Renix Pinging

After searching and reading all the threads I could find on pinging, I decided to ask.

1987 Renix Auto with most electronics replaced/adjusted. New TPS set at 83%, CPS, O2 sensor, MAP, coolant and air temp sensors, knock sensor, new orange top Ford injectors, new fuel pump (fuel pressure is by the book - 31psi/39psi). Ignition timing shows 14 degrees advance at idle(800rpm) and 30 degrees around 2500rpm. Runs great and gets 16mpg on my daily commutes (9 miles each way) and around town. Passed emissions with really low numbers. EGR diaphragm is blown, but valve stays shut. Vacuum line to EGR solenoid plugged.
Anyway, at low load/rpm, it is nice and quiet. No noticeable pinging, but put a load on it, and she pings bad. Constant pinging at highway speeds (anytime over 50mph). Yes constant.
I can't tell for sure when this started as I changed a bunch of parts at the same time. The XJ has been pinging since we bought it July 07, but never this bad. It also has a 180 degree thermostat, from the previous owner (could it be in constant warmup mode?), 93up radiator,hoses,expansion tank, Bosch Platinum plugs, Highly modified Pacesetter header, new high flow generic cat and Magnaflow catback exhaust. Intake is still stock.
I know the computer controls the timing and there is "no" adjustment, but are those numbers right? Is that too much advance?
I have tried Seafoaming the engine twice with no noticeable change, except the black mark on the driveway getting bigger and probably killing the new cat.

Any ideas?

have you tried filling up with higher octane gas to see if there's a difference?

This jeep has lived the good life of caviar and premium fuel since the day we bought it.

Stock ignition? If it is start by using regular run of the mill plugs. Our Jeeps don't like platinum.

Click to expand...

I was wondering that. I also have an MSD 6T box I am considering installing if it might help.

Champion? NGK? Autolite? Other?

Alot of guys like NGK and champion. I run the autolites just fine.

Our ignitions are very strong stock as I hear. As long as you run regular plugs.

Off to Autozone I go. Will report if changing the plugs cures it.

If it still pings, then perhaps maybe it's not pinging? Not sure what else could make that noise though.

Pinging can be caused by three major things. Running too much spark advance, running too lean, or hot carbon preiigniting the fuel.

You didn't mention that you replaced the ping sensor. That backs off the timing advance when it senses a ping event.

Replace the EGR valve. It's purpose is to inject a small amount of exhaust gas into the intake, thereby reducing the combustion temps. You said it passed with flying colors. You may be running too lean. Headers with no other changes will tend to make an engine run lean. Running lean causes excessively hot combustion temps.

Take it to a mechanic and have them do a tailpipe sniff to see if you are running too lean. A very experienced eye can tell by reading the spark plugs and tailpipe, but the sniffer is the most reliable way.

Fix it now, as running it like this can permanently damage your engine.

old_man said:

Pinging can be caused by three major things. Running too much spark advance, running too lean, or hot carbon preiigniting the fuel.

You didn't mention that you replaced the ping sensor. That backs off the timing advance when it senses a ping event.

Replace the EGR valve. It's purpose is to inject a small amount of exhaust gas into the intake, thereby reducing the combustion temps. You said it passed with flying colors. You may be running too lean. Headers with no other changes will tend to make an engine run lean. Running lean causes excessively hot combustion temps.

Take it to a mechanic and have them do a tailpipe sniff to see if you are running too lean. A very experienced eye can tell by reading the spark plugs and tailpipe, but the sniffer is the most reliable way.

Fix it now, as running it like this can permanently damage your engine.

Click to expand...

Uh,

New TPS set at 83%, CPS, O2 sensor, MAP, coolant and air temp sensors, knock sensor, new orange top Ford injectors, new fuel pump (fuel pressure is by the book - 31psi/39psi).

Click to expand...

He replaced it. Also, wouldn't exhaust mods and such only make it run lean on carbbed vehicles? Modern FI should auto adjust for it. Also the knock sensor is only used when there is a knock, which really there shouldn't be. I don't even have a working knock sensor on my '89, and I got rid of my EGR valve. It runs on 87 octane, and doesn't ping even under serious engine loads.

