Hi from So Cal

[jeepaddicted]

Hi, I have been reading and learning about EFI from Gearhead and have now run into a snag so I would like post my first request for help.

I have 2 project Jeep CJ's and have found some great help here.

[dave w]

Hi, I have been reading and learning about EFI from Gearhead and have now run into a snag so I would like post my first request for help.

I have 2 project Jeep CJ's and have found some great help here.

I have a CJ, maybe I can help? What kind of help are you looking for?

dave w

[jeepaddicted]

My 79 CJ7 (Chevy 5.7l TBI 1227747) recently failed the Calif. Smog test with high HC at Idle. I found that the pintle on the IAC had stuck in the TB and replaced it and now I am having trouble getting it to idle normally. I have shorted AB on the ALDL and set the base idle at 650, my final idle is set at 800 in the bin (ARJU 5.7l 700r4.bin) because the smog tech suggested a higher idle for the next test. The first startup on the idle is fine it runs at about 800rpm but the second idle run doubles the IAC count and it jumps to 1000rpm. Included are logs of each run. The only hack enabled is spark. Thanks for any feedback.

[dave w]

I'll look at the data logs soon, but might be a day before I can post back with feedback. What I'm thinking...I'll look at the IAC counts maybe something there is clue? I'll look at the .bin and see what the idle settings are. I'm wondering if your using a Park / Neutral switch? I'm wondering if your using a VSS? On some .bin files, I've set the all idle tables to the same idle RPM, because the Park / Neutral switch and VSS were not being used. I'm thinking you have a catalytic converter? I'm wondering if you have a single wire O2 sensor? I'm wondering if you have headers?

dave w

[jeepaddicted]

I'll look at the data logs soon, but might be a day before I can post back with feedback. What I'm thinking...I'll look at the IAC counts maybe something there is clue? I'll look at the .bin and see what the idle settings are. I'm wondering if your using a Park / Neutral switch? I'm wondering if your using a VSS? On some .bin files, I've set the all idle tables to the same idle RPM, because the Park / Neutral switch and VSS were not being used. I'm thinking you have a catalytic converter? I'm wondering if you have a single wire O2 sensor? I'm wondering if you have headers?

dave w

Hi Dave,

You helped me tune my 72 CJ5 304 several months ago it is running great!

I increased the idle as suggested by the smog tech. I have included the original bin and my modified bin for you to compare.

Yes there is a P/N switch (Dakota shift indicator) as well as a VSS, catalytic converter, heated O2 sensor and CARB approved Edelbrock headers.

Thanks for taking time to look at the logs.

Bill V

[EagleMark]

My 79 CJ7 (Chevy 5.7l TBI 1227747) recently failed the Calif. Smog test with high HC at Idle. I found that the pintle on the IAC had stuck in the TB and replaced it and now I am having trouble getting it to idle normally. I have shorted AB on the ALDL and set the base idle at 650, my final idle is set at 800 in the bin (ARJU 5.7l 700r4.bin) because the smog tech suggested a higher idle for the next test. The first startup on the idle is fine it runs at about 800rpm but the second idle run doubles the IAC count and it jumps to 1000rpm. Included are logs of each run. The only hack enabled is spark. Thanks for any feedback.

High HC is unburned fuel and usually a spark issue in a sound engine, could also be vacuum leak, weak cylinder or 2, burnt valve on unsound engine.

If smog tech suggested higher idle it is likely not very high HC? His suggestion of raising idle would work because of hotter Cat.

But your IAC count is higher at low RPM and lower at higher RPM, opisite of what you stated and wrong? I'd do the minimum air adjustment again, but cross A and B, turn key on, disconnect IAC wire and leave off, turn key off, remove A and B jumper (or idle and spark are wrong) and then start vehicle. Do all this totally warmed up and set RPM to 100 below Idle setting in bin. Turn engine off, reconnect IAC, clear codes and restart to check IAC counts.

Or cheat and open throttle blades 1/4 turn to lower IAC counts. Turn engine off for minute (to reset TPS% back to 0) and restart to check IAC counts. 10 to 30 is great.

Also second log of 1000 RPM idle, the IAC steps drop but stop at 39. I've seen this before and the paremter "IAC - Position vs Temp" is what is hanging it up, cut that table in half and recheck IAC count and idle RPM. Rinse and repeat... or close throttle blades so IAC count is higher and works again to control idle, this works but more open throttle blades and lower IAC count is better.

Your going Closed Loop fast so the heated O2 is working great.

Where is the O2 sensor in those headers? Shorty headers I assume as they CARB approved and legal in CA. Point is the O2 sensor is still not in exhaust manifold and moved farther downstream, so adding 5-10% INT delay may help.

Lowering the O2 - Idle AFR Bias Value of 109.00 mvdc to 0 will lean out idle. I'm assuming the HC test is at idle? Rasing timing advance will also help reduce HC Idle and above which may be what this Jeep engine needs?

