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91 golf hesitation, exhaust leak

[Sorry if this is a repost, I posted this yesterday and it never showed up] Hi all, I have a 91 golf gl. I recently replaced her exhaust with the dual downpipe system and she was a dream to drive for about a month. Recently, however, she has begun hesitating on accelerations from idle and she sounds like an old truck when accelerating (I can hear the individual cylinder explosions well). Her power has also dropped significantly.

I think the o2 sensor is fine. I replaced it 10-20k miles ago, there was a bit of a struggle getting it off the old manifold and it is now located on the cat. She drove fine for ~1 month so I don't think this is the problem.

I was under the hood the other day searching for the exhaust leak. When I turned the throttle the engine would putter down for a second then rev up like it's supposed to shaking violently. I held my hand around the manifold/dp area right when I started it up and didn't feel any puffs, only some slight wisps coming from the dp/cat junction. I've read a few threads about the flex joint on the dp going bad, my dp is used but looked in good condition when I put it in.

I'd appreciate any help on resolving this matter.

thanks,

-Matt

Reply to
MasterChifa
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reposting reply

Might be a broken exhaust manifold stud on the cylinder head causing that exhaust leak. (Add) or it may be that flexing connection at the downpipe!

Hesitation.................. Check those ground wires at the valve cover or at the coolant pipe AND the wiring for the throttle body. Those usually break and cause running problems. I sometimes will check the wiring from the ECM harness plug. Bentley manuals make this process fairly easy! ;-)

Reply to
dave AKA vwdoc1

I think both problems began about the same time. Is it possible that the leak causes/caused the hesitation? She usually puffs a slight amount of smoke out the tailpipe first thing in the morning. I happened to notice a small bit of smoke emerging from between the intake and exhaust manifold which I will investigate next weekend (I've held my hand all around the flex joint and felt nothing, fingers crossed it's not the dp). The studs were all fine when I removed the manifold. So I know what I'm looking for, how would a broken stud cause a leak? I knew this job was too easy, something always happens... it's the law...

Thanks for the grounding/wiring tips.

thanks, Matt

Reply to
MasterChifa

Stud breaks and exhaust manifold moves further away from the cyl. head = slight leak. Usually it is a little louder when things are cold.

I vote wiring problems are causing the hesitation! Unless you have a vacuum leak or the intake boot is loose!

Reply to
dave AKA vwdoc1

Which side of the cat is the O2 sensor on? Also, an exhaust leak could have burned a wire or a vacuum line, which as others have said would cause rough idle.

Reply to
631grant

Sounds like a misfire. How are the plug, distrb. cap rotor etc?

SFC

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Reply to
SFC

Checked around for those ground wires this afternoon. Didn't find anything that was out of place. I did, however, see arcing at the ignition coil; between the center spark wire and the two negative terminals. It would arc every time she stuttered on a rev. I put a few layers of electrical tape around it and she revved fine for a few times, then the arcing returned with the stutter. Should I just clean the area and tape it well next time, or is there a better/more proper solution?

-The o2 sensor is on the forward side of the cat, toward the front of the car. At ~45deg from ground level toward the passenger side

-Distributor cap, rotor, plugs have all been replaced/cleaned within the past few months

-Checked vacuum lines, all are well. Checked them all when I removed the intake manifold.

thanks, Matt

Reply to
MasterChifa

AHHHH so you found the problem(s) You need a new ign coil and a good set of spark plug wires. Bosch ign coils should be excellent! I have not had good success with Bosch wires for these engines though. I prefer anything but the 09-005 wires, you find on the early Jettas and Rabbits, nor the shielded wires (09-152?). I usually install Beru or STI wires.

Reply to
dave AKA vwdoc1

I had a coil go on my Jetta in heavy rain. Just start the engine and spray water on the coil. Guaranteed to die immediately. Don't screw around. Just replace it! The hardest part is the fact that they have the nuts on the backside of the firewall in the 'gutter' and the nuts are not welded in place so you have to pry up the plastic screen over the gutter. Read that as 'pain in the ass'.....

Reply to
631grant

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