My L67 Fiero is running and I'm so happy. I was supposed to be going to the strip to tear apart my buddies lightly modded Mustang GT but upon scanning I ran into some problems. First one, which I noticed on first start, is its running very very rich, like the exhaust fumes make your eyes water rich.lol I know fuel pressure is correct now though. When I first scanned it my O2 sensor seemed like it didn't wanna go into closed loop mode so I assumed the engine was actually running lean and the O2 was telling the PCM to richen up the mixture. Well after I discovered a misfire in cylinder three I thought Ok maybe its not running rich at all maybe its getting the right amount of fuel but since the fual in that cylinder is just passing through then it truly is running rich. So I assumed maybe I botched a homemade plug wire since I had never bought a set you had to assemble yourself before. Well I redid that and its still misfiring. I havent pulled the plug out yet to look at it I'm gonna do that later and then check to make sure its firing, but I dont see that being the problem because the coil is brand new and also shouldnt the other cylinder on that coil misfire as well if the coil was bad? If all else fails then I'm gonna test the injuctor with a multi-meter to see if its firing. If its not then that would probably be why my O2 sensor is telling my PCM to richen the mixture....................wow I know that was a lot to absorb, but if you guys have any additional thoughts I'd appreciate it, I'd really like to see what this car can do because as of now, it doesn't impress me given what all I've put into it.

Is it OBDII? what are you using to scan it? is the PCM factory (GM) code?
Is this a fresh install? or a re-install? was it running OK before?

My 3800 runs real rich at startup. At worst, mine is around AFR 8.8:1. once I hit closed loop, I am at 14.7:1 I watch it go from 8.8 to 14.7 before I attempt to drive.
My short term and long term fuel trim vary about 10% once in closed loop.
The PCM should go into closed loop irregardless of the O2 sensor. (or so it was explained to me)
If the coil is bad, the two cylinders would not be firing. Like you were describing, pull the plug and make sure the plug grounding tang isn't touching the tip.
Are the injectors new / clean?

Bump for more knowledgeable people.

[This message has been edited by IFLYR22 (edited 03-02-2009).]

I don't know much about the 3800's, but when I first got my DOHC running, it was running so rich that the exhaust would shoot flames. It turned out to be the throttle positioning sensor. It was worn out, and was just dumping fuel into the cylinders.
Nick

Is the Fuel Pressure Regulator hooked up to the vacuum port under the supercharger snout?

It's OBDII, and a fresh install. It is a 2003 model ZZP V1.0 PCM. Yes the vacuum is hooked up to the FPR. I'm not sure what type of scanner it is though it belongs to my buddy and he just scans it when I ask him, but he's got his own shop so its some crazy expensive one that will scan anything. My short term fuel trim was around 20.3 at idle until it finally kicked into closed loop. The plugs are all brand new they are the NGK TR8IX's. As far as TPS, I'm assuming its good because I'm not getting any codes.

[This message has been edited by Khaos88GT (edited 03-02-2009).]

Trims dont really mean anything out of closed loop.... Shortterm trims never mean anything, ever.

If you have a missfire, then your O2 will be reading lean, and add more fuel (its a oxygen sensor not a fuel sensor).

Get a scanner on there, read cylinder missfire's, read long terms, and watch the o2. should bounce steady from 150 to 850 ish.

If it is completely dead missfire (would sound even more horrible than normal) then pull the plug because you most likely chipped a piston and smoked your motor.

Okay--First of all--Double check to insure the coils are in order on the ICM and that the plug wires are on there in the correct order. This may sound dumb but this issue gets almost everyone at one time or another. Find out what cylinder is misfiring and then troubleshoot from there by swapping coils, wires, injector, ICM, ect. Is you vacuum line for your FPR hooked up to the small nipple under the SC snout and does your fuel pressure read correct at idle with vacuum on/off? Check the TPS and see what it is reading at idle and WOT also.

Also don't assume the problem is not a certain part cause it is new---I have gotten new parts before that where bad right out of the box.

