We have a 98 LS1 from a 98 Vette in our 89 S10 pickup. Overall conversion has gone well. One issue that we have found is that NOX level is a bit high. It is 2.3133GPM VS <1.55GPM (where it should be). This engine did not come with EGR. Does anyone out there have any suggestions as to how to lower the NOX levels? The only suggestion that we have is that the cats may be on the edge & going bad. We used the original 98 C5 cats with approximately 45K miles on them. HC is .8110GPM & CO is 9.2GPM. No error codes.
Your input IS appreciated.

 

The C5 doesn't have EGR so you shouldn't need it either. How is the AFR and have you checked for vacuum leaks? Running lean and having high cylinder temps can cause high NOX levels.

Cleaning the MAF or replacing an older O2 sensor is reported to help sometimes.

 

Do you have any means of DATA LOGGING the PCM?

What conversion harness did you use and has anyone retuned or installed a CUSTOM PCM Tune into the PCM? Are you sure that the PCM TUNE that your using is correct????

The C5 LS1 engine does not have an egr valve, and does not have an IAC. It uses the throttle by wire to adjust the PCM determined idle.

Are you using the C5 Throttle by wire TB? If not, did you set the TB minimum air and idle air properly?

IS,, the ducting between the MAF and TB completely sealed so no unmetered air gets into the manifold? That includes vacuum leaks form hoses

You best bet is to datalog the PCM and see what your O2 sensors are doing and see what the Long Term Fuel trims are reading. I use an ACTRON CP 9180 hand held scanner for most of my vehicles and it has LIVE SENSOR DATA.

EFI Live and HP Tuners works better.

You can also use the predator tuner to data log.

Bill

 

Thanks for your time...We DID clean the MAF when we put things together (about 1500 miles ago). We tried to be careful of the lines when we put things together, but, I WILL check for vacuum leaks. It would be easy to overlook something, especially when things have been apart. The O2s came over with the engine. We monitored them last evening and they seem to be fluctuating about the same (the 2 front ones and the 2 back ones). Nothing is jumping out at me.

 

Thanks for your time as well...
We tried the data logging function on our OBD com setup (first time I've tried it). It saves it as an Excel spreadsheet. We monitored the O2s. They seemed to be very similar to each other....no anomalies. We also monitored the short term fuel trim and didn't see anything strikingly different from bank 1 to bank 2 (we didn't data log that).

We didn't use any conversion harness. What we did was to modify the Vette harness and the S10 harness so as to integrate the one into the other. (I had a front end spring compressor break loose and got my finger smashed, so I had a month of not being able to turn wrenches, which I used to sit at the table with both the Corvette & S10 manuals to figure out the wiring).
We stayed with the drive by wire throttlebody to keep thing operating the way they were designed to operate as much as possible.
We tried to be careful when putting things together, but I WILL check for leaks in the intake hose & vacuum lines. Something may have been overlooked.
This is my first experience with LS technology and I figured that an incorrect mixture would have thrown a code.
What we are using is OBD com. It is a program, loaded into our lap top that uses a cable from the OBD connector under the dash to a USB connector on the lap top. With it, you can read codes, view gauges, see graphs, and data log. We could let it collect data while driving (I think). The guy that programmed our PCM uses EFI Live. When he set up our PCM, we asked him to keep the stock operating parameters since we have to meet emissions (and it has plenty of power to move the S10 down the road anyway).
To data log the long term fuel trim, do we have to let the lap top do that while driving for awhile? I think that I watched (not data logged) the long term fuel trim last evening and it didn't seem to be doing anything (I think that the lap top display just displayed "N/A" for long term fuel trim.
Thanks again!
Denny & Ruth

 

Are you sure that you PCM is going into closed loop operation? The LS PCM does have and use the LTFT Values to correct the commanded cruise Air Fuel Ratio (AFR) Like I stated, the LTFT valye should be close to zero percent if the engine is running correctly

Do you have access to a Wide Band O2 meter?

