Misfire on '95 3800 Series 1 L67 ---BLM Issue in Cell 00

**darbysan** · 05-16-2016

I have a misfire that I have been unable to diagnose. Engine is a '95 Series 1 on ECM 16183247. Spark and Fuel all check out. Compression test shows one cylinder a little low, but within 10%. No leakdown on the valves. Symptoms get worse once car warms up and thermostat opens. Has a 180 thermostat. Car does have a CAI that runs to the inner fenderwell . MAF numbers are around 4.2-4.5 grams at idle speeds, and IAC bounces between 18-23. Tried unplugging the MAF, but no change. Checked all plugs, checked spark at the plugs using HEI spark tester (set at .060); Checked Coil Pack and ICM. Swapped in two spares with no difference. Coil Pack temps run about 117F, with one at 110F. Checked Injector flow, Checked injectors firing using mechanics stethoscope ( one injector is much quieter than the others, but I still think it is firing OK). All injectors cleaned and new filters, o-rings, spacers and pintles installed. Checked Fuel Pressure and Tested Regulator and pump ( new EP381 pump). Engine warms up to 200 where fan is set to kick on, and cools back to 190. No Error codes are being set. Only thing changed in programming so far is VATS delete and fan on/off temps ( VATS Delete required change using HEX editor ?? (See thread http://www.gearhead-efi.com/Fuel-Inj...C-16183247-ECM)).

Here's the only weird thing I can find using Tunerpro. At idle, it runs fine in BLM cell 16, with BLM's and Fuel trim about as expected. As it warms up, it starts to "hunt" between BLM cell 16 and 00, and immediately it runs bad as soon as it jumps to cell 00. When it hits cell 00, you can see the BLM drop to 100, and the fuel trim goes to 182. BLM's try to climb , but as soon as they hit, 110, they drop back to 100 and the climb starts over. Fuel Trim holds steady at 182. All the time it is in 00, it runs rough, and misfires. If I touch the throttle just enough to get the BLM cell to change, car goes back to running fine, and BLM's on the new cell are as they should be. If it drops back to cell 00, it reverts to BLM's of 100 and Fuel trim of 182. Eventually, if it stays in cell 00 long enough, it will stall out.

Anyone have any thoughts on this?

NOTES: Engine / trans installed in an '87 Fiero. Donor vehicle was '95 Buick Riviera. Trans is 4l60E. Using BIN BKZS ( downloaded from donor ECM). XDF file $5B 94-95 L27 L67 3.8.xdf . ADX file 5B7a.ADX

**Terminal_Crazy** · 05-16-2016

Originally Posted by darbysan

I have a misfire that I have been unable to diagnose. Engine is a '95 Series 1 on ECM 16183247. Spark and Fuel all check out. Compression test shows one cylinder a little low, but within 10%. No leakdown on the valves. Symptoms get worse once car warms up and thermostat opens. Has a 180 thermostat. Car does have a CAI that runs to the inner fenderwell . MAF numbers are around 4.2-4.5 grams at idle speeds, and IAC bounces between 18-23. Tried unplugging the MAF, but no change. Checked all plugs, checked spark at the plugs using HEI spark tester (set at .060); Checked Coil Pack and ICM. Swapped in two spares with no difference. Coil Pack temps run about 117F, with one at 110F. Checked Injector flow, Checked injectors firing using mechanics stethoscope ( one injector is much quieter than the others, but I still think it is firing OK). All injectors cleaned and new filters, o-rings, spacers and pintles installed. Checked Fuel Pressure and Tested Regulator and pump ( new EP381 pump). Engine warms up to 200 where fan is set to kick on, and cools back to 190. No Error codes are being set. Only thing changed in programming so far is VATS delete and fan on/off temps ( VATS Delete required change using HEX editor ?? (See thread http://www.gearhead-efi.com/Fuel-Inj...C-16183247-ECM)).

Here's the only weird thing I can find using Tunerpro. At idle, it runs fine in BLM cell 16, with BLM's and Fuel trim about as expected. As it warms up, it starts to "hunt" between BLM cell 16 and 00, and immediately it runs bad as soon as it jumps to cell 00. When it hits cell 00, you can see the BLM drop to 100, and the fuel trim goes to 182. BLM's try to climb , but as soon as they hit, 110, they drop back to 100 and the climb starts over. Fuel Trim holds steady at 182. All the time it is in 00, it runs rough, and misfires. If I touch the throttle just enough to get the BLM cell to change, car goes back to running fine, and BLM's on the new cell are as they should be. If it drops back to cell 00, it reverts to BLM's of 100 and Fuel trim of 182. Eventually, if it stays in cell 00 long enough, it will stall out.

Anyone have any thoughts on this?

NOTES: Engine / trans installed in an '87 Fiero. Donor vehicle was '95 Buick Riviera. Trans is 4l60E. Using BIN BKZS ( downloaded from donor ECM). XDF file $5B 94-95 L27 L67 3.8.xdf . ADX file 5B7a.ADX

Try reading Steveo's page here.

http://fbodytech.com/tutorials/charc...er-purge-evap/

Let us know if it helps any.

Mitch

**darbysan** · 05-17-2016

Thanks Mitch. I read through Steveo's page, but don't think much of it applies to me. First, I have fully functioning CCP ( not deleted). Second, no parameters exist in the XDF I'm using for any changes to CCP, so nothing I can adjust. On the Sensor Data screen, it shows CCP Cycle at 14.84, and that number stays constant when shifting from cell 16 to cell 00 ( in fact, stayed constant no matter what cell I was in, up to cell 5).

Still searching.....

**???** · 05-17-2016

random thought, I know nothing of the mask you're running but is the o2 in a header and a one wire? maybe it's getting at idle?

has a tpi car drive me nuts once over that.

**darbysan** · 05-17-2016

Thanks for the thought on the O2. Mine is a 4-wire O2, and I can see it operating normally when the cell changes from 16 to 00, and then back. No direct affect from the O2.

It just looks to me like there is a weird value in a table that the computer is trying to process for cell 00. It processes the info normally in all cells except for 00, so that tells me the ECM is probably OK, and that the program is working as designed. Just need to see if we can figure out if a table change somewhere might make this go away???

billygraves · 05-17-2016

Have you checked for intake or S/C gasket leaks? Common. Some draw air from the bottom of the intake with slight oil consumption. Esp if the engine has the plastic carrier. The Fuel trim is 182 adding fuel.