traducian

Struggling with what to do next. Here is what I have done:
1. Ecu capacitor fix
2. New cats
3. New plugs/wires/rotors/coils (all needed anyway)
4. New camshaft seals. (Timing verified correct)
5. New valve cover gaskets.
6. Cleaned throttle body

Since I first brought this home a couple months ago (248k miles), I have had an elusive #4 cylinder misfire code along with a related rough idle. I checked compression and the cylinder is solid, putting out roughly the same compression as the others.

can someone please give me some advice before I get too deep into this head? My patience is running thin on this car and I only want to break it down one more time. What should be my order of priority in finding this elusive misfire?

- change fuel injector to another cylinder and see if the problem arises on the new cylinder?
- physically inspect cam lobe?
- rerun compression check?
- change cam?
- pull head, replace valve?
- positively I'd any possible vacuum leaks?
Brian

Yamae

I'd check the waveform of the ignitor's output / ignition coil's input. Does it swing fully? It should be swinging nearly 400Vp-p. As is explained in the link. If not that much, it will simply mean that the power transistor inside has some leakage or the ignitor has some problem.

traducian

I am going to replace fuel injectors ($55 rebuilt Densos) and fuel filter ($13) first as I believe it feels like a fuel problem due to lack of power. While I do that, I'll pull the right bank valve cover and inspect the cam. Yamae, you are too advanced for this backyard mechanic I simply don't understand "measure waveforms" and I can barely use a multimeter, much less the magical tool you seem to possess.

The problem is on the right bank where the #4 cylinder exists. But the problem feels like its manifesting in many cylinders, based on the pulling under load, leading me to believe it's probably more than one bank. Both coils are new since I started and the problem existed since day one, even though i replaced both coils. I find it hard to conclude coils have failed since performance is the same as before the replacement.

my instinct is that if these changes don't fix it, then it is a valve problem.

frankly, I have no idea (or the tools) to understand waveform issues. And I will spend $55 to and an hour on fuel injectors to eliminate the most likely culprit.

other than that... I cleaned my throttle body, which was VERY DIRTY. Do I need to clean my Idle control valve too?

brian

Striker223

Let's do the simple fix first shall we? If you have individual ignition coils move #4 to number #1 and vice versa and if you have the wire based system swap the coils side to side and the #1 and #4 wire. Start it and see if the missfire moves to #1

Next if the miss occurs at idle enough for the computer to detect it or you to feel it then unplug the #4 injector to see how much worse or not it becomes. If it doesn't change much or you can't notice anything then replug it and replicate it on #1 and if #1 stumbles noticeably worse than when #4 is plugged in you have #4 injector starting to go totally bad.

Next if that that still doesn't come up with anything since you told us you already checked compression and it's even you need to buy two cans of brake clean. You are going to spray the clean at the engine while it's running starting from the back of the MAF sensor going to areas like the vacuum line connections and throttle body mounting flange on the intake. Also spray the intake at its base where it seals on the lower intake/heads particularly around cyl #4 and any connectors from vacuum lines in that corner of the intake.

If that STILL doesn't find the issue it's time for more serious steps that we can get into when you have tried those. Are you absolutely sure you timed it correctly? What belt did you use when you replaced the cam seals, if you have the right side (or whatever bank contains 4 in this engine since I honestly doesn't know and am used to mopar V8s) even one tooth off it will do what you are describing.

Striker223

Not everyone just has a scope laying around or knows how to use one lol!

deanshark

Striker223; The coil on plug didn't start until 98 on the ls400. But yes, switching wires would be the first and easiest thing for diagnosing where this misfire is. Just swapping the plug wire from #4 to any other plug and seeing what missfire code you get would be the way to go. That way you could also tell if it's a spark or fuel missfire.

If the timing belt was one tooth off it wouldn't have an "intermittent" miss fire, it would be a constant miss fire....or maybe even a catastrophic failure seeing how it's an interference engine.

RA40

iTrader: (6)

May be that injector. Check that the wiring harness is ok for that one. Replacing it sounds good. Have you tried any of the fuel injection cleaning agents? (I'm not generally a fan of those but for ~$8 it is a low cost option.) How did the plug look for that cylinder?