NOTE. The rear after the CAT O2 Sensors are only there to tell the PCM that the CATs are working properly. You can have those sensors tuner out of the PCM and not use them if you desire. They have ZERO effect on performance but if you dont tune them out of the PCM it will set an emission DTC

Do you have any set PCM DTCs??? Please list what you have..

Example P-0321 H or C The C means that the DTC is current and the H is History They are both important and will help figure things out


Here are some other common causes for high NOx emissions:
• Misfire
• Failed Oxygen Sensor
• Leak in exhaust upstream of Converter
• Excessive carbon deposits in combustion chamber
• Advanced ignition timing
• Blocked coolant passage
• Lean Air/Fuel mixture

 

The PCM IS in closed loop operation. A check of the fuel system indicates that.
As far as access to a wide band O2 meter, I will have to ask around. I don't know.
The rear O2s are NOT programmed out. For our emissions, everything that came with that year car must still be there and working, but the PCM shows no emissions DTCs, in fact no DTCs at all. We have disconnected the MAF and shown that a DTC will set, indicating that at least part of the diagnostics are working. The only thing "tuned out" of the PCM is the AIR system check or test, as we installed the AIR injection between the front O2s and the cats and the front o2s will no longer see the burst of fresh air that the pump injects.
Any past DTCs were the result of tangible issues that have been fixed, such as the AIR DTC (air being injected after the front O2s, showing a lack of activity in the front O2s) and DTCs for all of the O2 heater circuits (the power wire was missing in our integration). Since we fixed those 2 issues, we have been DTC free, around 1 1/2 months.
A leak in the exhaust in front of the converters may be a possibility. We used flexible exhaust tubing to get the truck up & running and haven't gotten it in to the shop to be fitted with rigid tubing. That was scheduled for the latter part of this month.
As far as a blocked coolant passage, I wouldn't have a clue. In building this project, I had read (in the GM LS1 conversion manual) that proper venting of the heads was critical. With that in mind, we tried to follow the original Vette cooling system hookup, including the factory surge tank. Not sure how we can check for a passage blockage.
The O2 voltages seem to follow each other pretty closely (front & front, rear & rear).
Not sure where timing should be at what RPM and not sure how to find a misfire. Plugs were all new when we installed the engine, not that that means they are good, just data.
Never thought to look at the plugs we removed from the engine when we bought it, so not sure about carbon buildup. We DID run a can of BG44K through the tank this last fillup.
So far, I haven't seen an option on our diagnostics that will show air/fuel ratio, so not sure if it is running lean. Test shows HC at .8110GPM and CO at 9.211GPM, and NOX at 2.3133GPM, if that is any help.
We are at around 5400ft altitude.
Thanks again!

 

Are your CATs even lighting off??

Do you have an Infred Temp probe that you can measure the inlet pipe to the Cat, The CAT body and the after the cat pipe to se if your getting the proper CAT light off and heat up.

The CAT body should be a LOT hotter than the inlet pipe if the cat is properly working. What CATs did you use?

You would or should know if your getting a misfire If you drive the car with the scanner hooked up, the PCM will set a P-0300 if it detects a random misfire and the engine will stumble under load.

Bill

 

Hi Bill,
I DO have an infrared thermometer. I will check that.
We are using the cats from the Vette that the engine came with. We were fortunate enough to get most anything else that we wanted when we got the engine. We had to cut the inlet pipes on the cats, about8-10" forward of the cats themselves. That section of pipe is where we welded in the AIR injection pipes.
We will try driving with the lap top hooked up and see what we get. As far as prformance, we get absolutely NO stumble or hesitation under load or acceleration. This engine runs smoother that any I've ever had. No sputtering at all, starts easy, runs smooth. If my memory serves me correctly, we have never seen a P-0300 code set at all, but we'll check. It may be tomorrow before I can get to it.
Thanks again!
Denny & Ruth

 

Hi Bill,
I checked the cats today with little success. I ran for 6 miles at around 2oooRPM and tested. The flex pipe coming from the collectors to the cats read around 150 degrees F. The inlet pipe (part of the cat read over 230 degrees F. I don't know exactly as the limit on our thermometer turns out to ba around 230. The cat bodies read around 180-200 F as it sat there idling as I read them. The outlet pipes (part of the cats) read over 230 also. What should we expect to see? If we need to get another thermometer, we can.

