Bogging after Coasting

[Paul Workman]

Originally Posted by Scrrem

Paul,
Did Marc H. do your chip by chance?
Rich

Yes, Marc did the open loop/dyno tuning. But, honestly I think the issue is maybe a "closed loop" issue. And, frankly I don't know if he had time to do any closed loop tweaking.

[Paul Workman]

Originally Posted by Dmod81

Ok, yep, it is the same. Mine seems to do it every time I get back on the gas though. What injectors do you have?

I'm running the Accel 150821s, right out of the box.

Dominic did an article and gave a talk at BG on the finer points of tuning. In it I believe he talked about "preset" and the affect on idle, among other things.

I don't know if he's experiencing the "bog" issue - we'd have to ask him. But, I can tell you that he has the smoothest idling, fully ported and I/E cammed LT5 I've ever heard. Sweet.

[secondchance]

Just in case - connect a volt meter to TPS, as if setting idle, and have someone slowly push the gas pedal as you watch the voltage increase. I had a TPS fail partially and the symptom was hesitation at about 5% throttle position. If you see voltage increase, sudden drop, followed by steady increase again it's TPS failure.
With this type of failure, under rapid throttle opening TPS will go past the damaged part of the potentiometer so fast there will be no stumbling. Slow throttle opening will confuse the ECM when the TPS voltage drops suddenly resulting in hesitation until past the damaged part of the winding.

[Paul Workman]

Originally Posted by secondchance

Just in case - connect a volt meter to TPS, as if setting idle, and have someone slowly push the gas pedal as you watch the voltage increase. I had a TPS fail partially and the symptom was hesitation at about 5% throttle position. If you see voltage increase, sudden drop, followed by steady increase again it's TPS failure.
With this type of failure, under rapid throttle opening TPS will go past the damaged part of the potentiometer so fast there will be no stumbling. Slow throttle opening will confuse the ECM when the TPS voltage drops suddenly resulting in hesitation until past the damaged part of the winding.

Holy rheostat! Good point!

[XfireZ51]

Originally Posted by Paul Workman

I'm running the Accel 150821s, right out of the box.

Dominic did an article and gave a talk at BG on the finer points of tuning. In it I believe he talked about "preset" and the affect on idle, among other things.

I don't know if he's experiencing the "bog" issue - we'd have to ask him. But, I can tell you that he has the smoothest idling, fully ported and I/E cammed LT5 I've ever heard. Sweet.

No, there's no bog. A"flat spot" on tip-in could require adjusting the AE pumpshot, just like a carb. Transition from decel to accel can be tricky, and you really want to make sure that the calibration doesn't have a lot of "choppiness" to it. You do some "smoothing" of the spark and fuel tables. That's a bit tougher w cammed motors because the transitions are more abrupt. So it takes time and gas to have a cammed motor behave more like a stock one. In the end, you give the motor what it wants.
Definitely make certain, as second chance suggested, ur TPS doesn't have a null spot. Usually right at the beginning since that's where the throttle sits for the major part of the time.
You should also note what the temps are when this happens, both ambient and coolant. Any chance you also moved the MAT sensor?

[Dmod81]

Good points guys. I did check the tps with my tech1. Seems good and it's new but I'll check again to ensure I haven't missed anything. I also put in a new MAT sensor when I first got the car back together and the output of that seems normal as well. I'll look for the exact air and coolant temperature that the issue starts the next time I have it out

[XfireZ51]

I was asking about MAT to see if you had relocated it to front of radiator.

[Dmod81]

Oh ok. No, it's still on the air horn.

[Hib Halverson]

I know I'm coming onto this thread a bit late but, I'd like to take a little different approach.

Originally Posted by Dmod81

I'm still having the problem with bogging on throttle after coasting. This started after I had the intake ported and removed the secondaries. It seems to not happen until the car gets hot (fully warmed up in the 190s). What happens is when I let off the throttle and coast, the o2s read full rich. When I get back on the throttle, they go to full lean and the car feels like it has no power and bucks. After a few seconds of that, it starts to clear up and drive normally.

Everything seems to check out. I've replaced the pumps (was getting instant leak down), fuel filter, o2s twice (though it might have been the issue), coils (I had a miss that the first set fixed, I thought maybe one was breaking up under heat. Second set had no change), wires, plugs twice, injectors (manual pointed to a slight leak after pumps replaced. FICs installed now), tps, iac, full exhaust (old exhaust had many leaks from bad welds and was kludged together).

Could it be that dfco is not enabled? Or an ECM problem?

First of all, in reading the OP carefully, based on the symptoms the OP posted, especially his comment about the O2Ses reading way rich, we can assume that under decel., rather than DFCO working and the engine going way lean, the engine is way fat.

After a long period of coast down, that would tend to load the motor up pretty bad so it's perfectly understandable that once loaded up "pig rich", on tip in, the engine is going to bog, but it's bogging not because of a momentary lean spot, it's bogging because the motor is big time fat. That's why, the engine runs well after a momentary "cleaning out.".

My suggestion would be to find out why the engine is going rich on coast down. I wouldn't bother with fuel pumps, O2S replacements, wires, plugs and all the other stuff that's been thrown out there in this thread because I don't think they are related to the problem.

Apparently, you have a scan tester. If it's one which logs data, run a "snap shot" which covers the period just as you step back into the throttle. Look at your O2Ses along with injector pulse width, fuel trims and TPS and see what those things are doing.

You mentioned you have aftermarket injectors...are they the same flow rate as before?

Finally, I see your on Lompoc. I'm in Goleta. If you don't have a data logging scanner, bring the car down here and we can use mine.

[Dmod81]

I finally had a chance to look at the car today. As I was driving the car around before I had the scanner hooked up the bogging issue was evident. When I got home I took a scan at hot idle to capture those parameters. Sometime as I was starting and restarting the car, a code 43 was set, which cleared on the next startup. I then went for a long drive to get a scan of the bogging issue, for the life of me, I could not get it to happen. I am dumbfounded.

Hib, to answer your question, I'm pretty sure the injectors are the same flow rate, I got them from jerry's. Since you are knowledgeable, and if you are willing, would it be possible sometime for me to come down there for you to take a look at the car and how it's running? Even if the issue doesn't creep up again (though I can't belive that it won't), I think it might be good to get another opinion on how the car is running before I have to drive a long distance when I move to a new base this summer.