

 

[fjwagon]

Pinhead suggested to check the manifold/intake for a leaks....spray carb cleaner is see if the engine raves up...it should not. Do the same to the carb's base. Have you repalced the fuel filter? Also are you getting enough gas to carb after it warms up. Also has the egr valve been removed entirely from the intake?

I have a 79 but it has all it's emissions. I something similar a couple of years ago. It would run fine but every now and then it had trouble idleing when it was warm. It seems to get wosre to the point that it did not run well at highway speeds. I ended up replacing the fuel pump. That fixed it.

 

[Rick '79 FJ40]

Pinhead suggested to check the manifold/intake for a leaks....spray carb cleaner is see if the engine raves up...it should not. Do the same to the carb's base. Have you repalced the fuel filter? Also are you getting enough gas to carb after it warms up. Also has the egr valve been removed entirely from the intake?

I have a 79 but it has all it's emissions. I something similar a couple of years ago. It would run fine but every now and then it had trouble idleing when it was warm. It seems to get wosre to the point that it did not run well at highway speeds. I ended up replacing the fuel pump. That fixed it.

Thanks for all of the help!

I think I've figured it out...

I tightened the clamp on the distributor for the Vacuum Advance hose, and that seems to have fixed it. I think I had some minor vacuum leaks before, as well as some fuel line leaks, because the thing cranks so much easier now its like a different truck! I think I have all of the vacuum and fuel related clamps tight now.

Next problem is my brakes seem to be going most of the way to the floor all of a sudden. I've ordered a new master cylinder and am going to do the front brakes and the MC next weekend. That's about the only thing that goes bad over time that I haven't replaced yet.

It's always something...

 

[Pin_Head]

Next problem is my brakes seem to be going most of the way to the floor all of a sudden. ...

If the pedal rises on a second pump, then your rear brakes need adjusting.

 

[Rick '79 FJ40]

If the pedal rises on a second pump, then your rear brakes need adjusting.

Hmmmm... That could be it. I'll have to check it tonight, I haven't been driving it because of the brake problem. The last time I got my tires balanced the guy said I was going to need front brakes soon, so I am going to do that either way, but I may be able to wait on the MC.

Thanks!