Renix power and mpgs problems

Longer post...sorry,

88 renix 4.0 ba10 manual trans basically stock engine minus 4 hole injectors. 2" lift with 30" tires. Nothing crazy or heavy like bumpers or axles.

So I've read a ton of posts about these renix problems. My problem is I've replaced or checked everything I can think of and I'm still burning through gas and have to downshift up every hill even tiny ones and I have a really hard time getting up to 65 mph.

I have replaced every relay and checked every sensor based on lunghd website. I have done all of cruisers tips. New cps, plugs, wires, swapped injectors, o2 sensor, iac, tps. When I got the jeep a few years ago it ran really rough and sucked down gas but it would hit 80 mph easy and had tons of power. Recently the power has been lacking but mpgs were destroyed and it was running crazy rich based on about 8 different cracks and holes in the exhaust manifold. So a few days ago a shop fixed the holes and replaced the head pipe o2 sensor and cat. I ran it for a while and then readjusted the tps to a good idle. Fixed the rich smell out the exhaust but it's still really lacking power and still sucking down gas.

Help!

Almost need a long detailed blow by blow run down on what you did and when, to help.

But my first thoughts are low fuel pressure at say WOT, low compression like mine (it is gut less) or a clogged exhaust. How about the pipe and muffler after Cat?

Have followed my O2 sensor tests thread and tested to see if it is rich or lean at various RPM?

What plugs are you using?

Is the Dizzy index off by one gear tooth?

Timing chain jumped (not likely, but never know)

Does it run smooth at idle and while accelerating, but just gut less?

So cat back is not replaced yet. the shop said they thought it was basically empty right now; like rusted/rotted out so when i get more money i will finish that job, but figured the cat was providing the needed back pressure and the muffler wasn't blocking anything.

I have not checked the o2 sensor for voltages since it was replaced a few days ago. the wires and plugs are napa and not super old, maybe 6 months. And the distributor cap has been replaced as well and the timing chain was actually one of the first things i replaced when i got the jeep. It was and should be all good and same with distributor timing. I did the cut off tab and reposition service bulletin from the fsm as well and timing seems to be ok but i will get a timing light in a couple days to check its still good.

compression was all good at the end of may(last time i checked and still low power at that time)

The IAC and TPS were replaced when i had a bouncing and high idle problem a while back and the cps when i had no start problems and it measured around nothing when it was failing but now its good.

Ill look into the o2 sensor in a little bit.

??? Post says you replaced the Cat? POst 3 says "So cat back is not replaced yet"

Cat Back? What is a Cat Back?

IF you have not replaced the Cat converter it is 99% probable it is the problem and welded shut seal off by excess temps from running rich too long. Ot the Cat guts are loose and blocking the exhaust

Disconnect the O2 sensor and run it. If there is still no power, gutless, the low power has nothing has NOTHING to do with the O2 sensor or circuit.

O2 heater relay, wiring or ground wires to the O2 sensor are good front drive shaft targets and exhaust manifold targets. Any problems with the O2 circuit or sensor of the heater in the sensor can cause low MPGs.

Sure sounds like a clogged exhaust system, IE a clogged cat converter.

First things first......what gear ratio are you running?

I don't know if this actually made more power or at least feel it. But when I changed out my battery cables and grounds it was like driving a new car. It really picked up after that. Might be worth a shot checking the grounds and such.

sorry about the confusion. New cat, nothing behind the cat is new. Limited funds only allowed for work on exhaust manifold and cat replacement. The o2 wires looked good but i will check them with a multimeter in the morning when i gets light. And all battery cables and ground wires are either new or verified low enough resistance to keep and contact points cleaned up to shiny metal. Thanks for the help guys.

So u have 30" tires on a jeep with 307 gears...that may be why it is so down on power,have u checked fuel pressure and have u checked to see it the fuel regulator is leaking fuel into the vacuume system..they will occasionally fail and do that,are the spark bugs grappled correctly and the right heat range

vacuum tests good but I'm not sure how to tell if the regulator is leaking or not. The fuel pressure was good last i checked but ill check again when i get ahold of a tester. Ive been actively looking for a cheap 8.25 axle to swap for my dana 35 so when i find that ill gear correctly but haven't seen the logic in dumping money into my 35.

I take it low power means poor acceleration? Or you mash the pedal at speed and it is slow to build RPM's?

One cause can be timing and timing is mostly controlled by the TPS and MAP. Check your MAP vacuum tube. It can rub on the harness and cause a tiny leak or crack. Make sure it is plugged into the correct outlet on the TB. The MAP can cause fuel/air mixture/timing issues. The issue is usually corroded connectors or a harness issues, rarely the MAP itself. Use a mirror and have a good look at the MAP connector on the MAP. Be careful of that MAP vacuum tube, old plastic gets really brittle.

