Slight surging while decelerating / coasting

[stuntmanmike]

Hey guys, noticed that my 90 tends to "surge" slightly when coasting and decelerating in gear, happens in any gear around 2400 rpm and again around 2200 rpm. It's usually accompanied by some light popping of unburnt fuel in the exhaust. (I have a borla cat back and radio doesn't work so I'm listening closely!) Above 3000 rpm car has a smooth, linear decrease in engine speed and seems that the computer or some sensor may be ever so slightly increasing RPM or changing timing or something below 3000 rpm?

Runs very smoothly at idle and no issues at all when on the gas. The car has replaced injectors and I put a Haibeck chip in last weekend...but pretty positive the car was doing this before chip went in. (it is nice to not have the CAGS and notice a quicker return to a lower idle!)

I'm new to ZR1s, is this normal or do you think something is up?

[S.hafsmo]

I've got a similar issue on mine while decelerating. Seems it cannot always deside whether to engine brake (cut fuel) or just coast/idle, which gives a slight jerking sensation. Also with Marc-chip, but I also believe this was present before.

[appelen]

My 90 does it as well, not worrying to much about it.


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[XfireZ51]

Is this w closed throttle? In gear? What about free wheeling decel?

[S.hafsmo]

Closed throttle, in gear. At lest in my case. Also in the transition between closed and slightly applied throttle.

[Young1]

My 91 yet has it slightly. Marc's chip lessened the surge for me. The stock chip was annoying in the mountains.

[tpr60]

I to have this surge. It all started after changing the stock exhaust to a flow master. I had the luck to sit next to Dave McClellan at a Corvette awards dinner decades ago and asked him about the surge. Seams the after market low back pressure allows the surge to be more pronounced when the computer tries to control idle on a coast down. Nothing to worry about, or go back to a stock exhaust system to hide the surge.

[appelen]

I installed a Corsa system and I think it might have increased at bit after that, but it is a bit louder maybe that is that I hear it more now. The better sound is worth it to me


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[Paul Workman]

My 90 started the rhythmic surging immediately after installing the SW headers and the necessary tune (Marc's chip). (Best description would be as tho the rpm was following a sinusoidal or smooth wave pattern, peaking ~ every 2± seconds, and @ ~200-300 rpm.) However, it is minor and only when coasting either in neutral or with the clutch depressed. No surging if engine braking, however. And, once (practicality) stopped, it quits.

I don't know if it is related, but after first starting the (cold soaked) engine when the outside temp is below ~ 60ºF, the engine will surge at the same cadence as (above described coast down). The duration and the depth* of the cycling varies; both increases the farther below ~60ºF the engine was at start up.

*The depth of the cycling when recovering from cold soak is typically as much as 1000 rpm, ranging from ≤ 500 to as much as ~1500 rpm. On rare occasion, the motor rpm will dip to the point of cut-off and have to be restarted.

Just another tid-bit, for ppl like Dom who might be reading, a very light - barely touching - throttle pressure and the rhythmic surging stops. When I asked Pete about it, he suggested I turn the TB idle air screw clockwise about 1/4 turn and reset the TB voltage to 0.4. My idle now is about 850-900 rpm, but the depth of the cycling is diminished significantly. (Now it is only a minor annoyance, but doesn't really cause any other issue besides annoying me a little.)

BTW, Ami's 91 with cams does NOT surge/hunt. But, then her idle is set around 950-1000 due to the cam overlap. Maybe that is masking the surging it may otherwise have?

However, far as my 90 surging goes, it's innocuous enough to fall below the radar (for now). I've "other fish to fry" right now...like Pete's 391 upgrade perhaps?? :dancing

[XfireZ51]

I’ll bet that if u have a fairly stock calibration and have ur car freewheeling down to a stop, that the surging stops at 5mph.

[stuntmanmike]

Closed throttle, in gear. At lest in my case. Also in the transition between closed and slightly applied throttle.
Exactly, closed throttle in gear. OK cool, seems like nothing is wrong with the car if others experience this! Thanks

[Paul Workman]

I’ll bet that if u have a fairly stock calibration and have ur car freewheeling down to a stop, that the surging stops at 5mph.