There's just no way adding an exhaust change is going to make his low compression engine (4.0L) ping on premium fuel, it just shouldn't be happening period. Something is definitely awry.

old_man said:

Replace the EGR valve. It's purpose is to inject a small amount of exhaust gas into the intake, thereby reducing the combustion temps.

Click to expand...

please educate my simple mind. how is injecting exhaust going to lower comb temp??? i see one of two things happening:
1: the hot exhaust is going to raise the intake temp, there-by also raising the comb temp.
-or-
2: the exhaust will cause it to run a little rich( injecting air with litttle to no O2) lowering temps.


i don't get it

-chris


sorry for the hijack

The basic theory leading to the EGR system is sound, but the EGR system itself is not - as I've said so many times before, it's not really needed anywhere under 9.0:1, only vaguely needed 9.0-9.5:1. And, there are better ways to do the job.

However, do this. Disconnect the four-bolt flange at the catalytic converter (you can get a new gasket for that join for a few bucks) and disconnect the hose from the airbox. Get a spray bottle, and fill it with clean water only.

Run the engine at idle. If you have an assistant who can hold a "high idle" for you (~1200rpm or so,) all the better.

Set your spray bottle for the finest mist you can, and give the open intake tube a cloud every 15-20 seconds until black clouds stop appearing.

If you're getting knock on a low-compression engine, it's probably because of a carbon deposit that is glowing once everything gets heated up. I've not used Seafoam, so I can't testify as to how well it works. I know this method works, is cheaper, and won't hurt anything. You're essentially steam-cleaning the combustion chamber by doing this (the water gets absorbed by the carbon deposits, gets flashed into steam, and blows the carbon right off of the chamber surfaces. That's the black clouds you should see. You're disconnecting the cat so you don't clog it with carbon.)

Since the knock sensor isn't doing its job (it should generate a signal when it reads a knock,) you'll have to check that wiring out later. However, this is where I'd start.

For plugs, I've been using Autolite platinums for years with no ill effects - I've been sticking to Autolite copper or Autolite platinum for a good long while. I quit using Champions when a set exploded in my Bug a number of years ago... I know Autolite is owned by the same outfit that owns Fram (Allied Signal,) but they do a much better job with spark plugs than they do with filters, believe me!

You might also want to go with plugs one step "colder" than stock - I believe that would be Autolite P/N 3923, or AP3923 (verify with the catalogue, tho. Every maker uses a different numbering system.) The plug could be retaining heat, and that could cause pre-ignition as well.

twoksl2 said:

please educate my simple mind. how is injecting exhaust going to lower comb temp??? i see one of two things happening:
1: the hot exhaust is going to raise the intake temp, there-by also raising the comb temp.
-or-
2: the exhaust will cause it to run a little rich( injecting air with litttle to no O2) lowering temps.


i don't get it



-chris


sorry for the hijack

Click to expand...

Makes sense to me. Exhaust is in effect an inert gas (mostly). I would guess you could use nitrogen, CO2, helium or another inert gas, exhaust is handy. They use exhaust to thin the air a little, primarily the oxygen percentage. In other words tailoring the air to the burn characteristics of the fuel.
It likely has somewhat the same effect as running at altitude, lowering compression or increasing octane, it slows the burn.
Injecting exhaust into the intake displaces some of the oxygen (thins it a little) oxygen molecules are a little farther apart, slowing the burn. Normal combustion doesn't use up all of the available oxygen, just most of it We are likely talking milliseconds here, but a good comparison might be black powder which goes boom and modern powder which has a controlled burn rate.
Slowing the burn some, can actually increase combustion by using more of the available air/fuel up. Slowing the burn, spreads the torque over a broader band. Less like a diesel, which goes off like an explosion.
Granatelli actually tried to explain the process to me in the early 80's, while I was trying to get one of his compressors to work right (without detonation and/or pinging) in my Dodge PU. Dumping a measured amount of (almost) inert gas, into the intake under certain conditions, can be good and is not necessarily bad for combustion.

