LoneGunman

iTrader: (2)

I need some help here fellas. I've got a '99 Z28 M6 with 137,000 miles on it, and I am having a problem with the way it runs. It absolutely HATES 1500 rpm's! It sputters, and surges kinda like the way bad plugs or bad gas would act. Cruising at 60mph in 6th gear is a total PITA! If there is a slight incline I have to downshift to 5th, otherwise the surging gets worse! When you get on it, it'll go but I can feel the motor just "laying down". It doesn't have the power or the smooth acceleration that it should have. I have changed the plugs (NGK TR55) and the wires, changed the fuel filter, ran a few tanks of 93 octane and two bottles of Lucas through it, cleaned the MAF and the TB and it still does it! My buddy hooked his 4 thousand dollar Snap-On Scanner up to it today, and according to that everything is functioning properly. The only thing he took notice to was that the bank 1 rear O2 sensor readings were a little erratic. I was thinking it could be blocked cats! It has a LM1 exhaust, and is not as near as loud as it should be! I am at a loss and need some expert advice, please help!

my bandit

iTrader: (10)

My G8 is doing the same thing with 50k miles on it. Ive heard it could be a blocked cat. What about a clogged fuel filter?

jimmyblue

iTrader: (11)

I'd begin with looking at knock retard and O2 (front) sensor voltages
during the misbehavior. This will tell you if you're over-lean. A tool
that would let you pull and review a log file is better but you can
deduce a lot from watching things in real time, or having someone
else do it from the passenger seat.

LoneGunman

iTrader: (2)

The front O2 sensor voltages were fine during real time. The only thing that was weird was the rear O2 on bank 2 (it was bank 2, I thought it was 1) The spikes were pretty erratic, and nothing like the one on the other side.

Steve83ta

Im currently going though almost the same thing with forum member HibachiZ28.

Do you self a favor and read though these threads to get some ideas, you need to do some real tests and not just look at it from a scan tool. Fuel pressure and a timed volume test, also go to pep boys or harbor freight and pick up a vacuum gauge to take a vacuum reading that you can see in real time with a needle. This will tell you what condition the engine is running in and tell you were to go next. Compression and leak down tests too test for things like cylinder leaks

http://www.ls1.com/forums/f6/wont-ru...ar-now-174163/
And
https://ls1tech.com/forums/general-m...nder-load.html

Sounds like there is a lot of the same symptoms, Follow the threads. Although Im supprised you don't have a P0300 code at least.

Also Mass Air Flow Meters will not often put off a code becuase its a primary sensor. If you can get on that scan tool again tell us what the air flow is at idel at what rpm along with 2,000 and 3,000. Cleaning MAF sensors is almost a gimic. They have a burn off program at startup where they take the wire to about 800 degrees or higher, memory is failig me right now, to bun all oils and contaminates off

As a lot of us techs like to say garbage in, garbage out.

Its hard to tell you anything without some information from a printout of the scantool or hands on testings you have done. Right now its like tossing the fuzzy fix it dice

Steve

99Hawk6spd

iTrader: (2)

Just gonna mention this, I had wires rub through on the back side of the passenger side head. There is a loom there with a bent in tab to hold the harness. After 130k miles and some rubbing, it wore into my coil trigger wire, and my alternator exciter wire.

Mine would only break up when the motor torqued around 1500rpms.

https://s3.amazonaws.com/ggaenzle/Wires/DSC01118.JPG

This is the tab bent into the harness that caused the shorts:

https://s3.amazonaws.com/ggaenzle/Wires/DSC01119.JPG

And here is how you get to it:

https://s3.amazonaws.com/ggaenzle/Wires/DSC01121.JPG

agentruley

I had sputtering with the LsX truck in situations just like this.
When I replaced the fuel tank with a smaller one, I noticed the old fuel pump screen had a piece of broken plastic in it and when there wasn't enough fuel in the tank or I was just cruising, the pump would suck on that piece of plastic, causing a horrible start off the line or bad bad miss firing while in 4th or over drive.
Check that out or the fuel filter. just my own .01

LoneGunman

iTrader: (2)

I checked the fuel pressure today. It held at 60 psi at idle and while reving the engine. It never dropped below 58 psi, so I am assuming that is fine. I read the "Sputtering Under Load" thread, and that car has way bigger problems that my car has. My car doesn't sputter or miss, it just seems like it falls on its face when you get on it. If you ease into it its really hesitant, but when you nail it it just feels like someone stuck a potato in the tailpipe..lol.

