Low Mileage with Reman Engine

[wohley8]

I have recently (1k) ago put in a remanufactured engine into My 98 Eagle Talon Tsi AWD. Car idles smooth, pulls nicely, but mileage is way down. I used to get 270-280 miles on a tank of 93 octane consistantly. Now on my last tank of gas, I got 180, can pretty much watch the needle move...

Previously my car was 100% stock... at the time of the reman engine install, I did get a Forge BOV, and now have a 3" turbo back exhaust system I got from Slowboy Racing. I would have thought the exhaust would have helped mileage. Temperatures have been about 30-40? F.

I read some threads on the Forge BOV, some people have leak issues, but I am running stock boost levels...

Any ideas on where to start to diagnose the issue? I'm hoping it's not an issue with the motor.

 

[talon210]

Have you tried checking the o2 sensor? I had the same bad gas mileage problem and figured out that it was a bad o2 sensor and it gave me a good 5-7 mpg when i replaced it. My car was burning so rich that people didnt want to be behind me because of the incredible amount of gas you could smell.

 

[wohley8]

Did you get a CEL that let you know the O2 sensor was dead/dying? I am not getting any lights at this point...

 

[hereitcomes]

Well your turbo back exhaust is going to increase output of the engine leading to more power - and a slight decrease in HP. But freeing up flow will help with mileage, so it should balance itself out. Your decrease is significant though. It could be the new motor working itself in, and adjusting to your driving habbits.

 

[nuclearpenguin]

http://members.shaw.ca/costall/1000Q/answers-O2andEGT.htm#whynocheckenginelightonO2

Sometimes you might get the CEL, sometimes you might not. Do you have a datalogger or anything to monitor the a/f and see if you're getting a signal? That's the best way to check

 

[hereitcomes]

AHH yes the data logger. Now why didnt I think of that? Silly me.
The A/F is a good generalization as well, but a wideband A/F with o2 sensor will give you the most accurate readings.

 

[Ultimatedsm]

Does your FORGED BOV Vent to the atmosphere or does it recirculate the air back to the intake tract?

 

[wohley8]

Does your FORGED BOV Vent to the atmosphere or does it recirculate the air back to the intake tract?

The Forge BOV is recirculating. I was down at a friend's today, and he gave me an 90 degree elbow to straigthen out a kink in the line. It was a EVOIII BOV, only difference is the position of the nipple, on top not on the side as with the stock 2g. He put his hand behind my exhaust and his hand near got black with soot. I'm afraid I might have some blow by, and I think I should get a compression /leak down test to make sure my rings are OK. I had quite an adventure with the rebuild... The shop told me 4-5 days, was 6 weeks till I got my precious back. I told them the mileage I was getting, they told me it's the way I drive.

I digresss... no logger currently. People are telling me it would throw a code if the o2 sensor was not picking up, but not everyone. I will probably have to take it into the shop to hook it up and see what the ECU says. That kind of mileage, I think something has to be wrong.

 

[Blueiii]

Hooking it up to check if you have a CEL still might not indicate anything. If the o2 sensor is on its way out you will see a decrease in mileage, however you won't see a CEL until it fails.

 

[wohley8]

Hooking it up to check if you have a CEL still might not indicate anything. If the o2 sensor is on its way out you will see a decrease in mileage, however you won't see a CEL until it fails.

I went ahead and ordered the (2) O2 sensors, a little past due on replacing them in any event, and they were taken out for the rebuild, so maybe being handled did not agree with them. Sure hopes this solves the problem.

Appreciate all the good advice, all... I will post again once I have them in and see what my MPG goes to.

 

[wohley8]

Well, I have the 2 new O2 sensors installed, no change whatever. Car is is running rich they tell me, oil gets dirty very quickly. I hate to think of awhat all the carbon is doing to the internals. I have to think I have some type of serious problem. The shop that did the install wanted half a grand to find out where they went wrong...