# 1987 GTI MK2 8v sensor wiring issues...



## furious_george (Apr 13, 2017)

Aloha,
I have recently acquired and am restoring an 87 Golf GTI 8v. It's CIS-E. So far, I have rebuilt the top end+rings, installed a ported head with the big valves, a slightly more aggressive cam, new water pump, new timing idler and belt, new oil pump, new fuel dizzy, new injectors+seals, poly motor mounts with the early captive mounting brackets, a stage 2 clutch, headers, catback, heated 02 sensor relocated to downpipe after headers, new cap and rotor, new idle air/ISV installed, and bought all new sensors/senders for the engine. I probably forgot a few things, but you get the gist...

I have arrived at only one point of confusion. It runs great and idles well after warm up (I adjusted my fuel dizzy and via DPR method on a meter), throws you back in the seat and hauls ass but doesn't warm up properly on it's own. Also, the temp gauge does not (yet) work. Gas gauge works, fan comes on after a while and after engine shutoff, low coolant level blink light works fine (checked before I put coolant back in after rebuild). I have put around 1000 miles on it since the rebuild and am happy so far, but want to get everything working. The original owner (he who shall not be named :screwy had left nearly every sensor wire dangling in the engine bay and several with no connectors attached to them anymore :banghead:. I have done my best to put things back in order, and have all new sensors/senders for this motor on hand. 

I have a Bently Manual for this model, but it is sadly missing the wiring diagram section (section 15) entirely. Ironically, the wiring diagrams are also missing from my Haynes manual, too (Haynes diagrams are usually useless anyway). Really pissed about both of these things now , but that's another story. I managed to track down some wiring diagrams for both 86 and 87 year golf and GTI from "VW Technical Site" that look like they are from the factory, but seem to be lacking crucial details about the oil water related circuits. I have combed the forums and internet looking for info about this, but most pics seem to be for digifant, and most advice about CIS-E mentions completely different color codes for the wiring (colors I don't even have at all).

This car has not had any crazy swaps or frankenstein action, just abuse. The colors of these wires are as the factory installed them. Just may not be properly connected...

What I could really use a bit of community feedback about is which wires attach to the various sensors/senders and whether I have even gotten them close to correct. Attached are various photos of each with a caption about what confuses me.

This GTI does not have the VDO gauge cluster...

Here goes:
This one is the oil pressure sender, which I am pretty sure it is wired correctly because the light does not flash. No reference for this one in the diagrams, worrying...









These are the senders on the top of the coolant outlet. I was under the impression that the one closest to the block is the thermo time switch and the small nail head one is for the fan switch. If the smaller one is disconnected the fan does not come on. I cannot find any reference to this smaller one in the wiring diagrams tho, which concerns me...









This is the one on the bottom of the coolant outlet, which I am pretty sure is the temp gauge. The temp gauge does not work tho. I also cannot find this at all in the diagrams, even under the dash wiring charts...









These are the ones by the oil filter, the closest to the block is the oil temp sensor (at least according to wiring diagrams that are suspect), and the front one is (another?) pressure switch or sensor? The front one is not in the diagrams either...









This one I have no idea about and is not in the diagram at all. It goes where the WUR goes on the older CIS engines. I am assuming it is an ambient temp sensor? (its not the knock sensor as I have already replaced that, connected it and checked it against the diagram).









I vastly appreciate and help that the community can offer, and will gladly support in any way I can. I am pretty experienced with older VW air and water cooled motors, but this is my first Foray into the electronically controlled systems other than the occasional CIS-E tuning for friends.

Aloha!


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## Fat Rabbit (Nov 18, 2001)

Aloha Furious George. Since you have had no replies -- I'll give your post a bump and perhaps add a bit of information.

As far as I recall from my '87 GTI the top two sensors on the center hose flange are for the gauge and for the thermo-time switch. The tall sensor is the thermo-time switch. That sensor operates the cold start injector if the ambient temp is cooler and does not operate that injector if the engine is warm. The bottom sensor is for the O2 sensor circuit. That causes the computer to look for O2 sensor input after the engine is warmed up. 

The bottom sensor picture looks like an after run sensor for the radiator fan. That sensor is a switch that turns on the radiator fan to help cool the engine after the car has been driven and shut down. You might try grounding the switch wire with the engine off to see if the fan comes on. I recall the after run wire being black and note that you have a black wire on the small water temp sensor -- for the cluster gauge and the gauge doesn't work -- hmmm.... Ground that one too and see if the fan goes on. That black wire was always a problem because the connector would corrode off and sometimes fall into a place where it could ground and cause the radiator fan to run until the battery drained. 

The sensor at the end of the cylinder head is an oil pressure sensor. The two sensors on the filter flange are for oil temp and pressure. 

Part numbers would be a good way to verify the sensors. The wire colors may not be original VW in some cases. Like you, I do not have a reliable wiring diagram for that car. Never have found a decent one. Hope this helps some. FR


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## sonikgti (Oct 12, 2001)

Bumping this up because I'm going through this same right now with my 86 GTI - CIS / 8V / 1.8l head with 2.0 block. I replaced both pressure sensors but still get the buzzing after about 3000 rpm. Oil pressure tests good - I just had the motor rebuilt with the addition of the 2.0L block. I'll post pics later. 

(photobucket has really made it a bitch to use any of the previous threads for help - I need pics!)


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## Fat Rabbit (Nov 18, 2001)

First I'd check the engine oil pressure with a gauge. (The control unit could actually be telling the truth. But since the buzzer is a common issue -- the oil pressure is likely good.) If the oil pressure is OK -- try changing to heavier weight oil -- 10W40, 10W50. Avoid 30 weight oils for sure -- 5W30, 10W30. In OR the heavier weight oil should not be an issue year round. If heavier weight oil fails to correct the issue -- you can replace the Dynamic Oil Pressure Control Unit. It is located on a Printed Circuit board in the cluster. To replace it you have to remove and open the cluster. It is a bit of work but not difficult. Using heavier weight oils fixed the buzzer issue my 91 GTI had. Here in Wisconsin I used a 50 weight in summer and a 40 weight in winter. FR


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