Weird cruising misfires

B6/7 S4/RS4
#1

About a week and half ago I was heading to the race shop to continue tearing apart the Mazda… as I am driving on the highway, cruising at about 75mph, I start hearing and feeling what sounded like the car misfiring. I could feel the car move and hear every time it would do it. It wasn’t consistent or repeatable. It wouldn’t do it under acceleration, only just cruising. I have yet to look at the car but I’m going up to the shop tonight to take a look.

I’m not sure where to start looking… I saw no flashing CEL, and no CEL even came on. I didn’t have my laptop with me last time so I didn’t run a scan. Ill bring it with me tonight to scan it.

I was gonna pull the plugs tonight and check them. Hopefully vagcom will show me something…

Anything you guys could think to look at while I am with the car? I’m not driving it until I know whats going on and I’m not at my shop everynight. So if anyone can give me ideas on what to check, I would appreciate it.

#2

Vag com engine measuring blocks 15-17 should help you figure out what cylinder/s are misfiring and then can go from there.

#3

Awesome, I’ll do some logging later hopefully. I have to pull the Mazda motor out so I am hoping I get it done quick

#4

Assuming you have pulled the Mazda motor before, what’s your best time for the job?

Sorry about the thread jack.

#5

Depends if my dad works on it or not. He’s 70 years old and doesn’t move with the swiftness I have at 24. With him it will take 2+ hours. If I do it with someone who can turn wrenches, I can have it out in less than an hour.

The transmission is already off it, I just have to drain the water, unplug the harness, unbolt the motor mounts and its basically out. Dad is helping tonight so I am guessing 2+ hours lol. I’ve been at the shop since 5 and haven’t gotten anywhere.

I had to called Mazda Motorsports and find out why I am missing parts I ordered. I got my new shocks, new control arm bolts, ball joints, rod ends and 6 of 22 bushings… Come to find out the guy who took my order lied about availability. Looking at 60-90 days to get my other bushings now >:(

And Dad just sat down for dinner. I think I’ll go play with the Audi while I wait for him to consume the food

#6

Stout Lad! Go for it.

Got two on your Dad.

#7

Well I’ll be first to admit I’m stupid. I should have just ran a scan so much sooner.

Here’s the results and I know what my issue is now…

https://drive.google.com/file/d/0B2CH9bsTUbkYR2dxNGNKa3VGMTA/view?usp=sharing

Chassis Type: 8E (8E - Audi A4/S4/RS4 B6/B7 (2001 > 2008))
Scan: 01 02 03 08 09 0F 11 15 16 17 18 25 36 37 45 46 55 56 57 65
67 69 75 76 77

VIN: WAUPL58E24A109530 Mileage: 214610km-133352miles

Address 01: Engine Labels: 079-910-560-BBK.lbl
Part No SW: 8E0 910 560 UM HW: 8E0 907 560
Component: 5.0 93Oct JHM G 0010
Revision: 00000000 Serial number: AUZ6Z0C0253642
Coding: 0007711
Shop #: WSC 12596 412 394822
VCID: 0407A2894497C0014B3-5140

1 Fault Found:
16586 - Injector: Cylinder 2 (N31)
P0202 - 004 - Circuit Malfunction - Intermittent
Readiness: 0000 1000

#8

That was easy.

#9

Also, I started a timer to see how long it takes me. I have everything disconnected and the engine hoist hooked up in 30 minutes. Just waiting for my dad to make his way to the garage to help me guide it out without hitting anything

#10

Motor is out! so overall it took an hour after I disconnected everything, then waited for my dad. The miata is so easy to work on!

#11

Check the clip and harnus maybe swap spots with another injector. Pull the fuel rail leave all the injectors plugged in and just run the number 2 injector then run the 5 injector. After looking at the two and hearing the two you should be able to tell if the injector is down. I usually measure how long it takes each injector to fill a small glass.

#12

I replugged the connector all of the injectors. Drove home without any misfires or anything. I am about to go outside and check to see if the code came back.

Injector #2 should be the front most injector on the drivers side correct? If the code came back, I will test the way you said. Is there a way to run specific injectors in vag com or another method?

#13

Injector is the second injector back on the passenger side.

Audi numbers their cylinders like this:

Back
4----8
3----7
2----6
1----5
Front

#14

Thanks Jimmy. I reconnected all of the injectors because I wasn’t sure. Just checked to see if my code came back and it hasn’t yet

#15

So was it just the wire to the injector was not plugged in

#16

I had a couple of misfires the other night driving in the snow storm. I was having fun pulling out of our new race shop for the Trans Am car and heard it again. The code came back for the same #2 injector. I’m going to be back up at my old shop for my race car on Friday so I want to pull my fuel rail and test the injectors like you suggested.

What is the best process to run the injectors like you suggested?

#17

Do you have a race car at a race shop?

#18

no i have race cars at the race shop

#19

It made sense in my head before I wrote anything… Not so much after reading it back.

I think I found I can test the injectors under selective output tests in vag com so I will have to give that a try

#20

Yes select engine then output test. Walk through the test but your going to need the fuel rail and injectors off or take the entire intake off and just test them all together