 

Bud

Im guessing that your CATs are not working. They should be around 500 deg Measure any car with CATs and compare.

Feel the heat around your CATs compared to any car with CATs. They will be the same if they are working correctly. If the piping around the header outlets and CAT inlets are not sealed, it will injest fresh air and the cats wont work.

What CATs are you running??


Try this.. Disconnect the outlet from the header collector. Smell the exhaust. Compare that to the exhaust that exits the tail pipe.

The CAT should SIGNIFICANTLY reduce the raw exhaust if the CATs are working correctly.

Bill

 

I had a car fail NOx levels because it had an exhaust leak. Just something to check.

 

Thanks for the replies, guys,
I haven't been ignoring the posts, I've just been working on a number of things....life gets in the way.
OK, the cats....they are from the 98 Vette that the engine came from. They are not getting near hot enough. I was going to compare them to one of our other cars, but they have heat shields and are pretty difficult to get to with a thermometer, but I WILL get to that. The other item (an exhaust leak) we are working on. It doesn't sound like it is leaking, but we DID use flexible exhaust tubing to get the project up & running, so we could take it to the muffler guy. I'm guessing that the opportunity for leaks is fairly high with this arrangement, although when we put it together, I didn't think of that. We are planning on taking it in next week to get that rectified. I may try disconnecting the tube between the header collector & cat at that time.
Another thing that we looked at is the idea of a drooling injector (causing the PCM to order leaner mixture). When a fuel pressure gauge is hooked up to the fuel rail, this is what happens: upon turning the key on, it immediately pumps up to 55-60psi and then drops to around 20 (almost immediately after the pump shuts off), and drops to 15-16 PSI in about a minute. Pressure regulator came to mind until we start the engine. While graphing the front 2 O2s, bank 1 bounces up & down several cycles and settles down and tracks bank 2 pretty closely. (My thought was that it might be trying to compensate for a bunch of extra fuel in one of the cylinders... any ideas?)Upon shutting the engine off, bank 1 voltage drops almost immediately and bank 2 drops more slowly. I didn't monitor the fuel pressure while running (didn't think of it), but it never seems to have a lack of fuel, even under high acceleration.
The search continues.........
Thanks again!

 

Is the distance from the cats to the exhaust ports about the same as on the vette? If they are placed too far back, it could cause them to not light.

 

As someone mentioned before NOX is the result of a burn temperature that is too high.
Lean A/F ratios, or excess timing will spike your NOX values.
Are all of the coolant, IAT, misc temps making sense? Not enough that there aren't any codes, verify the sensor values make sense for what the engine is doing.
EGR is also designed to lower the burn temp.

Fixing it is one thing, getting it to pass smog is another.
E85 or any alcohol additives will also lower the burn temp.

 

I tried to put the cats as close to the headers as they were on the Vette (not really knowing that that may be important), so as to have the entire system as close as possible to the Vette, figuring that that would give us the best chance of things working like they were designed to. They may be up to a foot farther away than on the Vette.

 

The PCM tuner programmed the PCM using stock 98 Vette timing tables and operating parameters. The only things different are the maximum speed that it will downshift into first gear and the AIR system self test is disabled (not the AIR system, just the self test).
AIT & ECT temps seem to be OK. The engine seems to be running plenty cool. I seldom hear the fans even running (usually only when sitting idling for an extended period. Even then, it is only the low speed). This system of course has no EGR and we are running fuel with I think 10% ethanol (state law, I believe). The only additives we have run are Lucas Fuel system cleaner (1x) and BG 44K (1x). The ECT gauge could be a bit off, but not too far. We calibrated the ECT sensor to the S10 gauge with a trim pot, setting the temp to 210 degrees when the thermostat opens (210 stock thermostat). Not sure of any other temperatures.