Renix Knock sensor, very rough vibs now

Installed a good used knock sensor on my 87 Wagoneer and it ran fine till I hit about 48 mph during mild acceleration and then the front end starting vibrating and shaking so bad at 48 mph it almost started affecting the steering.

The engine must have been retarded on the timing too much by the Renix ECU based on knock sensor and knock sensor wiring data (290,000 mile engine) as the front end is solid (not very old parts), and it goes away at cruise up to 60 mph (have not taken it any higher yet), it is worst at 48 mph during mild to aggressive acceleration.

Going to disconnect the sensor to confirm it is the cause. I have put about 70,000 miles on this beast in 12-13 years since I bought with out a knock sensor and with ever feeling this problem. I had death wobble on this jeep 4 years agao and replaced the entire front end suspension, and death wobble was bad even at 20-30 mph, not at exactly 48 mph like this new issue.

Any one ever run into this before. While it could be something else, I doubt it is anything else. Timing too close....

Cruiser54, we need discuss the distributor timing (replaced it about 12 years ago with one from Autozone), but It has always been a bit weak on power which I always assumed was low compression (130 psi average) and 2 bad valve guides, but we also need to discuss possible knock sensor wiring damage, and possible bad sensor issues here this week as to what could cause the violent shakes

Last time that happened to me it was a front axle U-joint. I usually catch them before they go way bad, this one I missed. Low speed I'd hardly feel it, if I accelerated past the bad spot (certain speed) it was again tolerable.

I've ran mine with and without a knock sensor. I've never noticed any difference.

I did read the torque on the knock sensor is important. I have no idea how you'd get a torque wrench on one?

8Mud said:

Last time that happened to me it was a front axle U-joint. I usually catch them before they go way bad, this one I missed. Low speed I'd hardly feel it, if I accelerated past the bad spot (certain speed) it was again tolerable.

I've ran mine with and without a knock sensor. I've never noticed any difference.

I did read the torque on the knock sensor is important. I have no idea how you'd get a torque wrench on one?

Click to expand...

In this case I could feel the source of the wild shaking was the engine itself, middle of the hood, under the hood, in 2WD. Unmistakable. All I had to do to change it was to change the throttle and the vibration change was immediate, instant response, came and went with no change in MPHs.

Sounds like you maybe dropped a cylinder, if the shaking is that bad, likely two cylinders. Funny about the inline six, it often still has decent balance with one cylinder not firing (though it kind of depends on which cylinder).

Bucking is usually transient and tends to show up first around peak torque 2000-2200 RPM or so while cruising. Sometimes the first sign of a bad (weak) O2 sensor. Or some other fuel issue.

Retarding the timing shouldn't really cause you many issues until you get to higher RPM's IMO. You loose some top end.

To much advance can cause what you are describing. Maybe unhook the knock sensor and forget about it. IMO the only time it really does anything is at low vacuum, open throttle conditions (going up hill) and the AW4 usually downshifts before that happens. Low octane fuel can cause some valve train rattles.

Mike, you have a tester correct?

View the knock sensor at idle. Should be 0 or so. Rev it to 2000 RPM and the sensor should act wild and at about 20 on your screen.

As for the "timing", I would do the following procedure to make sure the dizzy is indexed correctly:
http://cruiser54.com/?p=68

cruiser54 said:

Mike, you have a tester correct?

View the knock sensor at idle. Should be 0 or so. Rev it to 2000 RPM and the sensor should act wild and at about 20 on your screen.

As for the "timing", I would do the following procedure to make sure the dizzy is indexed correctly:
http://cruiser54.com/?p=68

Click to expand...

Thanks, Yes I do, I will do that this week when I get the chance.

Today we test drove it and the shake was a sometimes issue, not all the time, needed a specific speed, and some acceleration (35-100% of WOT) in 4th gear with the TC locked to get the shakes. No other time can it be made to shake at all. One time it shock so bad I thought I was going to loose control of it at 48 mphs. Tightened the lug nuts, that seemed to help, but the problem is not easily repeatable to begin with, happens only about 1 in 6 times on the test drives. Disconnected the Knock sensor, but can not confirm if it actually changed anything as never could the really get bad shake to repeat after tighting the tire lug nuts. But I know this shake was not the tires. Also it took about 10 -15 drive runs to get the bad shakes just once.

Did find the knock sensor has lost all of the aluminum mylar film wrap RF insulation on the last 3+ feet of wire to the sensor. Might be getting fake signals.

