L98 still running rough
Thread Starter
Race Director
Joined: Apr 1999
Posts: 13,002
Likes: 4
From: Paint Hill NC
L98 running rough: Bad MAF Mass Air Flow
SYMPTOMS:
Poor/no idle, hesitation, stalling, stumbling, backfire thru intake. Smooths out under heavy acceleration and WOT, but power is down. Symptoms came on suddenly. Sets no codes. Set a code 34 after egr, iac install but I believe unrelated, cleared, stayed off.
SO FAR:
Checked a couple plugs, they are fine (rapid fires). New plug wires, cap, rotor. 1st chevy dealer says no output from ECM, so I replaced ECM. Second chevy dealer says EGR, I replaced it. Also new IAC. Nothing has helped. Am going to check maf b/o relay today.
This has to be something simple. Please post if you have any ideas.
Thanks
Merry Christmas,
Harold
[Modified by TPFKATK, 12:25 PM 1/7/2002]
[Modified by TPFKATK, 12:37 PM 1/7/2002]
Poor/no idle, hesitation, stalling, stumbling, backfire thru intake. Smooths out under heavy acceleration and WOT, but power is down. Symptoms came on suddenly. Sets no codes. Set a code 34 after egr, iac install but I believe unrelated, cleared, stayed off.
SO FAR:
Checked a couple plugs, they are fine (rapid fires). New plug wires, cap, rotor. 1st chevy dealer says no output from ECM, so I replaced ECM. Second chevy dealer says EGR, I replaced it. Also new IAC. Nothing has helped. Am going to check maf b/o relay today.
This has to be something simple. Please post if you have any ideas.
Thanks
Merry Christmas,
Harold
[Modified by TPFKATK, 12:25 PM 1/7/2002]
[Modified by TPFKATK, 12:37 PM 1/7/2002]
Instructor
Joined: Dec 2001
Posts: 247
Likes: 0
From: San Diego CA
Re: L98 still running rough (TPFKATK)
I hope this is not it since you have already spent some cash, but have you replaced your fuel filter? The symptoms you are talking about could indicate a poorly flowing fuel system.
Rich
Rich
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 4
From: Austria
Re: L98 still running rough (corvette90)
ah, yes..check your fuel pressure-as mentioned before..fuel filter-or fuel pump connections
i´ve had a corroded electric contact at the fuel pump..same symptoms
i´ver had no backfires, but rough idle, aso..
good luck, again
i´ve had a corroded electric contact at the fuel pump..same symptoms
i´ver had no backfires, but rough idle, aso..
good luck, again
Le Mans Master
Joined: Dec 1999
Posts: 8,540
Likes: 1
From: And on the fifth day, subpoenas were served to Obama senior staff
Re: L98 still running rough
Well, seeing how you have replaced everything - time to get some equipment on that thing and see whats up.
Suggest scanner, fuel pressure guage and vacuum guage. Sounds like could be a fairly large vacuum leak, but could be a million things. I am suprised that a code does not set - so that is consistant with a vacuum or ignition /timing related problem. I take it this is an 88 auto. How are the brakes working?
Any mods to the engine / fuel injection system / ignition? How many miles on the engine. Was anything done just before the problem started? Have you checked every plug? Could firing order be off? Is throttle body hanging open? Messed with the MAF recently? Any leaks between the MAF and TB?
Could be so many things, have to narrow it down.
Good Luck,
Pete
Suggest scanner, fuel pressure guage and vacuum guage. Sounds like could be a fairly large vacuum leak, but could be a million things. I am suprised that a code does not set - so that is consistant with a vacuum or ignition /timing related problem. I take it this is an 88 auto. How are the brakes working?
Any mods to the engine / fuel injection system / ignition? How many miles on the engine. Was anything done just before the problem started? Have you checked every plug? Could firing order be off? Is throttle body hanging open? Messed with the MAF recently? Any leaks between the MAF and TB?
Could be so many things, have to narrow it down.
Good Luck,
Pete
Thread Starter
Race Director
Joined: Apr 1999
Posts: 13,002
Likes: 4
From: Paint Hill NC
Re: L98 still running rough (PeteL)
Thanks guys.
Forgot to mention above; new fuel filter, fuel press ok and no leakdown. Vacuum about 18 at idle, holds vacuum for some time after shutdown. Done the carb cleaner vacuum test several times. Had it to 2 chevy dealers for diagnosis, neither of which helped. Yep, 88 auto, brakes work ok. It actually idles after it gets warm and runs a little better. Runs the best under acceleration, no skips or misses etc but power is down. I cannot believe it about no codes either as bad as it runs.. About 135k on car, nothing done to bring it on as far as I know. Looking like I'm gonna have to quit working on it till after xmas. Maybe Santa will bring me a new one??? I have been a good boy except for a lot of swearing...:blueangel:
Harold
Forgot to mention above; new fuel filter, fuel press ok and no leakdown. Vacuum about 18 at idle, holds vacuum for some time after shutdown. Done the carb cleaner vacuum test several times. Had it to 2 chevy dealers for diagnosis, neither of which helped. Yep, 88 auto, brakes work ok. It actually idles after it gets warm and runs a little better. Runs the best under acceleration, no skips or misses etc but power is down. I cannot believe it about no codes either as bad as it runs.. About 135k on car, nothing done to bring it on as far as I know. Looking like I'm gonna have to quit working on it till after xmas. Maybe Santa will bring me a new one??? I have been a good boy except for a lot of swearing...:blueangel:
Harold
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Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: L98 still running rough (Bluevette85)
it sounds like a MAF/ECM to me, it has to be one of those two.
