tylertitus14

Hey guys, I have a 96 audi a4 that I bought recently. I'm troubleshooting a misfire problem and decided to have my friend with a paid version of vag-com data log the car for me.

After hooking it up we realized he only function that works is that vag-com is reading the ecm model number and manufacture. All the other buttons are shaded out, we can't program keys, or access blocks to data log. I'm sorry if I am using incorrect terminology with this, I'm from the GM world so a bit of this Audi lingo is Egyptian to me.

While searching forums I read somewhere if your ABS module is throwing a code it will cause toruble with vag-com. This sounds very far fetched to me, but we will be trying vag-com again tonight with the ABS module unplugged.

Does anyone have any ideas? Is it possible for these ECMs to "go" but still run the car? We did get a generic data logger to work on the car, and we encountered some strange things such as the ECM getting disconnected from the software. This ONLY happened when romping on the car. Grandma driving resulted in consistent communication with the data logging software. Another strange thing my friend noticed while data logging is that a few times the "engine load" reading fell to zereo, and fueling numbers tumbled down (not to 0 though). I did not feel the car buck, or fall on its face when this happened. It seemed as if the data logging software was getting false readings. This load/ fueling bug only happened with spirited driving, like the disconnecting problem.

When we cleared the random misfire, and individual cylinder misfire codes they did not come back as pending or as codes for our 45 minute data logging session. As soon as we started idling it for a few minutes they did come back (random misfire, and only one cylinder specific code this time). Slight miss in the mid 2k RPM range was still there while driving without the codes...

The tachometer needle wobbles at idle, the idle is stable but eratic, I would call it "pulsing". Almost sounds like it is slighlty cam'd. Car mainly seems to misfire at about 2600, but can misfire from about 2200 to 3200. Varying the load on the engine seems to change the characteristics of the misfire, although it seems there's not a consistent trend, and at times it will feel like its not misfiring at all. I can't peg anything unique about the times it feels like it isn't missing at all, and the times it feels like there's no missing are far and few between.

Can anybody shed some light on this for me? Why vag-com is giving me trouble, whats causing the misfire? Could it be related to my vag-com issues?

For backround info...
-96 A4 12 valve fwd 150k
New
-Coils
-(Swapped ICM with junkyard one, car acts the same.)
-Wires
-Plugs
-Fuel filter

-Exhaust consist of dual 2" through aftermarket CATs, then single 2.5" through a generic muffler. I can see through the CATs well and they are not loose inside.
-Checked for vac leaks
-Cleaned MAF, drove with MAF unplugged as well. (Misfire still there.)
-Compression test numbers good, all cylinders close.

turbo510

Since the plugs, compression, wires are known to be good, maybe either fouled injectors, air leaks, or the Ignition Control Module (on the air cleaner box). I have a '96 too, and routinly disconnect and use contact cleaner/WD-40 on accessible connectors. Common trouble spots are ignition switch contacts, engine coolant temp sensor. Ignition-related problems can cause trouble on the two cylinders sharing a coil, this engine uses waste-spark/three coils. Check the vac lines above the throttle-body, and I'd suggest removing the throttle body plastic duct to inspect the valve cover breather hoses for cracks that can leak in air. Also, this duct has a marginal seal arrangement to the throttle body in my opinion, so I use RTV to seal its rubber gasket to the duct. Otherwise, it looks like plenty of air could bypass the MAF sensor through gaps in the seal.

CRAZY_RUSSIAN

turbo, i have to suggest something else for that throttle body seal to intake, its called "telephone cord mod" STFA (Search the forum archives) for that, I've personally replaced that gasket and used the mod, just because =)

it sounds like you have gotten yourself an air leak or an failing ICM, i would replace all the vac lines (they are cheap, and that way you'll know that they are all good) and as turbo mentioned, check the vent hoses, you also may want to run seafoam, just to clean some of the carbon out;-)

tylertitus14

Well I changed all the engine bay vac lines and valve cover breather lines. The tb seal was indeed "shrunken". I did put a large zip tie in the seal and got it all to fit snugly. (Verified by installing without locating bushings first.) Car did have a post maf air leak, since fixing it the car is more lively, but the misfire is exactly the same. I tried unplugging individual injectors, then multiple injectors while running only to watch the rpm needle still pulse with each misfire. This seams like an electrical issue to me, unless all the injectors are "fouled".

I've never run into a fuel pump that worked consistently but had low pressure. I'm begining to wonder if this is my problem? Anyone sell a fuel pressure test tool for this car? There's no test port, and I've already made to many tools for this car lol!

Are the cam/ crank sensors or ecms known to partially fail on these? I am at a loss right now. It will be a little while until I have access to the supplies, but I will be vag coming it (new cable HOPEFULY should let me connect) then ill be thermal metering around each cylinder to see if I can find a problem cylinder.

Sorry my post is a little disoriented, I'm on my phone right now, our neighbors dug up our roads internet line fml. Ill report back after I vag com/ thermal test. Keep the ideas comin!

turbo510

CRAZY; I've heard of the phone-cord fix, wondered what it was, so now I'll look it up.

I see that you have a '79 GS750, thought you might like a pic of my '83 KZ-550 (10K miles). I keep it in my 2nd floor office, people contantly trip on how it got up there!

turbo510

Low fuel pressure would tend to make the engine bog as if running out of fuel. When you get your VAG-COM working you can check out fuel trims, which will tell you if the ECU is trying to push the mixture richer. While I've not tried it, does seem to me that if you disconnect the "return" hose at the fuel tank access cover, and arrange for that hose to dump into a catch can, then by running the engine you should see a continuous discharge of excess fuel from that hose, as the fuel pressure regulator bleeds off gas to maintain proper pressure. IF the regulator is working correctly, this would tell you that there is proper fuel pressure.

CRAZY_RUSSIAN

Turbo, holly crap, that is mint man!!! did you do the work? i got my up to almost 40k now:-) I'm thinking about pulling the engine and converting it to an 850, and do some paint work on the frame and the engine, i like how the black cylinder block/head and polished ribs look :-)

Tyler, sorry for hijacking your thread :-)

CRAZY_RUSSIAN

there is a tool for testing fuel pressure, plugs in between fuel line and the fuel pressure regulator IIRC. MAC, Matco, Snap-on =)
test your MAF, it might be having some problems, also i would recommend tacking your EGR valve off, and cleaning out that passage in the intake, that thing gets gummed up all the dang time :-S also check your EGR valve.
another thing i might recommend is take your injectors out, dump them in to that acidic carb dip, let them sit for 24 hours in the solution. throw new o-ring on the injectors and your good to go:-) Ive made a post about it a while back, i got different responses out of ppl that didn't try this, but personal experience, it helped, and its cheap:-)
keep us posted man