Increased fuel consumption after catch can?

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Yesterday I installed a Steeda 555-3710 oil separator on my Grand Marquis, after experiencing problems with detonation and some blue smoke out the passenger side tailpipe only (no smoke at all from the driver's side tailpipe).

The good news is, there's no more detonation and no more blue smoke no matter what you do. I don't know how relevant this is, but the car has much better get up and go as well. The downside is I noticed a huge drop in fuel economy.

I fueled up right after installing the oil separator. Generally, by the time I have ¾ of a tank left, I would have usually driven between 125-150 km (79-94 miles) depending on how much city driving I do. I did a lot of highway driving yesterday and whilst the car has excellent get up and go, I've got half a tank left with just 160 km (100 miles) on this fill up.
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Refueling every 320 km (200 miles) and 20 L/100 km (11.8 MPG) is a bit too rich for my blood. I used to average about 13-13.5 L/100 Km (17.5-18 MPG) with a bit of spirited driving, although with a light foot managed to get 12.5 L/100 km (18.8 MPG).

So this left me wondering if the catch can has anything to do with the air/fuel ratio and gas mileage. I was thinking maybe the PCM adapted to the issue, because there was quite a bit of oil going in. I thought about reseting the PCM to see if anything changes, although I was also considering leaving it alone to see if anything improved over the course of the next couple of fill ups. Any thoughts? Thanks!
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The precision with which you're measuring MPG leaves a lot to be desired...you can't go off how many KM you've gone by a gauge reading...To get an accurate MPG, you have to know the exact number of miles driven and the exact number of gallons (litres) added.

In this case, your one sample of a partial tank and rough estimate has lead to a faulty determination of MPG...I wouldn't worry about it. Take a few accurate measurements, I doubt this thing affected MPG at all...
 
Originally Posted By: Astro14
The precision with which you're measuring MPG leaves a lot to be desired...you can't go off how many KM you've gone by a gauge reading...To get an accurate MPG, you have to know the exact number of miles driven and the exact number of gallons (litres) added.

In this case, your one sample of a partial tank and rough estimate has lead to a faulty determination of MPG...I wouldn't worry about it. Take a few accurate measurements, I doubt this thing affected MPG at all...



Quite true. I keep a record of my fill ups and fuel economy both in an Excel spreadsheet and on Fuelly. I just have a rough estimate of where the fuel gauge would be at a certain mileage on the trip meter, which I reset at every fill up, and that's what I was going by. I'll be filling up again tomorrow, so I suppose that will help produce a more accurate reading as opposed to a gestimate.
 
How did the catch can stop massive smoke and detonation?

I don't get it.

I like and use catch cans, but they are to keep other parts clean of sludge.
 
The smoke wasn't massive, but enough to keep leaving an oily residue on the tailpipe. You'd have to rev the engine hard or drive at WOT to put enough load on the engine for there to be smoke. The tailpipe is now bone dry, and I've put just over 500 km (313 miles) on it since I installed the catch can.

The detonation is gone. I was recommended a catch can on the Crown Vic boards after posting about detonation, oil exhaust and blue smoke under load.
 
oil in the intake is in every newer car with a PCV.

As OP noted it only becomes a problem when excessive.

An Italian Tune Up works wonders, too.
 
first of all i had catch can on my 98 vic it was a little restrictive. then i found out that the 4.6 had a catch can type of setup under the valve cover....off it came..the flow of the pcv was alot better without. my experience...if this happens in morning starts then it is probably rich fuel especially when it it wet outside this is normal it smells really sweet and i little puff of blue smoke..
 
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If the catch can stopped smoke and detonation, there must have been massive blowby residue that was now trapped.

But to actually see smoke burning and have it stopped is a first - really rare!
 
Right, a bit of an update. When I was driving in stop and go traffic this afternoon at 48°C (118°F), I heard the dreaded detonation sound again! It certainly is considerably less than before (you have to pay really good attention), and it doesn't do it on the open highway. But subject it to stop and go traffic in excessive heat for a good while, and you will hear detonation at half throttle or more.

I don't know if the detonation has anything to do with adding TC-W3 to the fuel. I'm experimenting a bit these days, mixing MMO and TC-W3 together. I initially started with a ratio of 150 ml MMO to 50 ml TC-W3, but I recently upped that to 100 ml of MMO and 100 ml TC-W3. I'm running 91 RON/87 AKI gas, so maybe the 2 stroke oil is lowering the octane further, which causes the (now much, much less) detonation.

The exhaust, however, is still bone dry and there is definitely no blue smoke anymore. When I was bedding in my pads last week without the catch can, I would notice some blue smoke in the rearview mirror as I accelerate. Just to confirm, I drove the same way again today, and there was no smoke. The dry exhaust is good proof I suppose.

The catch can does have some oil in it at the moment, but nothing too excessive.
 
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