Thread Starter
Race Director
Joined: Apr 1999
Posts: 13,002
Likes: 4
From: Paint Hill NC
Re: L98 still running rough (Bluevette85)
Thanks Walter, I am going to try that for sure. I priced MAFs today, yikes. I am not just throwing parts at this and don't intend to start now. Everything to this point has been needed as I haven't replaced it since I have had the car or has been recommended by the so called "experts" at the chevy dealerships. I just read the thread by the guy who picked up his firebird (I think) $1300 bill for nothing. Sounds like the same symptoms I have.
THE LATEST
Car is idleing rough we pull a plug wire NO CHANGE! AHAH! Pull another, the same. Pull the plugs they are fine but black, too rich, wires are new. WTF. Spark is orange not blue and seems to have a problem jumping 1/2 inch. Coil? Ignition module?
Thanks again for the help.
H
THE LATEST
Car is idleing rough we pull a plug wire NO CHANGE! AHAH! Pull another, the same. Pull the plugs they are fine but black, too rich, wires are new. WTF. Spark is orange not blue and seems to have a problem jumping 1/2 inch. Coil? Ignition module?
Thanks again for the help.
H
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
Re: L98 still running rough (TPFKATK)
could be the coil, might as well change it anyway they don't last forever.
while your in there you can take the ignition module in and have it checked.
but you should have enough spark to jump a 1/2" gap easy ( wide blue spark )
actually it ( stock HEI ) can knock the crap outta you. :eek:
so I think you've found the problem, otherwise you'd have a sore hand and would think twice about ever pulling a sparkplug wire off again :D
RJ
while your in there you can take the ignition module in and have it checked.
but you should have enough spark to jump a 1/2" gap easy ( wide blue spark )
actually it ( stock HEI ) can knock the crap outta you. :eek:
so I think you've found the problem, otherwise you'd have a sore hand and would think twice about ever pulling a sparkplug wire off again :D
RJ
Instructor
Joined: Nov 2001
Posts: 154
Likes: 14
From: NY
Re: L98 still running rough (TPFKATK)
had the same problem with my 85. Went thru the same including new injectors. Drop the end of your exhaust. look/feel inside your cat. I had a broken piece that was blocking the exhaust. Some time it would run pretty good and others rough and stall. Gas milage went south and it lost power. I gutted the cat and everything was fine after that. Good luck
Burning Brakes
Joined: Jun 2000
Posts: 865
Likes: 6
From: Auburn Michigan
Re: L98 still running rough (TPFKATK)
I know it couldn't be this simple, but this summer, I bumped the timing a little on mine, and reconnected (so I thought) the connection you unhook when setting timing, but evidently I didn't get it fully seated and it came apart after about 5 miles of driving. Took me a while to figure it out. Your IAC connection o-tay?
Burning Brakes
Joined: Nov 2000
Posts: 1,040
Likes: 2
From: BowlingGreen KY
Re: L98 still running rough (cohocarl)
I don't think anyone has mentioned this yet so, Have you checked the dist cap,rotor button and rotor for wear or proper instalation?If you had the dealership put them in they might have messed them up, 02 sensor? Make sure its not cross wired, although you would have some serious backfire if it were. Good luck.
[Modified by KYVette90, 4:15 PM 12/25/2001]
[Modified by KYVette90, 4:15 PM 12/25/2001]
Racer
Joined: Apr 2001
Posts: 452
Likes: 0
From: Tulsa Ok, Racing the wind
Re: L98 still running rough (TPFKATK)
It actually idles after it gets warm and runs a little better. Runs the best under acceleration, no skips or misses etc but power is down.
Thread Starter
Race Director
Joined: Apr 1999
Posts: 13,002
Likes: 4
From: Paint Hill NC
Re: L98 still running rough (BigTodd)
Add new O2 sensor to the list, no help. The car is running a little better. Last night I floored it on the way home from xmas at the inlaws and the acceleration was great, as good or almost as good as it was before this all started. The stumbling and missing is not quite as bad but still bad. Bad gas, dirty injectors? When this first started we added water remover then drained the fuel to two bars, put in 3gals, drove that out, put in three gals, drove that out, filled the tank, drove that out, filled the tank , added injector cleaner which is where it is now. Cap and rotor and iac were replaced no help. Timing is good, wire is connected. Still have not checked the burn off relay, that is next then replace coil with known good and test ign module.
Thanks for the input, happy holidays.
Harold
Thanks for the input, happy holidays.
Harold
Melting Slicks
Joined: Mar 2001
Posts: 2,899
Likes: 2
From: Summerville SC
Re: L98 still running rough (TPFKATK)
Check your wire going to the knock senser mine was burned bare and grounding between starter and engine block :eek: :boxing :cry Took me a while to trace it down...Thank God I bought a dealers service manual :D
Advanced
Joined: May 2001
Posts: 57
Likes: 0
From: Yokosuka
Re: L98 still running rough (TPFKATK)
Hey same problem on my 89. Changed everything except the thottle block so far. Still there..... Let me know if you ever get this fixed....Could use some insight on what to do next. :mad