tentonhammer 10 Posted December 10, 2012 (edited) I have an ongoing issue with my 9A maybe someone can help me out, what I expected to be a simple fix has now become a bit of a head scratcher, see below. Fitted a new coolant temp sensor this weekend (1x Bosch TEMPERATURE SENSOR 0280130040) as I suspected it to be faulty, issue remains. Basically the car gets lumpy as hell when she’s warmed up. If you disconnect the coolant temp sensor the lumpiness disappears immediately, idle goes back to normal and the car drives great (albeit in default mode via ECU because the car doesn’t feel as smooth as it does with a working coolant temp sensor connected). By disconnecting the coolant temp sensor in this way I would have hoped this would isolate the problem. Simply replace faulty sensor, reset ECU and we’re all done – That would be far too easy though eh…! There seems to be something else at fault here but I don’t know what? It doesn’t look like fueling because as I said, when coolant temp sensor disconnected the car runs great. Fuel pump priming, injector spray pattern good. Plus there is no smell of fuel to indicate the car is over fueling and I’m not tearing through fuel either. Could be an issue with cold start injector perhaps although this seems to be working fine. More knowledge of the relationship between a 9A coolant temp sensor / ECU / and cold start injector needed (no thermal time switch on a 9A). It can’t be ignition as I ‘ve replaced everything with brand new components (OEM plugs, OEM leads, OEM distributor, new battery, ignition coil + module etc). If it was ignition I would expect the car to be lumpy all the time even with the sensor disconnected but it isn’t – only when sensor is connected. Like I said, disconnect the coolant temp sensor and the car runs fines, great in fact! Plug it back in and the car gets lumpy / misfires, idle drops off, throttle doesn’t want to engage / is hesitant. Anyone know the correct output resistance for a coolant temp sensor? Should reading go up or down as it is heated up? I’d like to be able to test mine to eliminate it. All ideas welcome. Cheers, C 16V 2.0 (9A) Edited December 11, 2012 by tentonhammer Quote Share this post Link to post Share on other sites
bmwcompact 10 Posted December 11, 2012 Sorry to hear the sensor replacement didnt fix your problem. Im not good on car electrics but I have noticed that sometimes problems are caused by broken wires/poor contacts rather than defective sensors. Have you thought of extracting the ECU, inspecting/cleaning contacts, checking cable continuity from throttle potentiometer, temp sensor, lambda sensor etc to ECU or even trying another ECU (if you can borrow one). It might be worth a try rather than continuing to buy/replace parts in the hope of a solution. Quote Share this post Link to post Share on other sites
tentonhammer 10 Posted December 11, 2012 (edited) Thanks it was worth a punt, at the very least I've added more new parts into the engine bay which can only be a good thing ;) I've been toying with the idea of swapping out the ECU, I don't have another one to hand though unfortunately so either way I'll have to throw more money at it regardless. I'm slowly rebuilding the engine anyway so all good. When I get some time (and nice weather!) I'll start stripping the the loom back to try to find any breaks, shorts, bad grounds, poor contacts etc between the coolant sensor / lambda / and ECU. Dry joints / poor contacts are always a problem on older cars and in fact I've fixed a few already so I can almost guarantee I'll find some more. In a perfect world I'd gut the loom out altogether and build a new one, fairly straight forward to do really - the cable manufacturing part NOT installing it back into the car! Edited December 11, 2012 by tentonhammer Quote Share this post Link to post Share on other sites
Supercharged 2 Posted December 11, 2012 (edited) What does VAGCOM say?? I'd look at the lambda and it's wiring around the rear engine mount - maybe unplug this and see if it runs better when warm. Usually this sensor becomes key on a warm engine (closed loop) but i'm no 16v / K-Jet expert. Edited December 11, 2012 by Supercharged Quote Share this post Link to post Share on other sites
tentonhammer 10 Posted December 12, 2012 Hi Supercharged, I thought VAGCOM was limited on a 9A? Heard you can only really find the ABS controller and that's about it which doesn't really help me much (could be wrong though). Haven't had it on diagnostics as a result. Will def check lambda and lambda wiring etc. Do you happen to know how to test the lambda to check correct functionality? Quote Share this post Link to post Share on other sites
