Can Hear Air Sucking Hiss when I Try to Start it

my 1996 ram 1500 overheated. I didn't have a temp sensor wouldn't you know and apparently I need one in case hoses spring a leak.

anyway, I replace both temperature sensors and the crank position sensor. It started up very laboriously with a lot of hissing and the first time it started then subsequent starts seem to go quick was just return of the key.

Now today I take it on a trip to the store and when I come out of the store it doesn't start. I hear a hissing noise when I try to start it and I let it cool down for 30 minutes. I was in the store (a 15min trip) for maybe 10 minutes.

now it truck barely starts - but I can get it running.
I can hear air sucking after it starts and when it runs for 10 seconds then the hissing stops and I seem to be able to drive it. but, if I stop then start it, the same thing happens all over. The hissing is on the right side of the engine. Cant pinpoint it.

Again, what happens is when you start it you can hear the air sucking sound and if you continuously crank it eventually starts up slowly once it gets going the air sucking sound goes away. So, that tells me perhaps when the trucks warm some sort of valve is staying open that should close when you shut off the truck and be closed when you start the vehicle. I think it's remaining open and causing the air to suck in. What would I look for in based on what I have described?
if anyone has solved a similar issue help is appreciated.
rr

Sounds like the IAC is sticking. Its located at the back of the throttle body. Apperently they get gunbed up, and need to be cleaned. Hope that helps.

You can try cleaning the IAC. If you have the money though, I would just replace it. While you're in there replacing that, I would also take the throttle body off and give it a good cleaning. Make sure to pay attention to the small passages for the MAP and the passages for the IAC. Also check the rubber elbow where the MAP connects to the throttle body for cracks.

ok I replaced the IAC but it does almost the same thing. I did not clean the throttle body yet. it is really hard to start. when it's cold it starts better than when it's hot. it will start but takes a lot of cranking/revving to keep it running . after about 5 or less minutes it will idle. then I can drive it fine. but, if I turn it off same deal.

when it does first start I have to keep giving it gas to keep it running. I can't figure this out.

until I overheated it would start as soon as I turned the key. I changed the CPS because it would not start at all after I ran it hot.

then there's the mystery of the gas. only happened once, but, it wouId not start at all. I thought the head gasket was blown and I had driven only 33 miles on a full tank of gas before the problems started and found the tank to be empty. There's an anti siphon ballcock in the filler tube so, I doubt anyone siphoned all the gas out. I'll let you know if this happens again.

any ideas?

The area where the iac goes may be getting dirty as well not allowing the iac to move freely.

Sounds like a bad vacuum leak to me. Check all hoses attached to a vacuum source.

I agree with OCTech on the possibility of a vacuum leak. I'm not sure where each of these things is located on a 96, but make sure you check your PCV valve and lines, your EVAP solenoid and lines, EGR valve and lines, cruise control vacuum lines if equipped, your ventilation vacuum control lines. If you can't visibly see any cracks or tears you might need to take the truck somewhere to have them smoke the system... Or you could also get a cigar, make yourself a walking smoke machine and blow smoke in the lines and look for leaks.

I should have warned you to be careful cleaning the IAC because the motors in that device are very fragile and don't react too kindly to any rough treatment.

If it isn't a vacuum leak here are some other thoughts and questions....

You said you overheated the motor? Have you done a compression test to see if either of the head gaskets are blown?

Also since you ran it out of gas, you could have sucked up a bunch of crud into the fuel filter and fuel lines. Have you tried doing a fuel pressure test as well?

crazykid1994 said:

The area where the iac goes may be getting dirty as well not allowing the iac to move freely.

Click to expand...

I cleaned that out. it does start better when cold. takes about 2minutes to idle after a bunch of playing with the gas pedal to keep the rpms up. but when turn it off, it's harder to start gotta floor the the gas pedal then be careful not to Rev it too high.. eventually it starts, same deal

SportRam00 said:

I agree with OCTech on the possibility of a vacuum leak. I'm not sure where each of these things is located on a 96, but make sure you check your PCV valve and lines, your EVAP solenoid and lines, EGR valve and lines, cruise control vacuum lines if equipped, your ventilation vacuum control lines. If you can't visibly see any cracks or tears you might need to take the truck somewhere to have them smoke the system... Or you could also get a cigar, make yourself a walking smoke machine and blow smoke in the lines and look for leaks.

I should have warned you to be careful cleaning the IAC because the motors in that device are very fragile and don't react too kindly to any rough treatment.

If it isn't a vacuum leak here are some other thoughts and questions....

You said you overheated the motor? Have you done a compression test to see if either of the head gaskets are blown?

Also since you ran it out of gas, you could have sucked up a bunch of crud into the fuel filter and fuel lines. Have you tried doing a fuel pressure test as well?

Click to expand...

thanks for all that.
don't hear or see any leaks. clean IAC installed from another ram identical year. cleaned orifice where it resides.
fuel pressure seems OK. squirts pretty good out of Schrader valve.
doubt it's head gasket or plenum gasket since it d
will idle fine after I get it running for a few minutes playing with gas pedal until computer "catches" and stabilizes the idle. then it drives fine.

also. I don't hear hissing anymore when I start or running.

I decided to purchase a new map sensor. It just arrived today so I'm going to swap it out and see if that is going to improve anything on restarts.

if it's not the map I don't know what is involved with removing the throttle body. are there any diagrams of it clear enough to make out what I need to have if I remove it?

also. removed fuel tank. only fuel filter on the truck is in that unit. it seemed clean. nothing unusual.

rr

just another thought could the breather element cause the sucking noise if it fails. going to try a new pcv valve.