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HELP

J

JEEP_cannible

NAXJA Forum User
Location
oklahoma
88 Xj,4.0,auto
I was making a left turn on my way home from work.When my jeep started running really rough,and missing.It acts like it isn't getting enough fuel,or not fireing on all 6 cylinders.I replaced the fuel filter yesterday no help there,and cleaned my reuseable airfilter.It will start,and run untill I go to give it gas then it falls on its face.I feather it it hits about 3 grand ,and smooths out for a while,but not for long.Then it falls flat on its face .Then starts running rough,and missing.
Anyone have this problem that can help.I'm at my wits end here.I was leaking fuel over winter from the first 3 injector seals.When it warmed up no problems,and no leaks never missed a beat.Untill the other day
Thanks for any help you can give me
 
you can try a new o2 sensor, sounds like the issues I had with the 98 xj I own, new o2 fixed it right away. gets to be a normal thing with it, must be the fuel we get here.
 
Thanks fulltimer.I looked into that a year ago,but never replaced it.I was also thinking it could be the TPS after reading some other posts.I know the o2 sensor is 80 bucks and a day or 2 wait.
 
I'd do an ohm test on the CPS. Maybe even clean the CPS if it is covered in oil or mud. Check the CPS pigtail to make sure it isn't cooking on the rear of the header. And spray out and clean the CPS connector.

Fix that fuel leak, engine fires aren't fun.

My 88 would run like **** just about the same place every morning. Only difference, between yours and mine, was mine was a right hand turn I took after dropping my son off at work every morning. It always started fine so I figured it wasn't the CPS, wrong. My CPS would go up to around 180 ohms after it got hot and was 125 ohms cold. When it hit around 180 ohms I'd have misfires, lurching and spew black exhaust soot. It acted a lot like a bad MAP sensor vacuum line

Cruiser had a write up on how to safely route the CPS wire. I do it a little differently, I tie it (with cable ties) to a section of the speedo cable. Just leave enough slack so the engine (and speedo cable) can move a little without straining the wire.

Could be something else, but sure sounds familiar.
 
Here's how to test a CPS

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8" from the stock 5/16", or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 01-26-2013
 
Might just try a fuel filter too.

Only $10 and affects fuel flow more than you might think...especially when under load.

EDIT: If the jeep starts and idles fine, I doubt highly it's the CPS. In my experience, CPS will affect the whole range of acceleration, not just under load or heavy acceleration. You might do a pressure test on the fuel line too. And have you pulled your plugs and taken a look at them yet?
 
Last edited:
SanDiegoXJ said:
Might just try a fuel filter too.

Only $10 and affects fuel flow more than you might think...especially when under load.

EDIT: If the jeep starts and idles fine, I doubt highly it's the CPS. In my experience, CPS will affect the whole range of acceleration, not just under load or heavy acceleration. You might do a pressure test on the fuel line too. And have you pulled your plugs and taken a look at them yet?
Click to expand...

I agree with a fuel delivery issue.
 
Check the vacuum line from the Throttle Body to the Map sensor. Mine had a small leak there and it had all the symptoms you are describing.

Ditch the old injectors before it catches fire.
 
If it is fuel and happened when you went around a corner, is it possible your fuel pump pickup tube is rotting out or has a hole in it? I've heard stories about alcohol blend fuel causing issues with fuel line rot. How high is the fuel in the tank?

Maybe do a volume and pressure test on your fuel supply.

When my O2 sensor was going it started fine and wouldn't really act up much until it *warmed* up (*above* about 1/4 on the temperature gauge scale). Then the trouble showed up while cruising with a steady pedal about 2200 RPM, it would buck and stumble and I also lost about 1500 RPM on the top end, it wouldn't rev anywhere near the redline. I'd try the EcoMike test and unplug the O2 sensor and see what happens.

I still think I'd look at the CPS first.

