What happens when you remove Oil Cap

[waldrtw]

Just wanted to know what happens to your FZJ 80 when you remove the oil cap with the engine running. My 1994 starts a rough idle and almost cuts off. My 1997 LX450 runs just fine with the cap off. Which one is correct??

Tim

 

[Bear80]

There will be an idle change when either somthing like the oil cap is off or the dip stick is not in. The pcv valve pulls pressure gases from the crank case and allows it to vent into the intake. If there is somthing missing, it will be like having an air leak on the intake.

As for just running around without the cap, you should never be able to tell. Well, other than when you open the hood a few days later to find a nice oil stain on the hood insulator. Yeah.....I know. :-(

 

[ThePookieBear]

So if there is not change, at least not easily perceptible does that mean there is a problem? Because if it should change and doesn't....hmmm. : ). Mine doesn't.

 

[Lka1988]

Just wanted to know what happens to your FZJ 80 when you remove the oil cap with the engine running. My 1994 starts a rough idle and almost cuts off. My 1997 LX450 runs just fine with the cap off. Which one is correct??

Tim

Usually it idles rough. In mine, you can see the lifters and stuff moving around.

 

[CJF]

Just wanted to know what happens to your FZJ 80 when you remove the oil cap with the engine running. My 1994 starts a rough idle and almost cuts off. My 1997 LX450 runs just fine with the cap off. Which one is correct??

They're both "correct".

That is, neither one indicates a problem. These rigs just seem to vary in how upset they get if you run them with the cap off, how long it takes the computer to adjust to it, etc.

Basically meaningless (in a good way).

Curtis

 

[ThePookieBear]

Ahhh very good. I think this sight is giving me a bit of the old OCD if you know what I mean.

 

[Grolar]

Just wanted to know what happens to your FZJ 80 when you remove the oil cap with the engine running. My 1994 starts a rough idle and almost cuts off. My 1997 LX450 runs just fine with the cap off. Which one is correct??

Tim

But why would you do that?
Oh, whatever.

 

[CJF]

waldrtw: My Cruiser runs like crap when I do this.

Grolar: Don't do that.

 

[badmuthatrucka]

My 93 shuts off within a few seconds of removing the cap. Freaked me out the first time I tried it. Chevy's will run all day without the cap on. I kind of like the idea of my Cruiser cutting out without the cap. Almost like a signal that I'm an idiot...

 

[Grolar]

Grolar: Don't do that.

I didn't even think someone would actually give it a try.

 

[kwikrnu]

I've never had a car or truck that would die when the oil cap was removed. My 94 will die when the cap is removed as well.

 

[SUMMIT CRUISERS]

It's good to do if your a potential buyer of a used 80 and you want to get the price lowered. Just raise the hood with the salesman, take off the cap, look for gunk under the cap and notice the engine not running right. Then use it to lower the price for a potential valve job.

 

[RavenTai]

Just wanted to know what happens to your FZJ 80 when you remove the oil cap with the engine running. My 1994 starts a rough idle and almost cuts off. My 1997 LX450 runs just fine with the cap off. Which one is correct??

Tim

those are both correct for their year. this has been talked about in the archives.


Your 94 has a door type AFM, the incoming air moves the door against a spring, the amount the door opens is proportional the Volume of air that is coming in, due to the spring pressure on this door if another air intake sources becomes available the door will move towards closed tricking the computer into thinking the airflow is reduced and it will meter fuel accordingly (incorectly) .


your 97 has a MAF meter, the air coming though cools a heated wire, the amount of current required to keep the wire at temp is proportional to the Mass of the incoming air, since this does not create as much restriction as the door type a upper intake tract leak (opening the oil cap) does not draw as much air and the reading of the MAF is not as much off from actual air consumption.

 

[waldrtw]

Thanks!!!

 

[dcFJ]

I just noticed this as well when I changed my oil a couple of days ago...took out the dipstick to check the levels when I got done, and the engine ran horribly.

 

[Brian Macgyver]

The difference between a 94 and a 96 is vast. A 96 is an OBD II system, and will compensate for a much higher number of problems. It is more reactive and generally "smarter". A 94 will react to increased or decreased crankcase pressure. It is similar to the system in my 83 Celica. That car has had a broken ring in #1 for 50,000 miles. It is to the point that the EFI is confused and the engine will not start readily. The EFI does not know what to do to compensate. In the older systems, a lack or an overage in crankcase pressure confuses the computer. Then it cannot decide how much fuel to supply, so it supplies no fuel at all until plain pump pressure forces it to supply fuel. At that point the system is supplying too much fuel to compensate. The pre-96 system is crude at best, even in a Toyota. This is why the 96-97 80 is preferred over the older trucks.