I'm about tired of this damn car... Here's the details.

Brand new GM crate motor, LT4 HotCam, custom tune from TWong. In the last month and ½ the car has received brand new PCM, O2's, plugs, wires, and opti. Car still has a missfire. It's always there, sometimes very slight, sometimes to the point where the car spits and bucks and barely accellerates. Car is running noticeably rich, from smell, and smoke from time to time. When I pulled the old plugs before changine, all driver sides were black they were so rich, #2, 4, & 6 were lean, and #8 was wet with gas. Car pops a lot through the exhaust too, probably due to unburnt fuel in the exhaust. Just went out and recorded a Datamaster file. Started the car, idled for a min, drove out the neighborhood, then a couple WOT blasts, then a little constant speed cruise. Anyone care to look at the file, and/or speculate on what to try next?

Got a low mile set of stock injectors I'm planning to swap into the car this weekend, as well as change the fuel filter and check all the engine grounds. Past that, I'm done, don't know anything else it could be.

Here's the link to the Datamaster file:
http://www.hi-psi.com/Corvette/Corvette.uni

Thanks in advance.

 

Don't throw any more parts at it until you figure it out. I'd look at your file, but I don't have datamaster.

How's your fuel pressure look? Is the needle jumping at idle? Did you ohm out all of the injectors?

Do you have service manuals? While the diagnostic trees don't always apply to modified cars, they often point you in good directions.

 

Is it just the one bank of plugs that are getting fouled with fuel? I looked at the DM file and its showing me that the Left bank O2 sensor is lean and thus the PCM is POURING fuel to compensate for the lean condition that it THINKS its seeing. I am suspecting that your 02 sensor is bad. When you removed the engins is it possible that the connector for the left O2 sensor was damaged in any way or even had oil or antifreeze that was possiblly spilled into the connector of either the sensor side or the harness side of the O2 sensor connectors?

If any contaminants have entered into the connectors it could be that the reference air which is received into the sensor has been blocked. This reference air is transmitted via the sensors wire insulation and if its blocked off the sensor goes nuts and will give a very lean reading to the PCM. What is stranges is that you are saying that the even bank (right side) is all fouled and the DTC I see is for the left side which is bank one. Is there a possibility that the O2 harness connecters were swapped somehow during the engine swap?

One way to check this is to disconnect the left O2 sensor connector, ground the tan/wht wire on the harness side, start the engine and observe the Datamaster record. Watch the left o2 voltage it should remain a constant value of between 350 to 550mV. When the connector is disconnected the PCM just sees its internal 450mV reference voltage. If you still see a low value it means that there is a short in the ppl/wht wire between the harness connector and the PCM. If you see the 350 to 550mV then it means that the o2 sensor is bad. Or you have a air leak in the exhaust system close to the sensor or in reality a very lean condition which I don't beleive seeing how you are fouling plugs to a point that you are misfiring. Make sure that the wire colors are as stated above. The right side bank O2 sensor should have a ppl wire instead of a ppl/wht on the left side.


[Modified by tjwong, 9:39 PM 5/7/2004]

 

If you need a diagnostic chart let me know I can scan and email you a diagnostic chart to help you.

 

Tom,

All the drivers side plugs were black when I removed them. On the passenger side, all but the back plug (#8) were lean to normal. The back plug (#8) was wet with fuel.

Thanks for your input and help.

 

Just realized something... With the long tube headers on the new motor, we had to extend the O2 wires to reach. I'm thinking it could be possible that while doing this a wire got crossed on the left side? Anyone have a diagram or can tell me the order/color of the wires on the left side, and their correspondence on the O2 sensor? THanks in advance..

 

Robert I am not home right now but in the morning I will post wiring information

 

Robert here is the pin out for the harness side of the left o2 sensor connector:

Pin A: Tan
Pin B: Purple
Pin C: Black
Pin D: Brown

The right side is the same with the exception that the tan and purple wires may or may not have a white trace on them. That is how GM differentiates between left and right sensors.

Pin A is the sensor low reference or sensor ground in the PCM, Pin B is the snsor output to the PCM.

Pins C & D are the heater element connection for the sensors, with the brown wire being the switch 12v ignition circuit and the black wire is ground.

