intake air leak

[dgrund61]

Need help with 98 1500 6.5 td. I keep getting a code for an air intake leak which happens sporadically ; no apparent rhyme or reason ; I'll clear it and it might come back two weeks later or two days later. when the ses lite comes on for it, it tends to be when I'm letting off the throttle, but not 100 % of the time I've checked all the clamp connections and it has new intake gaskets so I think that's not the cause. What sensor would cause this code? What is a easy or quick and safe way to find a leak like this. i.e. ( soap bubbles,spray gaskets and connections with oil) ?Any Help would be appreciated.

[john8662]

whats the code number?

[Robyn]

The incidence of intake leaks on these engines is very very low. I would suspect one of the sensors such as the map sensor (Turbo boost) or the atmospheric pressure sensor. or in these later trucks the Mass airflow sensor

There could also be an issue with the wastegate solenoid or the supporting vacuum lines that run from the vacuum pump to the solenoid and then to the wategate actuator.

On a gasser you can spray a somewhat volatile aerosol around any joints but the diesel generates no vacuum so this is of no value. You can easily pressurize the manifold with the rig sitting so to get soap to work is a tough one too.

I am very suspect of one of the sensors getting hinky on you and as the throttle is changed and the manifold pressure changes.

The system is not happy with something so its just a matter of figuring it out.
A tech 2 scan tool or its equal could really make the diagnosis a snap. Simply run the truck under operating conditions and check the sensor readings against the specs.

The mass airflow sensor or the boost sensor are most likely the sensor that is setting the code but the issue is why. Is it a bad sensor or another issue such as incorrect boost for the throttle position based on the amount of air thats flowing into the engine.

These sensors are not cheap items so I dont really recommend replacing them to see.


Let us know the code that you got and we can go from there and possibly narrow it down some.

When the MIL light comes on does the truck go into any sort of limp mode or does it seem to run ok??

Best

Robyn

[dgrund61]

The incidence of intake leaks on these engines is very very low. I would suspect one of the sensors such as the map sensor (Turbo boost) or the atmospheric pressure sensor. or in these later trucks the Mass airflow sensor

There could also be an issue with the wastegate solenoid or the supporting vacuum lines that run from the vacuum pump to the solenoid and then to the wategate actuator.

On a gasser you can spray a somewhat volatile aerosol around any joints but the diesel generates no vacuum so this is of no value. You can easily pressurize the manifold with the rig sitting so to get soap to work is a tough one too.

I am very suspect of one of the sensors getting hinky on you and as the throttle is changed and the manifold pressure changes.

The system is not happy with something so its just a matter of figuring it out.
A tech 2 scan tool or its equal could really make the diagnosis a snap. Simply run the truck under operating conditions and check the sensor readings against the specs.

The mass airflow sensor or the boost sensor are most likely the sensor that is setting the code but the issue is why. Is it a bad sensor or another issue such as incorrect boost for the throttle position based on the amount of air thats flowing into the engine.

These sensors are not cheap items so I dont really recommend replacing them to see.


Let us know the code that you got and we can go from there and possibly narrow it down some.

When the MIL light comes on does the truck go into any sort of limp mode or does it seem to run ok??

Best

Robyn
The code that it sets is 1191 which says intake air duct leak; it does not go into limp mode as it still runs fine. It seems to happen (as an example) when coming off a 4 lane on an exit and you pop the cruise off or take your foot off the throttle; not always but out of the 4 or 5 times I would say probably 3. As I said it might be one or maybe two weeks before it throws this code again. I would assume that if it was a big leak I would be able to notice it.

[Robyn]

The mass airflow sensor has to be on the inlet side of the turbo.
This sensor has to be pre turbo and I am going to say that it will be between the air filter and the turbo.

Be sure there are no leaks between the air filter assy and the turbo.
I personally have not had my hands on the late 6.5 (96 on) so I am not familiar with the MAF sensor and its quirks but I am thinking that this little creature may be the culprit.

I am not sure what the MAF sensor is doing on these as it is not used on the HD 6.5 but it must be part of the emissions package on the Light duty units.

Good bet that the sensor is spendy though

Robyn

[DA BIG ONE]

There are o rings on the MAP/Boost sensors check that they are good. (unlikely)

Then if the intake has ever been taken off to say replace IP then make sure the intake is not on top of one of the many small brackets in back of motor. (only if IP was changed)

If you are not running an IC then the hose between turbo and intake maybe has a rip in it that opens under boost then closes, a clamp that is not tight will cause this hose to lift at edge under pressure then close when boost lowers. (very likely)

If running IC then any of the hoses could be the issue......................

Good luck!

[dgrund61]

There are o rings on the MAP/Boost sensors check that they are good. (unlikely)

Then if the intake has ever been taken off to say replace IP then make sure the intake is not on top of one of the many small brackets in back of motor. (only if IP was changed)

If you are not running an IC then the hose between turbo and intake maybe has a rip in it that opens under boost then closes, a clamp that is not tight will cause this hose to lift at edge under pressure then close when boost lowers. (very likely)

If running IC then any of the hoses could be the issue......................

Good luck!

what are you referring to as the IC? and what is the extra plastic tube that goes nowhere on intake; just looks another thing to cause an air leak.

[Kenneth]

"IC": inter-cooler; used to cool the air after the turbo, before engine. You would definitely know if you had one. The stock setup involves a 3" hose connecting the turbo to the intake manifold.

[rustyk]

This is totally-off-the-wall, but I wonder if the culprit is the crankcase depression regulator valve...or its hoses.