Cant solve rough idle
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Im getting confused when i see over 50* adv at only 2000rpm and the knock counts dont change or increase. Dont know how to explain this. But i havent looked at enough OBD I data logs to make judgement.
Just looking at the data log i see the MAP, integrator (short term fuel trim), O2 mV output all switch at the same time and looks like timing adv does to - this is in closed loop when the O2 is controlling. They all move in step which should not be. The MAP follows throttle position and looks ok to me. The short term trim locks onto a steady O2 output. In closed loop the O2 should be swinging. I dont know why i didnt see this before. When was the last time u replaced the O2 sensor? Did u know they are a normal wear part and should be replaced 'bout the same mileage as the tires or brakes?
U can test the O2 by pulling a vac line and allowing a intake leak and u should see a lean output but u need to be monitoring the O2 output somehow - with a meter or datalog or whatever. Next u can use a propane bottle to add propane fuel the same intake leak and watch the O2 output again - it should go rich.
I know im saying 2 things here but i think the O2 sensor is the easier test here than any further ignition tests and overdue for replacement anyways. And i dont have an answer for the large timing adv - sorry. But for an O2 sensor that doesnt swing in closed loop i do - its bad.
Watch'a think?
BTW u need to update the ECM with the new injector constants when u change injectors. Did u do this? That shouldnt make all the variables lock into step though as logged here but something to correct when ready.
Just looking at the data log i see the MAP, integrator (short term fuel trim), O2 mV output all switch at the same time and looks like timing adv does to - this is in closed loop when the O2 is controlling. They all move in step which should not be. The MAP follows throttle position and looks ok to me. The short term trim locks onto a steady O2 output. In closed loop the O2 should be swinging. I dont know why i didnt see this before. When was the last time u replaced the O2 sensor? Did u know they are a normal wear part and should be replaced 'bout the same mileage as the tires or brakes?
U can test the O2 by pulling a vac line and allowing a intake leak and u should see a lean output but u need to be monitoring the O2 output somehow - with a meter or datalog or whatever. Next u can use a propane bottle to add propane fuel the same intake leak and watch the O2 output again - it should go rich.
I know im saying 2 things here but i think the O2 sensor is the easier test here than any further ignition tests and overdue for replacement anyways. And i dont have an answer for the large timing adv - sorry. But for an O2 sensor that doesnt swing in closed loop i do - its bad.
Watch'a think?
BTW u need to update the ECM with the new injector constants when u change injectors. Did u do this? That shouldnt make all the variables lock into step though as logged here but something to correct when ready.
O2 sensor is a couple of months old, Also on a 90 corvette the data comes from the ecm then goes to the ccm then to the aldl connector, from what i have read this cause trouble reading data, I dont have a teck 1 reader with the proper module, I have a tablet running ALDLdroid and have to use the adx files that are out there on the internet.
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Im getting confused when i see over 50* adv at only 2000rpm and the knock counts dont change or increase. Dont know how to explain this. But i havent looked at enough OBD I data logs to make judgement.
Just looking at the data log i see the MAP, integrator (short term fuel trim), O2 mV output all switch at the same time and looks like timing adv does to - this is in closed loop when the O2 is controlling. They all move in step which should not be. The MAP follows throttle position and looks ok to me. The short term trim locks onto a steady O2 output. In closed loop the O2 should be swinging. I dont know why i didnt see this before. When was the last time u replaced the O2 sensor? Did u know they are a normal wear part and should be replaced 'bout the same mileage as the tires or brakes?
U can test the O2 by pulling a vac line and allowing a intake leak and u should see a lean output but u need to be monitoring the O2 output somehow - with a meter or datalog or whatever. Next u can use a propane bottle to add propane fuel the same intake leak and watch the O2 output again - it should go rich.
I know im saying 2 things here but i think the O2 sensor is the easier test here than any further ignition tests and overdue for replacement anyways. And i dont have an answer for the large timing adv - sorry. But for an O2 sensor that doesnt swing in closed loop i do - its bad.
Watch'a think?
BTW u need to update the ECM with the new injector constants when u change injectors. Did u do this? That shouldnt make all the variables lock into step though as logged here but something to correct when ready.
Just looking at the data log i see the MAP, integrator (short term fuel trim), O2 mV output all switch at the same time and looks like timing adv does to - this is in closed loop when the O2 is controlling. They all move in step which should not be. The MAP follows throttle position and looks ok to me. The short term trim locks onto a steady O2 output. In closed loop the O2 should be swinging. I dont know why i didnt see this before. When was the last time u replaced the O2 sensor? Did u know they are a normal wear part and should be replaced 'bout the same mileage as the tires or brakes?
U can test the O2 by pulling a vac line and allowing a intake leak and u should see a lean output but u need to be monitoring the O2 output somehow - with a meter or datalog or whatever. Next u can use a propane bottle to add propane fuel the same intake leak and watch the O2 output again - it should go rich.
I know im saying 2 things here but i think the O2 sensor is the easier test here than any further ignition tests and overdue for replacement anyways. And i dont have an answer for the large timing adv - sorry. But for an O2 sensor that doesnt swing in closed loop i do - its bad.
