Poor Fuel mileage
Thread Starter
8th Gear
Joined: Sep 2013
Posts: 8
Likes: 0
Poor Fuel mileage
My 86 has always got great fuel mileage. Now all of a sudden the fuel mileage has dropped to about 10 mpg. I can't seem to find the problem. Any ideas? I know I am missing something. Thanks, 86Rono
Team Owner
Joined: Jul 2004
Posts: 28,464
Likes: 3,288
From: Hartford WI
Well, you can stimulate the economy for Obama or get a scanner and see what the sensor is reading. Why don't we start rounding up the usual culprits? What have you already tried? Have you checked the fuel pressure? Does it deliver proper pressure at WOT? Have you checked the plug wires for leaks? Plugs, cap and rotor condition? Those you have to do visually. 10 to 1, you probably haven't had your injectors serviced.
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Pro
Joined: Sep 2012
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From: the confused state CT
A scanner would be a great help. Is the check engine light on, any codes? The o2s could be slow, not switching or a vacuum leak can cause a lean 02 reading. As stated earlier, is the engine coming up to operating temp? An open thermostat or coolant sensor fault is another possibility.
Gary
Gary
Last edited by yd328; Jan 24, 2016 at 05:19 PM.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
I agree but the O2 or its wiring has to take a total dump and then the ECM will revert to the tables in the software for A/F mixture which is not optimum.
A scanner looking at the voltage swings of the O2s would tell you right away how things look.
Also check fuel pressure and the FPR for proper operation. Too much pressure and the mileage goes down. And if the vacuum line is leaking it will do the same which is easy to check.
A scanner looking at the voltage swings of the O2s would tell you right away how things look.
Also check fuel pressure and the FPR for proper operation. Too much pressure and the mileage goes down. And if the vacuum line is leaking it will do the same which is easy to check.
Team Owner
Joined: Jul 2004
Posts: 28,464
Likes: 3,288
From: Hartford WI
A scanner looking at the voltage swings of the O2s would tell you right away how things look.
Also check fuel pressure and the FPR for proper operation. Too much pressure and the mileage goes down. And if the vacuum line is leaking it will do the same which is easy to check.
Also check fuel pressure and the FPR for proper operation. Too much pressure and the mileage goes down. And if the vacuum line is leaking it will do the same which is easy to check.
With the scanner, if there is a leak, you can see it in IAC counts being lower than it should be and not adjustable. I set mine for 20-30 and anything less and not adjustable to 20 means a leak somewhere.
Thread Starter
8th Gear
Joined: Sep 2013
Posts: 8
Likes: 0
Poor Fuel mileage
Thanks everyone for all the ideas. the plugs and wires were replaced about 2500 miles ago. the injectors were replaced about 4000 miles ago and I replaced the fuel pressure regulator at about the same time as the injectors. So, maybe vacuum line? Thanks, 86Rono
Team Owner
Joined: Jul 2004
Posts: 28,464
Likes: 3,288
From: Hartford WI
Do check out the spark quality. It needs to have a blue flame. Are the wires leaking?
If the vacuum line is leaking, I would be curious as to whether you changed it recently. Still, get a scanner and see.
Last edited by aklim; Jan 25, 2016 at 12:49 AM.