Timing advance and distributor rotor

[Rubberup]

I have a 1998 TJ 2.5 4 cyl. The timing is reading 16 degrees BTDC when idling and goes up to 35 D BTDC when driving. I am monitoring it with my code reader. It lists it in red. It also seems high to me.

Does anyone know what advance typically reads at idle and driving?

Also, I lined up the 0 degrees BTDC mark on my flywheel, removed the 1 plug and checked for top dead center. I also used my compression gauge when turning to make sure I was in compression. When I removed the distributor cap, I was surprised that the trailing “tang” on the rotor was near the number one cap contact. So the main body of the rotor was already past the 1 cap contact.

Any ideas if all this is normal or if I should look at something specifically?

 

[hear]

The rotor position "kinda" doesn't matter, since the computer decides when it will spark. Which is different from other engines I've worked on, where the spark happens as soon as the potential can cross the gap to the distributor post, and the intial timing advance is set by rotating the housing and then locking it down.

That said, there is a "TDC" setting on your distributor. The 6cyl & 4cyl use the same distributor, but there are two sets of pinholes used to line up TDC depending on which engine you have. I'm not sure how to know which pin set to use, I wish I had paid attention when I replace my distributor a while back. Regardless, getting it pointing to 1 is the correct answer. We have seen cases here where you can be off by a tooth one way and still fire up and idle ok, but it may stumble at higher RPM where the advance is higher but due to the initial timing it can't actually acheive that advance. And also if you're one tooth the other way it may run weird as you don't have enough advance.

If you don't think it looks right, try to move it one tooth back and see if you like it better.

TL;DR I can't remember exactly where it needs to point...whenever I take mine out I just make sure to (a) not rotate the engine and (b) maintain the exact same orientation on the way back in.

 

[JKP]

When you were at TDC the trailing edge of the rotor was at terminal 1 because spark occurs BTDC.

 

[AaronPaul]

The rotor position "kinda" doesn't matter, since the computer decides when it will spark. Which is different from other engines I've worked on, where the spark happens as soon as the potential can cross the gap to the distributor post, and the intial timing advance is set by rotating the housing and then locking it down.

That said, there is a "TDC" setting on your distributor. The 6cyl & 4cyl use the same distributor, but there are two sets of pinholes used to line up TDC depending on which engine you have. I'm not sure how to know which pin set to use, I wish I had paid attention when I replace my distributor a while back. Regardless, getting it pointing to 1 is the correct answer. We have seen cases here where you can be off by a tooth one way and still fire up and idle ok, but it may stumble at higher RPM where the advance is higher but due to the initial timing it can't actually acheive that advance. And also if you're one tooth the other way it may run weird as you don't have enough advance.

If you don't think it looks right, try to move it one tooth back and see if you like it better.

TL;DR I can't remember exactly where it needs to point...whenever I take mine out I just make sure to (a) not rotate the engine and (b) maintain the exact same orientation on the way back in.

Your 16° BTDC at idle and 35° BTDC while driving do seem a bit high, but it's important to understand that:

• The 2.5L Jeep TJ uses a computer-controlled timing system, meaning you cannot manually adjust timing like on older distributor-based setups.
• The ECU adjusts timing dynamically based on inputs from the crankshaft position sensor (CKP), MAP sensor, coolant temp, and throttle position sensor (TPS).

• Typical Timing Values for a 2.5L TJ​

  
  
• Idle: Usually between 10°-12° BTDC
• Cruising (light throttle, steady speed): Typically ranges 25°-30° BTDC
• Acceleration (WOT - wide open throttle): Lower, around 15°-20° BTDC
• Deceleration: Can spike higher (sometimes over 40° BTDC) due to fuel cut-off strategies.

Your idle timing at 16° BTDC is a little high, but not necessarily out of range. However, if it’s consistently exceeding 35° BTDC under load, it may indicate a sensor issue or timing error.

 

[Rubberup]

Thanks for the info….

hear - yes I know, interesting about being a tooth off, I should check. But I guess it won’t affect timing, maybe fuel delivery??


Jkp - good info, it definitely will with 16-35 degrees of advance. Any idea how it may effect fuel delivery?

Aaronpaul - I have no codes and I recently reworked the intake/valve cover/exhaust and cleaned all the associated sensors and plugs. Do you know if the crank/cam/map/coolant/tps all throw codes when out of spec?

When runnning/driving yesterday the coolant temp was listed in red on my code reader. But, we had just started driving (less than 1 mile).

 

[AaronPaul]

Thanks for the info….

hear - yes I know, interesting about being a tooth off, I should check. But I guess it won’t affect timing, maybe fuel delivery??


Jkp - good info, it definitely will with 16-35 degrees of advance. Any idea how it may effect fuel delivery?

Aaronpaul - I have no codes and I recently reworked the intake/valve cover/exhaust and cleaned all the associated sensors and plugs. Do you know if the crank/cam/map/coolant/tps all throw codes when out of spec?

When runnning/driving yesterday the coolant temp was listed in red on my code reader. But, we had just started driving (less than 1 mile).

Yes, many sensors and components like the crankshaft position sensor (CPS), camshaft position sensor, MAP sensor, coolant temperature sensor, and TPS, can trigger diagnostic trouble codes (DTCs) when they go out of spec. However, whether or not they throw a code depends on the specific issue, sensor, and the vehicle's ability to detect the problem.

