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One Last Car Story?

mmm, maybe

     
5:53 pm on Jul 6, 2018 (gmt 0)

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I've been having a misfire problem with my GT500 for awhile. Very common reason is an air leak. Previously I went over my engine with a fine toothed comb. Made sure air intake was secure, and verified that all connectors were seated. Disconnected some things I no longer needed and redid connectors on vacuum lines (installed new lines where needed). Did everything I could think of.

I put off buying ignition coils because of the cost. However, problem was still there and I ordered some earlier this week. They came today. Changed plugs and put new ignition coils in.

I don't know why I did it, but rather than loosening the air intake and taking it off as one piece, I completely disassembled it. As I was reassembling and jiggling the air box portion and trying to get it to seat correctly, for some reason I noticed that the air box connector (air filter fits inside and tube to throttle body fits outside) was loose. What? I didn't even know it could come loose. Turns out there were 3 torx head screws holding the connector to the air box. NOW THERE IS A HUGE OPPORTUNITY FOR AN AIR LEAK!

Tightened up the torx head screws, finished assembling and took her for a ride. I could NOT induce a misfire, no matter what I did. I'm not saying no more misfires. I've been down that road - thought it was fixed only to have the problem recur the next day. BUT, I'm glad I found the air leak. Makes me have confidence that maybe this time misfires are gone. But dammit, wish I found that leak before I dropped $240 on ignition coils. Of course without installing the coils I never would have found the air leak.
6:24 pm on July 6, 2018 (gmt 0)

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Just talked to one of the Steeda guys (who made the air intake). He said unlikely that there was an air leak from those loose screws directly. Possibility that the loose connector could have caused it to wiggle in the silicone connector on the air tube and cause a leak there. So it looks like, if the misfire is indeed gone, it is because of the new ignition coils.
7:02 pm on July 6, 2018 (gmt 0)

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I don't know cars, but even I know that one: When all else fails, take it apart and put it back together again.
8:22 pm on July 6, 2018 (gmt 0)

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When all else fails, take it apart and put it back together again.

One of my all time favourite books ...
How to keep your Volkswagen alive: a manual of step by step procedures for the compleat idiot / by John Muir & Tosh Gregg; illustrated by Peter Aschwanden.
I've had a lot of beetles, some microbuses, campers, pickups, and even a Carmen Ghia, how to take them apart and put them back together again, plus the illustrations* ( especially the ones of the car entirely disassembled laid out on the grass with the dog(s) ..and the one with the guy walking up at night and thinking of the VW engine disassembled )..and..there were never enough paper bags ( is that the same with a GT500 ? )..I'm thinking that "here" your coils would cost at least 5 ( if not 10 times that price ) I'll ask a friend who imports "US muscle cars"..

* Those illustrations were in large part responsible fro my taking a medical, scientific and technical illustrator course as a secondary degree in the early seventies..they looked like car illustrations heavily influenced by Bob Crump :))
9:57 pm on July 6, 2018 (gmt 0)

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ps ( after reboot, due to 2180 tabs open )..I know that Carmen is not how one spells Karmann, but..I bought the car from a lady called Carmen..and..another of my all time favourite books , are a series of the Carmen Cru comic books..similar in style to Bob Crump...written and drawn by Jean-Marc Lelong, who also sadly is no longer with us.
10:48 pm on July 6, 2018 (gmt 0)

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How to keep your Volkswagen alive...
You could easily do that with VWs. I had a few myself. Several bugs, a '71 square-back and a '67 van.

Had a '69 bug with an 1800cc I had bored/resurfaced with over-sized pistons, extended rods & a larger chamber carburetor . That thing really moved. I had to add weights to the bonnet to keep the front wheels on the ground when I launched.

I would often pull to the side of the road, disconnect the fuel pump filter, take it apart & clean it up, put it back together then back on the road in 15 minutes. Did the same with the distributor, cleaning it out, resetting the rotor, then back on the road.

I miss my bugs.
4:21 pm on July 7, 2018 (gmt 0)

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Car story continuing. Test ride this morning. Misfire #4 cylinder - same as ever.
10:57 pm on July 8, 2018 (gmt 0)

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A Bluetooth fault code reader from ebay can be a gem of a thing to have. You simply plug it into the OBDII port and connect it to your phone or tablet. With things like misfires, there can be quite an extensive diagnostic approach, but getting any error codes from the ECU can give you a good starting point.

They are dirt cheap to be honest and have helped me out on a number of occasions.

Mack.
11:25 pm on July 8, 2018 (gmt 0)

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Doesn't even need to be bluetooth.

