# '98 Dodge vacuum leak?



## cwby_ram

I'm trying to get the bugs worked out of my plow truck and looking for some advice. It's the '98 in my sig. Seems to be an intermittent vacuum leak. A big one. Sometimes when I start it it'll start sucking air (it sounds like), then stall out unless I give it gas. Other times it'll run fine for awhile then suck air and stall out. We sprayed carb cleaner all around the intake as best we could and couldn't find a leak there. I was gonna rip the intake off and replace the gaskets, but before I go to all that trouble, I thought maybe someone out there has had similar issues and might be able to point me in some other direction? Thanks in advance!


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## leepotter

I believe the IAC valves get dirty/worn out and can cause this. located on the back of the throttle body. Can get them for like 15 free shipping on ebay.


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## cwby_ram

Thanks, Lee. That sounds like a good place to start. I replaced the TPS today, but the problem came back. It sure sounds like the hiss is coming from back there. I've got a whole list of possible causes piled up. I'll try the IAC tomorrow before I yank the throttle body. Do you know if the '98's still have EGR valves, I looked around for one, but I sure couldn't find it.


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## DAFFMOBILEWASH

If it backfires through the intake when you get off the throtle then I would suspect the intake gasket.


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## USMCMP5811

Is the check engine light on? any stored codes?


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## mnglocker

98 shouldn't have an EGR IIRC. Sounds like a bad TPS sending incorrect signal to the IAC valve. Common problem on these engines. 

Check the TPS for proper voltage range and replace if needed. If needed replace the o-ring on the throttle shaft, as it has worn likely allowing dirt to enter the TPS and cause malfunction. 


If the TPS checks out ok, the magnum MPFI engines have plenum leaks often enough. You need to remove the intake manifold to fix that. If you do go that route I'd recommend replacing the original "beer keg" intake with a Mopar Performance M1 single plane air-gap manifold. It's a direct bolt in and has no plenum to leak.


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## cwby_ram

Thanks for the tips guys. I replaced the TPC yesterday, though I never drained the battery. No backfiring. The engine light is on. Maybe I'll try to drive it in to get that read today too. If I remember right, I think something (presumably the issue I'm trying to work out) has tripped an O2 sensor code.


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## mnglocker

You don't need to drive it in to get the code. 

Dodge you can do the 3 turns of the key trick:

Turn the key on and off several times (on, off, on, off, on), ending with the engine on. Do not crank the engine. The digital odometer will read out the P0 codes which you can look up in a shop manual or online.


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## cwby_ram

mnglocker;1380489 said:


> You don't need to drive it in to get the code.
> 
> Dodge you can do the 3 turns of the key trick:
> 
> Turn the key on and off several times (on, off, on, off, on), ending with the engine on. Do not crank the engine. The digital odometer will read out the P0 codes which you can look up in a shop manual or online.


That makes it easy. I'll do that when I head over in a few. Thanks!


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## cwby_ram

Ok, replaced TPS yesterday, IAC today. Sounded better for while, but the hiss and stalling out came back (though maybe not as bad?). I need to pick some more starting fluid tomorrow, but I'm suspecting throttle body gasket now? My last little spurt of carb cleaner seemed to ramp the engine up, but it was a quick little spurt and couldn't been the engine catching itself. Looked into the M1 thing, I don't think I wanna put that much into it if I can avoid it. Still have ball joints and tie rod ends to address at some point. I'm kinda leaning away from the intake itself leaking, it's so intermittent. I dunno, starting to get a little frustrating...

EDIT: I also replaced the PCV and it's hose just for good measure today.


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## leepotter

There should also be a gasket where the are cleaner attaches to the throttle body.


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## cwby_ram

leepotter;1382369 said:


> There should also be a gasket where the are cleaner attaches to the throttle body.


I need to check that, I keep forgetting to look when I have it off. I think (crossed fingers) that I found a vacuum leak around the throttle body gasket. I sprayed it with starting fluid tonight when it started sucking air and it seemed to catch, although it wasn't as definitive as I'd have liked. Gonna replace that gasket tomorrow, and see if the one on top is there. If that doesn't work I guess I'll rip the intake off. It seems to be getting better, but it's still there.


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## justme-

grab and wiggle the vacuum and emissions lines while it's running- at that age the rubber is breaking down- could be a line anywhere in the engine compartment that has a break which could vary in size due to engine vacuum, vibration, etc.


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## cwby_ram

I'm still coming up empty, guys. Replaced the TPS, PCV, IAC, throttle body gasket, along with a good cleaning of the throttle body. was going to replace the gasket between the throttle body and the air cleaner, but CarQueset couldn't find one, and it seems that if that were it, the hissing would be more consistent. Sprayed around with carb cleaner, quick start fluid and propane and came up empty. Can't seem to reproduce the hissing, just have to wait for it to show up. Always at idle (giving it throttle makes it go away), sometimes it comes quick, other times it takes awhile. I have vacuum at the PCV at idle (is that right?) Could it be an internal vac leak? The cat has a leak where one side of the exhaust enters, could that be related? I'm at my wits end!


