Have since changed the tune in the car (and changed the cats) which brought the AFR curve leaner about +0.5-0.7 along the curve. Still quite conservative, thing is the supercharged engines need to be a little richer than a naturally aspirated, so they tell me...

 

My twin turbo 300zx was actually about 12:1 in the upper rpms

 

What is the compression ratio on the 4.2?

 

9:1 for the 4.2

 

I think that's the (off boost) SC 4.2. The NA is higher (er, 10.1:1?)

 

Talking static compression, no boost. The N/A 4.2L are 11:1.

 

I was involved in the calibration of these vehicles. They run rich to protect the catalytic converter.


Ideal AFR would be about 13.3 at low rpm going up to about 12.2-12.5 at higher rpm.


The S/C cars will run richer than the NA cars and tend to run 11.1:1 at high rpm. The Range Rovers run richer for further protection because they are more likely to be used at high load (towing and such like) for prolonged periods.


In the Range Rovers cases they're protecting the exhaust valves so the heads don't drop off due to excessive temperatures.


It's a very dangerous game that Avos and all the other self proclaimed 'forum gurus' are playing- but please go ahead.


Nice to watch and learn and I myself am interested in a solution to be able to edit the ECUS

 

Ehum, not sure why you sneer at me, I have never proclaimed myself like that nor do I consider myself like that for the record, but I can’t help if others do.

 

Wow

 

I seem to have hit another snag. I got my pulley installed, finally corrected the reversed polarity at the supercharger coolant pump, and replaced the pump. That cleared up my periodic "reduced engine performance" mode. Couple that with the magnaflow resonated stainless exhaust, and she was really starting to wake up. While I was in there I did all new belts, updated idler pulley, and ac compressor, as well as new plugs (Denso iridium) and ignition resistor. Satisfied I was caught up on maintenance, I embarked on a 500 mile trip. On the way there I averaged around 23mpg (hand calculated) at 68mph, and everything was going swimmingly......

Until, on the return voyage, I heard some noise pulling into a toll plaza (the design of the walls amplified the clattering so that I could hear it). She's making a fairly pronounced clicking/rattling noise from what appears to be the passenger side top end. In my experience it sounds like a cam chain tensioner, I just haven't had any time to get the cover off and look.

Fortunately, it's still RUNNING well. Full power, no check engine light or misfire, so I don't believe the timing has jumped. Rather than wait on a tow I continued to drive it home, and the noise has not gotten worse. I haven't started it since, and have stopped driving the truck. With any sort of luck it's a simple repair.

I've read that this was a problem on the older engines with the plastic tensioners, but haven't seen it mentioned for the later AJ33's. Has anyone experienced this before? Is there somewhere else I should start before tearing the valve covers off?

Thanks!

 

Should have metal-bodied tensioners so maybe you could have a re-think on the problem.

 

Well, it gets weirder. I parked it for the week until I could make time to pull the front of the engine apart. Started it, silent. Pulled all the belts, checked everything, Let it run for an hour, silent. Checked the oil, it was 2 quarts low.

It's been silent for the past few hundred miles.

I have no idea what to do next.