9 mpg...

[Evil Jim]

Picked up the MJ last week, 90 long bed 4.0 AW4 3.55 347K miles on 235-75-15s.

First fill up, steady backroad driving at 55ish mph was 12 mpg.

Second fill up was more around town and it got just over 9.

 

It never starts on the first crank, but always on the second try... a few seconds apart on attempts.

Has a hesitation on initial tip in of the throttle, then picks up fine.

When going to WOT it blows black.

Just adjusted the TPS, really can't tell if it made a difference.

Checked the vacuum lines, didnt find any leaks.

Going to get a fuel pressure gauge and check the FPR and to check for leak down.

If that is OK, I plan on checking the O2.

I just picked up the truck and have no idea of its service history... other than the previous owner had it for 2 years and put around 2K miles on it.

Any of you more experienced with the Renix 4.0 have any other suggestions for me.

 

Much thanks.

 

 

Jim

[dunnc1991]

This man is the one to ask when it comes to renix engines. With age/mileage I'm sure a majority of those tips will be helpful.

 

http://comancheclub.com/topic/48463-cruisers-mostly-renix-tips/

[mikekaz1]

Black is probably all the carbon burning off. I'd fill your tank with premium fuel and add a quart of kerosene that will help a bunch with any sticky injectors and joints

[mikekaz1]

Or a can of seafoam. I love seafoam

[Evil Jim]

Not the FPR, 39 psi with vacuum disconnected, 29 connected, leaked down to 20 after about a half hour.

Dumped a can of seafoam in after the first fill up.

I am hitting the junkyard in the morning... as I was leaving sunday at closing time they had a ZJ with a 3.5" RC lift in it that I am going to try and grab... will test the O2 when I get home.

 

 

Jim

[Zebvance]

test the map sensor

[mik666]

O2 sensor

[MJCARENA]

I would think it could be the MAP sensor.  Make sure the vacuum hose is still connected to it and at the throttle body it is in the correct hole, can't remember if it is the top or bottom.

[Evil Jim]

Just tested the MAP sensor... it is plumbed correctly and functioning.

When I unplug the map and seal the line it idles VERY rough and tries to die... and sometimes does die.

 

 

Jim

[cruiser54]

Do Tips 1 through 5, along with a tuneup including plugs, wires, cap and rotor.

 

Make sure your intake manifold bolts are snug.

 

Closely inspect the MAP sensor tube.  

[Black89Comanche]

it probably would not hurt to replace the spark plugs and spark plug wires (stick with the copper spark plugs)