Next up: a miss and a "surge"... - ZR-1 Net Registry Forums

KILLSHOTS · 05-19-2014

So here's the next thing I need to figure out. When I start the car cold, it settles down right away but seems to idle a little roughly. Then after just a couple minutes, it smooths right out and everything is fine. I also noticed (only after I went to full-open exhaust; the mufflers were hiding it) that there seems to be a slight miss that I can hear intermittently only at the tailpipes...the engine itself sounds silky smooth. Lastly, when coasting to a stop with the car in gear, it seems to "surge" slightly. Imagine almost a light engine-braking effect that you'd feel on and off. I'm assuming these issues are related, but...??? (One thought: could the "miss" I hear at the tailpipes be because I have an H-pipe instead of an X-pipe? Are the pipes not "equalized" as well as they could be?)

Other than these small things, the car runs like a bat out of hell. No shakes, vibrations, hesitations or otherwise. Screams like a banshee to well past 7000rpm. Throttle response is smooth and instant everywhere in the range. It idles very smoothly after it warms up for a couple minutes. The car has only 16K original miles. Injectors just replaced with new (not reman) FIC stainless. Brand new OEM coil packs, brand new AC plugs, brand new fuel filter. I have Marc's chip. With ignition ON, vacuum pump stays on for 5-6 seconds and then runs for a split second, so I do have a leak but it's slight and certainly shouldn't be causing this.

This sucks, as I have neither the time nor the inclination to start ripping the car apart chasing gremlins myself, and I have yet to find a mechanic who isn't afraid of the LT5. Could this be something really simple?

Thanks in advance, guys!

Schrade · 05-19-2014

I'll take a stab here...

Plug in DataMaster, do incremental throttle increase with the throttle stop screw, and I guarantee you get the lope @ 1.6% Throttle Opening, until 2.4% TO, which Marc H says ALL LT5's have.

That COULD account for this:
"When I start the car cold, it settles down right away but seems to idle a little roughly."

and this:
"Lastly, when coasting to a stop with the car in gear, it seems to "surge" slightly."

TB secondary butterflys might also be letting in some UN-accounted for air, exacerbating the lope, and confounding diagnostics ...

WOT performance almost never tells anything of substance in any car...

Bearly Flying · 05-20-2014

It could also be when the car goes into closed loop and the computer starts adjusting fuel trims.

05-19-2014	#1
KILLSHOTS Join Date: Feb 2014 Location: AZ Posts: 860	Next up: a miss and a "surge"... So here's the next thing I need to figure out. When I start the car cold, it settles down right away but seems to idle a little roughly. Then after just a couple minutes, it smooths right out and everything is fine. I also noticed (only after I went to full-open exhaust; the mufflers were hiding it) that there seems to be a slight miss that I can hear intermittently only at the tailpipes...the engine itself sounds silky smooth. Lastly, when coasting to a stop with the car in gear, it seems to "surge" slightly. Imagine almost a light engine-braking effect that you'd feel on and off. I'm assuming these issues are related, but...??? (One thought: could the "miss" I hear at the tailpipes be because I have an H-pipe instead of an X-pipe? Are the pipes not "equalized" as well as they could be?) Other than these small things, the car runs like a bat out of hell. No shakes, vibrations, hesitations or otherwise. Screams like a banshee to well past 7000rpm. Throttle response is smooth and instant everywhere in the range. It idles very smoothly after it warms up for a couple minutes. The car has only 16K original miles. Injectors just replaced with new (not reman) FIC stainless. Brand new OEM coil packs, brand new AC plugs, brand new fuel filter. I have Marc's chip. With ignition ON, vacuum pump stays on for 5-6 seconds and then runs for a split second, so I do have a leak but it's slight and certainly shouldn't be causing this. This sucks, as I have neither the time nor the inclination to start ripping the car apart chasing gremlins myself, and I have yet to find a mechanic who isn't afraid of the LT5. Could this be something really simple? Thanks in advance, guys!

05-19-2014	#2
Schrade Join Date: Dec 2012 Location: NC Posts: 1,786	Re: Next up: a miss and a "surge"... I'll take a stab here... Plug in DataMaster, do incremental throttle increase with the throttle stop screw, and I guarantee you get the lope @ 1.6% Throttle Opening, until 2.4% TO, which Marc H says ALL LT5's have. That COULD account for this: "When I start the car cold, it settles down right away but seems to idle a little roughly." and this: "Lastly, when coasting to a stop with the car in gear, it seems to "surge" slightly." TB secondary butterflys might also be letting in some UN-accounted for air, exacerbating the lope, and confounding diagnostics ... WOT performance almost never tells anything of substance in any car... __________________ I'm getting my snappics / threads removed blindly as fast as I can, to get in compliance with copyright / license TOS on the boards here (lots of FSM pages and other copyright / license violations on my part; sorry guys). And thanks to all the guys who didn't whine when I posted those FSM copyrighted / licensed stuff in my threads... ( :thumbsup: [b]and to think I complied with a mod's request to delete a pic of him in a Challenge Car in NCM Museum, so he wouldn't get in hot water)[/b] Thanks to several guys here for sending parts FREE; BearlyFlying, WeGone, Geezer, GoldCylon, and more there, TonyD, mike100, fletchusmc... 1990 #2794; 4L60e Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless, Power Effects 3" [IMG]https://lh5.googleusercontent.com/-GHpfzty7DVU/UQn-0Ru2xAI/AAAAAAAAA14/08mz1p4QLD4/s445/Screenshot-5.png[/IMG]

05-20-2014	#3
Bearly Flying Join Date: Dec 2012 Location: Ponoka, Alberta, Canada Posts: 158	Re: Next up: a miss and a "surge"... It could also be when the car goes into closed loop and the computer starts adjusting fuel trims. __________________ 91 ZR-1 Arctic White/Gray 01 C-5 Magnetic Red/Black 85 FJ 1100 (Big Bore kit, Hooligan Bike) 05 FJR 1300 Yamaha (Long Distance, Sport Touring) And a whole whack of RC Planes