TheLoudestSilence

Well i checked the codes on my 88 today and one of the codes i got was 81 map has not changed normally and 41 oxygen sensor circuit indicates system always lean... along with some other stuff but these two inparticular worry me... If I had a vacuum leak somewhere that would keep the MAP from changing how it was suppose to right?? and having a vacuum leak would mean more air and less gas so my computer would try to add more gas to equalize it right?? meaning it burns more gas than needed witch results in my poor fuel mileage??

I have no idea what im talking abou though so i could be wrong if I am please tell me..

But if what i thinkis right I need to find out how to locate the vacuum leak and the best way to plug the line..

as i said in my last post the pollution stuff has been disconnected and that includeds this little canister that sits on top of the passenger wheel well I was told all this canister did was hold a vacuum which means theres no doubt there has been lines plugged around it that are vacuum lines.. how would I go about checking to see if their sealed good enough??

dewman

One way to find a vacuum laek is to listen while the truck is running. You should hear a hissing sound that is created by the compromised vacuum line sucking in air. If you find the bad vacuum line, you can use a temporary fix of wrapping electrical tape around the line. I did this on a Dakota I used to own and it held for more than 2 years.

Good luck.

06fordf150

you can go to autozone and get a stethascope to listen around also!

Strangerous

I always liked the carb cleaner method, ***don't do this on a hot engine*** on a hot engine though. When you spray around a vacuum leak, you can tell an audible difference in engine revs. Anything flammable from a spray can will work, carb cleaner was always in abundance in dad's shop.

TheLoudestSilence

Well that sounds easy enough.. Im going to try this either tonight or tommorrow.. I suppose starting fluid would work the best so ill pick some up today... Thanks for the help guys

bjafeman

Your bad MAP theory on fuel consumption is completely possible. Given what you've ruled out so far, it's a likely candidate.

The procedure for testing your MAP sensor involves applying a vacuum and taking tachometer readings (not the one on your dash, one of the expensive hand held ones). In general, you can unplug the MAP's vacuum line to see what happens while it's idling. No change in idle would point to a poorly or non functioning MAP. If you happen to have a vacuum application tool, you can apply a vacuum to it while it's at idle, that should definitely effect the idle.

Picking up a cheap vacuum gauge and connecting it into the system is a great way to keep tabs on older trucks like these. In addition to learning whether or not you've got a big vacuum leak (small ones might not show on a guage, hence starting fluid method) it can tell you a lot of useful info about your ride while it's in motion.

http://www.secondchancegarage.com/public/186.cfm

Curious if other people have tried this as well. I've installed a vacuum gauge on my dash and found that the vacuum that the engine is pulling is roughly what my mileage is as well (i.e. 15hg = 15 mpg). Tends to do a lot for keeping your right foot light weight.

TheLoudestSilence

Hmm I dont have a tach on my dash and i sure dont have an expensive one.. id like to put a guage on my truck though.. sounds like it come in handy.. can i get one as a kit or somthing from autozone or advance or do i have to order one?? and roughly how much do they cost??

Dominick

A vac leak on a MAP system = more gas
less pressure in the manifold it thinks the petal is being pressed and ignoring the TPS.



Vac leak on a MAF system = less gas
air getting in not being metered by the MAF it has no clue to add fuel.

TheLoudestSilence

well i went out started the truck up let it run about a minute then unplugged the MAP vac line and it died... i plugged the line back up and started the truck again and sprayed some starter fluid all around the lines i could see and didnt hear any noticable idleing difference... im once again lost as to whats causing this gas mileage... a 4.9 I6 with auto transmission and 3.08 rear end should get 15 miles a gallon right??? this 8 or 9 miles a gallon is killing me

Dominick

How old is the MAP and O2 sensors? And also you can use a hand help
propane torch just turn it low no flame and check for leaks that way.

Less messy and it does not hurt the O2 sensor thats to say if the O2 is good in the first place.