Well just to be clear firing order for the L67 is 1-6-5-4-3-2 correct? Also just to double check, and because I don't trust a chilton's manual, what would the correct orientation of the coils be on the ICM starting with the ICM harness on your left and moving from left to right?

quote Originally posted by Khaos88GT: Well just to be clear firing order for the L67 is 1-6-5-4-3-2 correct? Also just to double check, and because I don't trust a chilton's manual, what would the correct orientation of the coils be on the ICM starting with the ICM harness on your left and moving from left to right?

It goes on the ICM--Plug Side----1/4---5/2---3/6

The firing order if looking into the engine bay from behind:

5 3 1
Engine--Pulley side
6 4 2

U standing here!!!!

[This message has been edited by MstangsBware (edited 03-02-2009).]

Well firing order and coils are arranged correctly. So its not that. I pulled the plug it looked a little black on the tip but not that bad so it has been firing a little. I know that that doesn't mean that its able to fire under compression though. I'm gonna get a new plug tomorrow and see what happen with that. You know this sorta reminds me of that thread that Mathew_Fiero started about his misfire issues. He said his would run then just die on him. I guess I should double check my IAC and make sure its wired right because that was what he ran into.......dont know how that causes a misfire but if it does it does.

Checked the IAC its wired fine.

[This message has been edited by Khaos88GT (edited 03-02-2009).]

quote Originally posted by darkhorizon: Trims dont really mean anything out of closed loop....

Not true. If a fuel trim is stored in memory (long term) and displayed on the scan tool, that fuel trim is being implemented by the PCM; even while the engine is operating in open loop. The PCM will not make changes to the fuel trims until the system enters closed loop. Fuel trims are stored in engine operating cells. These cells are set up based on RPM and LOAD. So while in open loop you may witness the fuel trims changing as the engine RPM and/or LOAD changes. But the PCM will not be making changes to these trims until the system enters closed loop operation.

quote Shortterm trims never mean anything, ever.

INCORRECT.

Short Term fuel trims DO MEAN SOMETHING. They affect the fuel mixture being delivered to the engine the same as long term fuel trims do. The difference is short term trims are not stored in PCM memory and long term trims are. For example, if you have a short term fuel trim number of -4% and a long term fuel trim number of -5%; then you would add both those together to figure out what the total adjustment the PCM is doing to the fuel delivery to the engine (which in this case would be -9%).

While in closed loop and fuel learning operation, the PCM will always try to attain a short term fuel trim of 0%. It will do this by adjusting the long term fuel trim accordingly. But the short term trim is the first to react to changes in engine operation. So you will see the short term fuel trim number moving first before the long term number moves. But as the long term trim number moves, the short term trim number should start migrating back towards 0% or "no fuel adjustment". The long term fuel trim is stored in the PCM's keep-alive memory and reused for consecutive startup cycles. Short term trims are cleared every time the key is turned off and/or during other operating conditions.

DarkHorizon, PLEASE go get a proper education about this stuff BEFORE you confuse people by posting misinformation. Thank you.

-ryan


------------------
5+ years on this same swap -- NO engine or transmission failures...

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 03-02-2009).]

Read what I said...

Out of closed loop, the numbers dont MEAN anything in context of troubleshooting, but it doesnt say that they are not doing anything. Its very difficult to troubleshoot a problem in this situation using those numbers...

Short trims on a very accurately tuned stock setup will bounce around significantly.. and also makes it misleading for a troubleshooting in this situation.

I just noticed that entire post was just to troll me, and not to help this guy out... hmmm.. I am flattered you took 10 mins from working on Joe's car to yell at me about something you didnt read correctly.

quote Originally posted by darkhorizon: Read what I said... Out of closed loop, the numbers dont MEAN anything in context of troubleshooting, but it doesnt say that they are not doing anything. Its very difficult to troubleshoot a problem in this situation using those numbers... Short trims on a very accurately tuned stock setup will bounce around significantly.. and also makes it misleading for a troubleshooting in this situation.