Ya know...I just realized that I also converted my FW to a Fidanza at the same time I installed my SW headers...when the surging first appeared. Hmmm....

NOT intending to hijack the thread, but my Z surges on decel a little too, and the Fidanza FW thing is just another "potato" for the stew pot!:icon_scra

[S.hafsmo]

Mine is all stock clutch/flywheel wise. But some monkey amongst the previous owners did cut away the resonator to make way for nasty welding and straight pipes (I see most others has a cat-back or more).

And the issue isn't really when coasting to a stop, but when letting off the throttle due to a downhill descent or any similar reason you'd want to slow down a bit (annoying people in the way, for instance).

[jss06c6]

My '91 had a "hunting" rpm upon deceleration with clutch in and Fidanza FW. Like Dom said mine went away at about 3-5 mph. I changed back to dual mass setup and the "hunting" has all but vanished. Nothing else was changed. Just a data point from my experience.

Since the engine is unloaded with clutch in, the anomaly is tied to vehicle speed and I would guess could be addressed in the tune. My situation wasn't bad enough to chase in my tune. This was present with both Marc's tune and my revised tune. Never had stock tune loaded to compare.

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[XfireZ51]

My '91 had a "hunting" rpm upon deceleration with clutch in and Fidanza FW. Like Dom said mine went away at about 3-5 mph. I changed back to dual mass setup and the "hunting" has all but vanished. Nothing else was changed. Just a data point from my experience.

Since the engine is unloaded with clutch in, the anomaly is tied to vehicle speed and I would guess could be addressed in the tune. My situation wasn't bad enough to chase in my tune. This was present with both Marc's tune and my revised tune. Never had stock tune loaded to compare.

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It comes down to this. When you play w the LT5 configuration, the stock tune is "built" to manage the motor as is. Change that and the values of the parameters end up overdoing the compensations that are built in. Enhancing fuel and airflow etc. really requires a toning down of the tune if that makes sense. Otherwise the stock tune will compensate to the level of de-stabilizing the motor. So, as an example, the stock cal will reduced timing by "x" if idle is too high. On a modified motor, you want to reduce the amount of timing taken out to achieve this, otherwise the stock reduction can kick in the stall saver and now you have a see-saw idle.
In the case of an oscillating free-wheeling idle, one thing to modify is by bringing in Closed Throttle spark advance sooner rather than the stock 5mph.

[jss06c6]

Had not looked at the Closed Throttle Spark Advance Dom.. I don't have an issue but will look at the value in my tune. Thanks!

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[rkreigh]

try tuning the DFCO the stock car calibration cuts the gas for mileage and this can lead to some slight rubber banding and bucking on decal.


if you have a light flywheel the loss of decal intertia has an impact on the smoothness as well


it's not a problem. and tuning can smooth this out in many cases unless you swapped the flywheel and then it's much trickier IMHO

[BurnRubber]

My car is bone stock with only 15000 miles and it sometimes hunts on clutch in and engine decelerating. Sounds like there may be some hiccups in these speed density computers.

[tiegsd]

I have the same minor "surging" in gear during decel. My 90 is stock other than Haibeck chip. Always smooth otherwise in gear, figured it was just normal adjustments by ecu. Feels a bit like my MV Augusta motorcycle when the compression release kicks in on closed throttle.

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[stuntmanmike]

Drove the Z for 200 miles this weekend and found myself putting car in neutral more than I'd like to avoid this phenomenon. The car rips when on the gas.

This is a California car and when I put the Haibeck chip in I didn't remove the old one, was a "piggy back" situation I believe, wonder if CA-delivered cars have extra smog equipment that could be contributing?

Can you recommend anyone in NY metro area that is an expert in tuning ZR1s? Would like to try changing closed throttle spark advance as suggested above but no idea how to mess with that. Thanks

[Ccmano]

This is a California car and when I put the Haibeck chip in I didn't remove the old one, was a "piggy back" situation I believe, wonder if CA-delivered cars have extra smog equipment that could be contributing?

California cars are no different technically. Can you post a photo of the “piggy back” set up. That should not be there. I wonder if your running a Haibeck CA smog board with a chip on top. There should only be one chip in there. Either an original or the Haibeck.
H
:cheers:

[XfireZ51]

Hans,

I think he is describing a Haibeck prom on a Moates g2 adapter.

