hz900

'90 auto, 383, SR, 219 cam, Long Tube headers, Heated O2, PCMforless custom tune


I think my car is running rich, reason for me saying this is that there is a strong odor of gas when the car is running coming from the tail pipes. I think I have a vacuum leak because the car surges alot at idle and when I put it in gear it almost wants to die until it adjust to the lower idle, which would also cause a the car to run rich.... Right? I have tried to find the vacuum leak by using a propane torch and running it along the SR gasket surfaces, and along the vacuum lines, even though the lines are brand new.

Is there any easy way with out taking it to a tuner (which is out of the question around here) to tell if it is running rich and is there another reason for a surging idle than a vacuum leak.

Also is there a way to tell if the heated O2 is working properly?

BTW I have no Service Engine Soon light coming on so I assume the computer has no codes set.

bogus

carb cleaner. Spray that everywhere. that should help.

More then likely, if you have an SR, you have a leak.

AZC4Guy

Exactly how would a vacuum leak cause a motor to run rich?

cerino2000

Ya, vacuum leak would make you run lean. What preceded the issue? I mean, did you just got the PCM for Less back and now all of the sudden it is having problems? What's changed recently?

bogus

uh, lean, right up until the O2 kicks in and feeds more fuel.

cerino2000

Depends, if the leak is significant, the O2's are only allowed to adjust so much. If it is that bad and the o2's are maxed more than what's needed to balance it, then it's still lean.

hz900

Oh nothing has changed, its been a project car that I just took for the first long drive this weekend. Ever since I first got the car running it has not idled right. I tried the stock chip only to see it for sure run pig rich, and that was proven by the plugs fowling out after the car idling several times for 20+ minutes in the driveway, although it did seem like it idled smoother. So you see I have no basis to go on because it is a completely rebuilt engine top to bottom, with all new vacuum lines and all new sensors.

BTW it only starts to run funny, ie surging, after the car is warmed up.

cerino2000

You may want to invest in one of the wide band setups so you know for sure what it is doing AFR wise. Personally, I could never consider any tune without a wideband to verify what I think is going on, or prove otherwise. I don't know much about the pre ODBII scan tools but see if you can get hooked up with one. That way you KNOW what it is doing. Lotsa $$ to put into it and have it go to the chitter for not knowing what it is doing. Ya know what I mean?

hz900

I know exactly what you mean, guess I need to visit the scan and tune section.

tdr1919

The Scan forum has great info, you can build an ALDL cable dirt cheap and download great scanning software, only need a laptop, I suggest get a used one with a serial port because it is difficult to get a USB-to-serial cable to work, but you might be ok with your 90 because your ECM runs at a higher data rate than my 86 so the USB-to-serial might be OK. Once you run a scanner on your car you wont want to be without it. you can see just what is happening real time.
Tom

glide

"Oh nothing has changed, its been a project car that I just took for the first long drive this weekend. Ever since I first got the car running it has not idled right."

If its been sitting a long time, running a fresh tank of gas through it can do wonders. Just my two cents worth.

RRT vette

A vac leak introduces unmetered air into the exhaust stream. While in open loop it will likely cause a idle surge. After closed loop the O2 picks up the increase in O2 and sends a lean signal to the ECM. The ECM uses the info to adjust fuel delivery by adding more fuel. Therefore making it run rich.

hz900, where in Louisiana do you live. Craig Moates is in Baton Rouge and is a very good tuner. He can scan the ECM/engine and put it on a dyno if need be.

Square

I had a lazy O2 sensor that would not throw a code, but a mechanic friend of mine took his scan tool and noticed that the O2 sensor was basically always claiming the mix was lean and thus causing it to run rich.

As for finding vacuum leaks in the intake, try this. Someone else on this board clued me into this and it worked for me. Find yourself someone who smokes and a piece of tubing about 4 feet long. Remove the intake snorkle and then slip one end of the tube through the throttle body. Tape up the throttle body with duct tape and seal around the tube as best you can. Have the smoker enjoy a cigarette/cigar and exhale into the tube. It will take a few minutes for the smoke to fill the intake, but once it is full any vacuum leaks will be easily found by the smoke coming out of them. You can also have the smoker exhale with more pressure as you get in close with a flashlight to determine the exact source of the leak.

mseven

If you are rich/lean I think having some real data would help, download tts datamaster or Tuner pro RT freee you will have to buy some cables from someone like Moates.

tequilaboy

Several things can contribute to a surging idle. Once surging begins, the ecm can't do much to stop it, and it will likely make things worse.

As the rpm oscillates up and down, the calculated load changes inversely with rpm. As the load and rpm change, the spark advance, fuel and IAC position begin to oscillate as well, since they are a function of rpm and load. This is likey to amplify the rpm oscillation making the surge worse.

You may need to stablilize the load influence on the spark advance and fueling in the region of idle rpm to prevent further forcing of the oscillation.

One thing that is easy to try is reducing the influence of the IAC by increasing the min air adjustment so that it approaches the desired warm idle rpm.

Open the throttle stop and readjust the TPS voltage to 0.54 volts so that the desired warm idle rpm occurs with minimal IAC counts (maybe 10-20 counts). This can help to eliminate one of the variables that can contribute to the surge.

When adjusted in this manner, the IAC cannot reduce the rpm very far below the target rpm. This will help to stabilize the load calculation, which should also help to stabilize the spark advance and mixture.

Mixture and spark advance vs load may need to be addressed in the tune, if the min air adjustment doesn't help on its own.

GlennS87

My mechanic has a smoke machine which basically does the same thing but a little quicker. Only problem is you don't get to enjoy a fine cigar Turns out I had a small leak on the throttle body where plate that sits on top wasn't secured properly after I changed over to a billet one.