Hey guys,

Finally found the time to break out the PDU and go for a drive with the datalogger on.

I'm finding my Heated 02 Sensor Feedback voltage is stable at around 3.3V - 3.8V. which according to the AJ6 Engine Management Manual is a bit lean.

I did replace all four tires recently (had 4 snows mounted - my XJ12 was my summer car, the XJ6 was my winter) with Sumitomo HTR A/S P02's which are so much quieter. I originally thought I was due for new wheel bearings up front, the snows had gotten that loud. Anyway, with the new near-silent tires, I'm noticing a lot of exhaust noise up front, inside and out, when cold, and also inside the cabin at highway speeds, hot or cold.

I also having the long-standing issue of a higher than normal idle at times, requiring more effort when braking. Adjusting my idle speed per the proper procedures requires that I *completely* shut the idle air bypass, which I know shouldn't be the case. I have gone through the idle air plumbing, housing, control valve, gaskets, and the intake plumbing more than a handful of times to no avail. I'm getting extra air into the intake somewhere, though, and possibly also into the exhaust as well, causing the lean mixture.

So here's my plan so far: New intake and exhaust gaskets. I did have the intake off years ago to replace the coolant rail hose. I did not replace the intake manifold gasket then. Perhaps that's the culprit? And the elevated exhaust can definitely be caused by bad exhaust manifold gaskets.

Does that sound like a reasonable plan to start with?

Nick

 

Since you dont mention it specifically, did you check the evap canister in front of left front wheel. It has a port somewhere toward the front of the intake though i forget exactly and there's a vacuum valve on top of it. Mine had broken in half making an excellent vent.
And the exhaust noise.- I had a Y pipe split at the joint, but around back where it wasnt obvious.
If you suspect a leak at the intake or try the old carb cleaner spray test. maybe try using a mirror to see the exhaust mating area to check for telltale soot. I suspect youve gone over all this, but just throwing it out there. Good luck..

 

Run a smoke test and find the leak. Or ekse you risk creating different ones and thinking theyre your problem.

 

Thanks guys!

I forgot all about that EVAP canister. I remember trying to gain access to it, however I recall having an issue with the plastic speed nuts that hold the "underscuttle" panel, and gave up before I broke something. I will have to investigate that further. I have verified the vent valve holds vacuum and does not leak, but you are right, the canister could very well be split in two!

I have sprayed just about every cm of the intake down with carb cleaner, listening for a change in RPM to no avail.

Aarcuda, thanks for the advice on a smoke test. I have been meaning to either buy or build one of the cheap "paint can" style smoke machines to test this very issue out, but never got around to it. Is it as simple as shoving the hose into the intake plumbing and checking for visual leaks?

Thanks again guys,
Nick

 

I bought a cheap one off ebay and its shown my leaks twice. I put the smoke into the pcv line at the pcv valve. I found spraying carb cleaner made no audible engine changes. I believe the ecm corrects for it too quickly so theres no rpm changes. That why I got the smoke tester.

 

Wow, look at that! That's very impressive.

I think that might be the path I choose!

 

I tried EVERYTHING to find the leak before and was not getting anywhere. This one was obvious with the smoke. Then I found a couple more small ones which took some hunting but sure enough the smoke was there!

 

Hi Nick,

Just a bunch of random thoughts:

The smoke needs to be pressurized with compressed air to force it into all the recesses of the intake, crankcase breathing system and evaporative emissions system and then out through the leak(s), which may be very small. But the pressure must be kept low to protect fragile components, especially in the EVAP system, so most of the better DIY smoke machine designs use the type of propane pressure regulator used on cooking grills that restrict pressure to around 1 psi for EVAP systems.

If I recall correctly, the torque spec for the intake manifold screws and nuts is fairly low, maybe 10 ft. lbs., and I noticed over the years that mine would work loose. It might be worth simply re-torquing yours to be sure they haven't loosened.

If you do wind up pulling your intake manifold back to replace the gasket, it would be a great time to clean your throttle body, and if you haven't done it already, drill drain holes in the throttle position sensor case and flush it with electronic cleaner. Also, disconnect the EGR/purge valve port from the underside of the intake manifold and clean all of the carbon out of it - I used drill bits and wire brushes to clean ours.

Have you cleaned the carbon out of your IACV and from the stepper motor pintle? If not, it may not be able to completely close sufficiently to inhibit air flow when it is supposed to.

Since the crankcase breathing system feeds air into the intake past the MAF sensor, leaks at the breather hoses can cause lean running and high idle, but also leaks at less intuitive places such as the oil filler cap gasket and dipstick O-ring and dipstick tube seal.

A problem I had more than once was that I overtightened the large hose clamp where the plastic air intake elbow met the accordion hose leading to the TB. This caused the plastic elbow to collapse slightly on its underside edge, forming a gap for unmetered air to be inhaled.

An exhaust leak can cause the O2S to read lean because unmetered air is sucked into the exhaust by the venturi effect. Manifold cracks are not unheard of, but can often be repaired with the paste available at auto parts stores.

Anxious to learn what you discover.

Cheers,

Don

 

Thanks Don!

With your guidance over the years, I've tackled pretty much all of those points. Off the top of my head, the throttle body has been removed more than 8 times, the intake plumbing about 15 or so. I have drilled cleaning/drainage holes in the TPS per your advice years ago. I removed the IACV housing and replaced both gaskets, cleaned them out, and replaced the motor as well, swapping the original back in to see, as well. I am unfortunately all too familiar with the finesse it takes to tighten the large clamps on the accordion hose. I have epoxied a crack in the intake elbow year or two ago, and replaced the accordion after a split was found there. Copper pipe sleeve in the IACV fitting to keep it from collapsing, cleaned gunk out of the PCV hoses, even bought a factory throttle body gasket that was used on older XJ40s between the manifold and the throttle body (later ones have machined surfaces to seal) hoping it might be there.

I think the smoke machine will definitely point me in the right direction. I have always been thinking about getting one for this car, and I think the time has come to finally just get one and do it.

Interestingly enough, in the stack of repair orders I have for the car, my great aunt had a valve job done:

"Customer states car running poor - feels like it is missing" "Renew exhaust and inlet valves"

Parts included 3 exhaust valves and 1 inlet valve, head gasket, 14 head bolts, spark plugs, coolant, oil, etc.

This was done in April 1999 at 38,900 miles. $2,648.05

I definitely do not want to keep going with a lean mixture that could cause burnt exhaust valves again!

Nick