Cleaned the two NGK spark plugs on the #1 and #2 cylinders with bad valve guides that leak oil past the new valve seals, and they looked pretty good, not black wet oil on the them like the other plugs had. BUT, they had orange rust colored crud on the ground and some of what looked like flash rust on the first 1/4" of the insulators. It litteraly looked like orange rust? A year ago it was heavy white crusty stuff on the plugs, then change the valve seals, and plugs and it became wet oil on the plugs. They changed to the FR-5 NGK hotter plugs on those cylinders and they looked pretty good the first two check ups at 300 and 600 miles. Now after 300 more miles red rust? WTF?

Oil and coolant and transmission fluids are perfectly normal. 0-35 mph acceleration is the best it has ever been on this well worn engine in 70,000 miles since I bought it.

I cleaned the Cap and rotor of traces of brass dust from early wear under the cap, but the two are still in very good shape. Test drive could barely get the shakes at all, but it seems to be there just a wee bit at WOT in 4th gear with the TC locked. At 48 mph at WOT it stays in 4th gear with gear with the TC locked and does not down shift. Have to shift to 1-2 manually to force it to down shift at WOT at 48 MPH.


Before all the work I just did, I could not get over 60 mphs at WOT. Easily got to 70 mphs after all the work. I did mess with the Knock sensor wiring and disconnected the sensor. Cleaning the 2 plugs and cap and rotor helped a little. But the 2 plugs were no where near as fouled as others in the past that had to get seriously fouled to cause any problem.

Oh, and I think the Knock sensor wiring was hung up on the throttle cable causing an issue? Un-hung it, but not sure if that was the issue of not being able to get over 60 mph at WOT or an issue at all.

OK, I have an update, so lets start from scratch. Could not get the really nasty vibration any more, so far, after disconnecting the Knock sensor, tightening the front wheel lug nuts, and cleaning the dizzy cap and rotor, and cleaning the #1 and #2 spark plugs, which actually looked very good compared to the past check ups (Orange color, not more oil fouling, black wet muck using NGK FR5 plugs) , after getting the knock sensor wires loose of the throttle cable and exhaust manifold (the outer corrugated plastic sheath had melted to it after the Knock sensor was installed and wiring connected, routing issue) and here is what I have now:

Acts great at start up and hot, idle is awesome, great power in gears 1, 2 and 3, from 0-35 mphs at 30-100% of WOT. Decent power at 35-45 mphs.

Variable and random (which suggests it is the engine, not tires) vib spots around 45-55 mph that give me some minor (no longer severe) engine vibration/shakes at all TPS settings, 0-100 WOT at 45-55 mphs, and I can not get over 60 mph in D-Drive even at WOT. All 4 gears and the TC lock up work perfectly, shifts perfectly.

But in 4th gear (In drive when it hits 4th gear) with the TC locked up, and at about 1800 to 2000 rpm at WOT it feels like I have no acceleration power left at all. I can hold it at WOT for 60 seconds and it sits at 60 mph on a flat run. If I drop her to 1-2 (or was it 3?), I can get up to 70 mphs... Odd.

In park I can run the engine at 4500 rpm with no problem, from 700-4500 rpm in park is a smooth fast response. No issues at all on decel from 4500 rpm back to idle.

So I think this is something new, I need a list of common causes to work through for this. The data at lower vehicle speeds makes me think it is not a fuel or CPS or O2 sensor issue or even a TPS issue, and it shifts and runs as good as ever till I get to about 45-50 mph. It runs much better in a lower gear at higher rpm power wise.

I feel like I am missing something here. But what is it? Most every thing on it, except the coil and ICM is under 5-10 years old and under 70,000 miles old.

When plugs 1 and 2 would get fouled, I would get low power at higher throttle positions and even pinging if it was in 3rd-4th gears at low rpms, like under 2500 rpm at 40 + mphs. In the past new or cleaned plugs fixed it. Also in an emergency running it in a lower gear at high rpms, like 3000 rpm would clean the plugs enough to get me home so I could clean/replace them. This time the plugs did not look very bad at all in fact they looked pretty good, orange rust like color and red rust color junk on the back side of the ground electrode, but the gap area was clean. I checked some online plug color guides and they were listed as very good compared to before.

8Mud said:

Sounds like you maybe dropped a cylinder, if the shaking is that bad, likely two cylinders. Funny about the inline six, it often still has decent balance with one cylinder not firing (though it kind of depends on which cylinder).

Bucking is usually transient and tends to show up first around peak torque 2000-2200 RPM or so while cruising. Sometimes the first sign of a bad (weak) O2 sensor. Or some other fuel issue.

Retarding the timing shouldn't really cause you many issues until you get to higher RPM's IMO. You loose some top end.

To much advance can cause what you are describing. Maybe unhook the knock sensor and forget about it. IMO the only time it really does anything is at low vacuum, open throttle conditions (going up hill) and the AW4 usually downshifts before that happens. Low octane fuel can cause some valve train rattles.

