ImWildBill

My 1990 LS400 had a slight miss a couple of weeks ago. Wasn't too bad, figured a fouled spark plug. Within less than a week it was running very rough, no acceleration, sucking down the gas, horrible idle.

I changed out the plugs and wires and it helped a little, the old plugs and wires were very old and shot, but still runs horrible. The check engine light isn't on, so there shouldn't be any codes to pull I believe.

I don't know much about these computerized cars, still learning. Any help I can get will be greatly appreciated!

PureDrifter

iTrader: (10)

check rotors, firing order, coils (if one bank doesnt have spark), and ecu.

ImWildBill

How do you check the coil without getting zapped and the ecu?

PureDrifter

iTrader: (10)

no spark on one entire bank of cylinders=coil has died on that side.

deanshark

Pull the fuse for the fuel pump, (so the car wont start) take the coil wire off of the distributor, grab the boot part of the wire either with your fingers or some pliers, hold the wire about 1/16" away from the valve cover, have someone crank the engine, and see if there is spark. If you have spark, try the other side the same way. The drivers side coil usually craps out so check that one first.
Even though the engine light isn't on there can still be a code stored in there. Does the engine light actually work, when you turn the key does it light up?

ImWildBill

I believe it does light up when I start the car, I'll check in the morning when I get home from work.

1killerls

coil for sure.

union

i have this problem also,swapped coil,plugs and wires amd still runs terribly.any more help would be appreciated also!

vutown

Guys,

So I just did a tuneup and changed out the following items: (I have a 1995 LS400 with 230k miles)
Electric Coolant Temperature Sensor
Spark Plug wires (Denso)
Iridium Spark Plugs (gapped at 0.044")
Cap
Rotors

Initial start up had a check engine light on, so I decided to pull the battery for a bit and reconnected. Started up fine, no CEL. I let the car idle for about 10 minutes while I cleaned up the tools then took her for a spin. Here are the things that I noticed:

Car had a lot more power and smoother idling. But from a complete stop, there was some slight hesitation accelerating. No CEL.

So as I was leaving my friend's house, CEL came on as I was on the freeway - a lot of hesitation on acceleration. Got home within a few minutes and had the car towed to my mechanic for diagnostic this morning and he reported codes of cylinder #5 and 7 misfiring, along with Random Misfiring.

If I'm right, #5 and #7 are on different sides. If the coil is bad, as I've read on here, then the whole bank would have gone kapoot and not gotten any spark. What are the chances that both coils would go bad at the same time?

I dropped by my mechanic today to have a talk with him and he's starting to tear it apart (spark plug wires and will check other stuff). Looking at the Service Manual for our cars, it says to check the following:
Coil
Spark plug gap (mine is gapped at 0.044, where the manual says 0.031")
Fuel pressure
Fuel injector
ECS

Now, I know some will say check your spark plug gaps - and if indeed this was the case, then shouldn't all 8 cylinders be misfiring cause they're all gapped the same way?

I'm pretty puzzled. Hopefully my mechanic will find out what's wrong. I'm pretty flustered myself, as I've lurked on these forms for weeks and have read and reread all of the DIY posted on here and other links about changing out the ECS, spark plugs and spark plug wires.

Any inputs?

vutown

oh I forgot to add that it seems like once the car warmed up, that's when the slight miss went to a rough idle.

deanshark

vutown; It's possible that both coils can be bad at the same time, anything is possible. Yes 5 and 7 come off different distributors. Who did the original tune up? It's possible the rotors were put on backwards, 180* off. Lots of people have done that. Are you sure that the plug wires on 5 and 7 are correct? They could be just switched. Good luck finding the problem.

vutown

deanshark,

My friend who's pretty mechanically inclined and myself did the tuneup. There could always be a chance that I swapped up the wires, but here was my method of replacing the wires, cap and rotors:

1. I replaced the cap first by pulling one wire at a time. So essentially after replacing this, I had the old wires on the new cap.
2. Next I replaced the rotor.
3. Then I started to replace each spark plug wire one at a time, working from the most furthest to the front.

Again, there's always a chance I screwed this up. Is there a diagram somewhere that shows us which cylinder wire should be plugged to which connector on the cap?

I'm pretty sure the cap went on correctly. I'd imagine my chances of getting these 180* turned the wrong way slim on both. Now if one bank was misfiring....

Also, if the coil goes bad, would it exhibit symptoms of not firing on all cylinders? i.e. no spark on one bank? Or could a bad coil misfire on one cylinder?

PureDrifter

iTrader: (10)

did you ohm out the wires to make sure the old wires didnt get breaks in them when you messed with them?

vutown

PureDrifter,

I'm not sure what you mean by the old wires, but I currently have new wires on there. I guess I should consider ohming out the new wires? But again, what are the chances of the new wires being shipped bad?

I can see many of you rolling you eyes. alright, I'll suggest this to my mechanic if he can't find anything. My car is currently in the shop.

Stay tuned for updates...

deanshark

I think he meant if you used the same (old) plug wires, you might have ruined them when taking them off. (pulling on them the wrong way)
My last set of wires had one plug wire and one coil wire that were bad. They didn't read anything when I tested them on an ohm meter. Good thing I checked them before installing them. It's a good possibility you have a couple bad wires.
The rotors, depending on the brand, most brands have a little tip on them that fits into a notch on the cam pulley so they can only go one way, but some don't have it and you can put them 180* off.
At the bottom of this link it shows the plug wire diagram and the ohms of each wire.
http://www.lexls.com/tutorials/ignition/sparkplugs.html