Skipping and misfires

[HellCreek]

5 minutes ago, jdog said:

my apologies, I only did it as it seemed as tho no one wanted to help. But if we want to continue on this thread that is no issue as well. most people will not respond when it is directed at someone that is not them

ok here we go 12 and 55 are permanent codes, they will always pull up in the system, 12 is loss of battery or battery disconnected, and 55 is end of codes. the way it is being described it is a heat issue, so, other then throwing parts at it have you done any tests? What does the temp gauge say? last time a tune up was done (plugs wires filter)?

Hi, Jdog,

No sweat and no apology necessary.

The battery was disconnected when I replaced the cables, so that is a non-issue.  The temp gauge is a little off, and I need to replace the temp sender at the rear of the head.  I mistakenly thought that the gauge got its reading from the temp sensor at the thermostat housing, so I replaced that one and the thermostat while I was at it.  It started bucking and surging when I cranked it up with the engine still cold from changing those.  The problem is very intermittent, which leads me to think it is an electrical issue.  I drove it 120 miles last weekend with absolutely no problems. It drove smooth and got good gas mileage ( needle barely moved from full after 120 miles).  The plugs and wires were changed around 3000 miles ago, as was the fuel pump and the fuel regulator.  It occurs when the engine is hot or cold.

[jdog]

did you change the cap at the same time?

[HellCreek]

 

No, I didn't, but I can, and I probably need to.  It has been my experience over the years (my first car was a 1966 Chevy Impala that I got new after graduating High School) that bad plugs, wires or caps would result in a missing problem pretty much all of the time.  This problem is extremely intermittent.  It may not show itself for weeks at a time, which makes it very frustrating and almost impossible to track down.  Nowadays almost everything is controlled electrically, making those kind of issues even harder to fix.  Boy, do I miss the days when the only wires under the hood went to the headlights, and one wire to the distributor.

[jdog]

Don't blame ya there, only reason i asked about a cap, wondering about condensation. next would be test the tps, and reverence voltage, but if we can figure out a way to get it to do it so you can test it without being on the side of the highway, we just have to figure out what triggers it.

[HellCreek]

Thanks, Jason.  How would I test it when the problem occurs, or how do I make it act up so that I can test it in the garage?

[jdog]

borrowed from Dons post

 

The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine

[jdog]

to make it act up again, you gotta figure out the factors that is causing it to run poorly, whats the weather like, how long have you been driving, what kind of driving, stop and go or steady traffic?

[HellCreek]

Thanks, Jason.  I will check this out and let you know.

[jdog]

did you wash the engine when you changed the parts?

[HellCreek]

Um, no.  Why would I?  If these engines will only run right after they have had a bath, then most of us are in real trouble.

 

By the way, I mentioned earlier that this is my son's vehicle.  He brought it to me to fix, because he was just dumping money into it at the mechanic's shop.  They couldn't find the problem, because, as I said, it is very intermittent.  He has been having this problem for a few months now.  I have been working on it off and on for about a month, and the problem with the surging and missing has only happened once, but he doesn't want it back until it is reliable.  I will be testing the throttle position sensor this afternoon and will let you know the results.

 

 

[cruiser54]

Just a thought. Inspect the wiring path for the CPS harness.

 

 

[jdog]

only reason i asked if you washed it was if the cap had a crack and water got in it it would have the same issue

[HellCreek]

I thought that is where you were going on the washing thing, LOL  O.K.  I tested the voltage with a digital VOM and got 5 VDC at the constant tap and 0.75 VDC at the idle setting and 3.27 VDC at WOT.  Then I hooked up the analog VOM and there were no fluctuations throughout the sweep.  Then while tapping on the CPS with a screw driver handle, the sweep was smooth  as well.

 

Hi, Cruiser.  The CPS harness is as shown in your diagram, and the wire is not laying on the exhaust manifold                .

[HellCreek]

On 4/4/2020 at 1:47 PM, jdog said:

to make it act up again, you gotta figure out the factors that is causing it to run poorly, whats the weather like, how long have you been driving, what kind of driving, stop and go or steady traffic?