Ok, I changed out the Bosch Platinums for regular Champions (RC9YC)and it still pings. The color on the plugs is interesting.
Dry black carbon just below the threads, the center conductor ceramic(white) with almost no color, maybe a little tan and a medium tan colored deposit right around the conductor tip and the ground post. They were also gapped at .040 insterad of the .035 they should be. Hmmm.

I am willing to try the water mist thing. I already have a spare cat gasket so that would be easy.
I just drove to work and the one thing I did notice is a smoother idle in park and in gear. Maybe closing the gap helped there, but it still pings the same places as before.

If you're getting knock on a low-compression engine, it's probably because of a carbon deposit that is glowing once everything gets heated up.

Click to expand...

It will ping on acceleration from my driveway when first starting it in the morning.

have you tried a top end cleaner like seafoam or gm top end cleaner. could be a lot of carbon build up. i would put the old o2 sensor in if you do this. replace with the new one afterwards and clean off the plugs.

Im just throwing some stuff out there. Check the play in your distributor check the cap and rotor while your there. IDK

The knock sensor is nearly trouble free from what I've seen. In facts its usually the only sensor that doesn't go bad. If its retarding timing, you'll be missing alot of power. Are you? Are you also certain that this is ping from ignition and not a mechanical noise?

x2 on Seafoaming it. Back in the days of carbs, particuarly the older webers you would run the engine at high rpm/high load (like, hard acceleration up hill) to burn off any carbon. I've done this on both of my cars (both at MPFI) and it has little to no gains whatsoever, but Seafoam did make a difference.

old_man said:

Pinging can be caused by three major things. Running too much spark advance, running too lean, or hot carbon preiigniting the fuel.

You didn't mention that you replaced the ping sensor. That backs off the timing advance when it senses a ping event.

Replace the EGR valve. It's purpose is to inject a small amount of exhaust gas into the intake, thereby reducing the combustion temps. You said it passed with flying colors. You may be running too lean. Headers with no other changes will tend to make an engine run lean. Running lean causes excessively hot combustion temps.

Take it to a mechanic and have them do a tailpipe sniff to see if you are running too lean. A very experienced eye can tell by reading the spark plugs and tailpipe, but the sniffer is the most reliable way.

Fix it now, as running it like this can permanently damage your engine.

Click to expand...

Sorry I didn't see the "knock" sensor was changed. If you guys don't believe me about the EGR, do some research. I've been doing this crap since before most of you guys were born. I stand by my comment about taking it to have the tailpipe sniffed. 5-90's method with the water is an old school trick, but it scares most people so I didn't mention it. If carbon is the problem, then I recommend a can of BG44K. It will clean the injectors (possible source of lean) and cut the carbon. Renix systems tend to run on the lean side and have high combustion temps. It is believed that this lean run and high exhaust temps is the main reason for so many exhaust manifold cracks.

old_man said:

Sorry I didn't see the "knock" sensor was changed. If you guys don't believe me about the EGR, do some research. I've been doing this crap since before most of you guys were born. I stand by my comment about taking it to have the tailpipe sniffed. 5-90's method with the water is an old school trick, but it scares most people so I didn't mention it. If carbon is the problem, then I recommend a can of BG44K. It will clean the injectors (possible source of lean) and cut the carbon. Renix systems tend to run on the lean side and have high combustion temps. It is believed that this lean run and high exhaust temps is the main reason for so many exhaust manifold cracks.

Click to expand...

What? 5-90, me, and a bunch of others have completley blocked off the EGR with no ill effects. I think 5-90 says it actually made his put out less emissions. There have been absolutely no side effects to it other than a more reliable engine..

Like I said earlier, there is something extremely wrong about stangrcr1's engine. Maybe distributor play like that other guy said?

Also that's the first time I've heard of "Renix is known to run lean and thats why the exhaust manifolds crack". As far as I know, the manifolds crack on every single XJ (87-01) just as commonly.

Not trying to be offensive or condensending, this is just my experiences/what I've heard..

Stangrcr1, perhaps you have a big vacuum leak? That can cause a motor to run lean. You don't get any high idles do you?

Hey, when's the last time you changed your timing chain?