misfire

I've used the search engine and found a little bit on this topic, but I figured I would ask about my specific situation.

I acquired a misfire on my way home the other day. It was about 15 miles after refilling. The misfire only occurs under load. I can leave the car in neutral and it revs fine, in first gear it's fine unless i'm going up a hill. All other gears it's pretty noticeable until I'm cruising. I replaced 5 of the plugs and wires (pita for those back ones). The only one I didn't replace was the drivers side back wire (would love some info on how to get to that. IE what side of the car, where to slide your hand through...). The number 5 plug (i think that's the number...it's the middle one in the back) had gas on it, so I figured, maybe that's the plug/wire causing problems. Yet after swapping the plugs and wires I still have the problem. The way that the car is running, I can't believe it would be more than one cylinder missing. I bought a new coil thinking maybe the coil for that cylinder was bad. Car still ran bad, so I swapped it into the other two places and still didn't fix it.

Is the only thing left to check the injectors? How hard are those to change, and would a bad injector show signs of gas on the plug?

The plugs I got were AC Delco Professional 41-101 iridium plugs (6.99 a piece) and the wires were duralast.

The car is a 97 with 199300 miles. Replaced the fuel pump over the summer, other than that no changes to the ignition system.

Oh, forgot to add. I had a new fuel filter put on 2 years ago

Fuel injectors would not cause this problem, imo. It seems ignition related. You have the right idea with plugs and wires. The iridium plugs are not necessary but do not hurt. Keep these in.

Unfortunately, the plug wires may still be the issue. We have seen supercharged 3800 engines behave erratically (misfire) with cheaper ignition wires (Duralast, Bosch, etc.). AC Delco/Delphi wires can be had for $35 shipped from Rockauto with 5% discount offer. These are the only reasonably priced wires that have been proven to work for our ultra high voltage demands. They typically last 100k miles or more.

I would replace the wires with a set of Delco/Delphi and make sure to do all of them. Make sure all the plugs are replaced as well. Then if the problem continues, swap the new coil pack to all 3 locations and check for changes. Good luck.

I agree with Aaron on this one. Duralast wires could very well be the culprit. You can get the delco's form Advance auto (if they have those by you) in case you cant wait for shipping from rockauto.

I would also double check the plugs are all going to the right cylinder. You'd be surprised how well the car will run with two cylinders swapped (ask me how i know). Its also hard to get them back right if they are all off at the same time since the aftermarket ones are normally not labeled.
Since you didnt replace the #6 plug or wire, how many miles are on it?

Lastly you may want to have autozone/advance run a scan on it when you go back for the wires. they should be able to see a pending P0300-P0306 code depending on which cyl(s) are having the issue.

Thanks for the responses. I'm glad it probably isn't the injector. I'll have to get that last plug in. Any suggestions on how to get at it? It's the drivers side back firewall side plug.

The other day when I did the other plugs it was 6 degrees out and after pulling the one that had gas on it and fidgeting with the last plug and not being able to get to it I was just fed up and figured the one that had gas on it was probably the culprit cylinder. I don't see any other reason why that plug would have gas on it.

Would it be easier to get that last one from under the car?

Also, I don't think the plugs and wires are crossed or anything, because I bought the car with 160k miles on it and hadn't done anything to the wires until this problem came up. It also happened while I was already on the road for 15 miles, so it just doesn't seem like that could be the culprit. The coils all look factory (all have the numbers on them still, aside from the one I bought). The car hadn't had a tune up for at least 39k miles. Who's to say if the plugs and wires were replaced at the dealership I bought it from. Probably not since I bought it without brakes as well.

My dad has an OBD2 scanner somewhere. I'll have to find it and hook it up. Just figured it was probably due for plugs and wires anyway so I went ahead with that.

duster_do_little wrote:

Thanks for the responses. I'm glad it probably isn't the injector. I'll have to get that last plug in. Any suggestions on how to get at it? It's the drivers side back firewall side plug.

The other day when I did the other plugs it was 6 degrees out and after pulling the one that had gas on it and fidgeting with the last plug and not being able to get to it I was just fed up and figured the one that had gas on it was probably the culprit cylinder. I don't see any other reason why that plug would have gas on it.

Would it be easier to get that last one from under the car?