 

If you just unplug the sensors all together and drive it around in open loop and the car drives "normal", then you can rule out tons of mechinical problems. Just trying to help.

 

I tried to look at the file with DataMaster, but I really couldn't make heads or tails out of it. Maybe the file was corrupted or something, because it made no sense whatsoever to me. What am I doing wrong? It showed rpm around 25-75 most of the time and I saw your engine temp go from 53 degrees down to a couple of degrees in a matter of a minute. Anyway, I couldn't read it, but I tried.

 

Here's an update guys...

Swapped the injectors out, and then unplugged the driverside O2 sensor and took her down the road. There is still a VERY slight miss there, maybe a fouled plug or something, but the car is running noticeably better. Looks like I'll be rewiting the O2 sensor, then changing the plugs. Hopefully that will be it. I'll update again once I have that done.

 

Sounds like to me that your not using heated O2's and you don't have a Cat. When the O2 is too cool, with free flowing exhaust, it is usually a lean output to the PCM, thus the BLMs go typically to the mid 130's or even a tad higher thus the PCM then is stuffing fuel in, when in reality the motor isn't looking for more fuel.

However, when flooring the car, it should be smooth and feel normal, because it will be in open loop at this time. But here again, if the Fuel Pressure is too high, then at WOT it'll puff black and maybe be down on power, but shouldn't buck,

A buck is a usually a miss-fire or a lean condition.

My 2 cents
John

 

Hi John, Robert is using heated sensors. He has a 95 LT1 car and they are standard 4 wire units on these cars. Sometimes the problem is the sensors in these cars, the connectors are very susceptible to contamination. As the sensor needs to breath in order to get its reference air, and to be able to breath they breath through the wire insulation. Yes, thats right these sensors must have a O2 reference and in order to get it, they breath minute amounts of air via the insulation of the wire. Air travels through the insulation like a hose and into the reference chamber. Without this reference air the sensor goes nuts and will show a very lean condition.

Sometime ago I had my connectors apart while servicing the knock sensors. Well when I pulled the KS I blew coolant all over the O2 sensor connectors. Not thinking much about it I cleaned the connector out with brakeclean, and compressed air. The car ran about 20 miles before crapping out, running extremely rich to the point of smoking and fouling plugs. The scan tool showed DTC44, and a very lean output reading (below 200mV) from the sensor just like Roberts problem.

 

I know what your saying is true about the insulation, however I have never seen it to be an issue, but I'm not argueing with you, it sounds like it could be a problem.

What is his timing doing? Just curius if he is getting any advance, I know the PCM can call for timing based on what you flash, but how do you tell if your getting any advance. The data you get through the ALDL is PCM data.

I am experienceing this on a 93, I believe the OPTI may be the coulpret on the 93, because its also flagging a quad driver fault, 26, 43, and 36. and if the fuel is kept on the lean side, it runs OK, as soon as I richen it up, it loads up and is blowing smoke.

John

 

Hi John, the first thing I would do is to clear the codes and see if they return, any one that comes back can be considered a hard failure. The code 26 quad driver failure is not the cause of the black smoke and rich condition. That code monitors the driver circuit that activates 4 solenoids. Now if anyone of the solenoids are grounded or shorted out, that will cause this code. The ECM monitors current flow to the devices and if they pull more than 2 amps then a code sets.

Code 36 is an distributor high resolution signal DTC and code 43 is a knock sensor DTC. Either one of those could cause a problem. If 43 is present the ECM would go to lower timing map to prevent detonation as a safe gauard because it thinks the knock sensor is inoperative or defective. Code 36 with a missing high res signal could also cause misfire and other ignition problems which means Opti replacement.

I don't know of any way to really verify timing, as you probably know the LT1 engines do not have any timing reference marks on the balancer. However one could mark it someway and one could monitor the advance with a conventional timing light. Other than that all one can do is to trust the scan tool data.

You are right, the air reference problem I mentioned is not a common problem. It does happen from time to time and mostly if some one decides to extend the sensor cables by cuttling and splicing and or soldering the wires together. Or do as I did by dumping antifreeze all over the open connector.

If you need any diagnostic charts for the above codes let me know I can email you a copy.