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## DAFFMOBILEWASH

Has the CEL ever illuminated?? Perhaps check for codes clear them and run it. How does it run when cold?? Better or worse??


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## cwby_ram

CEL does light. Seems like it lights when the hissing thing happens. It's not always on. As far as idling, it doesn't seem to matter hot or cold. We took it a couple miles down the road this afternoon to pick up my father-in-law's truck, and it was a little herky-jerky before it got up to temp. But after it warmed up it drove better.


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## mnglocker

Double check and make sure it doesn't have an EGR. I may be wrong you're right at or before the change year. 

If it has an EGR the EGR tube will come off the rear of the passenger side exhaust manifold. 

Also when the truck is hissing, does it idle really low and rough?


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## cwby_ram

mnglocker;1387206 said:


> Double check and make sure it doesn't have an EGR. I may be wrong you're right at or before the change year.
> 
> If it has an EGR the EGR tube will come off the rear of the passenger side exhaust manifold.
> 
> Also when the truck is hissing, does it idle really low and rough?


I'll look again. I'm pretty sure mine is after the EGR was gone, but now I know where to look for sure.

That's exactly right, idle's low and rough, often to the point of stalling.


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## doo-man

Subscribed 

Same issue on 2000 Ram with 5.7L Mag :-(


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## mnglocker

How's the oil consumption?


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## cwby_ram

It uses more than it should. I haven't driven it since August probably, so I can't really give a good definitive answer, except to say that I'd have to add a quart every so often during plowing season. I did look into the intake while I had the TB off. There was oily residue , however no puddles. and I did reseal that pan 2 years ago when I swapped the other engine in.


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## mnglocker

This is why I love the M1 intake manifold. No more plenum leaks.

I still have the keg style manifold on my half ton, but it's got a *fabbed* plenum plate and it's been ported like nobody's business.


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## cwby_ram

mnglocker;1387647 said:


> This is why I love the M1 intake manifold. No more plenum leaks.
> 
> I still have the keg style manifold on my half ton, but it's got a *fabbed* plenum plate and it's been ported like nobody's business.


If I could find some way to determine that that's really what it is, I'd just rip it off and redo it. I'm not convinced that's the issue though. I know those go bad, but after only 2 years (and only really driven in the winters those two years)? It seems that if that were the case too, it would be more consistent than it is. I guess I may resort to pulling it apart here soon, if nothing else just to be sure.


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## mnglocker

Driving it only in the winter can also be the source of the problems. Trucks need to be driven so oils move around and condensation cooks off.


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## cwby_ram

I hear that. I drove it around a couple times over the summer, but not nearly enough, I'm sure. It's been the source of many headaches, sticky hinges and latches and the like. Once I take care of the driveability issues it'll get driven more. I had a dump insert in it that I'd like to get more use from.


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## mnglocker

cwby_ram;1387675 said:


> I hear that. I drove it around a couple times over the summer, but not nearly enough, I'm sure. It's been the source of many headaches, *sticky hinges and latches and the like.* Once I take care of the driveability issues it'll get driven more. I had a dump insert in it that I'd like to get more use from.


Perfect application for Fluid Film. _ (I'm still waiting on the hat Dano50) _

I let a friend drive my 1500 most of the summer. It was a cool trick, he doesn't put more than about 4k miles on in a summer, so he's not wearing the thing out and his car blew the transmission so he was more than willing to drive that old dumpster on wheels.

It got things moving and adjusted and all the bugs have been worked out before the snowy season. (all we need now is snow.)


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## cwby_ram

mnglocker;1387728 said:


> Perfect application for Fluid Film. _ (I'm still waiting on the hat Dano50) _
> 
> I let a friend drive my 1500 most of the summer. It was a cool trick, he doesn't put more than about 4k miles on in a summer, so he's not wearing the thing out and his car blew the transmission so he was more than willing to drive that old dumpster on wheels.
> 
> It got things moving and adjusted and all the bugs have been worked out before the snowy season. (all we need now is snow.)


Good thinking, good way to keep it moving. I'll have to pick up some of that fluid film. My Chevy's gonna be in the same boat before long.


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## festerw

Easiest way I've found to diagnose the plenum leak pull off the hose on the breather and stick your finger on it, there should be a slight pressure if there is vacuum the plenum is blown.

Have you checked the MAP and temp (both air and coolant) sensors they can cause driveability problems also.


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## cwby_ram

festerw;1387821 said:


> Easiest way I've found to diagnose the plenum leak pull off the hose on the breather and stick your finger on it, there should be a slight pressure if there is vacuum the plenum is blown.
> 
> Have you checked the MAP and temp (both air and coolant) sensors they can cause driveability problems also.


