Very intermittent unpredictable stalling issues

[Snowstorm87MJ]

Hello, I currently daily my 87 4.0.

over the last 3 years i’ve had these issues rarely but the last few months or so it’s been getting more and more common. I recently just cleaned the IAC based off of others advice and it appears to have helped my idle and make it feel more like my 2000 XJ. But every once in a while at the worse possible times it will stall at an intersection coming off the throttle or idling for a while usually in drive. instantly restart or chug for a few moments and clear out. Earlier this morning on my way to work  it mid chugged like half a second while cruising at 40 mph and than instantly starting firing again could feel it how the truck shook from the misfire. Coming home today i stopped at the store came out and it chugged like it had a heatsoak issue like a later 2000 xj and would die, try again, die and pump the pedal and it would eventually clear out like nothing is wrong. This is becoming more and more frequent noticeably more on warmer days. IAC was dirty (cleaned) i’ve replaced the cap and rotor. NGK plugs done within 3000 miles. Exhaust Manifold was recently replaced. EGR doesn’t exist. Injectors are 4 hole boschs (original leaked) fuel pump, filter and tank was done during first getting the truck. Sending unit seen better days but we filled in the problem areas with fresh metal but  this happens regardless of tank fuel level. The problem grounding areas were cleaned except C101. I do have sound system so I haven’t ruled out grounds. 
 

i’m at a loss because usually 4 other parts can mimic problems but i don't want to throw money at non broken parts it’s been a good truck to me when it cooperates. Thanks for any input helpful -Tyler
 

edit: a year ago or so i did have an issue where it wouldn’t start at all after driving fine cleaning the cps connector helped this.

[Ωhm]

32 minutes ago, Snowstorm87MJ said:

but i don't want to throw money at non broken parts

 

Oxygen Sensor is a maintenance item. I think replace every 89.5K miles. How many miles on your O2S?

[Snowstorm87MJ]

1 minute ago, Ωhm said:

 

Oxygen Sensor is a maintenance item. I think replace every 89.5K miles. How many miles on your O2S?

As far as I'm aware its either original or been replaced clock says 166k. 

[gogmorgo]

Does it cut out cleanly like the key was switched off, or does it seem like it’s bogging down before it quits? A quick shutdown would indicate a loss of spark, likely an electrical problem. 

If it seems like it happens with a sudden change in throttle, like when you hit the gas to pull away or come off it to step on the brake, I’d be suspicious of the throttle position sensor. Cruiser54.com has test/adjustment procedures for the TPS as well as other sensors. 

[Ωhm]

Without the use of a REM (Renix Engine Monitor + unit is out of stock), it will be hard to tell. Wiggle testing is about the best you can do. Perform @cruiser54 testing.

 

cruiser54 | True tales from "The Book"

 

NickInTimeDesign – Home of the Renix Engine Monitor!

 

[Snowstorm87MJ]

1 hour ago, gogmorgo said:

Does it cut out cleanly like the key was switched off, or does it seem like it’s bogging down before it quits? A quick shutdown would indicate a loss of spark, likely an electrical problem. 

If it seems like it happens with a sudden change in throttle, like when you hit the gas to pull away or come off it to step on the brake, I’d be suspicious of the throttle position sensor. Cruiser54.com has test/adjustment procedures for the TPS as well as other sensors. 

Most occasions its instantly once it will chug and stall. I also wouldn’t be surprised if its multiple issues considering its age.

[cruiser54]

Refresh grounds and connections per my website. Clean out the C101 connector. 

[pizzaman09]

You recently changed the manifold I see.  Go and double check that all of your manifold bolts are tights.

[cruiser54]

Also, the hose/piping from throttle body to MAP sensor may have a crack/split in it. It flexes under engine torque. Check it carefully!!

 

CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY TO MAP SENSOR HOSE FIX

JANUARY 23, 2016 CRUISER54 51 COMMENTS

The Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase.

The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause major starting and driveability issues.

There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket ( Napa FPG 60742 ), a vacuum fitting (Napa 05703-B102), two vacuum elbows (Napa CRB2670), and a length of new plastic piping (Napa CRB2672).

Remove the throttle body and take it to the workbench.

Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body where the old fitting was plugged in. Don’t go too deep. These are pipe threads.

