S4 has developed a bad "miss", and occasionally backfires.
04-19-2012, 12:13 PM
#1
Racer
Thread Starter
S4 has developed a bad "miss", and occasionally backfires.
History: Well maintained 88 S4 Manual. All new fuel lines several weeks ago. Top end refresh within last two years. 2 year old Nology wires. Beru S5 plugs, about 2 years old. Caps and rotors of same age. Grounds cleaned and replaced within the past 6 months. Fuse panel "sorted out".
No recent ignition work that would have reversed a wire. Ran great until two days ago. Sudden, mysterious "flubbing" miss sound at idle. Stutters on acceleration, but performs well at 3rd gear and above. If you are a 2-stroke person, then I can best describe it as the sensation you get when a 2-stroke engine is loaded up and you have to blow it out. Occassional minor backfire at deceleration. All lights on dash are cleared. Came on so fast after fueling that I thought it might be bad gas. Drained that crap and threw it in the Volvo(it'll run on anything
) Topped it off with fresh Sunoco, but no real change.
Went through the wires looking for short. Pulled the plugs, and all 8 are chocolate brown. Electrodes all appeared worn at a slight angle. Not sure if the Berus are like that from the factory, or that is how they fire in the 928. Pulled cap and inspected for cracks and carbon fouling.
Any ideas?
No recent ignition work that would have reversed a wire. Ran great until two days ago. Sudden, mysterious "flubbing" miss sound at idle. Stutters on acceleration, but performs well at 3rd gear and above. If you are a 2-stroke person, then I can best describe it as the sensation you get when a 2-stroke engine is loaded up and you have to blow it out. Occassional minor backfire at deceleration. All lights on dash are cleared. Came on so fast after fueling that I thought it might be bad gas. Drained that crap and threw it in the Volvo(it'll run on anything
) Topped it off with fresh Sunoco, but no real change. Went through the wires looking for short. Pulled the plugs, and all 8 are chocolate brown. Electrodes all appeared worn at a slight angle. Not sure if the Berus are like that from the factory, or that is how they fire in the 928. Pulled cap and inspected for cracks and carbon fouling.
Any ideas?
04-19-2012, 12:49 PM
#3
Racer
Thread Starter
04-19-2012, 01:08 PM
#6
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Check your fuel regulator and dampers (pull off vac hoses and check for fuel or fuel odors) ... if the diaphragms start leaking engine vacuum will pull extra fuel into the intake ...
04-19-2012, 01:11 PM
#7
Drifting
Make yourself a fuel test gadge.
Screw in a Tee, and a 5 foot hose with the gadge on the end, feed it under the back of the hood and hook the gauge under the wiper arm so that it is visible while you are driving.
This is a good way to see if the pump is keeping up while under load.
Screw in a Tee, and a 5 foot hose with the gadge on the end, feed it under the back of the hood and hook the gauge under the wiper arm so that it is visible while you are driving.
This is a good way to see if the pump is keeping up while under load.
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04-19-2012, 01:52 PM
#11
Drifting
I don't use the brains for my Auto 89 euro as I installed the electromotive Tec-4 GT controller.
comes with new plug wires, 4 coils, new unassembled harness, and software so that you can tune in on your laptop.
The install is not for a person that has 2 left hands (If ya no what I mean)
But its not that bad either.
Point is I have a EZK and LH that sits on the shelf, If someone gets in a bind, I would be willing to talk as I do not think ILL ever use them again.
Brad
comes with new plug wires, 4 coils, new unassembled harness, and software so that you can tune in on your laptop.
The install is not for a person that has 2 left hands (If ya no what I mean)
But its not that bad either.
Point is I have a EZK and LH that sits on the shelf, If someone gets in a bind, I would be willing to talk as I do not think ILL ever use them again.
Brad
475hp/460lb.ft
04-19-2012, 01:57 PM
#13
Racer
Thread Starter
By the way, did you ever resolve the wheel hub issue with your C70 after I PM'd you back?
04-19-2012, 01:59 PM
#14
Rennlist Member
Bill Ball just went thru this.
Looks for cracks in the rotor..just came outta nowhere, and missing esp load based, I tend to find as simple bad spark on most of my cars.
Looks for cracks in the rotor..just came outta nowhere, and missing esp load based, I tend to find as simple bad spark on most of my cars.
04-19-2012, 03:10 PM
#15
Race Car
nice
^^ rotor, that would be nice!
I'm on about my fifth hub bearing R&R at this point..one of the last pair was defective....but yes, you were right in that the used knuckle I installed from supposedly the same year/model appeared the same, but placed the ABS sensor a few mm higher above the tone ring and that threw off the ABS sensor and all that it feeds data to- TCU, ECU, etc.. And, replacing the ABS sensors has calmed the trans down a bit, though it is still marginally whacked.
I'm on about my fifth hub bearing R&R at this point..one of the last pair was defective....but yes, you were right in that the used knuckle I installed from supposedly the same year/model appeared the same, but placed the ABS sensor a few mm higher above the tone ring and that threw off the ABS sensor and all that it feeds data to- TCU, ECU, etc.. And, replacing the ABS sensors has calmed the trans down a bit, though it is still marginally whacked.