I've got my '87 (see sig for details) running fairly well. I run 100% in open loop and that has solved many of the issues I was having. Fueling is pretty good at all conditions (verified with wideband).

However, I'm getting some minor "pops" out of the exhaust at lower rpm cruising (1500 - 2800) with very light throttle (less than 1.0 volt). What causes this? Would increasing the timing in this area help to eliminate this? I know with my cam, this "range" of driving is going to be difficult to get perfect, but I'd like to at least get rid of the pops.

Also, I get some lean pops when I let off the throttle right before DFCO. How can I eliminate these?

Thanks!
Dan

 

Check for exhaust leaks by mufflers.

 

Thanks Dominic - I should have mentioned that in my OP; no leaks in the exhaust (checked and re-checked).

 

In that case, I would bring DFCO in sooner and lower my VEs in Low MAP, and low rpm cells. I'd play with fuel first. where do you hear the popping, towards tthe back, or closer to the motor?

 

Do you mean bring in DFCO sooner as in how many seconds before DFCO is enabled, or at a higher rpm?

I've got the stock MAF set up (using a $6E mask); are you saying to decrease fuel in those areas (using MAF tables) that I experience the popping?

Tough to gauge where it is coming from, but if I had to guess, I'd say towards the middle / back.

Sorry for all the follow up questions - I really appreciate the help!

Dan

 

Running rich perhaps? I don't know how much you can advance the timing you might have to pull some fuel. I don't know much about tuning so thats my guess.

 

According to the wideband, it is running pretty close to where it should be (14.3:1 to 15.1:1), so I think I'm ok for now.

I could swear I remember reading a post about the relationship between timing and these types of exhaust "pops" or "gurgles", but can't seem to find the thread for the life of me .

 

Yes, but if you're running C/L, what are the BLMs?

 

I have it running 100% open loop now.

When previously running closed loop, the BLMs settled in at 124 in these cells.

 

If DFCO was working in C/L, you're BLMs should have been somewhere in the 160s running lean since fuel would be cutoff.

 

Interesting - in my data log, for DFCO, all BLMs and INTs went to 128 (this was during closed loop operation); injector pulse width was "0", and O2 sensor mv went to 4.44 (I guess that is the lowest possible). I am definitely getting the pops in the exhaust right before DFCO, as I can see the injector pulse widths get really low (.6 - .7). Once they go to 0, no more pops. That's why I was asking earlier about bringing in DFCO sooner as in how many seconds before DFCO is enabled, or at a higher rpm, in order to help get rid of them. But, this is all with no throttle.

I am more concerned with the pops I am getting when there is very light throttle in lower rpms. Any suggestions for that?

 

Did the O2 go to 4mv/.004volts or 4volts? OK if everything went to 128, then its in DFCO and freezes BLMs. Try taking a little fuel out at the MAF where you are at light cruise or trailing throttle. Does your mask have a Decel Enleanment table as well?

 

It went to 4.44 mv / .004 volts .

Yes - I see a bunch of decel enleanment constants, but I have not altered them at all from the stock settings.

What do you mean by "trailing throttle"?

 

Can you post a pic of the DE tables in your mask? Trailing throttle is a very light throttle as in when you are on a slight decline. Its a low MAP situation with very little TPS.

 

I'm too much of a computer dope to figure out how to post a pic of those tables, but here is what I have for DE in TunerPro (figures in " " are enterable fields, all of which are unmodified):

Decel Enlean enable if Load is <= "38"

Decel Enlean enable if RPM above "900"

Decel Enlean enable delta TPS threshold "93.75" % TPS

Decel Enlean enable delta Load threshold "245"

Decel Enlean BPW factor (Low DRP's) "1.00"

Decel Enlean BPW factor (High DRP's) "1.00"

Trailing throttle sounds like EXACTLY where I'm having the issue

 

Based on this looks like DE is basically disabled. Looks like you need a 93.5% delta in TPS change to enable DE and almost an infinite change in load.Drop those 2 say to 10% TPS and 10 load. See what happens.

 

As I was typing that out, I was thinking the same thing - thank you for confirming. I'll make those changes and see if there is a difference.

Thank you so much for your help!