If the CPS is malfunctioning, it can cause erratic timing and stalling, but it will usually trigger a code, such as P0335 (Crankshaft Position Sensor A Circuit). This sensor is crucial for engine timing, and if it's misaligned or failing, it might not always throw an immediate code, especially in cases of gradual degradation.

Camshaft Position Sensor: Similar to the CPS, a faulty cam sensor typically triggers a P0340 (Camshaft Position Sensor Circuit) code. If this sensor fails, you may notice poor engine performance, stalling, or difficulty starting, and the code should be present in the ECU.

MAP Sensor: If the MAP sensor is out of spec or not functioning correctly, it will often trigger a P0107-P0109 code (for a low or high voltage reading). These issues often manifest as poor fuel efficiency or rough idling.

Regarding your coolant temperature reading in red while driving less than 1 mile, this could be due to a sensor reading that was temporarily out of range, potentially caused by sensor warm-up time. However, if the coolant temperature fluctuates between normal and abnormal readings quickly, this could point to a sensor malfunction or an issue with the coolant temp sensor or wiring.

If you’re not seeing any codes despite this, it could be worth clearing any stored codes and observing any future patterns. If the issue persists, it might help to check the actual coolant temperature with a gauge and compare it against the reading provided by the ECU.

 

[Rubberup]

Does anyone have advance readings from their 4cylinder? Idle and driving?

 

[Rubberup]

Could someone check their advance at idle with a code reader and let me know what it is please?

 

[macleanflood]

I don't but I'll bump the post.

-Mac

 

[AaronPaul]

Could someone check their advance at idle with a code reader and let me know what it is please?

I do not but the Expected timing advance readings (Degrees BTDC) should be as follows:

• Idle (Warm, No Load): ~10°–14° BTDC
• Cruising (~2,000–3,000 RPM, Light Load): ~20°–30° BTDC
• Full Throttle (WOT, High Load): ~15°–22° BTDC

These values can vary slightly based on engine load, altitude, fuel quality, and PCM adjustments.

Not sure if that helps at all.

 

[hear]

I do not but the Expected timing advance readings (Degrees BTDC) should be as follows:

• Idle (Warm, No Load): ~10°–14° BTDC
• Cruising (~2,000–3,000 RPM, Light Load): ~20°–30° BTDC
• Full Throttle (WOT, High Load): ~15°–22° BTDC

These values can vary slightly based on engine load, altitude, fuel quality, and PCM adjustments.

Not sure if that helps at all.

What's your source on this? Is it in the FSM?

 

[AaronPaul]

What's your source on this? Is it in the FSM?

No, not the FSM, this is just based off of my experience. If you want something very similar to the FSM but don't want to pay the high price, I suggest ALLDATADIY. It's an outstanding and thorough source that practically mirrors the FSM.

These are good baseline numbers (I think) but you can use a scan tool to compare real-time data against known baselines if you are unsure.

 

[hear]

No, not the FSM, this is just based off of my experience. If you want something very similar to the FSM but don't want to pay the high price, I suggest ALLDATADIY. It's an outstanding and thorough source that practically mirrors the FSM.

These are good baseline numbers (I think) but you can use a scan tool to compare real-time data against known baselines if you are unsure.

You do realize the FMS's for every year are available for free here under the Resources section? No need to "practically mirror" the FSM when you can have the actual FSM. IJS.

 

[AaronPaul]

You do realize the FMS's for every year are available for free here under the Resources section? No need to "practically mirror" the FSM when you can have the actual FSM. IJS.

Ok then the OP can get the FSM. ALLDATADIY is updated with easier to read instructions, illustrations, all TSB's, diagnostic trees and much easier to read diagrams.

 

[macleanflood]

And our FSMs are the original versions I assume...and we already have a thread about errors and omissions...and not updated for TSBs.

-Mac

 

[AaronPaul]

And our FSMs are the original versions I assume...and we already have a thread about errors and omissions...and not updated for TSBs.

-Mac

Again, if the OP wants to use the FSM so be it. I do not.

 

[hear]

it's a flipping subscription? Yeah, you can miss me with that noise. I don't have any use for a rented service manual.

 

[lBasket]

I used AllDataDIY back in college and it was fantastic. IDK what happened since then, it seemed like it disappeared off the market for a years, then when it came back and I gave it another shot it was more like a Chilton manual than an FSM, completely useless. Maybe it was just the model that had no data for?

 

[AaronPaul]

I used AllDataDIY back in college and it was fantastic. IDK what happened since then, it seemed like it disappeared off the market for a years, then when it came back and I gave it another shot it was more like a Chilton manual than an FSM, completely useless. Maybe it was just the model that had no data for?

Maybe the model. I use it for many applications and most recently for a Jeep JL. It's fantastic. Full-color, detailed schematics so you’re not shooting in the dark when tracing wires, testing sensors, or fixing electrical issues.

TSB's that are super helpful.

Torque values, fluid capacities, and even OE part numbers so you can get the right parts the first time.

Code explanations and troubleshooting steps.

IDK i just find it to very detailed and easy to navigate.

 

[AaronPaul]

it's a flipping subscription? Yeah, you can miss me with that noise. I don't have any use for a rented service manual.

It's $60.00 for a year, that's .16 cents per day.