Engine pinging at low load

[Mkiisupra]

Hey guys out of nowhere my J has been running bad, over the past couple of days it has been pinging while driving at low load and upon initial tip in at idle. The parking brake light has been coming on and off as well so I am unsure if it is related or not. Also the idle seems to wander a bit, sometimes just 100 or so rpm sometimes varying up to 400 rpm. I have only been using 91 octane 76 gas so that shouldnt make any difference. It has been smelling like baking oil as well. The engine did heat up about 3/4 on the temp gauge due to the radiator being pretty low but it did not overheat.

Any advice where I should begin looking would be appreciated, Im going to do a compression check on it and check the base timing although there should be no reason for it to have changed. Id like to catch this before the engine blows the ringlands or something equally disastrous.

[fourdrinie]

1. when the brake light flashes intermittently....usually a sign the alternator is going....check the charging system, esp when the brake light is flashing....
2. knocking....you might want to relocate the knock sensor...there are old posts here about where it goes....
3. for the fluctuating idle...clean the maf...
4. for the burnt oil smell...check that your valve covers are not leaking oil

[Mkiisupra]

Its just the parking brake light, not the battery light as well.
Its not knocking, its pinging, such as timing too far advanced or poor gas quality.
The maf was replaced just 10,000 miles ago.

I removed the plugs to find cylinder #4's plug covered in oil so I may have found the problem, however the solution as to where the oil is leaking from is still a mystery to me. I went ahead and picked up some pcv valves but may end up removing the upper manifold to clean out the oil inside (there is a significant amount).

Compression test with throttle fully open is showing:
170, 165, 160, 178, 165, 180.

[EriCCirE]

The idle symptoms scream classic vacuum leak.

Are you speaking of the red light indicator on the dash, or the actual rear brake lights?

[Mkiisupra]

They do not scream vacuum leak because the idle is not consistently higher than normal, it fluctuates a small amount.
I am describing the parking brake indicator on the gauge cluster which is illuminated without the addition of the battery light, both of which when illuminated would indicate a faulty alternator.

Anyways after taking a couple hours to pull the upper intake manifold mostly in the dark (which is not nearly as difficult as some here make it seem), Ive discovered the spark plug tube seals to be crushed on one side of nearly all of them and what looks to be the exhaust valve cover leaking into the spark plug valley on the drivers bank. I have not yet removed the valve covers but will report the condition of the gaskets when I do so.

So far I am planning to replace the spark plug tube seals, all valve cover seals, pcv valves and all hoses, and spark plugs. The manifold gasket itself was undamaged when removed so I will likely leave it alone as it is stuck to the manifold surface.

One thing I did find was one of the metal pipes which carry the coolant around the rear of the engine had corroded so badly there was literally holes eaten through the metal. This will explain my loss of coolant and some green deposits I have found on the passenger bank spark plug valley. I might end up throwing the metal lines out and run rubber hoses all across the rear as it will make plenum removal incredibly easier in the future. The metal lines that are held together as one piece include the pcv system, coolant system and a short bit of vacuum lines. I will post pictures when I have a chance, probably after the weekend.

[GerryO]

It's also a good time to replace the WP and to ohm check injectors. Compression check too, as that degree of corrosion is probably a sign that the coolant was old/weak for a while, increasing the chance of some aluminum eating electrolysis. Have the coolant checked for oil and check the underside of the radiator cap for a chocolate brown coating.

If you remove the injectors, new o-rings are required, and that gasket between the manifold and the plenum is inexpensive and very important. Find a photo that I posted of my throttle body coolant bypass, as I went just one step too far with it, eliminating the metal tubing line that heats one of the idle control system components, as do a few other of those metal coolant lines at the rear of the engine. Someday I'll replace that one line and the two hoses connecting it.

My experience is that vacuum leaks cause low idle speeds, and that not fixing, but only compensating for them, requires higher idle speeds.

[Mkiisupra]

The water pump and timing belt was replaced 33k ago with oem parts. The compression results have already been posted. The injectors will be left alone. I have yet to decide exactly how I will replace the corroded lines but its a small matter.

Heres some pictures showing the oil on #4 plug and coil, the failed spark plug tube seals from cylinders 2 and 4(#4 fell on the ground), which may have been incorrectly installed from the factory, oil running out of the manifold angled downward after opening the throttles by hand, and the corroded metal line that runs behind the manifold.

[Mkiisupra]

Had to remove the fuel injector rails to chase a socket and nut and turns out most of the insulators are damaged and no parts stores carry them. Looks like Ill have to go to Nissan for those.

[Mkiisupra]

Parts came in this morning, replaced the insulators, the 3 rear pcv hoses and reassembled everything. Runs very well now. The old plugs were bosch platinum, the ngks make the engine feel a lot smoother than before I had this problem. Will change the oil soon even though its only been 3 or 4 thousand since I changed it last. I guess I should get around to finshing the suspension.

Gerry your photos appear to be 2 different manifolds. I did not delete any of the lines under the manifold, I just left things alone and put it back together.