Lt1Porsche

iTrader: (6)

This is what goes on. The car misfires in open loop only. Repeatedly happens day after day. The O2S's are decently new (6months) because of this same problem. Has changed plugs recently as well. So plugs are fine. Codes that appear during this situation deal with losing voltage and having no activity with either O2S. Only way to fix the problem is to reflash the PCM. Once I do that all problems cease and function of the O2S's return. Next time I am going to replace the PCM. Ideas?

jimmyblue

iTrader: (11)

Insufficient Activity codes probably just mean sleepy O2s, you
can try holding off closed loop until fully warmed up or just kill
the insufficient activity and heater codes. These will fault the
O2s and put you in open loop even if things are working OK in
general; just arbitrary test conditions leading to judgement,
against.

Now, why it runs poorly in open loop wants more diagnosis and
fixing. You don't want to depend on big trimming to be happy.
But this is all to do with data, not the PCM brick itself.

Lt1Porsche

iTrader: (6)

But if the problem is because of the data, not the pcm, why would reflashing the PCM take care of the problem for 6 months. Or was it just a coincidence? When the vehicle misfires, it misses on all cylinders. The coild packs fail to fire. I tested it with 8 spark testers. At idle all cylinders fire perfectly. When you power brake it, the cylinders fail to fire a few at a time. Just enough to keep the motor running. When the problem occurs when your driving, you cannot reach speeds higher than 35mph. Then the problem disappears and will not return unless you restart the vehicle. You can let it sit there and idle all day long and nothing with happen. Try to complete the 1st drive cycle and she goes nuts. I am going to replace my O2S's again to to eliminate that as a problem. Would false information from the O2's cause the misfire under load? I will put the car on the lift tomorrow and look over all of my wiring and make sure everything looks okay. Any other ideas?

Lt1Porsche

iTrader: (6)

Last time this problem occured, I installed new spark plugs and O2's and that did not change a thing. I then reflashed the PCM and never had a problem until now. I will also check voltages on the 02S harnesses to see if I may have a short. But I figured if the problem was a short, reflashing the PCM would not change a thing because the short would still exist.

ssvolvo

Deal with the low voltage problem first. I'm guessing you have a homeade harness. I learned this the hard way. Kept popping a low voltage code. While doing my VE tune I had to add 20% more fuel. Once I cured the voltage problem my VE went back to normal.

Keep this in the back of your mind: Your engine under full power full load requires around 55 amps. At idle it only requires about 8 amps.

Ask anyone who builds LS harnesses for a living and they will help you out.

Stick with it, be perstant, patient. Good luck

Lt1Porsche

iTrader: (6)

The username may be throwing you guys off. This is a 2000 TA with a ls1 bolt ons. Nothing homemade on this car. All is stock wiring.

ssvolvo

post up your code #s.

Schantin

iTrader: (6)

I'd check the low voltage condition (ie check for a short, ground, etc). The PCM should not be using O2 data in open-loop. Open loop MAF uses the MAF, Ve table, MAP, and IAT. Open loop SD deletes the MAF.

Closed loop incorporates the O2's with the above-mentioned parameters for short term/long term fuel triming.

Good luck finding your problem. It can be frustrating to diagnose/fix wiring/sensor problems.