Go Back   LS1TECH > CHASSIS, SUSPENSION, APPEARANCE > General Maintenance & Repairs
Sign in using an external account
Register Forgot Password?
Search

General Maintenance & Repairs
Leaks | Squeaks | Clunks | Rattles | Grinds
Sponsored by
Gearstar Performance Transmissions

Hesitation/misfire

Reply
 
Thread Tools Search this Thread
Old 09-16-2008, 05:27 PM   #1
12 Second Club
 
ZexGX's Avatar
 
Trader Rating: 28
Join Date: May 2007
Location: under a JEGS hat
Posts: 2,753
Send a message via AIM to ZexGX
Exclamation Hesitation/misfire

Getting a random misfire... On startup it sometimes revs high, then idle goes down and it lopes (stock GM cam), then stalls unless I give it some gas. When driving along at speed, it'll miss ocasionally and even more under load. When this happens (and when it lopes), RPMs/volts will drop in sync. Volts are fine when running normally before this happens.

I have changed:
MAF (bad - replaced with new which helped and stopped the error codes - also tested the new one by unplugging)
Fuel filter (was good - keeping the old as a spare)
Front O2s
Plugs + wires (I can get pictures if anybody wants of the removed parts)
Air filter is K&N drop-in and has been recharged recently
Two coils have been replaced and the control module have been replaced twice recently!
Camshaft position sensor has been recently replaced with proper matching part

I am thinking it's either the fuel injectors or the TPS. I'm open to other ideas. If you think it's fuel injectors or the throttle position sensor (?), how can I check or have it checked? I have been trying to fix this for weeks now and it's driving me crazy! The MAF screen may be SLIGHTLY bent (no fault of my own - have pics if requested) but it is clean and air flows through. The MAF sensor on the V6's are removable units housed inside the throttlebody before the valve. Not sure if the bent screen would cause this. It was running fine for a LONG time with the bent screen.

Car is a '99 with 115k miles on it. It has an electronic throttlebody (drive by wire).

It's a 3.8L V6 f-body but I figure maintenance is maintenance and an F-body is an F-body. I've asked in the V6 forums but haven't gotten much feedback.

P.S. NO CODES HAVE BEEN THROWN
__________________
'99 Firebird: Under the Knife
February 2012 GMHTP Street Heat Car

Last edited by ZexGX; 09-16-2008 at 06:10 PM..
ZexGX is offline   Reply With Quote
Old 09-16-2008, 10:14 PM   #2
TECH Apprentice
 
Trader Rating: 0
Join Date: Jan 2008
Posts: 330
Default

i am having a similar problem, but mine is when I push the pedal all the way down really quick, it hesitates or has even popped. Really weird.
__________________
94 Trans Am GT
LT1Formula26 is offline   Reply With Quote
Old 09-18-2008, 10:31 AM   #3
12 Second Club
 
ZexGX's Avatar
 
Trader Rating: 28
Join Date: May 2007
Location: under a JEGS hat
Posts: 2,753
Send a message via AIM to ZexGX
Default

No ideas?? This car is my DD right now so having it not running properly is a pain... At this point I'm thinking fuel pump or injectors, cause it can stall immediately after starting up, as if fuel was cut to it. Also when I was on a roadtrip recently, I'd come to a stop but still hear a loud whirring sound coming from the rear end that would eventually go away. Oh yeah, and the fuel gauge is sometimes wacky (shows more than there is, or less than there is), and for some reason when I put gas in it sometimes (at 1/4 or less), the pressure stop on the pump activates after like 0.4 GALLONS...

Is there a way to test the fuel pump/fuel injectors?
__________________
'99 Firebird: Under the Knife
February 2012 GMHTP Street Heat Car
ZexGX is offline   Reply With Quote
Old 09-18-2008, 10:55 AM   #4
LS1TECH & Trucks Sponsor
 
Scoggin Dickey's Avatar
 
Trader Rating: 33
Join Date: Mar 2002
Location: Lubbock, TX
Posts: 3,332
Send a message via AIM to Scoggin Dickey Send a message via Yahoo to Scoggin Dickey
Default

Sounds like a vacuum leak or something similar. Where do you get that it's misfiring if no codes have showed up?
__________________

800-456-0211 ext 358 / PM /E-mail Facebook AIM or Yahoo: JSSDPC
WHIPPLE Superchargers, Procharger, Magnuson, Powerbond Sale, HPTuners packages!, Trickflow, AFR, PRC, Yella Terra, $100 7.400" pushrod set, Custom Cam of your choice
Scoggin Dickey is offline   Reply With Quote
Old 09-18-2008, 11:19 AM   #5
12 Second Club
 
nemss1's Avatar
 
Trader Rating: 0
Join Date: Jun 2008
Location: Edmond, OK
Posts: 2,587
Default

there are current threads on misfire in the other secitons/forums
__________________

'00 SS A4, Bolt-Ons/Weight Reduction-SOLD
nemss1 is offline   Reply With Quote
Old 09-18-2008, 03:59 PM   #6
12 Second Club
 
ZexGX's Avatar
 
Trader Rating: 28
Join Date: May 2007
Location: under a JEGS hat
Posts: 2,753
Send a message via AIM to ZexGX
Default

