Bogging after Coasting
 

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?

Re: Bogging after Coasting
 

Check map sensor hose and make sure it's correct one - hard plastic hose with rubber ends. I've seen this piece substituted with rubber vacuum hose. This will work fine for awhile until the rubber soften. Under deceleration, increased vacuum will collapse the hose sending wrong vacuum reading to the MAP sensor.

Re: Bogging after Coasting
 

Who modded the calibration?

Re: Bogging after Coasting
 

I've a new oem map hose on the car. It's all good

Re: Bogging after Coasting
 

Marc did the cal.

Re: Bogging after Coasting
 

Sounds familiar...

Mine is fully ported, SW headers n X-pipe, POS Magnalfow muffs, sans secondaries (see my signature).

Sometimes...not every time...when I coast down or down-shift too, especially during some aggressive driving scenarios, it sometimes will cut out on me as well. And, as you pointed out, temperature (i.e., fully warmed up) is a factor.

If I have the clutch disengaged and am decelerating when it happens, the motor will stop. However, if the motor stalls with the clutch engaged and in gear (i.e., such as when downshifting prior to a turn), a quick blip of the throttle and suddenly it's "all good again"!

I don't recall if it had this behavior prior to the mods/porting, etc. - that was 7 driving seasons ago. But, I definitely noticed it after completing the porting and tune, as well as some hunting at idle with the clutch depressed as I'm rolling to a stop. (Soon as speed reaches ZERO, the hunting stops.)

Dominic is always tweaking his tune - I think partly because he enjoys the challenge of ever-so-fine tuning his LT5. But, none the less he seems to have achieved success and feels he has a handle on the issue. I may give him a shot next season and see what he might be able to do for my 90.

However, in the mean time,I've learned to anticipate the quirk, and deal with it should it occur - almost w/o paying attention much at all: I'm living with it...for now.

All this said, Ami's 91 ZR-1 does NOT display this phenomenon (yet). And, in addition to mine, the "TURQ MONSTER" has also been blessed with Pete's cams and tune: difference in chip and/or tune Perhaps?? We'll see...

Re: Bogging after Coasting
 

Paul,
Yes, my car motor is fully ported as well and does exactly what you describe. I notice it at BG at high RPM and decelerating on a down hill slope and the motor will just die but like you said, a simple blip on the gas and it cleans up. I have chalked it up to the tune. Mark did my Chip base on the modes I gave him, but this can probably be cleaned up with a formal tune.
Rich

Re: Bogging after Coasting
 

Pretty interesting about the MAF hose ...When I was putting mine back together after the porting,one of the rubber ends came off, could not find it....Of course I improvised and cut a piece of hose that fit really well....

Did not know that could lead to maybe a glitch if you want to call it down the line....I will order the part from Jerrys and replace....

Interesting...

Re: Bogging after Coasting
 

2012 (I think...) drive to Carlisle my car kept stalling out as I slowed to a stop. I ran it by Marc at Carlisle and he pulled my MAP hose which was pretty soft from fuel vapor and heat. Replacement fixed that issue.

Re: Bogging after Coasting
 

Paul,
Your issue does sound similar, but mine never stalls. It just hesitates bad as I tip in the throttle after decel. If I mash the throttle, it'll jolt back to normal, almost like a really bad shift. I'm now wondering if it in fact can be tuned out. I've got a military PCS coming in a few months, and I'll need to get this fixed before then. Since I'm in CA now, I'm looking at a mid (CO) to cross-country (VA) move.

Re: Bogging after Coasting
 

Ummm.... I'm not sure it isn't the same thing. When I first noticed it, it would bog on throttle tip-in, and sputter and jerk a bit before catching and running normally again.

Now, having lived with it a while, I'm able to detect it before I have to get back on the "gas" and take steps to clear it before I actually experience the bog.

It's in the tune, I'm pretty sure. Fortunately, it doesn't occur every time or it would have risen to a much higher priority by now. Just a nagging little irritation is all. Nothing as bad as a beautiful girlfriend with a chipped front tooth might be! :eek:

Re: Bogging after Coasting
 

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

Re: Bogging after Coasting
 

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?

Re: Bogging after Coasting
 

It's not injectors. You're taking in more air. Need to adjust fuel as 1 parameter.

Re: Bogging after Coasting
 

Oh ok. That's good. Is this something that can be tuned out long distance?

Re: Bogging after Coasting
 

Not a fan of long distance tuning. First of all, I would want to make sure that everything is mechanically correct. Things like Min Air, TPS v, . Would want to do a scan just to see that everything tests out. How far is mike100 from u in CA?
I have a 92, so I have a number of calibrations I did for it at a similar level of mod.

BTW, I notice u are using 2piece rotors w Z06 brakes. I am just now upgrading from the stock Z06 rotors to 2 piece Paerformance/AFX rotors. Any thoughts or impressions?

Re: Bogging after Coasting
 

Looks like he's about 4 hrs 15 mins away. Kind of far. I could do a tunerpro log.

I never had stock Z06 rotors on the car, so I can't compare to those. They're pretty light ( lighter than stock ZR-1 rotors I think) and stop the car well. No fading so far at all and they seem to be wearing really well. With hawk HPS pads I get a slight squeal very infrequently. I painted mine off of the sweep area so I don't get any rust and even that has held up well. In short, definitely worth it.

Oh, and one issue I had was that the bolts on the rears rubbed the outer rim of the street shop adapter. A bit of time with the file took care of that.

