TCW

iTrader: (3)

Last night after about 2 minutes of driving on my way home I noticed a sudden loss of power and began stumbling or surging. It was a light rain and had been raining all day. About 30 seconds later the service engine light came on. It didnt flash like I assumed it would if it was misfiring. I stopped and checked the wires to make sure they were tight and continued home as there wasnt much I could do. It seemed to level out after about 5 minutes or I just got used to it. Well today after getting home(other car) I took it and got the codes checked. P0300 multiple/random cyclinder misfire. Well since It seemed to be driving fine I decided to clear the code by disconnect the batter and hitting the brakes/turing on parking lamps. (Advanced said they couldnt clear them...) Well code is still there so whats the problem?

Thanks

PS oil pressure stayed good as well as temps, oil looks good too & no smoke

joshp14

iTrader: (5)

Probably an O2 sensor issue. If the problem is still there, remove all of your oxygen sensors swap their positions by putting the fronts in the back and the backs in the front. If your problem goes away you have a bad front O2 sensor.

TCW

iTrader: (3)

Would an o2 throw a misfire code instead of its own tho? O well I guess I will do that as well as change the plugs tomorrow. Should I be good if I rotate them since the backs arnt rly needed?

MagnaTransAm0098

iTrader: (10)

also can have a bad temp switch...somtimes they make cars throw a fit..

joshp14

iTrader: (5)

It can...I have had it happen on several occasions w/o a single O2 code. If you had a way to monitor misfires that would be best...usually you will get misses on only 1 bank...ie 1,3,5,7.

TCW

iTrader: (3)

I will try clearing the code at and Advanced where they know what they are doing and see if it comes back, just want to know if I can drive it in the mean time. If it does I will rotate the o2 like you said and then plugs and eventually wires.

Thanks

markyde

HEY TCW,
Just curious! Did you get the problem fixed? Was it the O2 sensors? I have a 99 Ragtop Z-28 and I thought I got a bad tank of gas. Now, even with a new tank of gas, I am still getting the loss of power, sometimes even a popping in the exhaust under heavy acceleration. Let me know PLEASE!!
Thanks!
Mark.

Chief Z

Bump
Same problem!
The O2s are both reading high voltage codes as well. I understand this is because they are reading rich exhaust? Engine surges and rough idle too, but seems to be running fine other wise.
Intermittent codes, but surging is driving me crazy.
Thought it was crap in the fuel system. changed the fuel filter, plugs and wires look good, maf looks clean. I even ran FI cleaner through the gas and Sea Foamed the top end.
Anyone? What kind of damage is this doing to my motor?

Barr6505

Same problem
99 formula
97000 miles
Popping all four o2 sensors. (Can't remember whether they were high or low voltage)
Replaced fuel filter = nothing
Replaced plugs and wires = slightly better
Still throwing sensors and surging. Mine will start to accelerate (but not like it used to) then completely die out and sound like it is trying so hard to run, then start to accelerate again (all this time-pedal is in the same spot) and as it accelerates it gets more and more powerful. This has been a gradual problem getting worse and worse over the past two years. Yeah, I'm lazy as hell, but it wasn't that bad at first. It just started out as the surging problem that got more and more powerful after the accelerator was held constant.
Whatever this **** is, it is ruining my life. That and premium gas price. Hope we get it figured out Chief.

Seth

hndakilr

I keep the gas pedal in the same spot and the car will lag in accelerating, then all of the sudden it will just pick up and go like it should be. while its lagging the rpms will rise but at a slower rate. it seems to catch at about 4k. it almost makes me wonder if its a timing issue. i know my clutch isn't slipping because i just replaced it. im always throwing o2 codes but im not sure how that will apply to the problem im having.

wickedformula

iTrader: (1)

haha wow my car is starting to do this to... im thinking bad opti or an o2 sensor problem

sic2001

iTrader: (5)

I had the same problem with my car for years. It runs like a top now though after deleting !AIR!,replacing the crank posistion sensor and tuning out the rear cats. If you still have your EGR and AIR hooked up Id try tuning those out. I cant begin to tell you WHY my car did that but one of the thing mentioned definatly got rid of the problem.

92SilverSHO

iTrader: (3)

cracked pluged? hole in spark plug wire? Obviously seems ignition related.

wickedformula

iTrader: (1)

i deleted my a.i.r. and egr setup when i put the race headers in. it ran great the first day but now it will run fine when the motors cold (open loop) and once it reaches operating temp (closedloop) the idle lowers and it pops, misses, and backfires. when im driving it at low rpm it will buck and lose power then all of a sudden regain power. in the higher rpms it seems to go smooth out but feels underpowered. usually snaps my head back but not anymore. I changed the thermostat to a 160 degree powerstat. new plugs (gapped correctly) and the wires are fine. just put brand new o2 sensors in and that didnt fix the problem either. Thought it would have been that for sure... only thing left is the original opti but it ran fine before the header install. still got no check engine light

wickedformula

iTrader: (1)

hey heres something interested i found!

----Is Your Opti-Spark Failing?---

LT1 owners have dealt with the Opti-Spark distributor for 11 years now, but there is still much confusion regarding the causes and symptoms of a failing unit. Tapping into the PCM with a scan tool is a good way to start, but sometimes no codes will be set. Before diving into the Opti-Spark, be sure to verify that your grounds are good and the coil and wires are not the source of the problem, as they are much easier to change.