Click to expand...

My memory is foggy. The knock sensor should delay the spark if it senses knock, pre-ignition, but is that retarding or advancing the spark? I forgot which it is. The bucking is at around 2000 rpm, but only in 4th gear at over 45 mph. Fuel economy has dropped some this year, but that could be changes in driving habits.

8Mud said:

Sounds like you maybe dropped a cylinder, if the shaking is that bad, likely two cylinders. Funny about the inline six, it often still has decent balance with one cylinder not firing (though it kind of depends on which cylinder).

Bucking is usually transient and tends to show up first around peak torque 2000-2200 RPM or so while cruising. Sometimes the first sign of a bad (weak) O2 sensor. Or some other fuel issue.

Retarding the timing shouldn't really cause you many issues until you get to higher RPM's IMO. You loose some top end.

To much advance can cause what you are describing. Maybe unhook the knock sensor and forget about it. IMO the only time it really does anything is at low vacuum, open throttle conditions (going up hill) and the AW4 usually downshifts before that happens. Low octane fuel can cause some valve train rattles.

Click to expand...

Ran the Snap-on MT-2500 scanner on the beast, and it seems it is running lean according to the ECU data, open loop and the O2 sensor is not operating normally.

Reads about 4-4.8 Volts at idle. At steady 1800 rpm for 2-3 minutes it slowly drops to 1-2 volts, very slowly. Claims it is always lean, which seems odd based on the voltage at idle verses 2-3 mins at 1800 rpm. The snap on scanner was awesome, love it

More details later. My computer is crashing now, ugh.

Theoretically when you get detonation or knock, retarding the timing is the cure. Or you can add some fuel and richen the mixture up a little. Or a little of both.

That 2000 RPM bucking on mine turned out to be the same you found, cooked harness and questionable O2 sensor. Sounds like you have it worse than I did.

Low fuel can cause the same thing, either pressure, plugged injectors and /or something electrical causing the low fuel.

To much air can cause detonation, vacuum leak near one or two cylinders.

Not something you want to ignore for long, physical damage to the motor can happen.

8Mud said:

Theoretically when you get detonation or knock, retarding the timing is the cure. Or you can add some fuel and richen the mixture up a little. Or a little of both.

That 2000 RPM bucking on mine turned out to be the same you found, cooked harness and questionable O2 sensor. Sounds like you have it worse than I did.

Low fuel can cause the same thing, either pressure, plugged injectors and /or something electrical causing the low fuel.

To much air can cause detonation, vacuum leak near one or two cylinders.

Not something you want to ignore for long, physical damage to the motor can happen.

Click to expand...

very bad damage can happen IE melted piston rings a bell with me.

Does the mt2500 show it at all going into closed loop then jumping back out? what are your fuel trims look like? if the fuel trims are normal it might not change the rich lean designation until it resumes closed loop.

OK, I'm in to follow progress. At the moment I have no suggestions.

I snapped my Knock sensor off doing an engine mount change years ago. I glued, taped and zip-tied it back on to avoid having a dangling connector. Rapid tapping with a hammer on the block while running does nothing so I doubt it works. However, It runs fine.

90xj06 said:

very bad damage can happen IE melted piston rings a bell with me.

Does the mt2500 show it at all going into closed loop then jumping back out? what are your fuel trims look like? if the fuel trims are normal it might not change the rich lean designation until it resumes closed loop.

Click to expand...

I caught it trying to go closed loop right after start up only if I ran it at 1800 rpm for 1-2 minutes. That implies the O2 electric heater is not working (burned out or no power to it). But it did not stay closed loop for more than 1-2 seconds. I think it stayed closed loop when I first started (cold engine) running at 1800 rpm and stayed there till I went back to idle, but after further cycling the ECU was having non of it, would not go closed loop again after it ran a bit no matter what I did. I got some very VERY slow changes in the O2 sensor voltage at 1800 rpm early on, but after a while IIRC I think it wanted to set at one voltage no matter what I did to the throttle. It locked in at 4.8 Volts the last 5-10 minutes of testing on the O2 sensor. The Exhaust read out said lean 100% of the time, and never changed even when I got the voltage down to 1 volt early on at 1800 rpm. Idle fuel trim was 128, or close to that when I checked it and recorded it a few times.

sounds like to o2 sensor is not working or the heater is bad. after awhile i believe it gives up trying to go back into closed loop. check to make sure your getting 12v to the orange wire. and that the black wire has continuity to ground.

Port A 12V
Port B Ground
Port C Signal

Had 12 volts to the O2 sensor, but the heater wire in the O2 sensor read 250,000 ohms, (should be about 8 ohms as I recall) as in it was dead. Swapped out the O2 sensor, and it went closed loop in seconds of start up. But now had a rough idle??? WTF??? Still had fuel trims of 98(ST) and 128(LT).