Watch'a think?
BTW u need to update the ECM with the new injector constants when u change injectors. Did u do this? That shouldnt make all the variables lock into step though as logged here but something to correct when ready.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Well then thats the place to start. U have to have good data to read it or dont use it at all. I believe u can measure the O2 mV swing directly with a meter and if not moving from 100mV to 900mV while in closed loop at idle then something wrong with the O2 circuit. FYI the ECM doesnt start out in closed loop but has to warm up first so dont expect a good O2 reading w/o warming the motor up a bit. O2 sensors can get damaged just by sealing them at the wire entry location - they have to breath there.
The timing results then maybe not bad at all. Myself the 15.5* at 3000rpm when in neutral does seem low though and i would expect closer to 30*-35*.
U can do the manual test for each sensor one at a time - u already know timing numbers are low and u could try bumping the initial timing to observe results. But w/o reliable data i think its a waste of time to even look at the data log as it will take u in the wrong direction.
Good luck.
The timing results then maybe not bad at all. Myself the 15.5* at 3000rpm when in neutral does seem low though and i would expect closer to 30*-35*.
U can do the manual test for each sensor one at a time - u already know timing numbers are low and u could try bumping the initial timing to observe results. But w/o reliable data i think its a waste of time to even look at the data log as it will take u in the wrong direction.
Good luck.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
You will get error code 42 after you disconnect the EST connector to set the timing.
Set the base timing to 6°. The ECM will add approximately 14° for an total of around 20° at idle. The exact amount depends on the year (and if there is a tune in the ECM).
Set the base timing to 6°. The ECM will add approximately 14° for an total of around 20° at idle. The exact amount depends on the year (and if there is a tune in the ECM).
Cruising
Joined: Nov 2014
Posts: 12
Likes: 0
c4 runs rough at idle in park or drive
I have a 96 lt1 that has a rough idle in park and drive. I have taken it to multiple shops and everyone is scratching their heads. It has had new oem plugs and wires, fuel filter, pressurized fuel cleaning service, compression and vac lines checked, valve springs checked. Fuel injectors swapped from one position to the other, and the code did not changeto another cylinder. Only thing it shows in diagnostics is a misfire in cylinder 3. This was the case even before all the work was done. Timing and spark are reading correctly according to the mechanic.
Any ideas? Optispark?
Any ideas? Optispark?
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
I have a 96 lt1 that has a rough idle in park and drive. I have taken it to multiple shops and everyone is scratching their heads. It has had new oem plugs and wires, fuel filter, pressurized fuel cleaning service, compression and vac lines checked, valve springs checked. Fuel injectors swapped from one position to the other, and the code did not changeto another cylinder. Only thing it shows in diagnostics is a misfire in cylinder 3. This was the case even before all the work was done. Timing and spark are reading correctly according to the mechanic.
Any ideas? Optispark?
Any ideas? Optispark?
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
The code 42 is fixed, one of the 4 wires that come in through the back of distributor was shorted out on the distributor housing. She seems to be running pretty good.
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Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
I would try and help but have no experience with opti spark.
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Since I put in the new fuel pump and injectors its a lot smoother and I can idle in gear. Its still a little rough, the code 42 is fixed, that was a separate issue, My throttle body shaft is way to loose so I may try and remove the shaft and mill it out for a new bushing or purchase a new one and as far as I now the only new ones are aftermarket.
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Race Director
Joined: Jan 2012
Posts: 17,062
Likes: 166
From: United States
Have you put a meter on your IAC yet? It will not set a code, and even though the scanner will show counts, it only shows what the ecm is telling the IAC to do, not what it actually is doing..This pic shows where to test, technically same schematic.
http://shbox.com/1/iac2.jpg
http://shbox.com/1/iac2.jpg
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,280
From: Hartford WI
Have you put a meter on your IAC yet? It will not set a code, and even though the scanner will show counts, it only shows what the ecm is telling the IAC to do, not what it actually is doing..This pic shows where to test, technically same schematic.
http://shbox.com/1/iac2.jpg
http://shbox.com/1/iac2.jpg
Thread Starter
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,280
From: Hartford WI
Race Director
Joined: Jan 2012
Posts: 17,062
Likes: 166
From: United States
The datalogger shows the circuit is good as far as ecm telling IAC what to do. It will never show you what the IAC is actually dong. Many months of torture in my vette till i found shbox .
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,280
From: Hartford WI
If the meter doesnt show the correct reading, the iac is bad. Lots of people clean and adjust this item and that is when it brakes. Very fragile. It will adjust itself upon initial ignition cycling when new.
The datalogger shows the circuit is good as far as ecm telling IAC what to do. It will never show you what the IAC is actually dong. Many months of torture in my vette till i found shbox .
The datalogger shows the circuit is good as far as ecm telling IAC what to do. It will never show you what the IAC is actually dong. Many months of torture in my vette till i found shbox .
I understand all that however, how does the DVOM tell you what the IAC is doing? All you can see is that the coils are good. Remove the pintle and the coils will still be good so you don't really know how to tell other than "The coils are good or bad", right? How do you know it is actually doing what it is supposed to be doing if you all you can tell me is the coils are good?