Gerrot

Just bought a project car that has been LS1 swapped. I bought it with a misfire. It does not make any abnormal engine noise's. I have checked every coil pack with a ohm meter and they all read exact to each other if not very, very close. I have ohm read each injector and they all read exact also. Replaced spark plugs and wires(needed it badly, looked OEM). Cleaned the MAF, just to be sure.

I feel it vibrate when rev'ed up. It will not through any codes, but it will make the Check engine light blink while driving for a period of time. I hooked up my OTC Genesis and watched the misfire monitor. It would randomly misfire on cylinder 6 the worst. However!!!! It would misfire on 2,7,8 also. Maybe a count of 2-5 on the 2,7,8 cylinders, but counts up to 150 on cylinder 6.

So, I switched the coil for cylinder 6 to cylinder 2....Didn't change a thing. Misfire didn't move cylinders. Did the same for the injector, moved it to Cylinder 2, didn't change a thing. It has new plugs and wires, so i did not switch them.

I would not think it was a push rod being it is not reading a misfire every cycle. But I may be wrong.

I cleaned an added grounds, nothing. I am not lost, but getting there! Any help would be VERY appreciated.

The car, just because thread without pics suck!

http://www.flickr.com/photos/52474202@N08/7926108030/http://www.flickr.com/photos/52474202@N08/7926108030/ by http://www.flickr.com/people/52474202@N08/, on Flickr

http://www.flickr.com/photos/52474202@N08/7926113050/http://www.flickr.com/photos/52474202@N08/7926113050/ by http://www.flickr.com/people/52474202@N08/, on Flickr

http://www.flickr.com/photos/52474202@N08/7926110552/http://www.flickr.com/photos/52474202@N08/7926110552/ by http://www.flickr.com/people/52474202@N08/, on Flickr

http://www.flickr.com/photos/52474202@N08/7926115368/http://www.flickr.com/photos/52474202@N08/7926115368/ by http://www.flickr.com/people/52474202@N08/, on Flickr

93camaro_zzz

iTrader: (13)

I am sorry I don't have an answer to your problem, but my motor swapped TransAm is having similar of the same problem. How does your car run though? Does it run different before and after your detected missfires? Does it start detecting missfires on the 6 cyclinder right on startup? I am kind of curious if mine is in the ECM and am wondering where to get my ECM tested. I guess the dealership does this, but just don't know the price.

And last question for you. How are you measuring the resistance on your coils? Which wires are you using for the measurement, and what values are you getting for the measurement?

Thanks in advance, and also good luck on your situation. That is quite a sick looking S2K!!!

Gerrot

I just measured A-B A-C- A-D pins and checked them on everyone. It seems to do this right at if not a couple seconds into start up. I can rev it up(2k rpm) 10 sec into start up and fell the vibration. It takes 20-30 before it start to pick up the misfire on the misfire monitor. It will NOT through a code, EVER!

I will have to let you know the ohms on them as I do not remember.

The car came from Colorado, I live in Concord, MO(Close to St. Louis). Would this make a difference in the tune? I know the elevation it very different, but the Baro sensor should compensate for this.

MAF is read fine at idle 9gs and sweeps fine.

crainholio

iTrader: (2)

I'd go after the injectors next, suspecting they may be partially obstructed and under-flowing.

Swap 2 of the injectors from the worst misfiring cyls with injectors from non-misfiring cylinders, see if the misfire counts follow the injectors to their new locations.

After that, the spark plugs and wires are the next suspects.

Gerrot

I did this with Injector 6, I switched 6 and 2 around. 2 has never counter more than 1 misfire, so I switched it with this one. Same thing, high misfire count on cylinder 6. I will switch the plugs and wires today and see if that does anything.

wrp

Got any logs?

mike13

iTrader: (27)

1st I would check the mechanical condition of the engine by doing a compression check, especially no.6. I would spray some carb cleaner around the intake runner and injector on no.6 just to make sure you don't have a huge vacuum leak.

2nd I would take a wiring schematic and make sure all the pcm grounds are still part of the harness and grounded. Also I would take a look to make sure the injector harness is connected to the right injectors. Verify the color of the wiring on each injector matches which injector it's firing. It could be as simple as your have the injectors cross wired.

3rd. If none of the above gives any clues I would swap out the pcm just to rule it out if the above doesn't fix it. They aren't known for going bad but on a swap maybe something happened while trying to get it running. Like the ignitor or injector driver.

I would stand back and get a good reading of the quality of the swap, stuff like how hacked up is the harness if at all? If the harness has been cut what does the connections look like?, etc.

Hang in there you'll get it fixed.

Gerrot

Thanks for the replies!

I have just got done with a compression check, 150 across the board. Everything seems fine there. I Checked the spark plug on that cylinder, it was very dark. Not black in soot, but dark. I switched the spark plug and wire from cylinder 6 to cylinder 1, being cylinder 1 has never had a misfire. Took cylinder 1 plug and wire and put them in cylinder 6. Walla...i got it to switch cylinders, for a bit. I switched the wire back, and nothing changed. Therefor telling me I have a problem with that spark plug. If not more plugs.

SO!!!! I am using cheap cooper AC DELCO plugs. Do these LS engine get picky about plugs and gaps? I would think it wouldn't be this picky, but every engine has its own brand and style.

