Miss at idle

[94TrnsAm]

The car is a 94 trans am, stock motor with intake and headers(stock mufflar). The coolant was horrible sooo I drained flushed and filled. Upon doing this process I tried hard to keep the opti dry. The bleeder on the water outlet is a pain and i can't promise i didn't. The problem is as follows, The car misses at idle once the idle comes down, not necessarly warm. I was told the opti was replaced but the wires on the vehicle were not. I ordered new msd wires assuming the old wires began missing from heat off the headers and possible water from the coolant. Installed the new wires and the vehicle still missed. I have always ran 87 octane in this car, Somtimes premium. I realize this is not the best idea but my budget is a killer. The car continued to miss or seem so. Finally a ses light came on, I pulled the code and it was a lean right oxygen sensor....replaced the sensor(pulled battery cable also), all went well the old was was carboned up. Ran to the gas station threw some premium in and car was fine, premium ran though, threw some 87 in and bam the problem is back. No ses yet but same simptoms. Is it possible that the premium is avioding the the miss enough to hide the problem in the optispark? is this possible? I read several other optithreads (they are numerous) but didn't se anything related to gas. I also looked at the cars data and noticed the right bank injector pulse width is 4 and left is 0 and the left 02 runs higher numbers thant he right (mv). The old wires did have one cylinder where it had been burned from the header, but the car had ran great it wasn't untill I touched the coolant that it ran bad. When the car stated to miss again i could see black smoke when i start off, ussually the worse miss and lack of power obviously. Hopefully someone can provide some extra insight and help me out. Thanks guys!

[Z Ya Later]

Read your owners manual. It clearly states to run Premium for optimum performance, but 89 can be run if need be. The LT1 has too much compression to run 87 and have the motor run properly. Run 89 if you're on that tight of a budget. You might want to replace the plugs as well.

[94TrnsAm]

I have ran 87 with no problems for a while, i agree 89 would be better, it has new ac platinum plugs in it. what would cause the pulse width to increase on one side only? o2?

[Z Ya Later]

As I said, read your owner's manual. Run a minimum of 89 if you must. The compression on the motor is too high for 87.

[TraceZ]

I question why the injector pulse is 0 on the left bank. Cheap gas shouldnt make that happen. How do the O2 readings compare left to right?

[94TrnsAm]

the right had a lean (lower)mv signal, i just swapped the sensors left to right and the weaker signal switched also, looks like a bad o2. I am installing one right now, we will see

[94TrnsAm]

Ok, just test drove her, 02's are the same signal now, ijectors are both4, i did pull the battery cable so i will have to drive her a little more befor i can get good data. Idle is still seeming rough, may take the comp a little while to relearn. Could be the opti getting old too. The car does seem to run better and no ses yet. Hopfully the same tomm.

[Craig 94 TA GT]

Your car shouldn't miss when on 87 octane. The PCM should pull out enough timing to avoid detonation. Although that's why everyone recommends you put in premium, to run it to it's full potential.

Please elaborate on "The car misses at idle once the idle comes down, not necessarly warm." Do you mean open vs closed loop, or...? So when motor is completely cold, it does not miss, correct? What are your long term fuel trims? If your pulse width reading is really correct, then I'd suspect your BLMs should be all screwed up.

A miss is going to cause your O2s to read more oxygen, thus telling the PCM to add more fuel to that side bank.

Something isn't adding up. What are you using to scan? Are you using O2 extensions?

[Firebirdcrazy]

I suggest you get yourself a 4 banger or a V6 Bird no offence because even my old 86 and 87 TA's could not run on regular gas. Those engine's just were not meant to run on regular gas, and I doubt they ever will in the future either if they make a come back. Get yourself a beater and save yourself some money that wat. Dont kill your birds engine because it will cost you more in the long run.

[TraceZ]

I suggest you get yourself a 4 banger or a V6 Bird no offence because even my old 86 and 87 TA's could not run on regular gas. Those engine's just were not meant to run on regular gas, and I doubt they ever will in the future either if they make a come back. Get yourself a beater and save yourself some money that wat. Dont kill your birds engine because it will cost you more in the long run.

Running low octane fuel is not going to do any harm to his engine. As Craig stated, the PCM will simply pull out a little timing so there is not any detonation.

These engines were designed to run on regular gas, they just were not designed to make maximum horsepower on regular gas.

[Firebirdcrazy]

If you look in your manafactures book on the recommended fuel it tells you the octane level, and it also states possible engine damage may occur if you dont follow that octane level. My 86 amd 87 TA's were carburated, and I did get away with using regular at times but it would ping and knock like crazy. Even with a carburated car. I am sure he can get away with it, but like I said in the long run he might be paying more for it by blowing his engine. I am sure he would like to get a good resale instead of junking it. That pinging and knock are your rods being thrown around due to bad detonation of the fuel.

[TraceZ]

If you look in your manafactures book on the recommended fuel it tells you the octane level, and it also states possible engine damage may occur if you dont follow that octane level. My 86 amd 87 TA's were carburated, and I did get away with using regular at times but it would ping and knock like crazy. Even with a carburated car. I am sure he can get away with it, but like I said in the long run he might be paying more for it by blowing his engine. I am sure he would like to get a good resale instead of junking it. That pinging and knock are your rods being thrown around due to bad detonation of the fuel.

Stop.

He is not going to hurt his motor running regular gas. These modern fuel injected cars have something called a knock sensor. If the PCM detects engine knock from low octane fuel it will retard the timing until the knock goes away therefore preventing damage to the motor.

Your older carburated car may have knocked like crazy because it did not have any means to correct itself.

When Knock occurs, the last part of the compressed fuel/air mixture ignites before the flame front reaches it, creating two areas of combustion within the cylinder. However, while the original combustion is proceeding at a carefully controlled rate, this new combustion is simply a sudden sharp explosion. This abrupt increase in pressure is what creates the knocking sound in the combustion chamber. The Knocking sound is not caused by the connecting rods "being thrown around".



Read the above taken directly from the owners manual. You can run mid or regular grade gas, the power output will just be reduced. This is because the PCM will retard the timing.

[Firebirdcrazy]

I stand corrected then, but from dealing with past experience I do know engines have failed, or gotten damaged due to improper octane. I will never take that chance of ever putting regular to my LS1. These engines just cost to much money to take any chances. Why risk it?

[TraceZ]

I stand corrected then, but from dealing with past experience I do know engines have failed, or gotten damaged due to improper octane. I will never take that chance of ever putting regular to my LS1. These engines just cost to much money to take any chances. Why risk it?

An engine can be damaged or fail if knock is allowed to occur. The abnormal combustion creates hot spots in the cylinder and that results in piston failure.

Your LS1 will protect itself from that. Its Knock sensor and PCM will work together to retard the timing and stop any knock it detects. If the PCM stops the knock, it cannot damage the motor. Your LS1 will not be damaged, it is advanced enough to protect itself from knock. There is no risk.

[Joe K. 99 Zeee!!]

I got the same code with a slightly rough idle once. Turns out there was an air leak after the MAF sensor. The PCM couldn't measure the extra air so it spit out a right bank lean code.

Here's another question...Has the PCM been reporgrammed or is it running the stock program?