Engine Misfire Detected

[norm8332]

I noticed that the car was idling rougher than it normally does today. Even when I rev it up and hold it at 1500 rpms it was randomly missing.

So I got out the HPT VCM Scanner and this is what I get:

http://forum.grrrr8.net/attachment.php?attachmentid=1562&stc=1&d=1239494997

Great.:puke:

I can smell gas at the tail pipe and the stability control was turning off and on randomly while I was checking it too all of a sudden.

What should I check first. It has all new plugs from Livernois when the maggie went in and I checked the coil connections. Wires?


Any suggestions as to where to start will be helpful.

Thanks.

[GRRRR8]

Check the vac hose that hooks to the brake booster. You have a lean misfire thats why it is not identifying a cylinder.

[norm8332]

I just checked..It's fine, as a matter of fact when I disconnected the hose there was still a trapped vacuum present. The sensor is in and connected. I ran over my fuel pressure gauge a few days ago so I cant check that.. Crap I dont want to run lean with the maggie. The vacuum is the same on the vac/boost gauge.

[GRRRR8]

Look at short an long term fuel trims. If they are + 24% you know its really lean from a vac leak. Anything more the + 8% can be an issue lurking.

[norm8332]

Well I tried everything we talked about and I still can't find a problem.

I did a scan and the LT fuel trims are always higher for bank 1 and I get a voltage drop (blip) on the B1 O2 exactly when i feel the misfire happen.

I don't even know witch side of the motor bank 1 is anymore.

As for driving it, it almost feels like it's going to stall when leaving a stop sign with a light peddle. cuts out/stumbles.

[GRRRR8]

Bank 1 is the drivers side.

[GRRRR8]

I think we need to address the P0556 code 1st. The definition of the code is:
The ECM detects brake booster vacuum as being less than the intake manifold vacuum for more than 100 milliseconds.

[BlownG8GT]

Put the factory brake booster check valve back in. Loose the one Magna Charger sends. What other mods do you have to the car? Possible bad injector? Do you have a scan tool that can look at each individual cyl?

[GTPprix]

Brian should I switch back to my factory check valve too? ;)

[norm8332]

I think the brake booster code was a blip. It never threw an actual code (it was preliminary) And once I cleared the codes that one didn't come back. The only one that comes back is the P0300. Random cyl Misfire.

I checked every single vacuum hose and connection and no leaks are found. I'm assuming that if it is indeed a vacuum leak that it's the maggie's connection to the intake manafold on the bottom of a port. I even switched the ECM just in case. Same result. I have yet to check the fuel pressure (need new gauge) but it drives ok except for the stumble/cut at light gas take off. Tha vac/boost gauge is around 20 at idle. (I did check the gauge too by disconnecting)

Mods are:

Maggie, 60# Injectors, Rotofab, KB boost a pump. (maggie and injectors installed by Livernois)

I don't have the stock valve for the booster but I tested it and it doesn't leak pressure back at all.

I just installed the BAP on friday night but I noticed problem starting about a week ago and it seems to be getting worse. It would only stumble when cold, now it keeps doing it all the time. Thats why I finally hooked up the HPT VCM scanner yesterday.

Thanks for your help. I guess the next step is a shop.....

HPT Scan (zipped HPL file) attached. At idle and 1500.

[Andy@Livernois]

norm, I will have dan comment as soon as I can, but have you tried bypassing the catchcan? it's a total long shot, but i figure it is worth a look... also is there any residue in any of the vacuum lines? have you pulled any of the plugs yet to look at them? have you tried to duplicate this in a controlled stand still environment, such as setting the e-brake and just giving it light throttle without moving? if you can do this to duplicate the situation you might want to try disonnecting the coil pack wire from each cylinder individually to see if there is any change in the stumble. by doing so it should get worse, if you find that one cylider effects nothing this will be your target cylinder to check the coil pack, wire, plug, and injector on.

[GRRRR8]

He bypassed catchcan, no change. Fuel trims are + 15% - +24%. He has a lean misfire/vac leak.

[norm8332]

norm, I will have dan comment as soon as I can, but have you tried bypassing the catchcan? it's a total long shot, but i figure it is worth a look... also is there any residue in any of the vacuum lines? have you pulled any of the plugs yet to look at them? have you tried to duplicate this in a controlled stand still environment, such as setting the e-brake and just giving it light throttle without moving? if you can do this to duplicate the situation you might want to try disonnecting the coil pack wire from each cylinder individually to see if there is any change in the stumble. by doing so it should get worse, if you find that one cylider effects nothing this will be your target cylinder to check the coil pack, wire, plug, and injector on.