Adjust the TPS to .8 volts. If that screws up your idle you have another issue. Check your adjustment voltage to both the TPS ground and battery ground just as a check.

Ohm check the TPS ground wire on the TPS side of the connector to battery ground.

The O2 harness has a habit of burning on the exhaust manifold behind the power steering bracket. Almost impossible to see back there. Happens a lot after a new water pump install, the harness gets rerouted wrong. Cruiser has a write up on the right routing.

Timing light is all but useless with the Renix. All I ever use it for is to check if it advances when the throttle is applied.

When your Jeep is cold check the engine temp sensor (lower drivers side block) and the manifold temp. sensor for ohm readings. On an overnight cold engine they should be the same or very close.

If all else fails you may have to check your initial cam timing setup, not as hard as it sounds. Renix timing is pretty darned flexible and makes it's own adjustments. The initial setup check is a pain but pretty simple. Turn the balancer, until you get compression on number one cylinder, last movement to the right facing the front of the motor, until you hit timing zero, If you go past, backup a quarter turn and try again. Check your rotor position, should be a little after "1". Like I said, a little off initial setup isn't critical (Renix will adjust), a lot off is. You may be a full position off on your rotor and/or even your firing order. Most distributor caps are marked for "1". You can be way off sometimes and it it will idle fine. I tried all sorts of wrong setups on purpose (curiosity) and was amazed at what I could get away with, sometimes/sort of.

If you are still having issues you may have to remove the valve cover and check your number one rocker positions. Something to think about if the easier stuff doesn't work out for you.

I know this initial setup thing is likely redundant. But worth a double check. May cost you an hour, may save you 20 hours.

I'll be watching this thread. 10 mpg wit 4.88's and 35's with ZERO power is less than ideal. But I have tons of blow by

In actuality the Renix is nearly as quick as the HO. The only real difference is the Renix has more grunt and the HO makes a little more horsepower higher in the RPM band. The difference in a quarter mile is negligible, different shift points.

My Renix scoots with 29.5 inch tires.

I feel lucky if I get 15 MPG. I do a lot of low speed driving. Straight highway at or near 2200-2400 RPM, steady pedal and it does a whole lot better on mileage.

Before my dad died and his/now my jeep sat for a couple of years he and my mother routinely go 20-22 mph with their daily driving. They live in the country and it is mostly highway driving. The Jeep is an '89 Renix 4.0 AW4 2 door.

So life happened and i haven't been able to do anything with my jeep except suck down gas.

I finally had a bit of free time but i now only have one arm free because i had wrist surgery so some stuff is either impossible or too hard to try. I rechecked the vacuum and its good. grounds still look good and shiny. unplugged the o2 sensor and drove a bit and nothing changed from a power or acceleration standpoint. I could smell it running crazy rich though so it is working. I also followed the wiring up and it looks good and is free and clear of hot contact areas. So next time my arm is a bit more functional or i can find someone to help me i will start checking voltages and ohms on all the sensors again. I do know that my tps is not close to the called for voltages but the idle is perfect so I'm assuming something else is wacky. If i adjust the tps to around 17percent of reference it is redline rpms at start/idle. I don't remember what the voltage is right now for it but i know its set pretty low.

You said you went with 4 hole injectors.....exactly which ones? Manufacturer/model#?

Honestly I'm not positive because it's been awhile but I'm pretty sure I got 703's. I have been thinking of taking them to napa to get them cleaned and tested but haven't done it yet.

ljobbins said:

So life happened and i haven't been able to do anything with my jeep except suck down gas.

I finally had a bit of free time but i now only have one arm free because i had wrist surgery so some stuff is either impossible or too hard to try. I rechecked the vacuum and its good. grounds still look good and shiny. unplugged the o2 sensor and drove a bit and nothing changed from a power or acceleration standpoint. I could smell it running crazy rich though so it is working. I also followed the wiring up and it looks good and is free and clear of hot contact areas. So next time my arm is a bit more functional or i can find someone to help me i will start checking voltages and ohms on all the sensors again. I do know that my tps is not close to the called for voltages but the idle is perfect so I'm assuming something else is wacky. If i adjust the tps to around 17percent of reference it is redline rpms at start/idle. I don't remember what the voltage is right now for it but i know its set pretty low.

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Begin here at Tip 1 and work your way through Tip 5. If these grounds are poor, it wreaks havoc with a bunch of sensors" signals to the ECU.

www.cruiser54.com

ljobbins said:

Honestly I'm not positive because it's been awhile but I'm pretty sure I got 703's. I have been thinking of taking them to napa to get them cleaned and tested but haven't done it yet.

Click to expand...

703s are not what you want for injectors on a Renix. Do the tips and see what you find. 746s are the injectors you want.

If the TPS is off it will affect the power and drive-ability while the idle is great.