Vacuum leak

vbrad511 · Sep 21, 2014

I can hear it, but can't find it. I've sprayed starting fluid (sparingly) around everything I can think of, nothing's telling me anything. A while back I had an intermittent CEL, would come and go. About 6 weeks back I had to change the front leaf spring mounts, so I dropped the tank for safety reasons. When i put it back together the CEL was on for good. I've had it scanned, and at first I got "purge valve and solenoid" and all 3 O2 sensors. I changed the purge valve and sensor then only had 1 O2. Changed that O2, jumped back to all 3 O2's. I can hear the leak, truck stumbles a bit when I'm moving and give it throttle. I don't know where to look now. Suggestions?

adsm08 · Sep 21, 2014

What engine is in it?

vbrad511 · Sep 21, 2014

It's a 4.0

vbrad511 · Sep 23, 2014

Changed plugs in it tonight, all six been burning lean. Gonna pull the plenum on Thursday to see what I can.

AgPete139 · Sep 24, 2014

Physically wiggle the hoses. You'll hear a change in sound with it.

vbrad511 · Sep 24, 2014

Tried that. Gets me nowhere.

AgPete139 · Sep 25, 2014

Did you try 250 lbs of TNT?

There's this little thing that you can clean out with brake cleaner. I have found this to occasionally clog (causing your previous CEL), and it had hardened hoses (with minute vacuum leaks) on both of my '97 4.0's.

Give this area a look-see, by the charcoal canister. Be gentle though; the plastic nipples can easily break off.

This is located near the battery, driver's side fender.

rags · Sep 25, 2014

Just had the same problem with mine also 95 4.0 - It kept giving me lean codes and ran like crap. cleaned and sprayed everything and could not find a leak in any hoses or intake. by accident I found a small hole right under the EGR valve leaking vacuum. plugged with JB weld for now and engine has never run smoother and no more codes.

vbrad511 · Sep 26, 2014

I just changed that purge valve and it's sensor. That did nix the codes related to them, but still got the lean thing going on. I pulled the plenum tonight after work, still nothing. Put a different plenum on it, just to see what it'd do....same thing. I'll check that EGR tube and surrounding components. I know things are a bit rusty there. Thanks..

AgPete139 · Sep 29, 2014

Are you getting the P0171 - P0172 Check Engine Codes? Which code are you still getting that's lean?

You could be anything from your check valve on your left rear valve cover, to the 90* 1/2" tube that inserts itself into the intake tube from the manifold.

Head leaks could cause a miss and a hiss, but I don't think that's your case.

It soulds like you just have to search your hoses, man.

vbrad511 · Sep 29, 2014

Not the 0171-0172. Getting p0155, p0135, p0141, but I may have found part/all of the problem. Like I'd said, when I pulled the plugs a few days ago they all looked like they'd been fuel-starved. I did a little more digging today after work and found that there's an actual fuse for the O2's, and sure enough, mine was blown. They say it goes sometimes when you have one O2 go bad, which I did. I replaced the fuse and let it idle a while in the drive. Sounds a bit smoother, quicker pedal response too. The CEL is still on, but I'd think if I've gotten it taken care of it should go out with a couple day's driving. Thanks for all the help folks, I'll keep you posted how it all goes.

AgPete139 · Sep 30, 2014

Fantastic. Glad it worked out.

downer · Sep 30, 2014

where did you find this fuse? i'm having similar problems

vbrad511 · Sep 30, 2014

It's in the power block under the hood. It's a blue 1amp. They're not labeled on the lid, or in my Haynes manual, at least not for my 97, but the location for the 95 was the same. It's only been a day but the truck seems to be running smoother, accelerating without hesitation, but the CEL is still on. If it's still there tomorrow I'll run it through Oreilys and have them scan it again.

AgPete139 · Oct 1, 2014

vbrad511 said:
It's in the power block under the hood. It's a blue 1amp. They're not labeled on the lid, or in my Haynes manual, at least not for my 97, but the location for the 95 was the same. It's only been a day but the truck seems to be running smoother, accelerating without hesitation, but the CEL is still on. If it's still there tomorrow I'll run it through Oreilys and have them scan it again.

O'Reilly's does not have a scanner. Only Autozone does.

Vacuum leak

Member

Senior Master Grease Monkey

Member

Member

09/2014 OTOTM Winner

Member

09/2014 OTOTM Winner

New Member

Member

09/2014 OTOTM Winner

Member

09/2014 OTOTM Winner

Member

Member

09/2014 OTOTM Winner

Sponsored Ad

Sponsored Ad

Today's birthdays

Member & Vendor Upgrades

Truck of The Month

Recently Featured

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals