I am trying to track down an idle problem on my LT1. It almost dies at idle once it warms up. It starts perfect and idles fine until warm. It hasn't died on me yet, but it is only a matter of time. I have a new opti, wires, plugs, cts and O2s. It was doing this before the new parts. It isn't throwing codes and I am stumped.

 

can you datalog or at least scan it?

 

http://www.mediafire.com/?4jfxt41jmth

 

Definitely a closed-loop problem.

Though I hate to recommend off site, go to cz28.com and place the datalog in the computer section. Then PM Injuneer and ask him to look at it, he is pretty good.

 

I posted it on that site and it was suggested that it is a wiring issue. I won't be able to check that until Tuesday. What looks wrong with the datalog to you? I am still new to datalogging and trying to learn.

 

I am no expert but the O2 readings looked a bit off on the right side. But don't take that to the bank.

 

Can you explain what you mean by off? I appreciate any knowledge you can provide. I don't just want to fix the problem, I want to understand it.

 

O2 sensors should have a constant sweep from 100-900mv usually when they start to go bad they get "stuck" at a constant reading or are slow to respond..

If they completely crap out or the wiring gets fried they stay a constant 450mv..

Just looked like the right one was a bit slow.. but like I said I am not an expert by any means and I frequently seek the experience of those with more knowledge, especially when it comes to tuning..

 

The funny thing is that the right one is newer than the left. I replaced it a couple of months ago. I am checking all of the wires tomorrow. I am going to ohm the wires out to the PCM, checking the power wire for 12 volts and the gound as well. I am going to wiggle the plug and check to see if it is just a bad connection. I think I have an old O2 that I can try. Is there a way to test an O2 sensor off the car?

 

Bingo

I have been experiencing this same problem with my car for a year now. When I first did my LT1 swap I had the computer done by Brian at PCMforless, and the car idled and ran great. Since then I strocked it to a 12.5:1 compression 383, and had the computer redone by Brian. Since then the car surges at idle the second the car hits closed loop?

I checked everything I could think of and called people across the country, and still the same problem. Brian always claims that it is not his programming but I am not so sure? I also changed a lot of sensors and chased a lot of my wiring and still the same problem. But when I hooked a wide band to my car I found that the second my car hit closed loop and included the feedback from the 02s the car surged lean from about 12afr - 17afr causing the surge or rough idle?

I knew that if I unplugged the 02s and ran in open loop the car ran great, and the afr stays at 12 or so with no surge. So, last summer I drove and raced the car in open loop.

I have checked everything from the plugs/wires to the vacuum and compression with no luck. But part of me still thinks that it is a undetected vacuum leak in the intake, but I do not now. I wish there was a good dyno around to test and tune my car.

Who did your tune? What wiring did someone suggest to be bad?

 

Ion at madz28.com did my tune. I have replaced my tps, iac, cts, plug wires, plugs and checked for vaccuum leaks. I have been told that it could be in my O2 wiring. I did the LT1 seap in 2001 and it ran fine with the first engine and first tune. I changed the engine and the tune in February and it ran fine until recently. In open loop it is great. When it hits closed loop it almost dies at stop lights. I was going to check the wiring today, but it rained all day. I am glad to see that someone has had a similar problem.

 

Bingo,

We are having the same problem, in closed loop mine would want to die at lights and when shifting reverse to drive or drive to reverse.

I also replaced just about the same things as you. For some reason though I keep going back to a vacuum leak? I did a leak down test with map gas, propane, carb and choke cleaner, and a vacuum gage and found consistent results. But it could be an internal vacuum leak, I think. And for some reason I doubt it has anything to do with the 02s. This problem drove me crazy in the past so I just ran in open loop, and was thinking to tune out closed loop. But this would be the easy way out, I want the problem fixed just like you.

Please keep me posted and I will do the same, you can email me at roeser123@comcast.net if you would like and we can see if we can work through this problem together.
----------
I forgot

Have you ever over heated your engine?

 

My engine has never been over 195. I also feel like it is a vacuum leak, but I can't find it. It is really hard to hear one on mine with my airbox right in front of the engine. I am wondering if it could be something with a sensor I have not replaced. The MAP sensor tested good, but I don't know about the mass-air sensor. I have literally replaced ALL the others. How would an internal vacuum leak work? Off topic, but do you have any pics of your setup? Keep me posted on your findings and I will do the same.

 

Unfortunatly when you start getting into bigger cubes and cams, the only true way to tune these motors are with a dyno tune. You can only do so much with a mail order tune. Might want to look into doing that, most run between $250-450 to do a good tune on it.

 

I understand what you are saying, but my car ran perfect for months with a mail order tune. I am trying to find out what caused the recent situation. Something has changed that is causing this and I want to find it. A dyno tune is on my wish list. Right under a Moser 9 inch. These cars are never done.

