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Topic: rough low speed running, poor mileage '85 5.0 CFI (Read 667 times) previous topic - next topic

rough low speed running, poor mileage '85 5.0 CFI

Need a little help. Car is '85 Thunderbird with 5.0 CFI and auto, stock. I've had it since it was new, been a great car.  Has 143,000 miles on her now.

Several years ago put new oxygen sensor on it, also replaced TPS some 10 years ago for some reason.  About three years ago the EGR kept getting stopped open with carbon deposits I think related to faulty oxygen sensor, I eventually blocked the EGR altogether as going to have to remove intake and clean it good to alleviate carbon deposits blocking EGR open.

No oil use problems, trans is in great shape, TV cable is OK.

Anyway, been running OK, mileage in mid 20s on the road. 

Lately however, mileage has dropped to 19-20 mpg and at light part throttle she seems to shift and the engine surges.  Idle is not always steady either.  At heavy throttle or wide open she seems OK. 

I suspect the TPS. 

Was wondering however if any need or point in overhauling throttle body, having injectors cleaned, new oxygen sensor along with it????

Thanks ......

rough low speed running, poor mileage '85 5.0 CFI

Reply #1 –
i cant say it enough,,

anyone with CFI applications needs to eventually remove the carbon deposit on the base of the CFI.

i have a write up in my diy link below.  Basically go buy the cfi gasket kit (conssts of two gaskets) and remove the cfi and egr base.

locate your gold vac fitting on the rear driver side of the cfi. Up inside there is where the bottle neck is. 

Its pretty simple,, if the egr diaphram can not get vac signal due to blockage at the egr base, the EVP sensors range of motion can not send a good voltage to the eec, which ends up being a circle of madness eventually causing fuel consumption problems.

while you are at it,, replace your injector screens or just yank them out.  Doing this will fix the often complained about "hesitation" issue.
 

rough low speed running, poor mileage '85 5.0 CFI

Reply #2 –
Quote from: jcassity;230137
i cant say it enough,,

anyone with CFI applications needs to eventually remove the carbon deposit on the base of the CFI.

i have a write up in my diy link below.  Basically go buy the cfi gasket kit (conssts of two gaskets) and remove the cfi and egr base.

locate your gold vac fitting on the rear driver side of the cfi. Up inside there is where the bottle neck is. 

Its pretty simple,, if the egr diaphram can not get vac signal due to blockage at the egr base, the EVP sensors range of motion can not send a good voltage to the eec, which ends up being a circle of madness eventually causing fuel consumption problems.

while you are at it,, replace your injector screens or just yank them out.  Doing this will fix the often complained about "hesitation" issue.

Hmmmmm. 

Well, I replaced the TPS, it runs smoother, mileage helped a little .... but tomorrow I'm going to stop by either NAPA or Ford and get those gaskets and clean that bugger out too!  :bowdown:

Thanks for the tip.  :cheers:

I did do a search before asking, I guess I overlooked it or I used the wrong search terms.  What you say  may well be a big part of it at 143,000 plus miles.