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Paul Workman · 05-03-2015

Whenever someone says "use Mobil 1", I can't help but roll my eyes, just a little. Which one??????

See link...

https://mobiloil.com/~/media/amer/us...ecs-guide.ashx

It is the Mobil 1, "HIGH MILEAGE" oil...but there are several. I use Amsoil AMO 10W-40 myself - and have for the past 7 years in the z. But, I also use Mobil 1 15W-50 in my wife's flat tappet 1969 motor (after a cam went flat on that relatively low ZDDP in API "SM" Mobil 1. The 15W-50 High Mileage is a full synthetic and has the higher phosphorous/zinc additive flat tappets desire.).

220ºF is "normal" for the stock LT5, although Marc does provide a calibration that turns both fans on at ≈ 205ºF and then off at ≈ 200ºF

The miss above 5000+ rpm" could be a few things:

I'd want to look at the plugs (especially if it misses under a heavy foot...which I assume is the case! (ohming out the plug wires is always a good idea too.) Marc recommends an NKG plug w/ rare earth electrodes, but I've been running the AC Delco copper core 41 602s which have been working fine for a lot less money and cheap enough to replace for the cost of a couple craft beers at the local pub!

Plugs OK would have me looking at the fuel pressure next (easiest ≈ 53 psi at WOT).

That being OK, it could be the "accordion" air duct between the filter housing and the air horn collapsing (they've been known to get soft with age and heat). Marc can supply some wire hoops to insert in the tube to support it and keep it from collapsing. OR, (like I did) fashion an aluminum liner to be placed on the inside of the tube.

That being OK, I'd be checking the resistance across the injectors (HOT) to see they're all w/in a window of about 1.2 ohms. Depending on the injectors installed, the resistance would average around 12 ohms, or 14 ohms, I've found. But, if you have one that is a couple - 3 ohms low, that one is going south. And if it is in the 8 ohms or less, it's time for a new set!

I was experiencing a miss when it got up to operating temp which turned out to be a coil(s) issue. A new set from GM fixed that; been good ever since. I know you said the miss was rpm-related; NOT temperature. But, I threw that in b/c it also caused me to have a miss at the higher end of the tach.

More in-depth info is available, but these are some of the "new to me" glitches I had to deal with when I first got my Z. Nothing out of the ordinary for a 25 year old car, and NONE of the problems have returned...Well, except for the injectors that a dealer replaced with NOS parts when I bought it. (Yep...the originals were susceptible to ethanol, and so were the "new, old, stock" ones they replaced the originals with!)

I've been fussing with carburetors since the late 60s, up until recent times. Armed with a scanner or laptop, I'd take the computer over dealing with "the black art" of carbs any day!

Welcome to the Brotherhood of the Beast!

05-03-2015	#9
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Newbie Here Whenever someone says "use Mobil 1", I can't help but roll my eyes, just a little. Which one?????? See link... https://mobiloil.com/~/media/amer/us...ecs-guide.ashx It is the Mobil 1, "HIGH MILEAGE" oil...but there are several. I use Amsoil AMO 10W-40 myself - and have for the past 7 years in the z. But, I also use Mobil 1 15W-50 in my wife's flat tappet 1969 motor (after a cam went flat on that relatively low ZDDP in API "SM" Mobil 1. The 15W-50 High Mileage is a full synthetic and has the higher phosphorous/zinc additive flat tappets desire.). 220ºF is "normal" for the stock LT5, although Marc does provide a calibration that turns both fans on at ≈ 205ºF and then off at ≈ 200ºF The miss above 5000+ rpm" could be a few things: I'd want to look at the plugs (especially if it misses under a heavy foot...which I assume is the case! (ohming out the plug wires is always a good idea too.) Marc recommends an NKG plug w/ rare earth electrodes, but I've been running the AC Delco copper core 41 602s which have been working fine for a lot less money and cheap enough to replace for the cost of a couple craft beers at the local pub! Plugs OK would have me looking at the fuel pressure next (easiest ≈ 53 psi at WOT). That being OK, it could be the "accordion" air duct between the filter housing and the air horn collapsing (they've been known to get soft with age and heat). Marc can supply some wire hoops to insert in the tube to support it and keep it from collapsing. OR, (like I did) fashion an aluminum liner to be placed on the inside of the tube. That being OK, I'd be checking the resistance across the injectors (HOT) to see they're all w/in a window of about 1.2 ohms. Depending on the injectors installed, the resistance would average around 12 ohms, or 14 ohms, I've found. But, if you have one that is a couple - 3 ohms low, that one is going south. And if it is in the 8 ohms or less, it's time for a new set! I was experiencing a miss when it got up to operating temp which turned out to be a coil(s) issue. A new set from GM fixed that; been good ever since. I know you said the miss was rpm-related; NOT temperature. But, I threw that in b/c it also caused me to have a miss at the higher end of the tach. More in-depth info is available, but these are some of the "new to me" glitches I had to deal with when I first got my Z. Nothing out of the ordinary for a 25 year old car, and NONE of the problems have returned...Well, except for the injectors that a dealer replaced with NOS parts when I bought it. (Yep...the originals were susceptible to ethanol, and so were the "new, old, stock" ones they replaced the originals with!) I've been fussing with carburetors since the late 60s, up until recent times. Armed with a scanner or laptop, I'd take the computer over dealing with "the black art" of carbs any day! Welcome to the *Brotherhood of the Beast!* Last edited by Paul Workman; 05-03-2015 at 01:18 AM.