I found that the easiest way to get to the rear plugs/wires is to put front of the car on ramps (or stands if you don't have ramps) and slide in from the front. You may have to wait for the exhaust to cool off a little bit b/c you will have your arm all over it trying to get to that #6. As everyone who responded has said, it's amazing how much better a quality plug/wire combo solves so many problems.

Probably wouldn't hurt to check the firing order too. I had ignition problems and after having the coils off umpteen times that I was POSITIVE i had the wires correct, there were a couple times that I had one or two switched. As Mr. Riviera said, the car will run surprisingly well with a couple wires switched.

Maybe someone with a little more knowledge can tell me if this graphic applies to a Series II, but here's the graphic I found online for a Series I that I printed out and stuck to the wall beside my workbench to help me keep it straight.

diagram is correct for L67's

1 on my coil is going to the 1 plug, 4 seems to be going to the 2 plug, 5 to the 5 plug, 2 to the 4 plug, and 6 to the 6 plug. When i swapped the 2 and 4 wires the car barely started and ran really rough. I didn't look really hard as to where the wires are going. It's snowing, really cold, and I'm about to go to work. Just going off memory of when I pulled the plugs. So, the 4 could be going to 4 and the 2 could be going to 2. I'll pull the 240z out of the garage when i get a day off and put the car on ramps in there.

Make sure the coils are in their correct locations, else the numbers may not be correct if coil packs have swapped. Correct locations should look like this (agrees with above diagram):



If yours doesn't look like this, may want to swap coils or wires to correct locations.

the numbers i gave were looking at the diagram above and not the numbers on the coils

102 - MAF or VAF A Circuit Low input
141 - O2 sensor heater circuit malfunction
304 - Cylinder 4 misfire

The first two have been there for a couple of years. Cylinder 4 is the plug that had fuel on it when i pulled it out. Replaced that wire and plug and that's where i first put the new coil.

I'm pretty sure it's not the coil, because the new coil is now at the 2/5 coil, the 2/5 coil is where the 1/4 coil was, and the 1/4 coil is where the 6/3 coil was. Yet it's still giving me a misfire at 4 and no other cylinder

Also, I confirmed my wiring...according to your diagram my wiring is...

coil - cylinder
1 - 1
4 - 2
5 - 5
2 - 4
3 - 3
6 - 6

As soon as I swap the 2 and 4 it stutters and sounds like it's going to stall out

the misfire is more persistent when the car warms up

could an injector clip or wire for #4 have been damaged while doing the change?

I don't think so, I was pretty cautious when changing. I'm thinking the problem isn't plug, wire, or coil, because the car has the same exact problem right now as it did before I swapped all of those things. I'm looking for other causes for a misfire on cylinder 4. It's supposed to warm up to 50 tomorrow, and I have the day off, so I'm going to go out and take the plug out for cylinder 4 and make sure I didn't get any gunk or anything on it and put it back in. Then anything else that could possibly be the problem would be great to work on then, because it's supposed to cool right back down to the teens after that.

Sorry for the long wait on a response. I found the problem. Kind of. The reason I was having a huge misfire was because the way the wires are that I installed, the metal boot wouldn't fit over it enough to allow the wire to seat properly on the plug. I'm running the car without the cover for now. I have a new problem though. The car runs perfect until it reaches 190 degrees. When it finally warms up I have my misfire back under load.

duster_do_little wrote:

Sorry for the long wait on a response. I found the problem. Kind of. The reason I was having a huge misfire was because the way the wires are that I installed, the metal boot wouldn't fit over it enough to allow the wire to seat properly on the plug. I'm running the car without the cover for now. I have a new problem though. The car runs perfect until it reaches 190 degrees. When it finally warms up I have my misfire back under load.

whose wires did you install?

Reason I wonder is - the standard ignition on the SC engine is among the highest energy ignitions on any production car, and it *w i l l* quickly lunch on your wires if you install standard wires. If the metal boots are not fitting, then you probably don't have standard wires. The boots fit fine on the Delco wires; on the Magnecors they are not necessary due to the materials used. Taylor spiral wound I hear are good too, never used 'em.

Do tell.