[Ccmano]

Hans,

I think he is describing a Haibeck prom on a Moates g2 adapter.

True, that’s what Haibeck used for his CA emissions chip set up. Like this one...
H

https://www.ebay.com/itm/Haibeck-Technology-1991-ZR-1-ZR1-LT5-Emissions-Improvement-Chip-p-n-BFXBDR/163050464298?hash=item25f690a42a:g:3VwAAOSwEaBZ5hc O&vxp=mtr

[XfireZ51]

Right. I can erase the original prom and burn it w a modified cal, although that is a PITA. Spoiled I guess w Ostrich.

[Vetman]

Mine does it too. Put Marc’s chip in in 2015 and it still does it but idles slow now and runs much cooler with ac on!!!

[jss06c6]

Right. I can erase the original prom and burn it w a modified cal, although that is a PITA. Spoiled I guess w Ostrich.
I use this setup.. not too cumbersome... Ostrich definitely better, but need to find a decent place to locate it if you're going to make it permanent..

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[Norwegianmopar]

This is what Marc Haibeck told me regarding this subject:

"Yes it is normal. It's more noticeable on some cars than others. It is the deceleration fuel cutoff mode activating when you close the throttle to coast. When the throttle is opened the fuel is turned on causing a small surge in torque. The deceleration fuel cutoff mode can be turned off in the engine calibration chip"

[lfalzarano]

I had a similar problem (2200 - 2500 RPM’s coming to a stop) and replacing the ICAC didn’t fix it. So, I sent the throttle body to Mark for a rebuild and also get his chip. He found some “gunk” behind the throttle body plates on the manifold side. It is unknown how it got on that side, but it caused the plates to stay partially open and the high idle during deceleration and coming to a full stop.


Lou

[XfireZ51]

I use this setup.. not too cumbersome... Ostrich definitely better, but need to find a decent place to locate it if you're going to make it permanent..

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Steve,

I locate the Ostrich up around the wiper motor. There’s a spot there where it tucks in nicely. I also put it in a ziplock bag to keep any moisture away from usb port. One other alternative is to remove the stock prom and solder in a EEPROM.
I have the SST 27F512. This allows u to flash the cal without needing to UV erase things. I use the Moates Burn2 for this. However, to use the 512 chip, you need to “stack” the bin because its looking for a 64kb block not 32kb.

[jss06c6]

Steve,

I locate the Ostrich up around the wiper motor. There’s a spot there where it tucks in nicely. I also put it in a ziplock bag to keep any moisture away from usb port. One other alternative is to remove the stock prom and solder in a EEPROM.
I have the SST 27F512. This allows u to flash the cal without needing to UV erase things. I use the Moates Burn2 for this. However, to use the 512 chip, you need to “stack” the bin because its looking for a 64kb block not 32kb.
Thanks Dominic. If/when I put an Ostrich in, I'd like to try to get it in the center console and wire up from there. It would be nice to have for my upcoming tuning after the ported top end is finished.. having my laptop and TunerPro in the car with me would make it nice to log data and make changes while I'm in the Dyno and on the road (stopped to make changes of course!).

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[Norwegianmopar]

We have the Haibeck chip and the mentioned surge. However, when we pulled the plugs the other day we discovered the gap was 1,25 mm, not 1 mm like Haibeck told me they should have. After correcting this the surge is now way less noticeable, and the car runs way better too, feels lighter and more responsive if you know what I mean, especially on lower rpm's. It also "dances" with the rear tires struggling to grip at 6000 rpm like it did around 7000 rpm before this adjustment. Funny how much the plug gaps could mean power wise.

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[S.hafsmo]

I'll might have to check the plugs then. The surge is rather annoying. When coasting down a slight decline, it cuts fuel every 4 seconds, for approx. 0.5 seconds.

I'm generally displeased with the fuel management of these cars, with the increased idle after start up (1-2 seconds?), high coast idle, surges etc. Doesn't feel as refined as one would expect from Lotus. Though it could ofcourse be that these things are promoted by wear and tear on mine. I'm also starting to speculate if someone gutted the cats, as it's incredibly loud with the Corsa exhaust, and not in the good way.