fuel blowing back into airfilter.

89 xj 4.0 400k

So this jeep is new to me, i fixed a lot of issues with help from this form and a few others. My main issue now is that i noticed is that its blowing gas into the air filter from the head. no oil at all, just gas.

i did a lot of searching and have found nothing.

it has also been having oil pressure problems. maybe they are related?

cold start is find, around 20-30 psi. once it warms up it drops to like 0

i changed the oil. put in 10w 30 and some lucas treatment. i replaced the oil sending unit, nothing, then got one of those mechanical guages and installed that, still same thing.

then i noticed the old oil smells like gas.

any ideas? im stumped...

thanks in advance!!

Check the Fuel Pressure Regulator, sounds like the diaphram is letting fuel get by and getting sucked into intake manifold.

It's at the front end of the fuel rail(my vacuum hose is disconnected in the pic).:gee:

That is very possible. Check your oil pressure with a mechanical gauge. Factory sending units are known to be faulty.

RyanKnol said:

i replaced the oil sending unit, nothing, then got one of those mechanical guages and installed that, still same thing.

Click to expand...

Usually even the engines with worn bearings will have cold pressure up to 40 or so. Every time I've seen pressures that low a new oil pump tends to be a good start.

Gas in the oil is indicative of a leaky injector. If you pull the dipstick and smell it, see if it smells like gas. If so, you REALLY need to fix this or your engine will be trash shortly. I will try and follow up later with more info.

If you can, leave the vehicle parked and don't start the motor. relieve the pressure at your fuel rail ... should be a schrader valve that allows you to do that. Wait further instructions from Old-Man on locating the leak.

I have just a minute so I will give you a bit of followup info. When you turn off your rig, a leaky injector will continue to leak fuel into the cylinder until the fuel pressure is reduced. It will wash the oil off the cylinder walls and will lead to scoring of the walls and galling of the piston skirt.

One by one pull the plugs. You should be able to tell fairly easily which injector is leaking as the plug should probably be wet or at least look radically different. The corresponding injector will need to be replaced or you might be able to get a shop to clean it and get it working.

Besides causing scoring and galling, it will dilute the oil and lead to crankshaft, rod, and cam bearing failure.

You will need to change the oil and the filter as well. Be more careful than normal with the oil as it will contain quite a bit of gas and it will be quite flammable.:flame:

Hope you caught it early and no major damage done.

I think your right. There is a ticking sound when i shut off the engine sometimes too that come from around the fuel rail. This might explain that too.

Would i be able to pull the injector and clean it myself? maybe use some of that fuel injector cleaner additive?

I just replaced the spark plugs within 200 kms ago. Do you think there would be a noticeable difference yet? I still have the old ones in the garage, but i have no idea which is which.

Thanks alot for the help!!

Ill keep you posted

After some advice from other members here I just replaced my injectors outright. If yours have never been replaced they are a fire hazard and should be replaced ASAP. The injectors in these old Renix rigs are known to fail and cause engine fires... It just sounds like your injector failed and is letting fuel pressure to bleed off and drain down into your crank case. You should do some research on FoMoCo injectors as the early to mid '90's injectors are plug and play and are a much better design. I have done this (mine is a Renix rig also) and while the hp and mpg haven't changed, the throttle response is a little crisper and startups are almost instantaneous now. BTW the injectors I picked up (from a junkyard) were Ford P/N: FOTE-5DA or Bosch P/N: 0280150943. Good luck with it!