HTH!

[dave w]

I've looked at the .bin files and data logs. I'm thinking I'd try increasing the original idle speeds by only 50 RPM's not by the 225 ~ 275 RPM's I'm seeing with the compare feature of TunerPro. I think I'd try setting the Fuel Number to 129. The logs show the idle BLM's are 128 in closed loop. Maybe advance the distributor timing from Zero degrees for 2 degrees BTDC. I would only use the modified .bin and advanced timing to pass emissions.

dave w

[jeepaddicted]

High HC is unburned fuel and usually a spark issue in a sound engine, could also be vacuum leak, weak cylinder or 2, burnt valve on unsound engine.

I hadn't considered that since it is a recent rebuild, I did replace the plug wires, distributor cap and rotor. Checked for vac leak with propane and found none. I will do a compression test next.


If smog tech suggested higher idle it is likely not very high HC? His suggestion of raising idle would work because of hotter Cat.

Thanks for explaining this all he said is that it should help.


But your IAC count is higher at low RPM and lower at higher RPM, opisite of what you stated and wrong? I'd do the minimum air adjustment again, but cross A and B, turn key on, disconnect IAC wire and leave off, turn key off, remove A and B jumper (or idle and spark are wrong) and then start vehicle. Do all this totally warmed up and set RPM to 100 below Idle setting in bin. Turn engine off, reconnect IAC, clear codes and restart to check IAC counts.

Wow, you are right I mixed them up. I will do the minimum air adjust and data log again as you suggest.


Or cheat and open throttle blades 1/4 turn to lower IAC counts. Turn engine off for minute and restart to check IAC counts. 10 to 30 is great.

I will will try this too.


Also second log of 1000 RPM idle, the IAC steps drop but stop at 39. I've seen this before and the paremter "IAC - Position vs Temp" is what is hanging it up, cut that table in half and recheck IAC count and idle RPM. Rinse and repeat... or close throttle blades so IAC count is higher and works again to control idle, this works but more open throttle blades and lower IAC count is better.

Should I change the "IAC - Position vs Temp" before I do the items listed above?


Your going Closed Loop fast so the heated O2 is working great.

Where is the O2 sensor in those headers? Shorty headers I assume as they CARB approved and legal in CA. Point is the O2 sensor is still not in exhaust manifold and moved farther downstream, so adding 5-10% INT delay may help.

O2 sensor is on the drivers side just above the 3 bolt collector plate which is where the sensor was on the stock manifold.


Lowering the O2 - Idle AFR Bias Value of 109.00 mvdc to 0 will lean out idle. I'm assuming the HC test is at idle? Rasing timing advance will also help reduce HC Idle and above which may be what this Jeep engine needs?

I will make change the Bias Value to 0 with the other changes you are suggesting and burn a chip just for smog. The max allowed HC is 120ppm and the test failed at 350ppm. What is interesting is that when I had the engine swap tested at the Smog Referee station 2 years ago they did not do a stationary idle test but did a 15mph dyno test at 1570rpm and it passed at 91ppm. It is not a Jeep engine but an 89 Chevy 350 TBI. Do you think raising the timing advance might help HC on the 350? Thanks for your help Dave.

[jeepaddicted]

I've looked at the .bin files and data logs. I'm thinking I'd try increasing the original idle speeds by only 50 RPM's not by the 225 ~ 275 RPM's I'm seeing with the compare feature of TunerPro. I think I'd try setting the Fuel Number to 129. The logs show the idle BLM's are 128 in closed loop. Maybe advance the distributor timing from Zero degrees for 2 degrees BTDC. I would only use the modified .bin and advanced timing to pass emissions.

dave w

Thanks for the info and your time looking at these, I will get back to you when I get a chance to make the changes and datalog.

Bill V.

[EagleMark]

Should I change the "IAC - Position vs Temp" before I do the items listed above?

May not have to if idle was just increased 100, you were fine first log. But Yes if you open up throttle blades (which helps fuel mix with air) or it will stick again at 39 or? Like it is now.

I will make change the Bias Value to 0 with the other changes you are suggesting and burn a chip just for smog. The max allowed HC is 120ppm and the test failed at 350ppm. What is interesting is that when I had the engine swap tested at the Smog Referee station 2 years ago they did not do a stationary idle test but did a 15mph dyno test at 1570rpm and it passed at 91ppm. It is not a Jeep engine but an 89 Chevy 350 TBI. Do you think raising the timing advance might help HC on the 350?

120ppm to 350ppm is not that big, raising idle alone like Dave said by 50-100 may be enough, 2 degrees timing at idle may be enough, reducing Idle Bias may be enough.

That said I would raise idle 100, add 2 degree timing to idle area then back to making sure throttle blade min air is set so IAC controls idle whether it needs change to "IAC - Position vs Temp" or not would be determined then.

There'd be nothing wrong with leaving it like this...

