So two of the quirks I am working on fixing on my ABF swap at the moment are an erratic temperature guage and a hard start condition if the car is started after recently running. I know an erratic temp guage can be caused by failing temp sensors, thermostat problems or air in the system and that rough idling can be caused by a faulty coolant temp sensor. I'm going to check it out this weekend, but thought I'd get a head start seeing what you guys thought. Maybe the two problems are linked? The frustrating thing is that all the parts in question are brand new (new thermostat and temp sensor). I'm hoping that it's not a wiring issue as I have the ABF engine bay harness spliced into my existing 8v jetta harness. I've linked a video of the fluctuating guage just for an example. https://drive.google.com/file/d/1QpNI55lnkLrAxBB77JiLUb0YCRT4v4l5/view?usp=drivesdk
Additional info: -.Rad Fans do come on and the temperature guage does not go past 95. - Coolant temp guage can drop as much as 25 degrees celcius from idle to when I accelerate (thermostat or w/p issue?).
assuming this is in a MK2, what fusebox is it and what clock set are you using, if mk2 did it have factory fitted MFA? with the hard start, do you notice if the rev counter is jiggling or not
just watched the video, looks more electrical related to me but have a read of my coolant thread covers thermostat check: https://clubgti.com/forums/index.php?threads/coolant-system-faq.145091/ for clocks side theres an earth to the head from g1/5, its the brown/white wire on the side with ring terminal make sure thats clean and has good metal contact. for hard starting get diagnostics plugged in check for fault codes and look at your ecu measuring blocks
I transplanted the engine into my mk3 Jetta. Using the original jetta fuse lock (part num er is same as the abf one. Also using the original North American mk3 cluster. Reading your coolant system list, I'll start by replacing my black cap and see where it goes from there! I'll get back to you when I have ran diagnostics, I need to buy a new cable. Thanks!
Ok, its been a while, but I finally got around to looking further at the temp guage issue. It was thankfully an easy fix. I was about to look at the ground wire as suggested, but decided to look at the dash temp sender wire first as it is in front of the ground in question. Turns out the spade connector on the wire was too loose and easily moved even when connected to the sender. I imagine the connection was constantly losing and regaining connectivity due to engine vibration which gave me the erratic guage function. I had to remove the plastic clip that originally came on the wire as my new sensor had a different plug style. Either I bent the connector in the process or it was worn and old. I used some pliers to squeeze the connector back into shape and fitted it back onto the sensor nice and snug. Temp guage works perfectly now. As for the hard start issue, I do not notice my tachometer jiggling when I start the car. I'm wondering if I either have a leaky injector that causes the hard warm start or if my starter is starting to fail as this only happens when the vehicle is warm.
jiggly rev counter suggests its trying to spark, in the ECU measuring blocks you can look at the engine speed which is the output from the crank sensor, the coolant temp is worth a look too make sure its reading believable values both cold and hot start. make sure ecu vacuum line is good, wirign to throttle round back of inlet isnt split, isv buzzes etc