I replaced the O rings on my injectors, smear things up with a little vaseline and it slides right on in there.:)
 
I've all ready replaced the fuel filter,and cleaned my air cleaner.I did the unplug the cps for 5 minutes and plug it back in a couple of times.to be sure it had a good conection.I even took the battery cable off for 24 hours to reset everything.NO difference.While I was under the hood I replaced the old starter relay,because I all ready the new replacement in the back of the jeep.Its running the same hot or cold.and through all the RPM ranges up to about 2 grand.At 2 grand it starts upwards like a monster.then it spits after alittle while stumbles,and falls flat on its face.
To me it acts like its not getting the fuel it needs,or one cylinder isn't fireing at the low RPMS.It also dosn't want to really idle on its own after it stumbles at the higher RPMs.I have all the new injector seals,and that was going to be my next project.Right now though there no fuel leaks.
 
Put 5 gallons in the tank and see what happens.

Been there before, fortunately I decided to throw the contents of my jerry can in it on the side of the road right before starting in on diagnosing other stuff.

Oh, and if it's not just running out of gas, I bet your fuel pump ballast resistor is on the way out.
 
I sprayed around the injectors,and the rpms never went up.So i'm guessing thats a good thing.I'm going to install a new TPS today,and try unpluging the O2 senser if that dosn't work.I tryed getting a fuel pump resistor yesterday,but they didn't have a listing for it.Imagine that,so they suggested I take it off and bring it in.Then they might be able to match it.
 
Ask them for the "Ballast resistor"

You need to check the spark plugs, all of them, get photos if they do not all look normal. Test every spark plug and HV Coil wire with and ohm meter, post up the readings, and check or replace the rotor and cap. At night in the dark, look for sparks HV leaks from the Cap, coil or plug wires.

Check the CTS and O2 sensor wires for damage, heat or cuts from contact with bad things like the drive shaft or exhaust. Lot of other good advise here already so follow it to.
 
I replaced the TPS,and nothing.I keep thinking its a fuel problrm.I think I better go old school.I'm doing the plugs cap,and rotor in the Am.Hope this works.I'm pulling my hair out here.
 
It will do that for various reasons. All I can do is give you the most probable cause, eliminate that and move on to the next best guess.

CPS develops high resistance internally, it starts missing beats (pulses) and can act a lot like a severs ignition miss. Test the CPS, do like Cruiser recommended. The CPS will eventually get worse and you will have a no start. They tend to be temperature sensitive and get worse the hotter they get. They also don't like being covered in mud, oil or metal filings.

Fuel, do a pressure test. And a volume test.

LIke I said it can be various things, there are often other tip offs to the cause, like MAP problems tend to run the motor over rich, it will spew soot out the exhaust and you can smell the unburnt fuel.

You need air, fuel and spark. First figure out what is missing or in the wrong proportions and then find the cause.

Swapping components out and hoping to get lucky sometime works out, a systematic approach most always works out.
 
I bet ya it's the rubber hose in the fuel tank that connects the pump the metal line that exits out to the fuel filter.

Several Renix owners have had the hose clamp loosen up and this hose work its way off the fuel line under pressure.

You have to pull the pump/gauge assembly out of the tank to see thiNot that hard to remove with tank installed but a bear to get it back in correctly without dropping the tank.

Also, put a pressure gauge on the fuel rail test port and drive around and see what the gauge reads when it boggs down.
 
kastein said:
Put 5 gallons in the tank and see what happens.

Been there before, fortunately I decided to throw the contents of my jerry can in it on the side of the road right before starting in on diagnosing other stuff.

Oh, and if it's not just running out of gas, I bet your fuel pump ballast resistor is on the way out.
Click to expand...
did you ever try this?

I'm not kidding. I felt like a total retard after I found out I was freaking out about my engine/electronics being FUBAR when it was just running out of gas earlier than I expected.
 
I'm down to my wits end here.I put plugs,rotor,and a new cap nothing.I had no fuel in the fuel rail,so I replaced the fuel preasure regulator,nothing.Next I'm guessing is the fuel pump.I don't have see or smell any gas leaks.I can here the fuel pump pumping hit the gas,and it falls flat on its face.So I checked the fuel rail at the port,and like a slap to the face no fuel.I'm guessing I need a new pump,but I'm going to take it outto check things out first.
What a waste of time I could have done this two weeks ago.I hope this works.It almost doesn't look like the same jeep with all the new parts under the hood.$%^& !!!!!!!!:sad1:
 
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