 

They are never done.. Klortho is right though, a dynotune was the single best investment I made after my head and cam swap.. we were able to diagnose problems right on the rollers.

 

Bingo

I just beat you to it, I just installed my moser 9 inch last week end. It has 35 spline axels, spool, for d disks, and a nodular case. I also just installed spohns pro drag coil over kit up front.

But back to the engine problem. I agree with the dyno tune but there is not a good one around me. And like you said my car ran great before off of a mail tune. I replaced my map sensor and it had no affect, as you said my mass air is unknown but I think it is ok. I think that I am going to pull the intake and heads off soon and reseal everything and see what happens. If there was an internal vacuum leak it would leak between intake ports possably causing problems.

Have you tried to unplug your 02s and and start it up while monitoring it with a scanner? Mine runs great cold but the second it hit closed loop and the 02s go online in begains to stumble and my air fuel ratio bounces lean.

I also talked to Brian at PCMforless, Ed Write, and multiple other tuners and I stumped them all whith this problem.

I will send pics ASAP

 

I am working every day except Wednesday, so it will be a while before I can touch it. I was told my problem could be faulty O2s. I am running Bosch O2s and they apparently have a high fail rate. I am going to unhook an O2 and scan my car next week. I hope I don't have pull heads.

 

I believe that I also have Bosch 02s right now, but they are new and I had the same problem with my previous set that are NGK or what ever their electrical name is, NTK?

Either way you can take the 02s out of the car mount them in a vise, plug a digital multi meter to the voltage wires (not the heating wires), heat them up with propain or map gas, and watch the voltage rise. 02s make their own voltage when heated that will ramp linear if the sensor is good, with no spikes or dips. Which is why you can only test with a digital meter.

 

Bosch O2s are terrible. NTK are much better, but GM ones are still the best ones, and dont cost much more.

 

I checked my wiring today and all is well with it. I pulled my passenger side O2 and it was black and sooty and smelled of raw gas. I may have an ignition problem. I am going to pull some plugs and check them when I get a chance.

 

I have had this same problem on my L98. I couldn't it diagnose for anything. Then, I took it to my mechanic and it turned out to be the TPS. After he replaced that. It hasn't wanted to die at all. I have replaced the O2 sensor since then and cleaned out the IAC; and it runs like a brand new car. I would check the TPS sensor next.

 

IAC=new, TPS=new. I am starting to suspect the ignition.

 

Dang man that sucks. I was hoping the TPS was the fix. Good luck and I wish you the best.

 

It is never the easy things with my car. I am going to pull the coil and module tomorrow and test them both.

 

I also suspected the ignition when all else was replaced or checked. But the box is a new Mallory and the coil resistence checked good?

I am planning to pull my intake off and reseal it over the holidays, and see what that does.

 

What should the coil resistance be? I checked mine between the 4 low voltage pins and the high voltage post and they were all 10.8 (10,800) ohms. I thought this was a little high. I am testing my module today at work. My intake gasket was replaced in September. I pulled my intake because I thought it was leaking. It made no difference. If it stops raining I will pull a couple plugs and check them.

 

I tested the module 7 times and it passed each time. I am running out of ideas. Fuel is right, ignition seems ok, wiring is ok, no vacuum leaks I can find...

 

Check the ignition coil primary coil resistance by connecting an ohmmeter between the positive and negative terminals on the coil. The resistance should be 0.4 to 0.6 ohms.

Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal (coil wire gets attached to) and the ignition coil negative terminal. The resistance should be 5000 to 7200 ohms.

Your resistence shold be close to the above it you get no resistance or it is very out of range you have a bad coil.

 

Between the positive and negative reads 1.2-1.4. Between the primary and secondary side it is 10.8 (10,800 ohms). It is a Borg-Warner coil, I am going to see if I can warranty it at work. It was working fine for two years. I put it on when my MSD coil broke. It didn't fail, it broke.

 

I put a new coil on it and it seems to be better. I am going to drive it some more and wait before I say for sure. The plugs looked fine.

 

Nope, no better. It just starts better. I am out of ideas. Anyone have any suggestions?

 

Everytime I had this problem it was an exhaust leak. Mine was always the 2nd o2 bung that was fabricated for the swap. I remember using seafoam as a smoke machine to trace the leak. The o2 sensor would detect the xtra oxygen from the leak and dump in more fuel to compensate. It drove me crazy at first since the o2's would read lean but i'd have fuel everywhere, and fouled plugs. Hope this helps

 

I disconnected the O2s to see if it was indeed a closed loop and there is no change. I thought about an exhaust leak, but I can't find one. It only does it when warm. I have replaced everything except the MAS and MAP. I am at a loss.

 

man I feel for you, I went through alot of stuff with mine. Do you have a spare pcm to plug in to see if your tune might be the problem? I always kept one handy in case I did a bad flash or something. I also scorched my o2 wires once in a difficult spot , didnt see it till I had it up on the lift...