[jeepaddicted]

High HC is unburned fuel and usually a spark issue in a sound engine, could also be vacuum leak, weak cylinder or 2, burnt valve on unsound engine.

If smog tech suggested higher idle it is likely not very high HC? His suggestion of raising idle would work because of hotter Cat.

But your IAC count is higher at low RPM and lower at higher RPM, opisite of what you stated and wrong? I'd do the minimum air adjustment again, but cross A and B, turn key on, disconnect IAC wire and leave off, turn key off, remove A and B jumper (or idle and spark are wrong) and then start vehicle. Do all this totally warmed up and set RPM to 100 below Idle setting in bin. Turn engine off, reconnect IAC, clear codes and restart to check IAC counts.

Or cheat and open throttle blades 1/4 turn to lower IAC counts. Turn engine off for minute (to reset TPS% back to 0) and restart to check IAC counts. 10 to 30 is great.

Also second log of 1000 RPM idle, the IAC steps drop but stop at 39. I've seen this before and the paremter "IAC - Position vs Temp" is what is hanging it up, cut that table in half and recheck IAC count and idle RPM. Rinse and repeat... or close throttle blades so IAC count is higher and works again to control idle, this works but more open throttle blades and lower IAC count is better.

Your going Closed Loop fast so the heated O2 is working great.

Where is the O2 sensor in those headers? Shorty headers I assume as they CARB approved and legal in CA. Point is the O2 sensor is still not in exhaust manifold and moved farther downstream, so adding 5-10% INT delay may help.

Lowering the O2 - Idle AFR Bias Value of 109.00 mvdc to 0 will lean out idle. I'm assuming the HC test is at idle? Rasing timing advance will also help reduce HC Idle and above which may be what this Jeep engine needs?

HTH!

Did everything suggested relative to the idle and the IAC still got stuck at 39. I disconnected the p/n wire the tag went from Park to Drive and now it at idle and IAC count of 22. What's up with that and how should p/n work. Thanks again for the help.

Bill V.

[EagleMark]

Just a guess but you have a Painless harness and read the instructions?

Your log was idle only so I didn't notice. Those wires should be wired into the Jeep shifter. There is IAC movement to smooth the transition from Park to Drive etc... If there's no way to do this then leave Org/Blk open so ECM thinks it's in drive. There is very little IAC idle control in Park/Neutral, lots more in drive.

Although the Painless wiring instructions say to wire the Org/Blk and Blk/Wht together if not using a VSS? They should never be wired together with or without VSS. Open so it's in drive or to a park/neutral switch so the ECM knows the difference.

[jeepaddicted]

I think I understand why the IAC stopping at 39. With the engine warm and a start-up in park (P/N grounded) the ECU locks the IAC counts at 39 and when you put it drive (P/N open) it drops below 39 and stays that way (P/N or drive) until the next restart.. I would assume that the developers had their reason for doing this with an automatic since someone would drive very soon after starting the engine anyway. Is there a program setting that would change this?


I will have it smog checked tomorrow and let you know how it goes. Thank you for all the help!


Bill V.

[gregs78cam]

P/N to D IAC counts should go up due to the increased load of trans in gear.

[EagleMark]

I think I understand why the IAC stopping at 39. With the engine warm and a start-up in park (P/N grounded) the ECU locks the IAC counts at 39 and when you put it drive (P/N open) it drops below 39 and stays that way (P/N or drive) until the next restart.. I would assume that the developers had their reason for doing this with an automatic since someone would drive very soon after starting the engine anyway. Is there a program setting that would change this?


I will have it smog checked tomorrow and let you know how it goes. Thank you for all the help!


Bill V.

Well no, read response to Greg below

There are lots of IAC settings but none will help in P/N. IAC position when turned off parks at 145, when started decays to IAC - Position vs Temp table where it is adjusted for AC, Baro and ? But because there is not full IAC logic in P/N it can hang high. This is where this table being lowered helps. Nothing helps more then a P/N - Drive switch hooked up or left in Drive. I don't know why GM would not use full IAC logic in both? Probably emmissions better if idling higher?

P/N to D IAC counts should go up due to the increased load of trans in gear.

Yes, if idle is at desired idle RPM setting, like fully warmed up and put in D then P, but not in these old C3 ECMs and surely not while warming up. Even after fully warmed up they will idle higher then Desired Idle setting if in P/N. So you can't really use IAC counts as a tool there.

Newer C4 PCM like $0D is way better!

Idle IAC control in these is really limited in P/N, I think RBob described the algorithm once as P/N IAC is a high and low so it sticks somewhere in middle based off IAC - Position vs Temp paremeter. No other IAC Logic like desired Idle RPM. But fully active IAC logic in Drive.

You know what? I just figured out why people have so much trouble getting Min Air Setting done. It's always done in P/N, but when done and checking should be done in D. They set it correctly but when IAC is plugged back in Idle and IAC counts are not correct because of the P/N or D IAC logic!