Running rough - MPG dropped
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
HI folks. I need a little advice.
Monday the vette (stock 86 w/aluminum heads, auto)was runnning great. Smooth, lots of power.
Tuesday, no warning, it starts running rough (all RPMS), small decrease in power (SOTP). avg MPG dropped to 12 from 15 in just 55 miles. Stays at 12 - 12.2 now. Driving around town - no freeway.
Did a fuel pressure test this evening. Looks good. FPR seems to be working. Stop the car and it takes 45 min to drop from 38 to 5 psi.
Checked ECM - no codes.
In the past 2 months:
TB just cleaned, new: IAC, wires, plugs dist cap, dist rotor, ignition module, fuel filter, air filter. Timing set at 6 ddeg BTDC and min idle adjusted to 500 RPM. Monday it was running great.
Any ideas, folks?
Just a thought:
I read some where that a malfunctioning cold start injector or cold start switch could make it run rich. Anybody have an experiences like that.
Monday the vette (stock 86 w/aluminum heads, auto)was runnning great. Smooth, lots of power.
Tuesday, no warning, it starts running rough (all RPMS), small decrease in power (SOTP). avg MPG dropped to 12 from 15 in just 55 miles. Stays at 12 - 12.2 now. Driving around town - no freeway.
Did a fuel pressure test this evening. Looks good. FPR seems to be working. Stop the car and it takes 45 min to drop from 38 to 5 psi.
Checked ECM - no codes.
In the past 2 months:
TB just cleaned, new: IAC, wires, plugs dist cap, dist rotor, ignition module, fuel filter, air filter. Timing set at 6 ddeg BTDC and min idle adjusted to 500 RPM. Monday it was running great.
Any ideas, folks?
Just a thought:
I read some where that a malfunctioning cold start injector or cold start switch could make it run rich. Anybody have an experiences like that.
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 60
From: Fremont Oh
Mike,
You state that your car didnt throw any codes,..
I had an instance on my 87 where it ran very much like you are describing, my problem ended up being the MAF sensor.
Mine threw a code, for prosperity sake you maytrysimpll disconnecting the MAF sensor and see if it runs any smoother.
Just a thought..
Mo
You state that your car didnt throw any codes,..
I had an instance on my 87 where it ran very much like you are describing, my problem ended up being the MAF sensor.
Mine threw a code, for prosperity sake you maytrysimpll disconnecting the MAF sensor and see if it runs any smoother.
Just a thought..
Mo
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Originally Posted by Mo_Bandy
Mike,
You state that your car didnt throw any codes,..
I had an instance on my 87 where it ran very much like you are describing, my problem ended up being the MAF sensor.
Mine threw a code, for prosperity sake you maytrysimpll disconnecting the MAF sensor and see if it runs any smoother.
Just a thought..
Mo[/color]
You state that your car didnt throw any codes,..
I had an instance on my 87 where it ran very much like you are describing, my problem ended up being the MAF sensor.
Mine threw a code, for prosperity sake you maytrysimpll disconnecting the MAF sensor and see if it runs any smoother.
Just a thought..
Mo[/color]
I was hoping it wasn't the MAF, they're not cheap. I try disconnecting it and see if it smooths out.
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 60
From: Fremont Oh
Mike,
I know this sounds corny, but Pep boys used to sell the MAF's if it doesnt fix the problem , they used to have a return policy on electronic parts
Yes if you disconnect yyou of course will kick a code but if it is the maf the car should smoothen righ out as the ECM is then compensating for the problem..
Mo
I know this sounds corny, but Pep boys used to sell the MAF's if it doesnt fix the problem , they used to have a return policy on electronic parts
Yes if you disconnect yyou of course will kick a code but if it is the maf the car should smoothen righ out as the ECM is then compensating for the problem..
Mo
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Originally Posted by Mo_Bandy:
[B
[B
Mike,
I know this sounds corny, but Pep boys used to sell the MAF's if it doesnt fix the problem , they used to have a return policy on electronic parts [img]http]//www.corvetteforum.cc/ubb/smile.gif[/img]
Yes if you disconnect yyou of course will kick a code but if it is the maf the car should smoothen righ out as the ECM is then compensating for the problem..
Mo
[/B][/color]
I know this sounds corny, but Pep boys used to sell the MAF's if it doesnt fix the problem , they used to have a return policy on electronic parts [img]http]//www.corvetteforum.cc/ubb/smile.gif[/img]
Yes if you disconnect yyou of course will kick a code but if it is the maf the car should smoothen righ out as the ECM is then compensating for the problem..
Mo
[/B][/color]
I disconnected the MAF, the ECM threw a code 33 and ... the car ran great!
Bought a MAF, installed it and problem went away.
THANKS!
Le Mans Master
Joined: Feb 1999
Posts: 6,631
Likes: 1
From: Stoplight City IN
S. Indiana Events Coordinator
Cruise-In I Veteran
Hey Mike. You describe almost to a 'T' what happened to my car yesterday: Running fine one moment, then burning fuel like a mo fo the next.
Closer inspection revealed that the MAF sensor wire had been rubbing the water pump pulley and wore through the insulation causing a possible short.
My car set a code, mileage dropped to 9 mpg hwy, and black smoke poured from its exhaust.
As a temporary band-aid, we taped the wires up and wire tied them to the bridge. It took about 5 miles to get the car running nearly right again, but I'm still getting a code.
I'm taking it to the shop next week to try to clear the code and get the wiring harness replaced.
At any rate, it sounds like you have a similar electronic problem.
*edit
Oops. I see you solved your problem. I'll shut up now
Glad you got it fixed okay!!
Closer inspection revealed that the MAF sensor wire had been rubbing the water pump pulley and wore through the insulation causing a possible short.
My car set a code, mileage dropped to 9 mpg hwy, and black smoke poured from its exhaust.
As a temporary band-aid, we taped the wires up and wire tied them to the bridge. It took about 5 miles to get the car running nearly right again, but I'm still getting a code.
I'm taking it to the shop next week to try to clear the code and get the wiring harness replaced.
At any rate, it sounds like you have a similar electronic problem.
*edit
Oops. I see you solved your problem. I'll shut up now
Glad you got it fixed okay!!
Drifting
Joined: Nov 2000
Posts: 1,722
Likes: 0
From: Big D Tx
Cruise-In II Veteran
it would be wise to go ahead and replace your MAF and burnoff relays at the same time so you dont have to buy another MAF sensor in a couple of weeks. one of those *could* be what caused your original MAF to go out.
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