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losing gas...

M

Micha

NAXJA Forum User
Location
Vancouver
87 4.0 xj
335.000 km, supposedly unaltered (as i got the car last year)
engine runs smothly for the age and after changing the o2 sensor about 5 month ago i had a consumption of about 19-20mpg (12l/100km)

now i have a sudden drop to >20l/100km or 11mpg
car starts up fine, runs good in idle and under load,
sparks are grey with a hint of brown so it seems to run ok to lean...

where the bleep does my fuel go?
i have a light smell of fuel on the rear of the car, around the filler.

any ideas? what would be the next step, how do i trace that problem?

thanks a lot,
michael
 
new cap a few months ago, fits nicely and tight.

o2 and egr: i thought about it, but wouldn't i feel a diffeerence in driving if the engine would get too much gas?
the spark plugs look just fine - they should be black if the o2 sensor is faulty and lets the car run in open loop all the time, or am i wrong about that?

plus: the car would still be running at about 14mpg, not as low as it is now?
 
The tank may be bad. I worked on an 88 Laredo last year that leaked badly. I replaced the tank with one from an 87 parts car that I was sure was good, and a month later that one leaked if filled above 3/4.

Another possibility is that the mounting flange for the fuel pump can rust through. I'm facing that on my 88 Comanche right now. Replaced the tank, filled it, and gas poured all over the ground. Looks like the pump flange is porous, but it won't get fixed until warmer weather.
 
Micha said:
jb weld as a quick fix in this case?
will it withstand the gas?
Click to expand...

I do know that epoxy resin will work on a small hole, so I don't know why JBWeld wouldn't. Quite a while ago I found that the tank on my 95 had developed a couple of little rust pinholes right at the top (very common, because mud and slush come to rest on the top). Since the rest of the tank was fine, I filed it down as well as I could to bare metal, needless to say I did not power sand or grind (!!!), laid on a little West System epoxy, a little patch of fiberglass and some more resin on the top, and never a leak since. While I was at it I cleaned off the other incipient rust spots and dabbed epoxy on them too. As I understand JBWeld, it's just thick epoxy resin with metal dust in it, so it probably wouldn't need the little piece of fiberglass (West System is very thin, paintbrush consistency).

However, as far as I know, there's no way to fix it if it's leaking at the seam.
 
Just drove my '90 XJ across from Seattle that I got from my brother. We found out that the tank had a leak at some point above half. Back home again, I've had it into the dealership to see what's up with it. Seems the leak is coming from the sender, and has to be replaced. Might be worth a check and see.

Good luck!
 
Check the fuel press. regulator on the fuel rail (front of the rail, round can @ 1" dia. w/ vacuum tube connected to it) Pull the vacuum hose off and see if it has liquid fuel in it(dripping?). Then turn the key on without starting engine and see if fuel is squirting out of the nipple where the vacuum line was connected to (do this w/ engine cool if you want to be safe). Other sypmtoms of bad regulator: rubber vacuum fitting swollen/mushy, hard starting like it's flooded because it is. I know you said it started OK but if the regulator diaphragm is just starting to leak it may take a combination of pressure on the rail and vacuum at the nipple to draw a substantial amount of fuel. This is about the only failure I have seen that can make that drastic a MPG change in that short of a time. Hope this helps.

Brian
 
just checked the jeep: there is no gas in the vacuum line, no gas dripping out the open regulator... if i suck on the vacuum line connected to the regulator (at the manifold end) i get a gas smell but no actual fluid. it does seem to hold the vacuum, but then again that's just me sucking :)

still: you might be on the right track, as i don't have puddles under the car (no matter what fluid level ) and a small hole in the top part would probably not lead to such amounts of evaporation that i end up at 11mpg...

i will try to get the fuel pressure regulator tested with the proper tools, would like to not have to take the tank down...

