Alright a buddy of mine has a 1996 Z28 and Im pretty familiar on the LT1's even after moving to an LSx Z. But the car is very hard to start and he thought it was the Opti which we tested spark from the coil and opti and all is good. Once it starts it wants to die and you cant really keep it running, he removed the thermostat (stupid idea) and it threw a code for that but that wont make it run bad after it gets warmed up but at cold temps it will run funny for that reason alone. Its running lean sometimes and rich sometimes but I believe more lean than rich. Here are the 8 codes it is throwing.

P0101 - MAF System Performance
P0125 - ECT Excessive Time to Closed Loop
P0131 - H02S Circuit Low Voltage Bank 1 Sensor 1
P0174 - Fuel Trim System Lean Bank 2
P0300 - Engine Misfire Detected
P0372 - Crankshaft Position Sensor Fault
P0400 - EGR System Fault
P0420 - TWC System Low Efficiency (CAT Bank 1)

Here is what Ive come up with, needs a new Crankshaft Position Sensor and both front o2 Sensors replaced. With those being bad it wont get the correct timing therefor throwing it off and running rich and sometimes lean so this makes the car misfire. We dont really care for the P0125 code because we know what caused that and the EGR system doesnt matter, its coming off. The CAT in Bank 1 is reading the code it is I think due to it being rich on that side. MAF is out the window, its brand new. Also new thermostat Im going to recommend 180 degree.

Anyone else have an Idea or what do you think. I just need some input on what direction to go from here. As far as experience this is what I think.

Thanks for any info.
Mike

 

Check the pink wire in the MAF harness connector for +12V.

I think maybe you meant you don't care about P0400. You should care about P0125, because it indicates the coolant sensor is not indicating the engine is warmed up as quickly as it should be, preventing the PCM from going into closed loop. I doubt it has anything to do with a 160* t'stat. It should go into closed loop at 140*F, well under the initial opening temp of either a 160* or 180* t'stat.

The O2 sensor is stuck below 200mV. That indicates either the sensor is defective.... OR... Bank 1 of the engine is running extremely lean.

Now we have an indication that the PCM is adding an average of more than 21.9% extra fuel above what it should be adding, or at least trying to add by increasing the long term fuel trim. Pattern is starting to emerge.... running lean on both banks.

Self explanatory. If you have access to a scanner with "GM enhanced parameters" you can see the misfire count by individual cylinder, which may tell you if there are specific cylinder problems, or if its truely "random".

Not the correct definition, so incorrect analysis. It may be what a "generic" scanner tells you the code means, but its not correct for an LT1. This code tells you the PCM can not find the high resolution pulse from the optical module in the OptiSpark distributor. Generally the engine will run with this code, with a small loss in timing accuracy (increased spark scatter). The crank position (CKP) sensor is on the lower part of the timing cover, reading a 4-pole reluctor wheel on the crank behind the damper hub. It is only used for misfire detection, not for any sort of engine timing.

Might be worth tracking down, but is often caused by a low back-pressure exhaust system.

Don't jump to conclusions. Could be a faulty cat (or missing cat??), or a faulty after-cat O2 sensor. Swap the after-cat O2 sensors side-to-side. If the problem follows the sensor (P0430) its a sensor problem, if the problem stays on Bank 1, its a cat problem (or possibly a wiring problem).

 

Well the ECT was changed awhile back and I know that code is thrown due to the car not warming up and this is because it has no stat and maybe because its running lean.

 

So what do you think is the issue here? Bad opti and maybe low fuel pressure or bad fuel pump?

 

Its either too much air or too little fuel.

It would make sense to check the fuel pressure. It would make sense to find out why the MAF isn't working right. If the MAF reading is irrational, based on a comparison to the speed-density derived mass flow, it sets the code. If the MAF is reading significantly lower than actual flow, its going to show "lean" to the O2 sensors, and the long term fuel corrections will not be able to correct the condition, setting the "lean" codes. I would check the MAF reading with a scanner, at various engine loads.

And, did you check to see if the EGR valve is stuck open? That would make it hard to start, and cause it to stall at idle.

 

Well check that, better yet well prob just pull it off.