Re: Bogging after Coasting
 

If you could do a TP log and send me a csv file, that could help. Do a log w just key ON to get the nominal sensor values, then a log of a situation where the motor shuts down. Do a decel, then tip in of accelerator.

Re: Bogging after Coasting
 

Sure, I can do that sometime in the next few days. Thanks.

Re: Bogging after Coasting
 

I have a similar setup as Paul with the Haibeck 350/510 HP package. I have never experienced regular stalling or stumbling but once in a while I get a little stumble on take off, almost as if the engine were getting a little flooded. It only happened when I have been say, coming out of a parking lot in which I have the old timer's habit of blipping the throttle (as if one needed to clear the plugs on a 68 Hemi Roadrunner). I think it was confusing the computer. It always cleared up immediately, maybe in 100 feet of driving. Marc suggested that behavior like that is often related to O2 sensors that are not 100%. He reminded me that he had not changed them when he did the work so they are 20 years old, although with only 30k miles on them. I have obtained some new ones but haven't yet installed them, and actually have not experienced the problem during much of the past year. Probably will put them in this spring just in case.--Bob

Re: Bogging after Coasting
 

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.

Re: Bogging after Coasting
 

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.

Re: Bogging after Coasting
 

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.

Re: Bogging after Coasting
 

Holy rheostat! Good point!:cheers:

Re: Bogging after Coasting
 

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?

Re: Bogging after Coasting
 

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

Re: Bogging after Coasting
 

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

Re: Bogging after Coasting
 

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

Re: Bogging after Coasting
 

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

Re: Bogging after Coasting
 

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.

Re: Bogging after Coasting
 

Sure. Call me at work sometime at 805-685-6864.

As for the injector, get in touch with Jerry and see if the injectors he sold you flow the same as stock.

Just curious...what is a "Banski" suspension?

Re: Bogging after Coasting
 

Thanks. Will do.

They are from Banski Motorsports: anodized aluminum rear trailing arms, toe rods, and camber rods, all with heim jointed ends.

Re: Bogging after Coasting
 

An old thread I know. I’m curious, was this issue ever resolved and if so what was the cause and solution?
H
:cheers:

Re: Bogging after Coasting
 

Re: Bogging after Coasting
 

That used to be my car... I sold it to him. I never heard from him again... Car was in really nice shape when it left my garage.. I think he sold it or traded it in. I was searching for it one day and saw it on a private lot someplace... Lost track of it since. :neutral:

Re: Bogging after Coasting
 

Interesting, he still shows as a member, which means he must have re-upped recently.
H
:cheers:

Re: Bogging after Coasting
 

Hmmm.. I wonder whats up... nice kid for sure. I had hoped to hear from him again at some point... kind of gave up when I saw it on the site where it was for sale...I know it was the same car because of the wheels and the suspension parts were pictured.... and VIN #

I bought the car from a guy in Tennessee name Perry... cant recall his last name right now.... I put the Samco hoses, SW headers, B&B exhaust and genuine Chrome A Molds I bought from a forum member on it and new injectors and coils, and a reseal of the top end when I had it. Jeff Flint got me all the parts I needed at the time... I really liked him allot as well... I dont know where he is currently. Cool guy though.

Re: Bogging after Coasting
 

I still get the bogging after coasting and stalling when coming to a stop occasionally. Although the car ran good, it was more pronounced on my 1000k mile trip to LA. last week at lower evaluations and higher temps. After I returned I replaced the injectors and coils, this was previously planned, and I’m now finding this condition a bit more often here as well. In doing some research I found this interesting piece from an old 2014 post by Bob, Warp_Ten with a reply from Mark Haibeck. I thought Marks reply was interesting. I’m going to doing more datalogging here shortly. Keeping in mind bogging and stalling could be two separate issues.


“Craig, I ran into the same problem on my 95 about a month or two after Marc Haibeck did his 510 package for me. I remember him attaching his computer to the OBD port and making a physical adjustment near the throttle in the front of the engine but did not recall precisely what he did. So I asked him and he responded with the following; hope this helps:

Hi Bob,

The adjustment that we made is the, "idle air flow". Basically the air flow through the throttle body at closed throttle needs to match the table that the calibration chip uses to control the IAC servo motor. Engine's with stock cams can use the OE table values. The OE IAC count at idle with a hot engine is 10 IAC servo steps. On your engine the IAC count was 30 at idle. That's because my larger 63 mm throttle body is tighter and leaks less air than the OE throttle body. There is another concern, that the IAC count could go to zero. Then the idle speed would go too high. I initially left the IAC at 30 because running out of counts is a more common problem than die out if the IAC count is not perfect. After your engine exhibited the die out problem. I adjusted the primary throttle plate stop screw to open the throttle until the IAC count on the scanner was 10.

An engine with big cams might idle at 850 rpm. Because of the additional air flow requirement, the IAC count is typically 50. In that case the table in the calibration chip needs to be adjusted to what the engine wants, that is 50.

When I figured this out ten years ago I probably spent 20 hours analyzing data to understand it. At first one might think that the problem is related to fueling or spark advance. I spent most of the time determining that I was barking up the wrong tree.

Regards, Marc

Re: Bogging after Coasting
 

Yeah Marc is always good for excellent advice and explanations. As noted, I had the problem after the 510 package was done and he fixed it right up when I stopped over for lunch one day.--Bob

Re: Bogging after Coasting
 

I’m going to be giving this method a try today or tomorrow. After I installed the Injectors and coils last week the IAC count was at 29. After resetting the IAC motor I got it down to 16. I can’t imagine it’s that critical but Mark certainly knows a heck of a lot more than I do.
H
:cheers: