4.0 motor pinging under load

[DaveB]

Well I finally got a temporary permit for my scrambler so that I can drive it to the muffler shop to get it ready for inspection and it seems to ping a lot under load. I compared the timing to my 92 cherokee and it looks to be the same. I don't have a tailpipe on it and the exhaust system that is on it is less restrictive than stock. Could the lack of backpressure contribute to pinging ? The motor has low mileage so carbon buildup isn't an issue. All sensors are stock and in the correct positions. The motor is a 99 TJ motor with 93 XJ wiring and injection system. Any ideas ?
Dave

 

[Caleb]

how old is the fuel and what octane did it start out as? Bad fuel can easily cause pinging...

 

[DaveB]

how old is the fuel and what octane did it start out as? Bad fuel can easily cause pinging...

There was some small amount of old stuff but I added 10 gal of new stuff a couple of weeks ago. I used regular 85 octane. None of the other 4.0 jeeps in the family ping with regular and I hope I don't need the high octane stuff. I checked the MAP sensor last night and it checked out good. Today I will check out the rest of them.

 

[DaveB]

Well the tailpipe didn't help, the MAT sensor swap helped a bit. The temp sensor checked out ok as did the MAT. Timing looks good. Ping happens more when the engine has warmed up and not much at all when cold. The fuel rail pressure is exactly what my manual says it should be. So I guess I need to test the oxygen sensor next. Any other ideas ?

 

[Badger]

stupid question but what plugs are you running.jeep is known not to like certain plugs that might burn a bit hot.

 

[waynehartwig]

O2 sensor could do it... Look at the plugs, though. See if they are lean... Also the hotter the engine is the higher octane of fuel you will need. So if the motor is running 210* you would need a higher octane than a motor runing at 140*. I guess what I'm trying to say is, is the thermostat restricted? Water pump not pumping like it should? Etc... Like Badger said, too hot of plugs will also require a higher octane fuel.... Basically anything that causes combustion chamber heat to increase, so needs the octane rating of the gasoline being used..... What about the crank position sensor? Or anti knock (if it has them?)?

 

[PBandCJ]

May be some thing else to look at?
my manafold was loss at the block and it sounded like it had a ping under load (going up hills) .found it one day and tighten it up and stopped that problem

 

[waynehartwig]

May be some thing else to look at?
my manafold was loss at the block and it sounded like it had a ping under load (going up hills) .found it one day and tighten it up and stopped that problem

True... Or a cracked or a leaky intake gasket...

Come to think of it, it might not even be a ping... Maybe you have an engine knock. Ping happens when throttle is applied, a rod knocks when throttle is removed....A rod won't knock when cold, but will when warm...

 

[DaveB]

Thanks for the replies, I am running 4412 Champion plugs. They do look like there is a bit of a lean burn (tip is a white) but they haven't been in long. I am pretty sure the rods aren't knocking, it just has the standard spark pinging sound on acceleration. I will check for manifold leaks. I didn't ever take the manifold off and the motor has only 19k miles on it. I bought some octane booster and will be trying that to see if it makes the ping go away. This motor was from a TJ with OBD2 and the bigger intake manifold, I put on OBD1 injectors, fuel rail and sensors. The map sensor is hooked up to the throttle body like the TJs have it rather than the plenum like the cherokees do. I'm not sure if that would make it run lean. I can move the vacuum feed on the MAP sensor to see what effect that has. I could also "adjust" the MAT and coolant sensors with an external resistor to richen it up.
Thanks again for the help.
Dave

 

[waynehartwig]

Thanks for the replies, I am running 4412 Champion plugs. They do look like there is a bit of a lean burn (tip is a white) but they haven't been in long. I am pretty sure the rods aren't knocking, it just has the standard spark pinging sound on acceleration. I will check for manifold leaks. I didn't ever take the manifold off and the motor has only 19k miles on it. I bought some octane booster and will be trying that to see if it makes the ping go away. This motor was from a TJ with OBD2 and the bigger intake manifold, I put on OBD1 injectors, fuel rail and sensors. The map sensor is hooked up to the throttle body like the TJs have it rather than the plenum like the cherokees do. I'm not sure if that would make it run lean. I can move the vacuum feed on the MAP sensor to see what effect that has. I could also "adjust" the MAT and coolant sensors with an external resistor to richen it up.
Thanks again for the help.
Dave

Definately move the MAP hookup, if that's where it should be with your computer and MAP sensor. If it's not detecting the right vacuum, it can do funny things. And there is a difference between manifold and venturi vacuum.

The different injectors could be a problem, but I'm not sure. I know they are different, but I don't know in which ways. White tip on the spark plug may not be a concern. Best way to check them is run it down the road and then immediately check them. Before it has a chance to run through city lights and idling. You may even want to put a 93 XJ throttle body on it, those are different as well.

What tempurature is the engine running at? or do you have just a light?

 

[DaveB]

Definately move the MAP hookup, if that's where it should be with your computer and MAP sensor. If it's not detecting the right vacuum, it can do funny things. And there is a difference between manifold and venturi vacuum.

The different injectors could be a problem, but I'm not sure. I know they are different, but I don't know in which ways. White tip on the spark plug may not be a concern. Best way to check them is run it down the road and then immediately check them. Before it has a chance to run through city lights and idling. You may even want to put a 93 XJ throttle body on it, those are different as well.

What tempurature is the engine running at? or do you have just a light?

I just have the standard cj temp gauge which doesn't show numbers just C-H. I did check with a thermometer in the thermostat housing when it was warm and it read about 190 degrees. I'll try moving the map sensor feed and also try an xj throttle body. The throttle bodies look very similar and I used the TJ one since it was a great shape. I had the injectors professionally cleaned and tested before I put it together.
Thanks for the suggestions.
Dave

 

[PBandCJ]

I will check for manifold leaks. I didn't ever take the manifold off and the motor has only 19k miles on it. Dave

never took mine off but, bolts loosen and back

 

[waynehartwig]

I just have the standard cj temp gauge which doesn't show numbers just C-H. I did check with a thermometer in the thermostat housing when it was warm and it read about 190 degrees. I'll try moving the map sensor feed and also try an xj throttle body. The throttle bodies look very similar and I used the TJ one since it was a great shape. I had the injectors professionally cleaned and tested before I put it together.
Thanks for the suggestions.
Dave

I've never compared bores (I'm 99% sure they are the same) between a pre 96 and a post, but I know vacuum ports and sensors are different.
I'd move the vacuum first and try the throttle body later. Which you probably already did

190 is good...If it was 220 I'd say it was hot, but....

 

[DaveB]

I've never compared bores (I'm 99% sure they are the same) between a pre 96 and a post, but I know vacuum ports and sensors are different.
I'd move the vacuum first and try the throttle body later. Which you probably already did

190 is good...If it was 220 I'd say it was hot, but....

Haven't done it yet, had to go to work. My son also bagged a nice buck over the weekend so we will be cutting it up tonight. I plan on moving the vacuum line first, then check the TPS which can also cause pings according to what I read, swap the throttle body, and check out the exhaust sensor with my oscilloscope now that I know what to expect on it. I discovered that when it is warm it will ping just off idle without any load on it which should make it a bit easier to find.

Dave

Edit
Changed the vacuum line for the MAP sensor, changed the throttle body, tested the TPS and nothing helped. I'll be testing the oxygen sensor tomorrow after work.

 

[DaveB]

Well the oxygen sensor made no difference, neither did replacing the computer. I put in some premium gas and some BG44k cleaner that is supposed to be really good. It is getting better than it was but will still ping if I let it go into overdrive on hills. The wife took it in for emissions testing and inspection and said they spent about 45 minutes on the emissions machine which made her worry. When they finally came out they handed her the results and said it was VERY clean. I looked at the results and can't believe the numbers. I think it is running lean but the numbers they measured look impossible, maybe thats why they spent so long, they couldn't believe the numbers either. the results were:

