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92 1.8L Jetta (RV Engine) - ignition problem driving me nuts...need help!

Hi everyone,

I have a well-worn 92 Jetta with a 1.8L RV engine. The car starts fine and for the first ten minutes or so works flawlessly. Once everything heats up however I am getting erratic misfiring on all cylinders. It doesn't seem to matter where the throttle is or how much load is placed on the engine. The misfiring can be a single blip or a full-blown 10+ second epileptic seizure to the point the engine quits. Along with the misfiring the tachometer also wanders through almost it's full range.

My first thought was that the ignition coil had a broken wire or dodgy internal connection that got worse as the unit heated up. I replaced the coil, distributor cap, and rotor - no change. The grounding strap from the coil bracket to the engine is also fine.

I'm stumped and don't want to start replacing everything in the car till I find the right component. There must be a procedure I can use to isolate the problem.

Can anyone offer advice as to the next steps I could take?

TIA for all the replies.

DarylS

Reply to
DarylS
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Check the Hall sensor inside the distributor, or try a replacement.

SFC

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Reply to
SFC

Make sure the ground wires that are attached to the valve cover stud nearest the master brake cylinder are clean and not corroded. I had to replace mine once with the same problem. It started out as a very rough idle. Check the ground wire at the computer as well. TEMiller

Reply to
Corrado Daddy

Make sure the grounding straps to the body and engine are clean and tight. Possibly ignition module just over the ECM?

Make sure you use a BOSCH distributor rotor & distributor cap. Cheaper rotors can create some nasty running or non-running problems.

Might be a defective 02 sensor. You might try testing with the sensor unplugged. Check wiring to the throttle body switches and that ground wire to the cylinder head coolant flange or intake manifold.

Not sure about what is affecting that tach though unless the tach is bad or the ECM? :-(

Reply to
dave AKA vwdoc1

Thanks to everyone who replied. The problem turned out to be the Hall Sensor as SFC indicated (Gold Star for SFC!). I had checked the grounding wires and all were OK. Given the problem only happened after the motor got up to operating speed I was certain it wasn't a faulty ground.

I installed a reman'ed distributor a couple of days ago and retimed the engine - engine now works perfectly! The distributor performance must have been degrading for some time and I never noticed - the car seems to have a lot more power now. The engine runs smooth all the way to redline.

The weird tachomoter behaviour also went away - apparently the signal the hall sensor sends the ignition ECU for firing the coil also is used for the tach. So what I saw on my tach was what the ECU thought the motor was running at, no wonder the engine was stumbling so badly.

Thanks again everyone. SFC, I owe you one...

Daryl

Reply to
DarylS

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