I DID read what you said. You said:

quote Trims dont really mean anything out of closed loop.... Shortterm trims never mean anything, ever.

What is YOUR definition of "EVER" and "NEVER"? Regardless of context, your use of absolutes will only serve to confuse people unless you are very specific. If you wanted to make your post factually correct, you should have worded it better and said: "IF you have a misfire, then any fuel trim numbers you see on the scan tool could be invalid." But just jumping in the thread and saying "short term trims never mean anything ever" is a blanket statement that is not correct the very way you worded it.

O2 readings can be invalid if you have a misfire. An incomplete but partial burn CAN result in RICH O2 readings. I have had this happen. Of course misfires can also result in LEAN O2 readings; BUT NOT ALWAYS. In any case, if the O2 readings are invalid or erronious then the fuel trims will not be based on "good" data either.

Short Term Fuel Trims on a "very accurately tuned" setup MAY NOT bounce around significantly; they may in fact move very little. If they do move around a lot and by big amounts, then the tune IS NOT very accurate.

quote I just noticed that entire post was just to troll me, and not to help this guy out... hmmm.. I am flattered you took 10 mins from working on Joe's car to yell at me about something you didnt read correctly.

Don't tell me how to do my job and don't tell me what to do. I would not have said anything in THIS thread if you would have been 100% factual in your post. And for the record I did help this guy by correcting the misinformation you were feeding him and everybody else reading it.

So are you agreeing with me? I really dont understand what you are trying to say... If my "blanket statments" are considered bad information, then fine.. I really would rather post an answer quickly and bluntly then making 3 paragraphs to explain why looking at trims is usless in a thread like this...

quote O2 readings can be invalid if you have a misfire. An incomplete but partial burn CAN result in RICH O2 readings. I have had this happen. Of course misfires can also result in LEAN O2 readings; BUT NOT ALWAYS. In any case, if the O2 readings are invalid or erronious then the fuel trims will not be based on "good" data either.

Sounds like an expanded version of "you cant rely on trims to troubleshoot misfires"... If I am wrong correct me but thats the way I read it.

In obd2 we have very accurate misfire detection... so I dont see why you would want to talk about trims at all.

Now if you want to argue something with me... I have never been able to use short term fuel trims for anything useful when tuning/troubleshooting on obd2. I think the short terms are too finicky and when trying to do a tune using them usually results in a very choppy maf curve when using "weak" metrics to make the adjustments. So I do think that short terms are 100% junk, and I havent scanned a STFT in more than a year on any of my tunes. I do think there is a use for them if I had a different style of tuning.. as they are accurate at finding instant rich/lean situations without waiting for the LTFT's to populate with accurate data. But I think this discussion is better of in email or another thread....

quote Originally posted by Khaos88GT: Well firing order and coils are arranged correctly. So its not that. I pulled the plug it looked a little black on the tip but not that bad so it has been firing a little. I know that that doesn't mean that its able to fire under compression though. I'm gonna get a new plug tomorrow and see what happen with that. You know this sorta reminds me of that thread that Mathew_Fiero started about his misfire issues. He said his would run then just die on him. I guess I should double check my IAC and make sure its wired right because that was what he ran into.......dont know how that causes a misfire but if it does it does. Checked the IAC its wired fine.

A bad IAC probably won't cause just one cylinder to misfire. A single cylinder misfire is most likely caused by a bad spark plug, bad spark plug wire, bad injector, vacuum leak in the lower intake manifold or injector O-ring for that cylinder, leaky head gasket, or insufficient sealing of the piston rings for that cylinder. I have seen the ignition coils on these engines crack and allow spark to jump from just one tower to ground (thus bypassing firing the spark plug for that cylinder); but more often than not the entire coil goes bad and you lose 2 cylinders and not just 1.

First thing I would do is get a spark tester. Should be something that allows you to plug a spark plug wire into it and then has an alligator clip on it that will allow you to clip it onto the spark plug. There should also be a gap you can adjust and see where the spark jumps across it. I would install this at the spark plug on the cylinder where you are having trouble and run the engine and observe to see if you are getting spark. Should be a nice, strong blue-whitish spark. If so, then you are likely getting spark to the spark plug.