Quote:
Originally Posted by Scoggin Dickey View Post
Sounds like a vacuum leak or something similar. Where do you get that it's misfiring if no codes have showed up?
Well, it may not be caused by a misfire. It's sorta like a "popping" motion, and its chances of occuring increase with the throttle applied. Feels like it just loses power (like throttle dropping to 0%) and then instantly regains it (like a switch gets flipped) but it happens in a fraction of a second - faster than I can duplicate it by letting go of the gas and then punching it. I suppose it could be the fuel pump or an injector(s) now and its just starving for fuel. I checked all of the visible vacuum lines and they looked fine and were connected. I suppose I can check the other engine-specific forums for troubleshooting, but I figured general maintenance/troubleshooting would be able to provide some ideas for a resolution/cause to the problem.
__________________
'99 Firebird: Under the Knife
February 2012 GMHTP Street Heat Car
ZexGX is offline   Reply With Quote
Old 09-21-2008, 08:06 PM   #7
TECH Resident
 
peterock98's Avatar
 
Trader Rating: 24
Join Date: Dec 2002
Location: Bronx, NY
Posts: 976
Default

Bad spark wire or wires.I see you wrote you replaced them what kind of wire did you go with.
__________________
peterock98 is offline   Reply With Quote
Old 09-22-2008, 12:24 AM   #8
12 Second Club
 
ZexGX's Avatar
 
Trader Rating: 28
Join Date: May 2007
Location: under a JEGS hat
Posts: 2,753
Send a message via AIM to ZexGX
Default

Brand new Bosch pre-cut lengths & AC Delco Rapidfire plugs.
__________________
'99 Firebird: Under the Knife
February 2012 GMHTP Street Heat Car
ZexGX is offline   Reply With Quote
Old 09-22-2008, 06:53 AM   #9
TECH Resident
 
peterock98's Avatar
 
Trader Rating: 24
Join Date: Dec 2002
Location: Bronx, NY
Posts: 976
Default

I had the same problem I brought some cheap wires and my car had a bad misfire.My check engine light was flashing when I drove.I installed the msd's and so far so good.
__________________
peterock98 is offline   Reply With Quote
Old 09-22-2008, 09:50 AM   #10
12 Second Club
 
ZexGX's Avatar
 
Trader Rating: 28
Join Date: May 2007
Location: under a JEGS hat
Posts: 2,753
Send a message via AIM to ZexGX
Default

Yep... No check engine light and it's not 100% of the time... Only SOMETIMES on startup, idle, and increasing load - I also noticed last night that it increases when going uphill... Gonna throw on a fuel pressure gauge soon.
__________________
'99 Firebird: Under the Knife
February 2012 GMHTP Street Heat Car
ZexGX is offline   Reply With Quote
Old 09-22-2008, 03:43 PM   #11
TECH Resident
 
peterock98's Avatar
 
Trader Rating: 24
Join Date: Dec 2002
Location: Bronx, NY
Posts: 976
Default

Might be all of the crap there putting in the gas today...
__________________
peterock98 is offline   Reply With Quote
Old 09-24-2008, 11:21 AM   #12
Teching In
 
Barr6505's Avatar
 
Trader Rating: 0
Join Date: Mar 2007
Location: Michigan
Posts: 23
Default

I am currently trying to fix a similar problem on my 99 formula with 101,000 miles. It will hesitate under load and lose all of the power. I thought fuel pump and just checked the pressure. 57lbs so it isn't that. I was thinking injectors. I recently did a tune up to try and fix the problem and I had three plugs with black residue on them. Not oil residue, just sooty. Mine was doing this before I put the plugs and wires on so I don't think the cheap wires and plugs messed it up.

Anyone replaced a fuel pressure regulator on an LS1 with similar miles? Ignition control module?

*Oh, and all of my o2 sensors are throwing codes. I believe they were throwing rich and lean, but I can't remember what the guy at Autozone said.
__________________
Crop circles are Chuck Norris' way of telling the world that sometimes, corn just needs to lie the f*ck down.

"This is Papa Bear. Put out an APB for a male suspect, driving a... car of some sort, heading in the direction of, uh, you know, that place that sells chili. Suspect is hatless. Repeat, hatless." -Chief Wiggum

Last edited by Barr6505; 09-24-2008 at 11:23 AM.. Reason: Forgot
Barr6505 is offline   Reply With Quote
Old 09-24-2008, 09:31 PM   #13
TECH Fanatic
 
ghardester's Avatar
 
Trader Rating: 0
Join Date: Aug 2006
Location: Knappa, Oregon
Posts: 1,156
Default

Bad spark plug wires. Or you have another bad coil. Electrical problems tend to show up more under a load, when you are trying to excelerate. Go back and be sure of the plugs, coil, wires.
__________________
2002 Navy Blue Metalic WS6 TA A-4. Born on 7-24-2002. I drive it every day.
ghardester is offline   Reply With Quote
Old 09-24-2008, 09:31 PM
LS1Tech
Pontiac Firebird




Paid Advertisement
Reply


Tags
330, 38l, bmw, cuts, firebird, firehawk, hesitation, high, load, ls1, misfire, speed, throttle, troubleshooting, uphill, zexgx


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off



Join Ls1Tech

All times are GMT -5. The time now is 10:34 AM.


Powered by vBulletin® Version 3.8.7 AC1
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Advertising - Terms of Service - Privacy Statement - Terms of Service - JOBS
Emails & Contact Details