Hey Dustin,

Did you resolve your issue? I'm having misfires up around 50 MPH after changing wires and coils. Was thinking about going after fuel injectors next.

cheap wires was my problem. I ended up buying ZZPerformance 10.5mm wires and boy what a difference. A bit pricey, but I had the cash and figured why not. I no longer have any missfires. Next thing on my agenda is the MAF sensor. I believe that's what's giving me the hesitation at low rpms when cold.

Interesting. My misfire was initially caused by a bad ignition coil. After this was changed, it still hick-uped. So I changed wires and spark plugs. Still hickuping a little bit so going to replace the wires with the AC Delco's. Hopefully that get's it.

werdstrave wrote:

Interesting. My misfire was initially caused by a bad ignition coil. After this was changed, it still hick-uped. So I changed wires and spark plugs. Still hickuping a little bit so going to replace the wires with the AC Delco's. Hopefully that get's it.

I guess this means you saw the light... for the rest of you, I repeat: the standard ignition on the SC engine is among the highest energy ignitions on any production car, and it *w i l l* quickly lunch on your wires if you install standard wires. Probably the least pricey wires that would work would be the ACDelcos, which are not that pricey even from a dealer. Magnecor (http://www.magnecor.com), I use - have had a set on now for more than 150K miles. Others say Taylor, ZZP are good.

It is not the case that you have to spend a king's ransom on wires. It IS the case that you can not buy the wireset that goes on the non-SC ignition (it WILL fit but it WONT work long). It is also the case that you can not buy standard wires and expect them to work long.

By the way, on maintenance on my car, I noticed something that may interest you. I had what I though was a mild misfire (mechanic said it was my imagination) and it turned out to be that a while back I'd had a coil fail (an OE spark plug wire had failed) while I was traveling. The shop (a Firestone) did a real nice job of diagnosing the problem (they had several GM dealer techs who moonlighted there on weekends -- this was a weekend) and got me going with a Standard coil and a wire out of their packrat box (they would keep spares pulled off other cars for just this sort of problem). I replaced my wire set after I got back home. Anyway, if you listened to the engine idle carefully you could pick up a sort of an unevenness.

3800 series II engines don't lope.

I was out one saturday in a junkyard pulling maintenance spares where I came across a 99 PA with the 3800 S II SC engine that looked like it had a recently-installed coil pack etc. SO I bought the coils. And for grins I installed one in place of the Standard.

BAM. No more miniscule lope. I even balanced a nickel on edge on the engine cover while this thing is idling, just for shiggles.

What I learned (over the years):

- Never use crap wires
- make sure you are using the SC coils on the SC engine. You do not have to replace the coils in sets but you need to make sure they electrically match (check them with a meter).

Albertj

Thanks for the detailed response Albert. I have a question about coils. What initially set off my misfire was a bad coil for pistons 2 and 5. I have replaced all of the coils with AZ's duralast coils. Still misfiring and popping a bit. So then I replaced the wires with crap BOSCH. Still misfiring but a little less. Replaced the plugs with Platinum AC Delcos (The old ones were fouled really bad especially 2 and 5). Still misfiring a little bit. I just replaced the plug wires with AC Delcos as suggested and haven't noticed a misfire yet but exhaust smells a little funny. So basically everything is close to OEM except for the duralast coils.

My question, would you replace the coils with the AZ duralast coils vs. an AC Delco coil or OEM coil as I just did? You mentioned making sure they electrically match, how do I do this? I still have 2 good OEM coils, I just replaced all of them with the duralasts to be thorough.

The funny smelling exhaust is probably just the new setup burning off all the gunk that's built up inside the cylinder...I wouldn't worry about that. A couple of WOT runs will clear it all out.

As far as Electronically matching coils, I think he means the overall coil resistance. Once the car sits overnight, pull the wires off (one coil at a time), and measure the resistance across the terminals. They should all be within ~.5 ohms of each other.
The factory coils are far superior than the aftermarket versions IMO.

So I checked the resistance across the terminals. The newly installed AZ duralasts are 8.3 ohms vs the OEM 5.6 ohms. Sounds like a problem to me. I'm going to hunt down an OEM coil. Anyone know of a good place to get an OEM? I don't think I can trust these after markets. I think it's weird how when I went down to AZ that they didn't have one item # for SC 3800s and one item # for naturally aspirated 3800s. I'm thinking they just provide the one for the naturally aspirated 3800s. Lame.