Toad [totalcardiagnostics.com] is one of the best OBD tools out there. They may have a bluetooth version, but I have the software on a small notebook I use for tuning. I just sit in the driver's seat & plug the cable into the OBDP II under the dash.
2:35 am on July 9, 2018 (gmt 0)

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I have an SCT X3 tuner. Had it almost since I've had my car. Use it to upload various dynotunes stored therein. Also reads engine codes and clears them. Does a lot of other stuff too. For instance, last week I put some different (taller) tires on the rear. Set the rpm (revolutions per mile) with the box. When I changed gears in the rear end, I used the tuner box to set the change. When I put in a different thermostat, I used it to change temps for when fans come on. That kind of stuff.
3:32 am on July 9, 2018 (gmt 0)

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I was just talking about simple & cheap error code reading with Toad.

For tuning it's all about EFI Live for the ECM, Accel EFI for the Supercharger and Big Stuff 3 for the TCM.
8:07 am on July 9, 2018 (gmt 0)

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My mistake. I thought you and Mack were giving me some helpful advice. I was just explaining that I had a device that included code reading. Ancient by today's standards, but definitely not simple and cheap. Insofar as simple and cheap goes - I've had a cheap CReader since about 2006. The CReader has resided in whatever car my my lovely wife drives since about 2010.
11:19 am on July 9, 2018 (gmt 0)

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My mistake. I thought you and Mack were giving me some helpful advice
I always try to be helpful, no matter who it is that needs the help. I think Mac was being helpful as well.
12:01 pm on July 9, 2018 (gmt 0)

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Yes, I agree with Mack, they can save a great deal of time. Unfortunately, they don't always find the problem.
Vacuum leaks, especially, can be frustratingly difficult to find.
I'm not familiar with your set-up, but, if it's only on one pot that you're getting the misfire, the first thing i'd check would be if the misfire occurred at different revs, and different power scenarios. Is it a regular misfire, or irregular. The misfire can also cause other problems, too, so it really is worth trying to track it down, if possible, before it become costly.

Keep us updated.
12:28 pm on July 9, 2018 (gmt 0)

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Hello engine - I can usually induce a misfire in cylinder 4 by accelerating in 4th gear. Most common reasons for misfire is either a fuel (lean condition) or ignition (plug, ignition wire, or coil) problem. In addition to checking for air leaks, and changing plugs/COP, I have swapped positions of injectors in # 3 and 4 cylinders. Interestingly, whenever I do various changes/fixes, the problem seems to resolve only to reappear the next day. I haven't replaced the ignition wire harness.

And yes, thanks to this group's intervention, I think I'll seek professional help.
11:07 pm on July 9, 2018 (gmt 0)

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I think the next step is narrowing down the issue. Swap the plug in no4 with another cylinder. See if the misfire remains or moves to the new cylinder. Do the same with a coil pack (if they are standalone) right down as far as injectors (if you dare go that far). Are you running a stock map currently? pump fuel or E85? High octane with retarded timing could cause that if that air was dense. Like I said before misfires can have quite an extensive diagnostic route.

My best guesses would be Spark gap, ignition timing, an injector (or it's software) under-fueling, air lead in a vacuum pipe or inlet manifold gasket (not likely).

Interesting side story... An elderly mechanic once showed me a trick for finding vacuum leaks using a cigarette lighter. Run it close to the pipe with the gas on (not lit) when it finds a leak the engine revs will pick up because it will draw the butane in.

Mack.
3:52 am on July 10, 2018 (gmt 0)

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Hello Mack:

Last Friday I gapped new plugs and installed them concurrently with a brand new set of COP. Not stock map, but for good measure I reinstalled street dynotune for 93 octane. I used to race it and all tunes are designed to run slightly rich to help ensure no detonation (I had a problem with that once that led to a rebuild). Yes, have swapped out # 3&4 injectors. I have replaced and tightened vacuum lines. Air intake couplers are secure. I cleaned MAF. Replaced PCV valve. I have looked over, but have not replaced ignition wiring harness.

Thanks for putting some thought into it for me.
4:11 pm on July 10, 2018 (gmt 0)

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Another thing I would maybe test would be cylinder compression just to satisfy yourself that all cylinders are in the same ballpark. It's unlikely, buy cylinder ring blowby might be a factor. Especially if you have been running some power maps. I don't think that's the cause, but may be worth looking into. The more you can rule out the better. :-)

Mack.
5:29 pm on July 10, 2018 (gmt 0)

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Yep, compression and leak down tests are in my plan.