Yeah I bypassed the can, no effect. I even added spring clamps to the bypass actuator hose on the maggie because it was a slightly loose fit.

No residue found in any of the lines. I haven't tried the e-brake but it is missing detectably (with HPT and feel) at idle rpms and at 1500 rpms in park with temp having no effect.

The reason I haven't checked the plugs besides making sure the wires are secure is because the code is a P0300 random misfire, meaning the misfiring cylinders are changing randomly just like a lean misfire. If it were one cylinder I would get a specific cylinder code like P0301....P0308 for cyl 1 thru cyl 8 Misfire etc. wouldn't I? I did check all injectors for connection and seal to the manifold. All coil connections were also verified.

This problem seemed to develop slowly first it would only do it when it was really cold then it kept getting worse so it would do it more and more each day until now it does it all the time no matter the temp.


It's easy to explain like this dit.....dit.dit.dit......dit.dit......dit..etc

[Devilish34]

Uggg Norm is this your DD??

Is it possible for it to be a crank or Cam position sensor failing???

I

[Andy@Livernois]

try disconnecting the injectors one by one, the connections could be seated fully, and plugged in all the way, but still could be having intermittent contact.

[norm8332]

Uggg Norm is this your DD??

Is it possible for it to be a crank or Cam position sensor failing???

I

Yeah, it's the DD. It's still drivable. It is most annoying at stops etc..you think it's going to stall when you go to move on, but it hasn't done that yet. I definitely cant live with it. I have to get this fixed somehow myself or at a shop. I really don't feel like pulling the maggie to check the gaskets though.....

[norm8332]

try disconnecting the injectors one by one, the connections could be seated fully, and plugged in all the way, but still could be having intermittent contact.

Wouldn't I get an Injector Circuit Malfunction Cyl X DTC? I did press on the plugs while the engine was running once at no effect.... It doesn't seem to be the same cylinder misfiring each time. Wouldn't DTC show that? For example if I unplug the coil for cyl4 one of the DTCs I get is "P0304 Cylinder misfire cylinder 4"

I'll try, but it looked like you have to be very careful unplugging them because the socket is just snapped together and it looks like you could just pull the injector apart.

[norm8332]

Well.. I'd like to thank everyone for their suggestions..I have a couple things left to check but my list is pretty short now.

Plugs, Plug gaps - Will check today.
Maggie gasket leak.
Bad head gasket between cylinders (?) - need to have pressure check done. This may also account for the odd "exhaust noise" I here from inside the car.

I may check the maggie myself if it comes to that, but if the heads end up having to be pulled it's going to a shop.

Once again thanks for all the suggestions.

[Livernois Motorsports]

Norm,

What changed after it left here? The pulley and BAP?

Let me know if there is anything we can assist you with.

-Rick

[BlownG8GT]

Well.. I'd like to thank everyone for their suggestions..I have a couple things left to check but my list is pretty short now.

Plugs, Plug gaps - Will check today.
Maggie gasket leak.
Bad head gasket between cylinders (?) - need to have pressure check done. This may also account for the odd "exhaust noise" I here from inside the car.

I may check the maggie myself if it comes to that, but if the heads end up having to be pulled it's going to a shop.

Once again thanks for all the suggestions.

Headers?

[norm8332]

Headers?



Norm,

What changed after it left here? The pulley and BAP?

Let me know if there is anything we can assist you with.

-Rick

3.2 pulley on it now.
BAP installed in advance of planned install of headers and 3.0" Pulley.

I'm going to give a shop a call tomorrow and hopefully have them track down the misfire cause and fix it.

I pulled the plugs and re-gapped them to .035, They were .024. All the plugs looked identical as far as color. It did improve the misfire issue at idle, but it's not completely gone.

[Devilish34]

.024 is that not a little tight??


Good luck hopefully Mike can help

[GRRRR8]

Blowers use tighter gaps, but .24 is what I used with twin 66mm turbos on a 393 Mustang. I know the Maggie is good, but if it can blow a .35 gap spark out then I need one asap! :)

[09G8DC]

I know its been awhile but, what was the final verdict on this?

[norm8332]

Apparently my larger injectors required a higher rpm than the stock idle speed. 50 rpm more did it for me back then.

[09G8DC]

Apparently my larger injectors required a higher rpm than the stock idle speed. 50 rpm more did it for me back then.

Perfect, thanks for responding so quickly.