15 MPH MAX allowed Measured
HC 338 1
CO 2.43 0.01
NO 2288 1

25 MPH Max allowed Measured
HC 318 0
CO 2.46 0
NO 2188 2

Needless to say they passed it, but I always thought that when you ran something too lean the HC numbers would be low but the CO numbers would go up. Do they have different range settings on the testers for old cars vs. new ones that could explain the numbers ? It was tested as an 84 but has a 99 motor and catalytic converter in it. Anyway I still need to fix the ping since I don't want to have to shift it into third gear for every steep hill. I think I have narrowed it down to an intake manifold gasket leak or partially fouled injectors from the old gas that was in it.
At least the scrambler looks really good.

 

[Badger]

don't trust the emmision machine.they are crap and the reading are dependent on the day.my friend works for the company that tests the machines back in Jersey and he says that over 3/4 of the machines aren't running correctly on any given day.

as far as i know this state uses the same machine that we used to use

 

[waynehartwig]

What is the timing at idle, under load and at 3500 RPM? That will tell us the amount of advance and let us know if it's off.... You should be around 30-35* max and about 10-15* at idle.

 

[DaveB]

What is the timing at idle, under load and at 3500 RPM? That will tell us the amount of advance and let us know if it's off.... You should be around 30-35* max and about 10-15* at idle.

It is about 10-12 degrees at idle if I am reading the marks correctly, haven't checked it under a load, when I rev it a bit it looks like it goes up about 8-10 degrees more. I'll try to test it under load tonight. It doesn't ping much at high RPMs but more at low RPMs with a load. I may also pull an injector or two to see if I may have gummed them up.
Thanks for the help,
Dave

 

[waynehartwig]

It is about 10-12 degrees at idle if I am reading the marks correctly, haven't checked it under a load, when I rev it a bit it looks like it goes up about 8-10 degrees more. I'll try to test it under load tonight. It doesn't ping much at high RPMs but more at low RPMs with a load. I may also pull an injector or two to see if I may have gummed them up.
Thanks for the help,
Dave

10-12 at idle is pretty good....Does it bounce around much? It should stay pretty solid at whatever number it's set. If it doesn't, then you have ignition troubles, too.

Does the distributor have a vacuum advance on it? Or is it mechanical advance? If it's vacuum advance, make sure you check your timing with the vacuum line plugged. If it's mechanical advanced simply revving the motor up to 3500 RPM will engage full advance (if the weights/springs are rusted in place - another thing to check...). If it's vacuum advanced, then revving it up to 3500 and putting a vacuum on the advance mechanism will make it fully advance. Then you can read all of the numbers...Just don't pull a vacuum at idle - that's too much advance for an idle

Also pull #1 plug and put it to top dead center and make sure the harmonic balancer hasn't moved and still reads accurately. If you aren't sure how to find tdc, let me know and I'll try to explain it....

 

[DaveB]

10-12 at idle is pretty good....Does it bounce around much? It should stay pretty solid at whatever number it's set. If it doesn't, then you have ignition troubles, too.

Does the distributor have a vacuum advance on it? Or is it mechanical advance? If it's vacuum advance, make sure you check your timing with the vacuum line plugged. If it's mechanical advanced simply revving the motor up to 3500 RPM will engage full advance (if the weights/springs are rusted in place - another thing to check...). If it's vacuum advanced, then revving it up to 3500 and putting a vacuum on the advance mechanism will make it fully advance. Then you can read all of the numbers...Just don't pull a vacuum at idle - that's too much advance for an idle

Also pull #1 plug and put it to top dead center and make sure the harmonic balancer hasn't moved and still reads accurately. If you aren't sure how to find tdc, let me know and I'll try to explain it....

I checked the timing and it is usually 12 degreees at idle with an occasional drop to 10. The advance at high speed and under a load with the RPMs up is around 35 degrees. I put a piece of tape with half inch marks on the dampner to estimate the high speed timing so I could be a bit off. I'll look at TDC on the #1 cylinder. It doesn't have a vacuum or a mechanical advance. The advance is done by the computer. I wonder what sensors it checks to know how far to advance it ?
Dave