micha
 
I had a friend with the same problems: sudden fuel smell, bad mileage, no explanation. I went to visit the Jeep, & it reeked of gas. What have you done recently w/it? I asked. "oh, nothing." "how new is that subwoofer box in the back?" "3 days ago" . He had drilled holes in the floor for L-brackets to mount his sub, & the tank sits pretty close to the body in XJ's. We dropped it, (10 mins. & most, left everything attached except the fuel lines, which we were changing anyway) JB'd the heck out of it, & fixed his issues.
 
after you drive it and then park the jeep.... give it a minute then look under the jeep from the front and see if you notice any small wet spots under the drivers side. Look under the rest of the jeep too.. dip finger in and smell to see if it is gas... thats how I found my leak.... turned out to be at the fuel rail where the hose connects... leak was so small when parked it was hard to notice it at all.... back up to 18-19mpg now.
 
explorer said:
Check the fuel press. regulator on the fuel rail (front of the rail, round can @ 1" dia. w/ vacuum tube connected to it) Pull the vacuum hose off and see if it has liquid fuel in it(dripping?). Then turn the key on without starting engine and see if fuel is squirting out of the nipple where the vacuum line was connected to (do this w/ engine cool if you want to be safe). Other sypmtoms of bad regulator: rubber vacuum fitting swollen/mushy, hard starting like it's flooded because it is. I know you said it started OK but if the regulator diaphragm is just starting to leak it may take a combination of pressure on the rail and vacuum at the nipple to draw a substantial amount of fuel. This is about the only failure I have seen that can make that drastic a MPG change in that short of a time. Hope this helps.

Brian
Click to expand...


This sounds like what I've got. I just bought my XJ last week, and all of the vacuum lines are either mushy or so soft they won't hold the hard lines that fit into the elbow fittings. Idle isn't very smooth and it seems to go through gas pretty quick and I do get a little gas smell after it's been running a while. The fuel guage moves around quite a bit too. It's just a DD for now, but I've got to get it running better soon.

Later,
Keith

BTW... 1989 XJ Larado, 2dr 4.0, 149,xxx miles
 
Micha said:
just checked the jeep: there is no gas in the vacuum line, no gas dripping out the open regulator... if i suck on the vacuum line connected to the regulator (at the manifold end) i get a gas smell but no actual fluid. it does seem to hold the vacuum, but then again that's just me sucking :)

micha
Click to expand...

Did you try pressurizing the rail w/ hose off? When you are sucking on that hose, you are just sucking on the manifold and if you could develop a vacuum sucking there you either have some super lungs or there could be a collapsed line somewhere(SORRY just reread and saw where you were sucking). The other poss. is an injector leaking down. This would give some of the same symptoms, but usually the mileage would not drop that bad because they are always flowing some anyway when the engine is running.

Brian
 
You may have already checked, but it was not mentioned anywhere... Check the injector o-rings. Not uncommon, and the majority of the fuel can easily evaporate before it gets to the ground. This is extremely dangerous, and has caused a few to burn to the ground since they leak onto the exh. manifold. Ii believe they more commonly leak on the intake end of the injector rather than the fuel rail side.

Best of luck.

TheRasper.
 
TheRasper said:
You may have already checked, but it was not mentioned anywhere... Check the injector o-rings. Not uncommon, and the majority of the fuel can easily evaporate before it gets to the ground. This is extremely dangerous, and has caused a few to burn to the ground since they leak onto the exh. manifold. Ii believe they more commonly leak on the intake end of the injector rather than the fuel rail side.

Best of luck.

TheRasper.
Click to expand...

Indeed, it can be almost impossible to spot leaky injectors unless you watch them as the engine runs. The evaporation is very quick in a hot engine compartment. The Renix era injectors often leak at the electrical connection. In this case there is no fix but new injectors.
 
When it is parked, do you see signs of any leakage under the tank anywhere? Seems when mine is somewhere around 3/4 full or higher, it is seeping on the drivers side somewhere. [around where the tank is joined I suspect as it's in the back top of the tank] which is probably due to the rust, as the XJ originated in Thunder Bay. [Canadian winters in salt= rust!]
Looking at having to replace the entire tank now unfortunately.
 
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