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View Full Version : 99 xj, can exhaust feed into the cab via HVAC?


4x4JeePmaNthINg
October 4th, 2017, 08:30
Is there anyway that something on the 4.0 can fail sending exhaust fumes through the heater into the cab?

where does the hvac system pull air from, air box, intake. vacuum....?

thanks

Rob Mayercik
October 4th, 2017, 14:48
As far as I know:

Primary intake is under cowl on passenger side.

Secondary intake is wherever in the passenger front footwell it sucks from for recirc (MAX) in A/C mode.

Ewenm
October 4th, 2017, 15:59
the cabin air is picked up at the base of the windscreen, where the wiper motor is, so no exhaust gas should not be able to get in, unless you have the back of the hood jacked up and a serious exhaust manifold leak.

if you are getting exhaust in the cabin and the exhaust system has no leaks, check your tailgate seals , as you drive along you can suck fumes back in via a leaking tailgate.

Ivan
October 4th, 2017, 17:10
There is a foam seal that fits between the HVAC coil box and the firewall. It falls apart over time. This is also a common water leak point for water into your passenger side cabin through the engine bay, so exhaust from a leaky manifold is possible where the foam seal once was.

If you need to replace either your AC or heater coils anyway in order to replace the foam seal, there's a long process for removing the dash for access. Search other posts for that procedure.

However, you can stilll seal it from under the hood, by applying silicon sealant where the blower motor pokes out into the engine bay. Just move aside some emissions line, and apply sealer all the way around firewall and blower motor area....

Ewenm
October 4th, 2017, 22:45
yep that is correct, i had forgotten about that.

one of the first things i had to fix 18 years ago, when the factory converted the XJ to right hand drive, the lower part of the cutout for the blower was Below the inner guard, water would pool and run into the cabin, grrrrr that was hard to find.

4x4JeePmaNthINg
October 4th, 2017, 23:28
if you are getting exhaust in the cabin and the exhaust system has no leaks, check your tailgate seals , as you drive along you can suck fumes back in via a leaking tailgate.[/QUOTE]

Tail gate does rattle some, but I know the manifold is cracked near the front of the engine. Windows up I didn't think I should smell anything , but my way down the canyon I had the heater on and I swore I smelled exhaust.

Ewenm
October 5th, 2017, 05:30
i would be checking the blower seal as mentioned by Ivan

md21722
October 6th, 2017, 00:16
The exhaust manifold isn't that far from the throttle cable where it passes through the firewall. If that grommet is shot, that's another entry point.