Hesitation "Sigh"

[myfreeaudi]

For 2 weeks, my 2003 A4 B6 1.8t manual shift will intermittently give a little sigh of hesitation. It clears right up after a few seconds. This is worrisome as it feels like when the car runs out of gas, except very briefly.

I have searched and found suggestions which I plan to try. But I did not find this exact problem described.

It seems to be okay with a full tank. The symptom started up again when the tank was 1/2 full.

Done so far:

Code scan - 16684, random cylinder misfire, 16685 cylinder 1 misfire. Both can be caused by fuel supply or fuel pressure issues

Cleared codes, problem persists with no code set, yet

Replaced fuel filter which has internal pressure regulator

Added Seafoam to gas and filled tank to clean injectors


I have more things to try but I thought I would ask if anyone has advice or experience with this to share?

And how can the fuel pressure regulator be in the fuel filter? How does it get a signal to vary the fuel pressure?

Thank you.



Thanks for your input.

[cmoak1994]

I have a b5 1.8t and the fpr on my motor is located at the back center of the motor at the top


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[MetalMan]

B6 fuel pressure is fixed at 4bar, by the regulator in filter. B5 has "rising rate" fuel pressure regulator at back of fuel rail, which has variable fuel pressure according to pressure inside intake manifold.

How old are spark plugs and coil packs? Have you performed any air leak tests? I would tend to lean toward spark plugs/coil packs or air leak instead of fuel supply issue. Spark plugs/coil packs can directly cause misfires, and there are MANY hoses and check valves which are prone to deterioration with age.

[myfreeaudi]

B6 fuel pressure is fixed at 4bar, by the regulator in filter. B5 has "rising rate" fuel pressure regulator at back of fuel rail, which has variable fuel pressure according to pressure inside intake manifold.

How old are spark plugs and coil packs? Have you performed any air leak tests? I would tend to lean toward spark plugs/coil packs or air leak instead of fuel supply issue. Spark plugs/coil packs can directly cause misfires, and there are MANY hoses and check valves which are prone to deterioration with age.

Plugs are 5,000 miles old. Coil pack age unknown. Code shows misfire in cyl 1, I could replace # 1 coil pack. Will look at air leak testing, check valves and hoses.

But I have had coil packs fail before. That results in a very rough running car and flashing CEL light. This is just a lack of power which goes away as soon as I let up on the gas.

I thought about bad EPC gas pedal system but the EPC warning light does not come on. I'll recheck the codes.

Thank you.

[myfreeaudi]

I have a b5 1.8t and the fpr on my motor is located at the back center of the motor at the top


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The B6 1.8t is different, pressure is regulated in the filter.

[cmoak1994]

The B6 1.8t is different, pressure is regulated in the filter.

Ok im still kinda new to the audi world iv only had my b5 a year but it is good to know tho


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[MetalMan]

Plugs are 5,000 miles old. Coil pack age unknown. Code shows misfire in cyl 1, I could replace # 1 coil pack.

You can do a quick diagnostic here before spending any money. Pull the #1 coil pack, and spark plug. Double-check the gap on #1 plug. If it looks okay, then swap coil pack #1 with coil pack on #2. If the misfire moves to #2 with the coil pack swap, then you know it's the coil pack. If the #1 plug's gap is too large, then this could be the issue.

[myfreeaudi]

Solved - brake light switch!

I noticed that the ESP light came on frequently. Searches found other posters where the brake light switch failure will cause an intermittent loss of power. Other symptoms I had include lack of cruise control but tapping the brake brought it back; ABS brake system VAG COM code 00526, brake light switch.

Replacing the brake light switch has fixed all symptoms so far after 3 days. I need to drive for a week more as the problem was intermittent.

I believe the connection is that when the brakes are applied under certain conditions, the ESP reduces engine rpm to a high idle so the engine will not pull on the brakes. With a bad brake light switch, the ESP thinks the brakes are applied and when those conditions prevail, it cuts power to the engine.

I hope this helps others with this mystery.

[Dillon Clark]

Plugs are 5,000 miles old. Coil pack age unknown. Code shows misfire in cyl 1, I could replace # 1 coil pack. Will look at air leak testing, check valves and hoses.

But I have had coil packs fail before. That results in a very rough running car and flashing CEL light. This is just a lack of power which goes away as soon as I let up on the gas.

I thought about bad EPC gas pedal system but the EPC warning light does not come on. I'll recheck the codes.

Thank you.

I have a cylinder 4 misfire. I bought a set of coil packs from ESC tuning for $200, it's a conversion kit for 2.0t coil packs because they're longer and more reliable (the conversion is using a spacer plate to accommodate the longer coils). My engine runs better, but I've yet to install my new coil wire connectors (which are brittle and cracked). Hope this helps.

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