I got home today and went to check my oil and noticed a small fire on the back of the engine. It was actually on one of the vac lines. What could cause it to catch on fire?
If you look at where the acv was, you see 3 vac lines, 2 of which go towards the back of the engine bay and connect behind the engine. The fire was on one of those where it connected behind the engine.

 

leaking PD (Pulsation Dampner) is the most likely cause

 

I always thought that it leaked near the front of the engine, by the cap. Can it leak elsewhere, too?

 

oh yeah!...i had cracking fuel lines on mine but i cought them before they went completely

 

the plastic cap thing is towards the back of the engine bay

 

but its more on the front side of the engine, isnt it?

 

the thing is, this didnt really look like a fuel fire. It was a pretty small flame. I'd think it would be larger if there was a fuel leak.

 

Well, how'd it smell?

 

hmm interesting.....did you have any styrofoam or any other material near the back of the engine bay? because if it wasnt fuel( usually the thing that causes fires, duh) than it must have been something else like, a material that accually combustes at high temp....

if you heat styrofoam up to a couple hundred degrees then it will combust. so its possible if you got something close enough to exuast it could have caused it......

were you in the car when it happened????

 

ooooorrr it could be electrical.... you got a lot to check. what model is your car? take off the uim and start searchin

 

You're right. N/A's have the PD on the front of the secondary fuel rail, T2's have it on the back.
-John

 

Well, it wasn't really near the exhasut. It was right by the back of the intake manifold. The only other thing around it was some electrical tape that was wrapped around another hose. I think that whatever started the fire was burned off by the time I saw it, bucause there wasnt anything there. The fire wasnt much bigger than the flame from a match, just an inch or two tall.

It smelled like burning plastic, that was about it

There were no wire nearby, so I doubt it was electrical.

 

But the leaking fuel can run down the front to the back and drip down on non turbos (more so on S4 versions with the plastic cap) or back to front on the Turbos.

 

Oh, ok. Just for reference, how much is the cap on the PD supposed to move? I cant really notice it moving.

 

On the S4 PDs, the cap should never move. Its whole purpose in life is to only protect the calibration/stop screw from coming in contact with anything.

 

Good, I was hoping that was how it worked.
This might be a stupid question, but how are you supposed to check the PD? The FSM says to check that it pulsates, and the cap is the only part that is accesable.

 

you think it would be ok for me to tape the screw so that it never comes out???

 

ahh, gotta love them 87-88 PDs...

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/engine-fire-pics-352047/

 

No, the screw can not touch anything, that is the whole reason for the cap

 

man you got lucky that you caught it, glad it worked out in the end

 

Yeah, i consider myself very lucky. The only damage was to 2 vac lines, and I had spares sitting in the car so I had it fixed in about 2 minutes.
Now to get another one. Im guessing its recomended to get a new one and not one from a junk yard, right? I saw that someone (icemark?) said that they were about $100 on another thread yestartday. Where can I get it for that much? The mazda dealership said it was either 160 or 230, he claimed there were 2 different ones.

 

Before you jump to conclusions, verify that it is in fact leaking. Start the engine and let it idle, if its leaking it should leak right away, so check it with your hand and see if its wet with gas. If that is the case, replace it asap, don't drive anywhere when its like that.

My first impressions with this thread was that it was a grease fire? If your engine bay is just disgustingly covered in grease, its a possibility?

 

my banjo bolt used to leak... thats on the rear side of the fuel rail

 

Well, I didn't notice any gas anywhere, so I'm thinking its not the PD. There actually is a noticable amount of grease around that area so its a possibility. I'm gonna fix my exhaust leak tomorrow, and I'll look it over again then. Its so bad my eyes started burning when I was looking under the hood. I'll get back to you then.
I'd still like to know how you are supposed to check if the PD pulsates when you can't get to it.

 

On a non turbo S4 you can get to the PD without taking anything apart.

As far as replacing it, it should be replaced anytime it is leaking, I also consider it to be a maintence item and should be replaced every 100-120K miles or 10 years.