If you have a scan tool that displays current cylinder misfires, something else you can do is swap the spark plug and wire from the misfiring cylinder to one that isn't and see if the problem goes to that cylinder. If so, then either the plug or plug wire is bad. If not, you can probably rule out the plug and wire as being the problem. You can do the same for the injector. But I encourage you only swap one component at a time so you can verify what component is bad if the problem moves to the test cylinder.

-ryan

Interestig read - but if I were taking advice, Darth would be the man - His reputation speaks volumes in my mind.

DH on the other hand talks a lot and sounds like he knows his stuff - but all ever hear is talk, with not a whole lot to back it up.

I moved the "bad plug" from cylinder 3 to 6 so I can get to the dang thing easier just in case it is the plug. Here in about an hour im gonna get it scanned and pray that the misfire moved to cylinder 6. That would make life so much easier. Although it would be annoying that these brand new NGK TR8IX plugs would have a bad one in the batch , but I guess it happens. So we shall see. I appreciate everyone's help even if yall disagree. I'm kinda trying everything just to be sure. lol. I may just by a new IAC for preventive maintenance.

quote Originally posted by darkhorizon: So are you agreeing with me?

I didn't agree with the statement you made, the way you made it. And still don't.

quote I really dont understand what you are trying to say... If my "blanket statments" are considered bad information, then fine.. I really would rather post an answer quickly and bluntly then making 3 paragraphs to explain why looking at trims is usless in a thread like this...

I am trying to say that you SHOULD NOT just bluntly post something that isn't clear. Your so-called "quick" answers are not always clear and in many cases present misinformation the very way they are worded. Don't you think it is more important to be very clear by what you mean in your answer to somebody's problem vs. just posting a "drive-by" answer that can be confusing? We have enough "drive-by" posters on internet message forums, we don't need more. I encourage you to TAKE YOUR TIME and explain your answers. Some people reading your posts may want to know WHY; not just WHAT. This is a technical discussion and the goal is to educate the community.

quote Sounds like an expanded version of "you cant rely on trims to troubleshoot misfires"... If I am wrong correct me but thats the way I read it. In obd2 we have very accurate misfire detection... so I dont see why you would want to talk about trims at all.

You were the one that posted that short term trims don't mean anything, ever. Not me. If you meant something different, then you should have TYPED something different. That very statement in the way you worded it is FALSE in just about every context we can be talking about. Even with a misfire, the short term trim does mean something and does affect something. The VERY FIRST THING this guy complained about was his car smelled like it was running rich. Wonder what was causing that? Fuel trims being high perhaps? Sure, this could be the result caused by the root problem: misfire. But nonetheless, the short term trims still mean something, even in this case.

quote Now if you want to argue something with me... I have never been able to use short term fuel trims for anything useful when tuning/troubleshooting on obd2. I think the short terms are too finicky and when trying to do a tune using them usually results in a very choppy maf curve when using "weak" metrics to make the adjustments. So I do think that short terms are 100% junk, and I havent scanned a STFT in more than a year on any of my tunes. I do think there is a use for them if I had a different style of tuning.. as they are accurate at finding instant rich/lean situations without waiting for the LTFT's to populate with accurate data. But I think this discussion is better of in email or another thread....

Most people disable long term trims and just use short terms to do their VE or MAF tuning. The problem with just using long term trims for your tuning is the fact that they are usually slow to update/change. When looking at a scan tool you should see the short term trims moving more quickly and adjusting by larger amounts than the long terms do for a given time period. Basically to put it in different terms, using short term trims for tuning gives you better resolution on what the fuel is doing vs. long term trims just because of the update/change rate difference between the two. While operating throughout the RPM/LOAD range you could skip right thru a fuel trim cell much too quickly for the long term to update; so you may never see any adjustment on your scan log. And there are different update/change rates for Short Term vs. Long Term trims in the OS of the PCM programming. In every instance I have seen, the Short Term ALWAYS has the faster update rate.