Tried 3-4 restarts, about 8 cycles from run to off to run with out cranking, then suddenly she springs a fuel leak at the QC feed line to the fuel rail after tidying up the O2 and CPS and axle vent hose/wires with tie wraps to keep them from getting into axle shaft-steering column or exhaust manifold sudden death battles again. Must have bumped the QC too much and the 30 year old o'rings gave out finally. They were toast, inner one was rotted....

Replaced the 2 o'rings and spacer inside the 30 year old factory fuel line QC, stopped the fuel leak.

Oh, forgot to mention the fuel pressure was perfect before I changed the O2 sensor, I tested it first, FPR is working perfectly also before I swapped the O2 sensor. And O2 sensor ground was perfect.

Then the rough idle after replacing the O2 sensor, and multiple ign switch on off cycles and restarts stayed for 2-3 more restarts after fixing the fuel leak, and suddenly the jeep fixed itself.

I now have a self repairing jeep :clap: LMAO.

Drove her today, several short trips, runs smooth as glass, even the sticky lifter has gone silent, she never ever ran this smooth before, at idle or under power.

What did I do wrong? LOL

Now we wait to see how well the slightly hotter NGK FR5 spark plugs on cylinders 1 and 2 stay clean (leaking valve stem seals from worn valve guides...long story) with a working O2 sensor?????? Fuel economy should go way up, I was down to about 11 mpg average so I already suspected an O2 sensor issue.

Congratulations on your new genie jeep. Let us know how it goes.

Still can not get over 60 mph even at WOT

Still have a wee bit of the shakes engine wise at 45-60 mph.

Swapped the ICM and HV coil today (did not run the 60 mph test yet) but when I tested the TPS with the Snap-on MT-2500, engine off, ign on, I discoveredin my TPS test that while the idle is perfect, .82 Volts, 16% of WOT, I am only getting 57% of the 0-5 Volt range, 57% of WOT at WOT. It should be 87% per the FSM, so my 10 year old, Auto-zone TPS, 50,000 miles TPS is either bad or I have a 5 Volt/wire input problem. I will test the 5 volt input tomorrow and swap the TPS and run a drive test Monday.

Tortured myself today for about 3 hours today testing and swapping out the TPS, and had back probing problems at the connectors, test method memory problems (seemed my TPS sensors were wired backwards??), and I finally remembered I had a snap-on MT-2500, LMAO, silly me. I don't need no stinking multi-meter LOL.

So I attached the Snap-on tool and voila I had the correct idle voltage. Calibrated it, new sensor and as expected from ohm meter tests, and now the snap on scanner, I still could not get past 58-63% of WOT readings on the TPS at the ECU, just like the TPS I had just replaced.

Note: I tested 4 new TPS, one Mopar, two brand new $7 TPS sensors just bought from China on Ebay (yes, only $7 each DELIVERED!!!!!!), and the old one, and there was not a bit of difference worth noting between them unmounted or the old one (that seems to be Mopar?) and the new China one, which looks very well well made.

So I checked the Throttle body throttle cable linkage and throttle body. With the cable unconnected, I get a max of 63% of WOT reading on the snap on scanner. Cable connected is the same, but is only 58% using the gas pedal. But the FSM says it should reach 83% (or 87%???) of WOT.

I am shut down for the day already, but I plan to test the white 4x4, 1987 and the recently wrecked 89 that was running perfectly before it got rear ended and totaled, to see what the snap-on reads at WOT on them.

Lastly I found a loose enough O2 sensor wire splice that I knocked it loose today. Fixed it and test drove it as the last thing I did, and I still have the same lack of power at WOT to get past 60 mph, and some occasional engine vibes (not nearly as bad as bad as before I replaced the O2 sensor). Still have loads of power at 0-45 mph. No issues till it about 45-50 mph, in 4th gear with the TC locked, But even in 3rd gear with the TC unlocked it can not get past 60-65 mph at WOT.

OK folks, I need you other Renix gurus to post up your past data, using a volt meter or the Snap-on MT-2500, and / or test if needed, your WOT TPS voltage or % of input voltage to the TPS at WOT , with the ignition switch power on, engine off.

PLEASE!!!!

I need figure out why mine is not getting past 58-63% open when the manual says it should reach 83% minimum. Trying to figure out if all the new TPS sensors made today and the last 10 years are junk, or if there is a throttle body or linkage issue, or all of the above.

Do you wanna tell them, or should I? LOL.

BTW, I did test my TPS with the DRB and got 89% reading from the TPS output at WOT.