Symptoms:

* Car suddenly dies and won't restart
* Starts but immediately dies
* Extended cranking to start
* Rough idle
* Sputtering
* Backfiring
* Trouble reaching higher rpm
* Black smoke from exhaust
* Poor performance with car warmed up
* Weak plug wire spark
* Codes 16, 36, and 42 may be set

http://www.gmhightechperformance.com...ing/index.html

Barr6505

I have a 99 automatic, so I don't think mine has an opti on it, does it? The crank position sensor sounds like it might be the culprit. I know someone wrote that. I was thinking; check for vacuum leaks, check the coils, check the pigtail on the radiator temp sensor, mostly just the stuff the shop manual tells you to trouble shoot.

About the EGR and the !Air! code. Are there sensors I can replace instead of getting them tuned out? I would rather dump forty bucks into two sensors than spend $300 on a tune and have it not be the problem ya know?

I guess it wouldn't be a bad thing to look into though.

I am in Lapeer Michigan. I go to work in Troy everyday. Does anyone know of a good place in southeast Michigan to get tuning on LS1's done? How about cam, headers, ory, exhaust install?

*Edit: I just did plugs, wires, pcv valve, fuel filter, oil and filter. It runs better after the tune up, but still shitty... Maybe fuel pump? GM vehicle, 98000 miles, it's gonna need a fuel pump I guess.

Barr6505

Was your crank position sensor a bear or was it a pretty easy fix?

wickedformula

iTrader: (1)

heres some more about it.

-Many ignition problems can be realized as high rpm roughness. Check for intake leaks around the MAF and throttle body connections, tighten your plug and coil wires and use dielectric grease for better contact, maybe replace plugs and wires, but there's certainly a chance it's the the Optispark. If the problem gets worse as the engine warms up, to the point where the engine dies and won't restart, you might have a bad coil. In order of what's easiest to do, replace the coil first, then plugs (you might try gapping them down to 0.040" rather than the stock 0.055) & wires (including the coil wire). But if the problem remains after all this, you probably have a bad Opti.

- Low RPM vibration, especially in high gears: Perhaps the easiest resolution here is a loose or burned spark plug wire, or even a cracked plug. If you've just installed headers, it's almost guaranteed that you've got this issue. And it's also likely that it's wire #8. Check by looking in the engine bay at night, looking for stray sparks. The plug could be disconnected at the Opti, or the plug end, or burned in the middle. If you recently did headers, you may have also crossed some plugged wires. You can also test to see if any cylinder is firing by dripping water on each primary. On a hot engine, each should sizzle, unless there's no fire in there. The other way you may not get a cylinder firing is lack of fuel. Make sure the injector is plugged in, check injector harness

-Headers red hot: Rich fuel condition - fuel burning in your primaries. Can be caused by un-metered air being pulled in downstream of your MAF, dramatically retarded timing, low spark intensity (incomplete fuel burn), possibly a bad optispark, even a cam installed wrong.

-Cats red hot: Rich fuel condition (fuel burning in cat). A rich fuel mixture can be caused by a header/exhaust leak sucking in fresh air, causing the O2 sensors to read a lean condition and adding fuel

-Oxygen Sensors: At wide open throttle when the PCM is running in open loop, O2 sensor values should be around 880-900mv. In closed loop operation, it’s constantly richening/leaning things out trying to get to stoichometric, ~450mv, so you'll see readings jumping up and down hundreds of millivolts, centered around 450mv. A "dead" O2 sensor will read around 450mv all the time, and needs to be replaced.

If you're running really rich, you can even get flames out your exhaust. Especially if you aren't using catalytic converters. The most likely suspect is a bad O2 sensor (check them with a scan tool), or maybe a leak in your exhaust system in front of a good O2 sensor.

A hesitation or stutter at low RPMs can be many things. Try replacing your EGR valve first, then O2 sensors.

A hesitation or bog might be caused by a leak in your air intake. Check all connections from your filter all the way to your throttle body (throttle body elbow, MAF, etc).

Car not starting: The key turns, but all you hear is clicking? I assume that means the engine is _not_ turning over via the starter? If that’s the case, it can’t be your coil or ignition. It’s either going to be your battery (are you certain it’s fine?) or your starter/solenoid or your engine is seized up due to water in a cylinder, etc. If it’s clicking then I already ruled out a PASS key foul up. If the PASS key security feature locks you out, there’s no noise at all. If your starter won’t even engage, after ruling out a weak battery, check the gauge fuse in the fuse compartment on the end of the dashboard. Another possibility: if you know the battery is good, but no lights come on in the dash gauge and fuel pump doesn't run, you may have an ignition switch failure in the switch at the base of the steering column.

http://www.go-fast.org/z28/diagnosti...l#low-hesitate

i think i got this covered for you guys so try figuring out where your car falls in

sic2001

iTrader: (5)

Bro, I did the same thing, new fuel pump yadda yadda, problemm continued just as you describe untill I tuned out Air (and Egr if app.) and put
in a new crank pos sensor under the starter.
I feel your pain and wish ya luck.

Chief Z

Instead of an expensive tune, why not try taking the car to a competent mechanic?
I am beginning to think my problem is a failed driver side cat. because of my driveway, the cat scrapes every time I pull in or back out off the garage. I have repaired a hole twice. The headers, and catted Y are new, but since I just passed inspection I have a year before I would have to futz with it again.
I think a restricted or clogged cat on that side is causing my issue. It runs fine cold (closed loop) but it surges fuel when it warms up (open loop).
It could also be a vacuum leak, fuel pump, or a half dozen other things I am not prepared to deal with.
I think I will try a cat delete (Should have tried an ORY first) and see if that is the fix.
I will take a big freakin hammer to the pipe if it still scrapes.
Then into a shop if it still surges. I may like turning my own wrench, but I know when to turn it over to a pro.