[This message has been edited by Darth Fiero (edited 03-02-2009).]

quote Originally posted by topcat: DH on the other hand talks a lot and sounds like he knows his stuff - but all ever hear is talk, with not a whole lot to back it up.

That and his car looks like it was built by the kids from the local cub scout troop.

I have not seen anything at all from him - well not too recently. I do rememebr a hobbled together SC3800 that he posted pics of a long time ago, but I am sure it had been vastly improved since then.

quote Originally posted by topcat: I have not seen anything at all from him - well not too recently. I do rememebr a hobbled together SC3800 that he posted pics of a long time ago, but I am sure it had been vastly improved since then.

I seen it at the 25th and it still looked like it was ready for the wrecker to come pick it up.

quote Originally posted by MstangsBware: I seen it at the 25th and it still looked like it was ready for the wrecker to come pick it up.

You say this knowing that I painted it, and put a turbo on it...

Hey DH - got any recent pics of yyour work? I'd really love to see how much progress you've made since painting and turboing it.

Helps to lend credibility to all the advice you give.

Okay back on topic - any new results after switcing the plugs around? I know when I first got my SC3800, I tried fancy, expensive NGK Platinum plugs, and the car ran like CRAP. I swapped them out for regular cheap OEM plugs, and it has run great every since... I am not sure that is your problem, just sharing my experience with NGk plugs.

Well this is freakin GAY!!! I scanned the engine again and it still said cylinder 3 is misfiring. It wasnt doing it as bad but it still is. So I made sure all my plug wires were good and tight and then I was like well I'll go ahead and put my new IAC in. So I go to warm to engine up to operating temperature and it doesn't wanna start. I look and guess what like 10 PSI in fuel pressure. So I tried adjusting the regulator, which was pointless because it never changed, its like all of a sudden I'm not getting the fuel tranfer to the rails like I should. All lines are brand new, regulator, and TRE 255 LPH pump. The only thing that makes sense is the pump isnt putting out pressure like it should. It was just fine like 6 hours ago I don't understand this. Is it possible this brand new pump with less than an hour running time just screwed up. I know its getting power like it should so the only thing is it could just be not putting out pressure as it should. So now I can't fix the misfire because I can't get the car to stay running. This is becoming a nightmare.

Make sure none of the hoses are kinked. Also maybe the tube between the pump and metal tube slipped off. This is something that I have seen a few times. Kink the return line and see if pressure will build.

How did you wire you fuel pump? Did you exclude the variable rate fuel pump switch? Those have a tendency to go out. Just a thought.

I got it running today it was a bad kink as Mstangs mentioned. Now back to the same problem, but I do have something new to report. The SES light has always started flashing when I got on it because of the misfire, but I didn't notice till tonight that my interior floor lights flash and so does the power button on my radio, and its so weird because it does it with both doors closed. If you open the doors they come on solid, but no matter what my radio wont turn on. What in the world does this mean? It makes me think that under a load the car........injectors included are not getting enough power. I checked injectors resistance at idle and all injectors sit around 14.8 and I checked voltage at idle and each injector upon firing puts out around 25-35. Any thoughts?

Funny though I ran a rough 14 (odometer measured distance and stopwatch), with a class A misfire. lol Man with my mods if I can ever get this thing running right I should be able to put out a 12.5 max. lmao

[This message has been edited by Khaos88GT (edited 03-05-2009).]

The lights and radio is most likely a blown fuse

Have you swapped coils around to see if the misfire moved with it along with swapping the injector? I had this same issue and it was a plugged up injector. There are only so many things that can cause a misfire.

loyde's tech page is fairly comprehensive.

http://fastfieros.com/tech/stumble_L67.htm

I will swap a couple coils around today then scan if nothing changes then I'll move it back, and swap an injector around and rescan. I havent checked my fuses yet, but if it was a blown fuse wouldnt the lights and radio not work at all vs. flashing when the doors are closed?