Dry Black Spark Plugs

[flbob 97400]

I'm about to give up and go to the dealer. 97 LS400 - 148,000 miles really nice shape. My saga started with rough running. Took to local highly recommended independent. He "checked" ignition, compression and whatnot and said we must have gotten some bad gas. Drained and added a litttle. Said there was some "white stuff" in the gas but couldn't tell what it was. Also told me he would have changed the fuel filter but that "model didn't have one". He said it seemed better and I thought I'd better get her outa there before he tried to fix something else.

I had ordered a engine temperatute coolant sensor -that shows up a lot in the troubleshooting section of the factory manual - which I have - and I was blaming for very extended shift delay when cold so I changed that -seemed to help the shift, by the way. And I changed the fuel filter - in back above and to the left of the differential and dumped in a can of seafoam.

Ran OK for one or two short trips - then rough again. codes were 0300, 0302 and 0308. Random misfire, and misfire cyl 2 and 8. I started changing ignition parts - plugs and wires. NG - rotors and caps - NG. always would run OK for a minute or two - just long enough to get out of the yard but would shortly start missing again.

It would rev up OK, slowly, and always threw 302 and 308, so I figured the fuel system was OK and started working on the injectors. All new to me but with my trusty manual to guide me, I tested all of the injectors. Ohmed them - all met spec. Built a test rig to test fuel flow quantity - all tested OK -(kinda scary fooling with gas and sparking wires!). Put it all back together but moved injectors 2 & 8 to positions 4 & 6.

Different, but worse. Now missing on 3,4,5,and 6. But 2 & 8 OK so ordered two injectors and all of the o-rings and gaskets to put it together right. Got it all together this last Saturday, and still missing on 3,4,5,& 6. So I went thru all of the ignition wires to make sure they were all correct - they were and the plugs were firing (out of the engine).

Here's comes the interesting part. One of the checks in the manual for troubleshooting is to rev the engine to 4000 quickly, three or four times and then check the plugs. Wet would indicate getting fuel. Mine were dry but black with loose soot. I would read that as rich but firing. The interesting part is that I checked the old plugs and 3,4,5,& 6 were dark brown or black, like thay had been running rich for a while, and 1,2,7 & 8 were nice and clean - like they came from a different engine. In case you are thinking coil, I forget which is which but 3,4,5, & 6 share both coils.

One more hint - every time I've done something, she will start and run very smoothly for between one and two minutes, and then start missing.

Any ideas? Please help!!

[curiousB]

These cars are known for problems with one of the two ignition coil/distributor cap going out due to arc or shorting of the wiring. Car will still run but only on 4 cylinders hence a very rough ride. Maybe one side is dead for you. It could be an intermittent problem hence the coming and going nature of the problem. If your search this site on distributor short or something similar you should find many threads on this.

This sounds like ignition to me. I wouldn’t mess around with fuel injection until you run this to ground first.

Maybe get one of these and see if the spark comes and goes on a warm vs. cold engine

http://www.amazon.com/Thexton-404-Adjustab...f=pd_sim_auto_2

[flbob 97400]

Thanks for responding. Of the four cylinders missing, 3,4,5,& 6, two are fired from one coil, the other two from the other coil. Since the other four cylinders are firing fine, I'm thinking the coils are OK.

[jrbtn]

I'm about to give up and go to the dealer. 97 LS400 - 148,000 miles really nice shape. My saga started with rough running. Took to local highly recommended independent. He "checked" ignition, compression and whatnot and said we must have gotten some bad gas. Drained and added a litttle. Said there was some "white stuff" in the gas but couldn't tell what it was. Also told me he would have changed the fuel filter but that "model didn't have one". He said it seemed better and I thought I'd better get her outa there before he tried to fix something else.

I had ordered a engine temperatute coolant sensor -that shows up a lot in the troubleshooting section of the factory manual - which I have - and I was blaming for very extended shift delay when cold so I changed that -seemed to help the shift, by the way. And I changed the fuel filter - in back above and to the left of the differential and dumped in a can of seafoam.

Ran OK for one or two short trips - then rough again. codes were 0300, 0302 and 0308. Random misfire, and misfire cyl 2 and 8. I started changing ignition parts - plugs and wires. NG - rotors and caps - NG. always would run OK for a minute or two - just long enough to get out of the yard but would shortly start missing again.

It would rev up OK, slowly, and always threw 302 and 308, so I figured the fuel system was OK and started working on the injectors. All new to me but with my trusty manual to guide me, I tested all of the injectors. Ohmed them - all met spec. Built a test rig to test fuel flow quantity - all tested OK -(kinda scary fooling with gas and sparking wires!). Put it all back together but moved injectors 2 & 8 to positions 4 & 6.

Different, but worse. Now missing on 3,4,5,and 6. But 2 & 8 OK so ordered two injectors and all of the o-rings and gaskets to put it together right. Got it all together this last Saturday, and still missing on 3,4,5,& 6. So I went thru all of the ignition wires to make sure they were all correct - they were and the plugs were firing (out of the engine).

Here's comes the interesting part. One of the checks in the manual for troubleshooting is to rev the engine to 4000 quickly, three or four times and then check the plugs. Wet would indicate getting fuel. Mine were dry but black with loose soot. I would read that as rich but firing. The interesting part is that I checked the old plugs and 3,4,5,& 6 were dark brown or black, like thay had been running rich for a while, and 1,2,7 & 8 were nice and clean - like they came from a different engine. In case you are thinking coil, I forget which is which but 3,4,5, & 6 share both coils.