I haven't checked those sensors , I cleaned off the ports and connections around the MAP, where are the temp sensors? 
There is a decent amount of suction coming from the intake if i put my finger over the PCV, is that what you mean? I've been trying to figure out where there is supposed to be vacuum and when and just how it all relates, but really haven't been able to yet. I do know though that I have good suction from the hose that goes from the PCV into the intake.


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## festerw

cwby_ram;1387876 said:


> I haven't checked those sensors , I cleaned off the ports and connections around the MAP, where are the temp sensors?
> There is a decent amount of suction coming from the intake if i put my finger over the PCV, is that what you mean? I've been trying to figure out where there is supposed to be vacuum and when and just how it all relates, but really haven't been able to yet. I do know though that I have good suction from the hose that goes from the PCV into the intake.


Not the PCV line, it should have vacuum. The breather is on the drivers side valve cover.

Here's a link to a Dodge Service Manual for an 01 your 98 should be similar, it will give to the locations and how to test all of the sensors.

http://www.rm-indy.com/wavefiles/2001ramsrvcmanual.zip


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## cwby_ram

festerw;1387944 said:


> Not the PCV line, it should have vacuum. The breather is on the drivers side valve cover.
> 
> Here's a link to a Dodge Service Manual for an 01 your 98 should be similar, it will give to the locations and how to test all of the sensors.
> 
> http://www.rm-indy.com/wavefiles/2001ramsrvcmanual.zip


Awesome, thanks for clarifying, and the link.

Here's an update. I finally got out and put the salt spreader on the truck. Had to do a 20 mile round trip to get it. Didn't experience the hissing sound once. It was a little jerky at first like I described before. It bucked like mad going down the road sometimes worse than others. There may also be a slight ping or knock, could be unrelated. Also had a hard time starting it, cranked and cranked for quite awhile before it started. It was just started yesterday. Almost forgot, CEL was off on the way there, came back on on the way back. I'll try to get that checked here soon.

Anyway, some forward progress. Need to do tie rods and ball joints sometime here as well. It's almost scary to drive, but I'm getting there.


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## USMCMP5811

I'm leaning towards a blown plenum gasket. With the oil in the bottom of the throttlebody, that is your #1 clue. I've know guys who have fixed the plenum gasket only to have them blow out again 3 months down the road. With the check engine light on, you need to check the code(s). The magnum motors have a nasty habit of cracking their heads ( most times will show a # 7 or #8 cylinder misfire code)


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## mnglocker

USMCMP5811;1388515 said:


> I'm leaning towards a blown plenum gasket. With the oil in the bottom of the throttlebody, that is your #1 clue. I've know guys who have fixed the plenum gasket only to have them blow out again 3 months down the road. With the check engine light on, you need to check the code(s). T*he magnum motors have a nasty habit of cracking their heads* ( most times will show a # 7 or #8 cylinder misfire code)


Yep, take a wire brush on a drill and clean the chamber surface between the intake and exhaust valves to find your crack.


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## cwby_ram

I think we may be on to something. Found a good size crack in the exhaust pipe right in front of the cat. Welded it up today and it seems to have smoothed out a lot. Left with a mechanic to pull all the diagnostic stuff on it. Should find out tomorrow if that solved it or not.


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## b&b landscapes

i would love an update on this, as i am currently having this problem..... it is so random its wierd....


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## cwby_ram

Sorry, I forgot that I never updated this. Welding up the little hole in the exhaust seems to have resolved that issue. I don't recall having another similar symptom after we did that. Just started the truck for the first time in several months last night and it idled just fine. The randomness drive me nuts. Check the exhaust pipes up where they come of the manifolds, that's where the hole in mine was.


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## b&b landscapes

Ironically my I have exhaust leak right before the cat and manifold gasket leaks.... I will def get those fixed and see if that helps, thanks for the update


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## ram_tough2001

cwby_ram;1508345 said:


> Sorry, I forgot that I never updated this. Welding up the little hole in the exhaust seems to have resolved that issue. I don't recall having another similar symptom after we did that. Just started the truck for the first time in several months last night and it idled just fine. The randomness drive me nuts. Check the exhaust pipes up where they come of the manifolds, that's where the hole in mine was.


have a look here. the guys that mention plenum gasket could have been right

http://dodgeforum.com/forum/2nd-gen-ram/286307-end-all-be-all-plenum-thread.html


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## cwby_ram

I'll bet that'll do it, b&b. My turn to wait for an update! I'll check that other thread out, too. In think mine's all set on that front, finally.


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## mike8668

*Resurrecting please help*

Hey cwby_ram was the exhaust leak the fix to what ailed you many,many moons ago?
I have the same issue with my 98 5.9L Ram and am hoping for an update....


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