OSU Football Fan

iTrader: (23)

I had a problem similar to this once and it turned out to be a dirty MAF sensor. My car would hesitate and run poorly from about 2K to 3K rpm. Then after that it would run normally. I sprayed it down with electrical cleaner and it didn't help. I tried again a few days later and used a full can of electrical cleaner and several cue tips to clean the wires with. (Be careful cleaning the wires or they'll break.) After that it ran perfectly. I couldn't believe the difference it made. My K&N air filter was over oiled and it had coated the wires of my MAF sensor.

Anyways, make sure when you try cleaning your MAF sensor that you do it thoroughly. Good luck man.

Steve83ta

Pressure isn't the only thing. If you have a gauge with a fuel release button and tube, get a measuring container and record the amount of fuel released into the container with the ignition off for 15 seconds, you wil have to jump the fuel pump relay on side. Make sure you use a meter or a jumper with a fuse so you don't let the smoke out of the wires. Pressure is only one side. You can have great pressure but no volume.

You are correct. The car in the other thread has a number of issues. Im sure you can get it figured out. Try unplugging the mass aif sensor to force it into speed density mode, it will turn on the light but it will not use the mass air sensor for fuel control. See if that helps if you havent done it already.

Block cats can also cause that issue like you and someone else mentioned. See if you can find an adapter and a backpressure gauge

RockinWs6

I had a similar problem, 99 too. would hesitate and surge around 1500. I pulled the fuel rail off and the injector screens were full of rust from the fuel lines.

Hook the scanner back up and look at the fuel trims.

LoneGunman

iTrader: (2)

I didn't get a chance to do anything to it today. I had the ole cattle truck out today I had thought of the dirty injector thing. There was some pretty nasty looking gas coming out of the filter when I changed it out
I can hook the scanner back up to check the fuel trims. What exactly should I be looking for??

Steve83ta

Clear the codes, and look at long term and short term for 1/1 2/1 banks, its normally in % in most scan diag. tools. it should be close to 0 but -3 to 3 is normal. Anything outside those ranges there is an issure somewhere

RockinWs6

Look at the 02s and see how fast they are switching and look at the fuel trims. If the trims are high you may have blocked screens or a fuel delivery problem. Max on the fuel trims is 10% -or+ anymore than that and you have a problem that needs attention. Normally like steve says -3 to +3 is normal but I've seen them move around -8 after filling the tank because of the cold fuel is much denser than what was in the tank.

Example I recently was scanning my LTFTs and was around -1 to -4 and filled up the tank, the fuel trims went to -10 for a while then started to drop back down.

Steve83ta

RockinWs6 is right, a little off topic Im working on another members car and his LTFT was at 26% yeah 26%. Which if I recall this corectly, I believe when you take into whats "normal" is 126% because 100% is base which is 0.

Steve83ta

Any updates?

LoneGunman

iTrader: (2)

The car has been in the garage the last few days. I am up to my neck in window regulator issues I just got my headers and ory yesterday. I plan on tackling that this weekend, so we'll see if that helps at all.

RockinWs6

So before you find your problem you are going to put headers on it? Are you serious?

tjwashow

iTrader: (2)

Clogged cat may be his issue ^

LS6427

iTrader: (2)

Run a FULL can of SeaFoam in 1/8th tank of gas....run it almost out before adding new gas. That will clean the fuel system better than anything, including the injectors.

Clean the MAF with MAF cleaner........spray the IAT sensor in the lid while your at it with the MAF cleaner.

If that doesn't do it....your issue sounds exactly like a failing 02 sensor. Of course make sure none of your spark plug wires are touching any part of the metal exhaust piping....that will cause stumbling at different rpm's.

But I say it's an 02 sensor.

Ae you using more gas than usual.....?

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