Now, the computer. I do not know if it has been adjusted or is stock. Is there any good place's to send my PCM into to get a good tune(bin) on it? Shouldn't be hard, its close to all stock. But would like to know what is on it. Also, can we run in open loop at all times? I know I was able to adjust my Honda PCM's to do this, therefore I didn't have to run o2 sensors.

Gerrot

No logs, sorry. I do feel it hesitate while driving down the road too. I will be cruising at 35-40 and feel it load up, give it a little throttle and it clears up. Drive steady again, and it does it again.

mike13

iTrader: (27)

There's a few tuners who do very good mail order tunes, it sounds like your tune could be really off causing all your problems. You can run open loop all the time but I wouldn't. You could be so pig rich that it's misfiring, many people run cheap copper plugs without issue.

What's your fuel pressure set at? Should be 58psi running.

jimmyblue

iTrader: (11)

Manifold:head vacuum leak on just one runner (#6)?

I've seen people say that the indicated cylinder for misfires
is not always the actual one bugging. Not sure whether to
believe it, or how far off in # or firing order the bogus index
would be.

Gerrot

No vacuum leaks, checked with a smoke detector and with Brake clean. Neither indicated any leaks. I checked the FP and it is within spec also.

I am going to replace the plugs with some ngk plugs, gapped per spec and see if it changes anything.

Anyone have a link of a good mail order tuner? I would like to send my PCM in to get it done, so I know exactly what I am running off of.

Thanks for all the help once again guys!

mrvedit

As I understand it, the PCM detects misfire by calculating the expected amount of engine acceleration for each spark by using the crank and cam sensors. Sometimes high-overlap
cams don't run smoothly at idle and the PCM "thinks" it is misfire.

jimmyblue: Haven't I read that some high-stall torque converters also can result in misfire codes?

Therefore, you might not even have a real misfire. It could be a marginal crank or cam sensor, or an engine mod.

mike13

iTrader: (27)

roll a seal on the intake or a crack. Just trying to rule out the assembly related stuff since it's a new swap.

Also I would get some good datalogging before getting a tune. No.1 your tuner might want to see them before doing the tune. No.2 it's good to keep a base datalog for reference when your trying to solve a problem.

Gerrot

I feel the misfire, it shakes the car when driving and when rev'ed up. Manual trans, so no Converter failure.

I do need to get something to log, I have been using my OTC Genesis Scanner to read codes, watch datastream and test things. The swap has been done for a while and the previous owner says it did not do this before, it has only done it recently.

Like I stated earlier I have smoke checked the intake, and sprayed brake clean on it to check also. Did not indicate any problems.

I am about to go outside and try some NGK TR55 plugs and see if it switches anything. I will keep you all updated tonight.

I do have a small exhaust leak around a header flange, this is on the 1/3/5/7 side. my misfire is coming from the 2/4/6/8 side so I do not think this is the problem. Yes I will be fixing it soon to. with this, it will misfire before it goes into closed loop anyway, so the leak making an o2 sensor read wrong can't be the problem.

Gerrot

SOOO!!!!!!

I switched the BRAND NEW AC Delco plugs I put in to cure my misfire with some NGK TR55's. I checked the gap, they were at .60 and a left them right there as that is OEM spec. Sure as ****...start it up and no misfire! My good god you have to be kidding me right? Nope, I just had a bad BRAND NEW plug. Here are the pics of the Delco's I pulled out. I will never use a Delco in this engine again, not because there horrible, but because it made me pull my hair(that I don't have BTW) out!

So, to whomever this may help in the future, check your plugs even if you are 100% sure they are good. And then check them again, and again.

I will update this in a week just to be sure my problem is gone for good. Thanks for the help guys, it was much appreciated. Here one for you guys! Of course after a drive in the rain!

http://www.flickr.com/photos/52474202@N08/7952505088/http://www.flickr.com/photos/52474202@N08/7952505088/ by http://www.flickr.com/people/52474202@N08/, on Flickr

http://www.flickr.com/photos/52474202@N08/7952509136/http://www.flickr.com/photos/52474202@N08/7952509136/ by http://www.flickr.com/people/52474202@N08/, on Flickr

The plugs...

http://www.flickr.com/photos/52474202@N08/7952507822/http://www.flickr.com/photos/52474202@N08/7952507822/ by http://www.flickr.com/people/52474202@N08/, on Flickr

http://www.flickr.com/photos/52474202@N08/7952506466/http://www.flickr.com/photos/52474202@N08/7952506466/ by http://www.flickr.com/people/52474202@N08/, on Flickr

ss1129

iTrader: (16)

I literally know tons of people that run cheapie (myself being one of them) and have never had a problem. Something caused that plug to foul. Did you had the problem before the plug swap as well?

crainholio

iTrader: (2)

Great finding. I recommend Delco Iridium stock plugs for these engines and I've never been disappointed...except for the price tag. They aren't cheap, but they last a loooong time and perform well the whole time.

If you're short on cash, NGK coppers are fine but gap them precisely to spec before installing.

Fix this before moving on to PCM tuning. Then consider ECS for $150 or whatever if you want a decent mail-order tune. I've sent them several customers and every one has been very happy.

mike13

iTrader: (27)

I'm glad you got it figured out, now go out and enjoy it.

crainholio

iTrader: (2)

I posted above before reading the rest of the thread...congrats!