Tune up = worse gas mileage, wtf

I had the cam sprocket off, pretty sure that can only go on one way right

Yeah the factory cam gear only fits on one way.

What TEMPERATURE stock OEM thermostat did you install? I believe a 195F was the recommended temperature. If you got a factory 180, for example, you'd run cooler and possibly suffer some mpg penalty.
I don't remember if it was mentioned, but the incoming air and coolant temperature sensors feed the computer and it modifies fuel regimen accordingly. If your CTS or IAT sensors were on the way out, that could affect fuel use. The CTS is not the same sensor that runs your gauge or light, it is a second sensor all by itself, providing coolant temp. You can find 'acceptable' readings at different temperatures in the shop manual that would indicate if they are kerflooey.
tom

tomw said:

What TEMPERATURE stock OEM thermostat did you install? I believe a 195F was the recommended temperature. If you got a factory 180, for example, you'd run cooler and possibly suffer some mpg penalty.
I don't remember if it was mentioned, but the incoming air and coolant temperature sensors feed the computer and it modifies fuel regimen accordingly. If your CTS or IAT sensors were on the way out, that could affect fuel use. The CTS is not the same sensor that runs your gauge or light, it is a second sensor all by itself, providing coolant temp. You can find 'acceptable' readings at different temperatures in the shop manual that would indicate if they are kerflooey.
tom

Click to expand...

it was a 190 motocraft


I'm really starting to wonder if the carb cleaner damaged a sensor or something in the TB or IAC

I would get/rent a Fuel pressure gauge.
Start engine and see what pressure you have, should be 32-42psi
Turn off engine and key then watch pressure gauge, it may drop to maybe 30psi but then stay there, leave it for 20 min and check again.
If it is dropping slowly then you have a small leak and it is evaporating pretty fast or you would smell or see it.
Check fuel line connections at FPR(fuel pressure regulator) and main fuel rail connection.

Heck, put all the old parts back on and see if the mileage goes back to where it was.
If you don't like that idea, then go through all the steps you took in doing your work. Write them below in the "quick reply" box. Press the 'post quick reply' button.
tom

Don't have any of the old parts so that's not an option


0. remove intake tubing, air box, and battery
1. unbolt a/c compressor and bracket it's sitting on.
2. remove serpentine belt
3. Unhook radiator hoses and remove radiator, fan, and shroud shroud
4. remove timing belt cover
4.5 remove cam sprocket, replace camshaft seal
5. remove water pump and replace with new one
6. remove timing belt, replace tensioner
7. replace thermostat
8. remove throttle body
9. unbolt IAC from throttle body, spray IAC and TB out with carb cleaner
10. remove valve cover, put on new gasket
10.5 replace spark plugs and wires
10.75 put valve cover back on
11. put cam sprocket back on, put timing belt and timing belt cover back on
12. put everything together


I think that's it

RonD said:

I would get/rent a Fuel pressure gauge.
Start engine and see what pressure you have, should be 32-42psi
Turn off engine and key then watch pressure gauge, it may drop to maybe 30psi but then stay there, leave it for 20 min and check again.
If it is dropping slowly then you have a small leak and it is evaporating pretty fast or you would smell or see it.
Check fuel line connections at FPR(fuel pressure regulator) and main fuel rail connection.

Click to expand...

I called around and no one rents one. Is there any reason you suspect a fuel issue? I mean I don't think anything I did could cause a fuel pressure issue.

One possibility is the carb cleaner may have contaminated the O2 sensors or the catalytic converter. You mentioned the engine was misfiring for a while. The O2 sensors may be sending incorrect signal to the computer resulting in less mpg.

Before replacing the O2 sensors, you should consider running a product called Cataclean by Mr. Gasket through the engine per instructions on the bottle. A friend of mine used this product on his vehicle because the CEL light kept coming on and could not get his smog test done. His mechanic told him the cat was bad and needed to be replaced. He decided to try this product before spend all the money to replace the cat. After using this product, no more CEL and it passed smog with no problem. It is suppose to clean injectors and O2 sensors also.

Certainly no guarantee that it will help and it is not cheap but probably worth a try.

The carb cleaner had evaporated long before I put the TB back on. It was missing a couple weeks before I did the tune up because of a dirty MAF. I cleaned the MAF sensor before I did all of this and was getting the same MPG as I did before so I know it's not related to that. The upstream o2 sensor was replaced a few months ago and the cel isn't on.

gw33gp said:

One possibility is the carb cleaner may have contaminated the O2 sensors or the catalytic converter. You mentioned the engine was misfiring for a while. The O2 sensors may be sending incorrect signal to the computer resulting in less mpg.

Before replacing the O2 sensors, you should consider running a product called Cataclean by Mr. Gasket through the engine per instructions on the bottle. A friend of mine used this product on his vehicle because the CEL light kept coming on and could not get his smog test done. His mechanic told him the cat was bad and needed to be replaced. He decided to try this product before spend all the money to replace the cat. After using this product, no more CEL and it passed smog with no problem. It is suppose to clean injectors and O2 sensors also.

Certainly no guarantee that it will help and it is not cheap but probably worth a try.

Click to expand...

How many tanks have you done since the tune up, with this lower mpg result?

6.2 said:

How many tanks have you done since the tune up, with this lower mpg result?

Click to expand...

I did one tank and got the 17.5 and am on my second tank now. The needle is much lower than it usually is for the amount of miles since I refilled just like it was last tank.

I'd give it a couple tanks before I got to worried. Let it relearn your driving style etc. Since you had the battery unplugged it reset everything.

Since I have owned the truck I have never got less than 20 mpg and I have had the battery out several times. There is definitely something causing me to get bad mileage.

Because this problem only started when you did the tune up and you said the new wires have a loose fit and don't snap onto the spark plugs , I would squeeze the wire ends to m down to make sure they have a tight fit .

XLTsplash said:

Because this problem only started when you did the tune up and you said the new wires have a loose fit and don't snap onto the spark plugs , I would squeeze the wire ends to m down to make sure they have a tight fit .

Click to expand...

what you mean squeeze the boot that goes over the plug with pliers with it off the plug?

I'll try it but I took a 15%+ loss in mileage and it's not missfiring