96 N/A - Tracking down a vacuum leak...

Post by **SonicAdventure** » 23 Aug 2020, 21:32

This is a springboard from my prior problems starting as a consistent misfire in Cyl 1.

I've pulled the #1 injector and replaced it with like-kind. Resistance on all of the injectors is between 18.0-19.5 ohms. No real noticeable difference in idle or run with the replacement injector, but 1-2 days later, CEL again for a misfire in cyl #1. Pulled the Volvo sparkplug from #1, its been in there for 1 year. Replaced it with a used but good condition Volvo plug, no difference in running, no CEL yet.

While I've been under there poking around, I'm noticing a loud hissing sound, like a tire with a nail in it would make. Depending on where you stand, it always sounds like its in front of you. If I stand in front of the car, it sounds like it's coming from the PCV box area, but if I stand in front of the passenger tire, it sounds like it's coming from the vacuum tree. Maybe it's coming from both. The vacuum line from the fuel pressure regulator to the tree seems fine, I checked all that while the fuel rail was off. PCV is good, glove sucks in hard and harder when throttled.

This car does not have the little end outlet on the intake manifold (its just a solid plate), nor does it have any vacuum lines running into or out of the airbox. There are no holes in the airbox like I've seen on other same-year cars. With how loud the hiss is, I'm inclined to think its the intake manifold gasket, but wouldn't it throw a separate code for an intake vacuum leak?

Surprisingly, when I refilled the car's tank today, the MPG according to the app I'm using based on mileage and gallons since the last fuel-up went from 22.2 to 22.3 over the length of this issue the past few weeks, which doesn't make sense to me if it's misfiring.

Attached are photos of the one-year-old plug I pulled and a video of the hissing sound. Any ideas?

Post by **SonicAdventure** » 23 Aug 2020, 22:06

Thought I would add a quick vid of the exhaust. There are two concerning sounds (to me), one of which is the subtle (whuuump or whooo sound) that occurs randomly. I can't tell if I hearing the sound of a piston traveling in the block and randomly not firing or if its the sound of a valve, or neither...

Post by **abscate** » 24 Aug 2020, 04:54

Get a piece of hose, put one end in your ear, and poke the other end inthe gaps in the intake manifold to localise your noise. It will be the intake manifold or a vacuum hose running under there. High frequency hisses transmit great through hose so that will work well

Careful the vacuum doesn’t pull your brains out through your ear, I read on the internet that can happen.

callahanoffroad · Post by **callahanoffroad** » 24 Aug 2020, 05:28

abscate wrote: ↑24 Aug 2020, 04:54 Get a piece of hose, put one end in your ear, and poke the other end inthe gaps in the intake manifold to localise your noise. It will be the intake manifold or a vacuum hose running under there. High frequency hisses transmit great through hose so that will work well

Careful the vacuum doesn’t pull your brains out through your ear, I read on the internet that can happen.

Abscate: this is good advice. But don't forget to also include essential oils to promote wellness and chi balancing on the self healing chakras of the car.

Hey Sonic, I used to have a very similar car! There are really only four vacuum lines on the car. One for the fuel rail, one for the egr, a small jumper from the flame trap elbow, and one that goes to the charcoal cannisters. A simple, cheap fix is to simply replace all the vacuum lines with the cheap stuff at the auto parts store. See if replacing all those baby lines fixes it, plus the rubber is probably bad anyways.

Part 2 would be to check the flame trap elbow, idle air control valve connections and the brake booster hose.

Hope that helps!

Post by **SonicAdventure** » 24 Aug 2020, 10:31

Thanks Callahan and Abscate; two follow ups

Would a "car stethoscope" work good for this also? I've been thinking about buying one for a while, maybe this is a good time.

Does replacement small vacuum line need to be the same inner diameter of anything it's replacing? Or would buying a larger/smaller diameter throw off other sensors due to different pressure? I'm esp referring to the white lines with black elbow from the fuel pressure regulator in the rail and also the white one that goes to the relays above the fan shroud. Those lines both look original to the car so, 24+ years old...

Post by **abscate** » 24 Aug 2020, 11:24

A hose will work better than the stethoscope

Vacuum lines are forgiving on diameter, so just buy for the fitting end and use a zip tie if it is a bit loose