Drag Racing Tech - Eliminated a few possibilties, could really use some help!




Loudmouth LS1
12-20-2004, 11:21 AM
So my car is leaning out on the top end for some reason and can't figure out why! Put a fuel pressure gauge on it and it's perfect, holds 60 psi at idle and cruise, and drops to about 56 - 58 psi at wot and holds, so the fuel pump isn't bad! Dropped a couple bottles of fuel system cleaner through it to see if maybe injectors were gettin clogged, no change, so i'm pretty sure the injectors are good. Checked for air leaks, only thing I found was a little hole in the stock intake baffle, so I replaced with a fernco, still no change! So now the only other thing I can think of too try is replacing the o2's and putting on longer exhaust extensions (I currently have 18" extensions off of the collectors, probably lengthen to like 24" or so). So what do you guys think, is it possible the extensions are too short and causing the o2's to get messed up or read wrong or something? I'm also eatin a bit of oil, so I thought maybe rings, but one of my buddy's told me to get the leaning out situation solved first cuz with it running that lean it could cause the oil usage.


WhtLT1
12-20-2004, 05:02 PM
How many miles are on the car? Stock injectors still? It could be clogged injectors just to a point where plain ole fuel injector cleaner cant clean them. OR is there a possibility that ur just runnin outta injector on the top end? are u sprayin the car? stock pump? There's a lotta stuff thta it could be

GM Muscle
12-20-2004, 06:13 PM
I think your extensions should be ok. I run 16" extensions on my collectors without any kind of issues (a total of about 19" of pipe behind the O2 sensor).


MADMAN
12-20-2004, 07:32 PM
Have you looked at volume not pressure?????? The pump can produce pressure but no get the volume it needs.

Loudmouth LS1
12-20-2004, 08:45 PM
Have you looked at volume not pressure?????? The pump can produce pressure but no get the volume it needs.

No, how do I check that, and to answer all the other questions, yes, stock injectors, stock fuel pump (have an inline that i'm getting ready to install), about 60k - 65k miles on the car, not sure exactly, cuz the odo stopped reading at 47,xxx when I put the turbo 400 in last year. And I don't think the stock injectors are maxed out, only mods power wise on motor are a lid, filter, ls6 intake, longtubes with extensions, and a comp 228 xer cam, stock heads and a lot of other stuff stock still. I haven't sprayed it yet cuz of the leaning out issue on motor, I don't want to spray it and blow it up! If I was just running motor, I wouldn't worry so much about it leaning out, but since i'm gettin ready to spray it, I can't spray with it this lean, i've seen it drop as low as 810 on the o2's at the top of third.

SilverGhost
12-20-2004, 10:03 PM
you do realize that your 02's don't matter under WOT right? the car quits reading them..

Loudmouth LS1
12-20-2004, 10:49 PM
you do realize that your 02's don't matter under WOT right? the car quits reading them..

Huh, not sure what you mean by that one? I was always under the impression that you want ur o2's at wot between 890 - 900, which puts you around 12.8 - 13.0 area a/f ratio, am I wrong? :confused:

KCFormula
12-20-2004, 11:12 PM
Huh, not sure what you mean by that one? I was always under the impression that you want ur o2's at wot between 890 - 900, which puts you around 12.8 - 13.0 area a/f ratio, am I wrong? :confused:


Well the way I understand it is that at WOT the computer uses what it has learned from the LTerms and "guesses" how much fuel to add durring WOT. The O2 sensors are not read durring WOT runs. Thats why your BLMs should read 128 no matter what they are truely at durring WOT. I could be off here but that is the way I understand it.

Spencer Allen
12-21-2004, 12:30 PM
Devon,

Have you done a leakdown test yet as we suggested???

Check with your local auto parts stores if you don't have the tester as you can "borrow" most testing equipment from Autozones or Discount Auto Parts. You pay a deposit and then a rental fee usually.

A leakdown tester will tell you a lot and only takes a few minutes.

~ Spencer

Loudmouth LS1
12-21-2004, 11:50 PM
Devon,

Have you done a leakdown test yet as we suggested???

Check with your local auto parts stores if you don't have the tester as you can "borrow" most testing equipment from Autozones or Discount Auto Parts. You pay a deposit and then a rental fee usually.

A leakdown tester will tell you a lot and only takes a few minutes.

~ Spencer

Yeah, I haven't done one yet cuz I figured let me do the cheapest and easiest things first and like I said, I have no knowledge of how to do a leakdown test or the equipment to do it. I wanted to rule out a few things first (I guess I don't want to think about having bad rings, cuz if I do, i'm gonna be down for a while!). If longer extensions and new o2's doesn't work, I guess I will borrow the equipment and figure out how to do it and see what it shows me! Would it be easier to do a compression test first to see if any of the cylinders are bad on compression and then just test the one's that show up bad if any at all with a leakdown test? Cuz I saw a compression tester tool in sears and it wasn't too expensive and I heard a compression test is a lot easier than leakdown test. A buddy of mine from ny who is going to auto mechanics school told me that a leakdown is a pain in the ass.

Spencer Allen
12-22-2004, 07:31 AM
A leakdown test will show if your valve springs are shot, rings are shot, and in worse cases if you have a hole in the water jackets. We did my car in about 30 minutes start to finish.

It's a bit harder on a street car, but all you do is warm the car up, shut it down and remove all the plugs, crankcase breathers and radiator cap. Hook the gauges up to a air supply of 90-100psi and then thread in the air fitting to plug #1, bump the motor over until the piston is at top and pop the air line into the gauges, providing the piston is actually at top and the air does not roll the motor either way, the gauge will give you a reading. At 90psi supply, I usually see between 85-87psi on the cylinder side - showing a 3-5% loss, anything below 10% is acceptable.

We do one after every heavy nitrous day and periodically during the year. We got our kit from MAC of course, but if you can't find one to borrow, give me a shout and we'll work something out to get it to you to use.

~ Spencer

Loudmouth LS1
12-22-2004, 01:16 PM
Shit, I don't have an air compressor and I can't buy one, cuz I have no where to put it. Also, how do you know when the piston is at tdc? I'm gonna finish checking all the little stuff, and I guess this will be my last try, cuz i'll have to see if I can get with a buddy who's got an air compressor to do it.