That's the real problem.  There is no discernible  rhyme or reason to the occurrences.  it will happen in any weather, any engine temperature, idle and any rpm range, driving in heavy traffic or cruising down the highway, and not always in any of those conditions.  As I said very intermittent.

[cruiser54]

Ever done this?

 

CRUISER'S MOSTLY RENIX TIPS

CONNECTOR AND RELAY/RECEPTACLE REFRESHING

OCTOBER 30, 2015 SALAD 24 COMMENTS

 

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together.

There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.

Revised 1-31-2016

[cruiser54]

This?

 

CRUISER'S MOSTLY RENIX TIPS

IMPROVING THE FUEL PUMP GROUND

JANUARY 3, 2016 CRUISER54 51 COMMENTS

The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ.

Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture.

Locate the black wire on  the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire.

Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering.

At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces.

[HellCreek]

Hi, Cruiser,

 

I did the first one.  I printed out your Renix tips and have done them on both my '89 MJ and this '91 XJ.  The XJ is a HO, though and not a Renix.  I did not do the Fuel pump ground improvement, though, but that will be next.

[Tex06]

On 4/3/2020 at 3:19 PM, jdog said:

might start a new thread instead of bumping a 4 year old one, Don has passed and Tex hasn't been on in a couple years

Hey, HEY NOW!!!!  I've been busy guys....and mostly separated from my MJ for the past almost 2 years.  Focusing on my other project since I'm on assignment in Georgia (Pete, I'm in Snellville every weekend until August, fyi).

 

This is my response to HC's message if I ever fixed my problem:

 

I absolutely did.  I had a bad solder joint in the wiring harness.  The CPU sends a 5VDC signal to both the TPS and the IAC from the same wire which splits right above the valve cover in the main harness loom.  

 

You can test this pretty easily with a decent multimeter and a piercing probe (link below).  Figure out which wire is +5VDC from your computer to each of those sensors (I had +5V DC on each one as long as it was unplugged). Key on should be able to find this.

 

Next, hook the piercing probe to the wire (should still get +5VDC).  Hook the connector back up to the sensor and start the engine. Check voltage (rev the motor a bit too just to see if there's any change).  Do the same for the other sensor.

 

If the voltage drops below maybe 4.96VDC on either one you likely have a problem. Mine dropped to 1.77VDC with the engine running but if I unplugged one of the sensors it jumped back up to 5VDC.  You should also check the voltage coming from the ECU to make sure that it is +5VDC.....I want to say it's pin 26 but that's going strictly off memory and it's been a few years since I had any issues with this. I'd offer a wiring diagram to help but my books are all with my Jeep in Louisiana and I'm in Georgia on a project at the moment.

 

Seriously, once I saw the voltage drop it took me 15 minutes to trace out where the two wires came together, unwrap, resolder, and tidy everything back up.  I had thrown probably $700 in sensors, fuel injectors, etc in it at that point. Talk about a dumb, easy fix.

 

Hope this helps, if you have more questions, hit me up.  My MJ is separated from me at the moment but I'll tell ya what I can from memory!


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[Tex06]

This sounds EXACTLY like the problem I had.  If you can't get it to replicate, attach the leads like I suggested, tape the multimeter to the hood and go for a drive.  It shouldn't dip below 5VDC ever...if it does when it's bucking, I'd look real hard at that solder joint and the wiring coming from the ECU to the IAC and TPS.

[HellCreek]

Thanks, Tex.

I sent you a message response, but will post it here as well.  I will check this out and let you know.

Tom

   

[Pete M]

16 minutes ago, Tex06 said:

 (Pete, I'm in Snellville every weekend until August, fyi).

 

 

Of course you are.  I'm still stuck in Michigan.    But I am working on getting back.  

[jdog]

you could also set up the meter and grab the harness and wiggle it everywhere you can grab it

[HellCreek]

O.K. I checked the electrical connections, upgraded the fuel pump ground and confirmed that there were no loose connections or broken wires to the TPS and IAC.  What's next?

[cruiser54]

29 minutes ago, HellCreek said:

O.K. I checked the electrical connections, upgraded the fuel pump ground and confirmed that there were no loose connections or broken wires to the TPS and IAC.  What's next?

 

[cruiser54]

Drive it. You coulda fixed something and not know it.