code p0300 missfire cyl#4

[johnd89]

Hello,

I got this code (1995 riviera s/c vin 1) and using the scanner I got cyl#4 misfire. I noticed that if I bring the rpm's up to 1500rpm for a while and let go, the cyl will misfire, otherwise not-idle only-. then I revved a little more 2000rp and let go, it did not misfire again
I have new wires and plugs, but I will doublecheck everything-wire, injector-. I know I have spark at the coil at least.
Now the thing is that it did this after it stayed one day without use, and I know from another bonneville vin k that the same cyl was hydroloking. I also noticed maybe more than normal white smoke-could be only an impression-
I will take out the sparkplug and turn the engine over to see if I have coolant in it, also check coolant level
I guess I'm only trying to rule out the fuel injector.

PS; If I have to do the lower intake manifold gaskets, can the supercharger, LIM, TB, fuel rail/inj taken off COMPLETE in one piece? I'm trying to figure out if I need the extra tb gasket, s/c gasket and the two o-rings

Thanks a bunch for any hint

[willwren]

Swap the 4 and 6 wires (rear bank, two closest to the driver). They're the same length. See if the misfire moves to #6. Make sure the #4 wire isn't rubbing on a manifold or too close to the O2 sensor in the downpipe. This is a fairly common problem from time to time, especially on your Riv which has less room between the rear bank and the firewall than a Bonneville does.

Ignore the injector for now, failures are extremely rare. What brand/type of plugs and wires do you have, and what are you gapped at?

If you suspect a leak/coolant/etc, 'read' the plug. It should look noticeably different than the 2 and 6 on the rear bank. The L67 isn't as prone to these issues as the L36, but it can happen. Do you have Dexcool in the car? What's your coolant level?

Yes, you can remove the LIM, SC, and TB all at once, but I don't suggest it. This is a really good time to replace all those gaskets, and it really isn't that much more work to take each component off one at a time. Your TB should be thoroughly cleaned before reinstall, and it needs to be off the SC to do it properly (pay close attention to the idle air passage after you remove the IAC). Techinfo has a bunch of good info to read through before tackling this job. Do NOT attempt to clean the SC, other than the base where the gasket goes. It's also a good time to change the oil as you can gravity drain it when it's removed.

[johnd89]

WOW, thanks for the quick reply and the wealth of info!
Just to clarify, the cyl I'm talking about (thought #4, may be wrong) is front bank extreme left as you open the hood- towards the bumper and towards the belt(s)-
this is where I saw hydrolok on a non-s/c series II bonne.

Ok, I'm talking about cyl 1, my bad. the code reader gave me #4 though (means I has the coil the other way around). I have to check #4 now. sorry for the messup

the new set of wires is bosch and plugs are champions from walmart.
checked the coolant level in the tank and rad, the level is ok.
the cyl4 plug seemed to look gapped a little more than the one right beside. color wise looked the same. I regapped same as the other one and switched places. I'll scan again to see if the misfire moved. if not, I'll try with a different plug wire (this is the shortest though, but I have a second car)
measured the ohm on the injectors, look the same. maybe one it's partially plugged
I turned the engine w/plug off and nothing leaked. I will redo this after it stays longer.
I did see though right when u take off the oil filling cap some light brown deposits on the bolt right below. so antifreze may get there (I use regular green stuff, no dexcool).
so far my $$ is on the LIM gaskets.
thx for the tip about the other gaskets, I will do them too.

question is: can I still use the car with this slow leak or is this asking for major trouble?

Thanks!
PS: forgot to add, car has 160k miles

[willwren]

Facing the motor (front of the car), 1 3 5 left to right on the front bank (closest to the radiator, 1 is the closest to the belts).
2 4 6 are the rear bank, with 6 being the closest to the driver. You are talking about cylinder #1.

Bosch wires generally suck on our cars. Do you have an old wire of a different brand to swap in? Champion plugs are OK, but not preferred (make sure they're not platinum, they should never be used for a turbo or supercharged application).

If you were burning coolant in one cylinder and not the other, you would notice a difference. Pull one from the rear bank to be sure, or at least the far opposite end. Also make sure you have no corrosion on the coil terminals. It might also be a good idea to remove and re-seat the coil in question on the ICM. You'll need a 5.5mm socket.

[johnd89]

Thanks will, u're right, sorry for the messup. I meant cyl1 for the hydrolock but the scanner gave me #4 so I'll do the checks you said the first time around-at the real #4-.

[willwren]

Middle rear bank, right above the downpipe and O2 sensor.

Let us know if you discover anything.

Another good trick for your bag 'o tricks is to wait until dark, and mist a fine spray with a pump spray bottle (windex etc) over the motor. Use plain water (well water works particularly well) and watch for arcs in the dark. That'll tell you if a wire is shorting through the insulation to ground.

It goes without saying that you want things dark and the motor running for this to work.

[aCiD]

lol wow.

I haven't been on here in years, just signed in to ask THE EXACT problem right down to the cylinder!

I'm going to go switch my wires and see if it moves. I already replaced the plugs and the injector and the coil. (Had spares of all sitting around, and plugs needed to be done anyways.)

[aCiD]

Well... that was easy. It was the plug wire. New ones ordered!
ty

[willwren]

Good to see you again, bud. How's the SSEi running otherwise?

[johnd89]

took out the plug and it looked ok.
repositioed some the wires
if it does it again I'll swap the wires and
the windex trick is a good one
thanks!