One more hint - every time I've done something, she will start and run very smoothly for between one and two minutes, and then start missing.

Any ideas? Please help!!

For what its worth, a couple of years ago I had a similar runnability problem and took it to the dealer on a flabed to diagnose. It took about 2 weeks of searching, mechanic taking it home and such to find the problem. The first thing they went after was "bad gas" and even tried to convince me I had put E85 in it. I also had some black plugs. To shorten the story, it turned out to be a bad fuel pump and there was never a code related to that in the system.

[curiousB]

Thanks for responding. Of the four cylinders missing, 3,4,5,& 6, two are fired from one coil, the other two from the other coil. Since the other four cylinders are firing fine, I'm thinking the coils are OK.

Fouled spark plugs seems to indicate missing ignition (hence build up on plugs). It seems you're pretty comfortable and knowledgeable working under the hood.

What if you swap the distributor caps? I wonder if there isn't some contamination or carbon traces that are causing a discharge path on certain plug wires (spark is occurring but not at the plug). Do different cylinders act up when you swap cap? Can you clean it up in and out with some rubbing alcohol (use an old toothbrush to scrub it) and then dry it out. What about swapping coils? does problem move with coil? Can you run engine at night (in darkness) and see if there is any visible arcing along the plug wires?

If you unplug the plug wires to the cylinders you feel are bad does it still run about the same, ie rough, but no worse than when connected? If so then that would seem to confirm no ignition at these cylinders. If it gets much worse as you unplug the bad ones then it would cast some doubt on it being ignition (at least for those cylinders).

Hopefully you used new o-rings (with a dab a petroleum jelly to grease them up) with any injectors you pulled, replaced, or moved. Old deformed o-rings could create a vacuum leak to the cylinders and be another reason for rough running, particularly at idle speeds.

There are numerous things you could check on fuel side but given the codes you’re getting it still seems likely an ignition related cause. Dirty throttle plate and IACV are know contributors to rough idling but they wouldn’t create the codes you’re seeing.

Some of these ideas seem less likely than other. At this point ruling out possibilities is useful in getting to the root cause. Anyway just a few things to maybe try that wouldn’t take too much effort. Good luck.

[nc211]

What do those engine codes tell you the problem is?

[flbob 97400]

More info - after all the other work - I siphoned all of the gas out of the tank, ran the pump and drained the gas from the low pressure side, and then ran the engine until it ran out. Replaced with Shell hi-test. I put all of the old gas (not the original that the service station said they drained) in clear containers and let sit for a couple of hours. All clear with no trace of water or anything else.

[flbob 97400]

nc211 - codes indicate misfire in cylinders 3,4,5, & 6. Both distributor caps are new - as well as new rotors - old plugs indicate some kind of problem in the same cylinders before replacing plugs, wires. caps and rotors.

CuriousB - Thanks for your comments. While playing with the plug wires I got big sparks - like over an inch long so I assumed the coils were OK. On the way home last night I was trying to determine a commonality between the four bad cylinders not shared with the good four. One is that all four use long plug wires and are fired by the coil on the opposite side - maybe the coils are weak and the long wires are just enough resistance to be a factor?

I'm going to try to play with it tonight after dark to see if there are any fireworks.

[curiousB]

nc211 - codes indicate misfire in cylinders 3,4,5, & 6. Both distributor caps are new - as well as new rotors - old plugs indicate some kind of problem in the same cylinders before replacing plugs, wires. caps and rotors.

Could this be knock sensor related? Is it the knock sensor that is determining a misfire? That wouldn't necessarily explain rough running but I was wondering how the ECU determines a misfire? If the knock sensor is faulty I wonder if ECU is trying to compensate timing to such a servere amount that engine is running poorly. I'm not too up on how this works but again just some thoughts. Any knock sensor experts online?

Take a look here:

http://us.lexusownersclub.com/forums/index...rt=#entry365858

[flbob 97400]

Did a quick check last night after dark - no arcing anywhere. I pulled the plug caps off of 1, 3 and 5 (3 and 5 were indicated as misfiring, 1 was not), plugged loose plugs into them and they all threw a long spark - about an inch or so. - from the plug to the engine. I guess that means both coils are OK as are the wires on these three at least.

Again it seemed to run a lot smoother for the first minute or so - anyone know what the "open loop" control sequence does?

[curiousB]

Open loop refers to fuel injection control of engine mix. Before the car warms up and the O2 sensors in the exhaust system put out accurate readings the engine is controlled in open loop mode where it sets the proper air/fuel mix based on a predetermined setting. Once the feedback data is valid (O2 sensors warmed up and sending data) it then trims fuel air mix to get more optimal mix. In open loop mode the engine intentionally runs slightly rich so performance isn't too compromised. Of course you wouldn't pass an emissions test in this mode but its only meant for a couple minutes while engine warms up anyway.

[flbob 97400]

Thought I would come back and finish the story. I gave up and took the car (flatbed) to an small independent that was recommended by the Snap-on guy who comes to the garage near by. Turned out to be a bad ECU. Tried re-flowing the PC board - didn't work. Sent away to a guy in Miami for rebuild. All good as new! He had the car for about a month. Bill was $1400 or so - not as bad as I expected.

Took off on a 800 mile trip the two days later - new battery (dead),, a set of jumper cables (jump start), and new tires (tread separation) got me home. Otherwise great.

[eatingupblacktop]

Somehow I missed this thread completely. Props to you Bob for your determined investigation/testing. Thanks for posting your final results!