Stutter/heistation at low RPMs - ZR-1 Net Registry Forums

BigBiss · 06-05-2011

I had to change the alternator and now have a serious stutter at low RPMs even in neutral. The secondaries are kicking in, but stutter is there at low rpm in all gears. I did change some of the vacuum hoses at the same time, they seem tight, could this be the issue? I am showing no codes, so I am lost at this point. Is there something I missed during the alt change? Any thoughts or direction would be appreciated.

Jim

Demps · 06-05-2011

Could be a myriad of things. I would start with the obvious of what changed.

Did you happen to disconnect an injector connector?

Any vacuum leaks from your work--does it idle high? Take a flashlight (and small mirror) and look around under plenum and throttle body.

Ted

Also, are the electrical connections for the alternator secure?

ittlfly · 06-05-2011

Did you R&R the alt without removing the plenum? That might narrow the trouble down a bit.

Marc Haibeck · 06-06-2011

The most common cause of a misfire after removing the plenum is a fuel injector electrical problem. You might have pinched a fuel injector wire under the plenum gasket flange. The number one primary injector is the most common because it has the longest wires that are not in a sheath.

An easy way to find a fuel injector that is not working is with a stethoscope with a probe pin. With the engine running, touch each primary injector with the probe. A click can be heard when an injector is working normally. Try to find one that does not click.

BigBiss · 06-06-2011

Thanks all, I did change the alt without pulling the plenum,thinking that was the easier way to go. I had to pull the throttle body assembly though to get it off. I am going to check the injectors as Marc suggested, I will let you know.

Thanks for the feedback
Jim

BigBiss · 06-06-2011

Ted, the idle seems fine, but as soon as you touch the throttle it really stumbles. I have checked all around the throttle body and plenum and all looks ok. I am gonna take a closer look when I check the injectors and see if I missed something.

Thanks.

Demps · 06-06-2011

Quote:

Originally Posted by BigBiss

Ted, the idle seems fine, but as soon as you touch the throttle it really stumbles. I have checked all around the throttle body and plenum and all looks ok. I am gonna take a closer look when I check the injectors and see if I missed something.

Thanks.

Jim,
Arm chair quarterbacking here--any chance the connections for the throttle position sensor and/or idle air control valve on the throttle body are not making good connnection?

As Marc elaborated on, I've seen injection electrical connectivity cause a simliar issue but doesn't sound like you pulled the plenum. His trick of listening to the ticking is awesome! My father-in-law just got me a mechanics stethoscope as a joke--now I've found a use for it.

Ted

ittlfly · 06-06-2011

Quote:

Originally Posted by BigBiss

Thanks all, I did change the alt without pulling the plenum,thinking that was the easier way to go. I had to pull the throttle body assembly though to get it off. I am going to check the injectors as Marc suggested, I will let you know.

Thanks for the feedback
Jim

That's why I asked if you removed the plenum. That should eliminate a lot of things. That said, it is certinetly possible that something unrelated to the alt. R&R has happened.
FWIW.....I just did the same job a few months back in the same manor you did. Check all your elecrtical connections again. Did you replace the TB gasket and retorque all TB bolts to spec? I found that it became a critical issue when I did mine.

Marc Haibeck · 06-07-2011

Be aware that most LT?5 will stumble if the throttle is opened quickly in neutral. That?s normal. However the engine should run smoothly under heavy load at 1500 rpm. If it does not, and there is a choppy power delivery there is a misfire.

I can?t imagine how removal of the throttle body and alternator could cause a misfire. Does the engine run rough under load with the power key off?

06-05-2011	#1
BigBiss Join Date: Jul 2007 Location: Clarkston, Michigan Posts: 4	Stutter/heistation at low RPMs I had to change the alternator and now have a serious stutter at low RPMs even in neutral. The secondaries are kicking in, but stutter is there at low rpm in all gears. I did change some of the vacuum hoses at the same time, they seem tight, could this be the issue? I am showing no codes, so I am lost at this point. Is there something I missed during the alt change? Any thoughts or direction would be appreciated. Jim

06-05-2011	#2
Demps Join Date: Jan 2006 Location: Niceville Posts: 998	Re: Stutter/heistation at low RPMs Could be a myriad of things. I would start with the obvious of what changed. Did you happen to disconnect an injector connector? Any vacuum leaks from your work--does it idle high? Take a flashlight (and small mirror) and look around under plenum and throttle body. Ted Also, are the electrical connections for the alternator secure? Last edited by Demps; 06-05-2011 at 04:24 PM.

06-05-2011	#3
ittlfly Join Date: Jul 2009 Location: Redding Calif Posts: 223	Re: Stutter/heistation at low RPMs Did you R&R the alt without removing the plenum? That might narrow the trouble down a bit. __________________ 1994 ZR-1 # 0102...SOLD

06-06-2011	#4
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 243	Re: Stutter/heistation at low RPMs The most common cause of a misfire after removing the plenum is a fuel injector electrical problem. You might have pinched a fuel injector wire under the plenum gasket flange. The number one primary injector is the most common because it has the longest wires that are not in a sheath. An easy way to find a fuel injector that is not working is with a stethoscope with a probe pin. With the engine running, touch each primary injector with the probe. A click can be heard when an injector is working normally. Try to find one that does not click.

06-06-2011	#5
BigBiss Join Date: Jul 2007 Location: Clarkston, Michigan Posts: 4	Re: Stutter/heistation at low RPMs Thanks all, I did change the alt without pulling the plenum,thinking that was the easier way to go. I had to pull the throttle body assembly though to get it off. I am going to check the injectors as Marc suggested, I will let you know. Thanks for the feedback Jim

06-07-2011	#9
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 243	Re: Stutter/heistation at low RPMs Be aware that most LT?5 will stumble if the throttle is opened quickly in neutral. That?s normal. However the engine should run smoothly under heavy load at 1500 rpm. If it does not, and there is a choppy power delivery there is a misfire. I can?t imagine how removal of the throttle body and alternator could cause a misfire. Does the engine run rough under load with the power key off?