Flush the hole with carb cleaner and inspect for any left over cuttings.
This is an excellent time to do a complete throttle body and IAC cleaning.  See Tip 11.
Take the vacuum fitting (05703-B102 ) and apply a LITTLE bit of thread sealer on the threads only. I prefer Permatex #2 but almost anything is fine.

.

Carefully screw the fitting in until snug.

Install one of the vacuum elbows on the MAP sensor so it points toward the throttle body, and the other vacuum elbow on your new throttle body fitting so it points up to the MAP sensor.
Cut a length of the new plastic tubing (approximately 13 inches) to fit between the vacuum elbows and install it making sure there is enough slack for some engine movement. Route it according to the photo. We don’t want any rubbing or chafing with engine movement.  Not a bad idea to use some contact cement or Gasga-Cinch sparingly on the tubing to elbow connectors.

[Snowstorm87MJ]

On 10/7/2023 at 9:01 AM, cruiser54 said:

Also, the hose/piping from throttle body to MAP sensor may have a crack/split in it. It flexes under engine torque. Check it carefully!!

 

CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY TO MAP SENSOR HOSE FIX

JANUARY 23, 2016 CRUISER54 51 COMMENTS

The Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase.

The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause major starting and driveability issues.

There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket ( Napa FPG 60742 ), a vacuum fitting (Napa 05703-B102), two vacuum elbows (Napa CRB2670), and a length of new plastic piping (Napa CRB2672).

Remove the throttle body and take it to the workbench.

Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body where the old fitting was plugged in. Don’t go too deep. These are pipe threads.

Flush the hole with carb cleaner and inspect for any left over cuttings.
This is an excellent time to do a complete throttle body and IAC cleaning.  See Tip 11.
Take the vacuum fitting (05703-B102 ) and apply a LITTLE bit of thread sealer on the threads only. I prefer Permatex #2 but almost anything is fine.

.

Carefully screw the fitting in until snug.

Install one of the vacuum elbows on the MAP sensor so it points toward the throttle body, and the other vacuum elbow on your new throttle body fitting so it points up to the MAP sensor.
Cut a length of the new plastic tubing (approximately 13 inches) to fit between the vacuum elbows and install it making sure there is enough slack for some engine movement. Route it according to the photo. We don’t want any rubbing or chafing with engine movement.  Not a bad idea to use some contact cement or Gasga-Cinch sparingly on the tubing to elbow connectors.

Thanks for your assistance with this. I’ll clean the c101 next. I did order an 02 bosch sensor because its never been done. I did wiggle the tube on the map around and it did slightly change in idle. That tube inside the throttle body isn’t exactly in there very tightly it seems factory so i hope that will fix the issue. I do appreciate the help.

[cruiser54]

That tube can cause lots of issues. Did you see my fix? 

[Snowstorm87MJ]

13 hours ago, cruiser54 said:

That tube can cause lots of issues. Did you see my fix? 

I did

[cruiser54]

I know that fit of the rubber into the throttle body is sketchy, but make sure the plastic pipe fits snugly into the rubber. A little glue on the outside of the plastic pipe where it fits into the sketchy rubber part is good.

[Snowstorm87MJ]

Bit of an update i did replace the 02 sensor and the CPS sensor. Haven’t taken it on its maiden voyage but the idle sounds healthier with the cps replaced. I will update if it stalls again but i did notice before the CPS there was a very quick mili second miss in the firing you could hear it every once in a while and that no longer happens. 
if it was truly the CPS that part is just a nightmare of misguidance of symptoms. 

[Ωhm]

1 hour ago, Snowstorm87MJ said:

very quick mili second miss in the firing you could hear it every once in a while

 

Truthfully, I think your idle kick was caused by the O2S dropping out, causing the ECU to go from Open Loop (OL) to Close Loop (CL) or attempting to go from CL to OL. Either way, CPS or O2S, hope this solved your problem.

[Snowstorm87MJ]

11 hours ago, Ωhm said:

 

Truthfully, I think your idle kick was caused by the O2S dropping out, causing the ECU to go from Open Loop (OL) to Close Loop

It does smell a lot less rich too. Sensor was cheap enough and will hopefully boost MPGs.