Friday 17 December 2021

BMW E30 / E28 Diagnostic Plug / Socket Pin Out Diagram

11.5BrownGround Distribution G101
40.5Brown / VioletGauges / Warning Indicators,
Coolant Temperature Sender
50.5White / GreenFuel Control,
Injector Control Module (Fuel Rate)
70.5White / BlueService Indicator,
Service Interval Processor (Reset)
112.5Black / YellowStart, Start Signal
120.75BlueCharge System, Alternator,
130.75BlackIgnition, Ignition Coil
142.5RedCharge System, Alternator
151.5Green / YellowIdle Speed Control,
Idle Speed Control Unit

BMW E30 Fuse Box Layout + Diagram


17.5AHeadlights (also 2, 13, 16)
27.5AHeadlights (also 1, 13, 16)
315AAuxiliary Fan (also 18)
415ALights: Turn/Hazard (also 24)
525AWiper / Washer
825ALights: Dash, Rear Defogger, 
Seatbelt Warning (also 10), 
Speedometer / Indicators (also 12)
915AIdle Speed Control / Vacuum Advance,
Reverse Lights
107.5ASeatbelt Warning (also 8), 
Service Indicator (also 24), 
Tachometer / Fuel Economy Gauge (also 24), 
Gauges / Indicators, Brake Warning system,
1115AFuel Delivery
127.5ARadio (also 21), 
Speedometer / Indicators (also 8)
137.5AHeadlights (also 1, 2, 14)
147.5AHeadlights (also 1, 2, 13)
15-Not used
16-Not used
1715AAccessory Connector
1830AAuxiliary Fan (also 3, 19)
197.5AAuxiliary Fan (also 3, 18), 
Interior Lights (also 21, 22, 27), 
Power Mirrors
2030AHeater / Air Conditioning (also 28)
217.5AAuto-Charging Flashlight, Digital Clock, 
Glove Box Light, Ignition Key Warning,
Interior Lights (also 14, 22, 27),
Radio (also 12), Trunk Light
227.5AInterior Lights (also 19, 21, 27),
Lights: Front Park/Tail, 
Front Side Marker
237.5ALights: Dash, Front Park/Tail, 
Front Side Marker, 
Rear Marker / License Plate
2415ALights: Turn/Hazard Warning (also 4), 
Tachometer / Fuel Economy Gauges (also 10), 
Service Indicator (also 10)
2525ANot used
2625ANot used
2725AInterior Lights (also 19, 21, 22),
Central Locking
2825ACigar Lighter, Power Antenna
297.5AFog Lights
307.5AFog Lights

Thursday 9 December 2021

E30 Speedometer Schematic / Wiring Diagram / Pinouts

 ** For E30 speedometer / odometer troubleshooting and repair guide see THIS POST. **

The arrangement is the same with both VDO and Motometer type gauges. 

Pins are: 

R - 12v +

31 - Ground

31b - Speed sensor INPUT Pin 1

A - Speed sensor Pin 2 *NOT USED*

Bench testing can be achieved by powering the unit with 12v and simulating the pulse of the speed sensor over the two remaining pins, either way around. This is essentially done by creating a pulse across the circuit of pin A and A1. You can do this by just bridging the two pins together with a piece of wire and touching the wire against one of the pins on and off to make the ‘pulse’, as this is basically how the speed sensor works, but simulate any kind of actual road speed you will need to be doing the on/off pretty quickly. A far better way to bench test is to use some kind of ‘pulse-generator’, such as an oscilloscope or something set up using an Arduino, which is what I used to create a pulse with 5 volts. I will post a guide soon.

E30: Rebuilt and refitted instrument binnacle w/ new speedo/odo + more

  • Replaced speedometer / odometer.
  • Replaced back-light bulbs.
  • Checked and tested Si batteries.
  • Tightened brass-nut on temperature-gauge.
  • Bench-tested.

Sunday 24 October 2021

E30/E28: Faulty AFM (Air Flow Meter) repairs, worn carbon-track quick fix


The AFM or Air Flow Meter uses a metal flap that is opened air entering the engine to move a brass arm up and down a carbon-track. The position of the arm along the carbon track alters the electrical resistance through the circuit and this lets the ECU know how much air is coming in, so it can deliver the right amount of fuel to the injectors. The E30 uses a BOSCH AFM unit, also used in many other BMWs with Motronic or Jetronic injection systems.

The analog electrics in the BOSCH AFMs rarely ever fail, but there are two areas that are failure prone after higher mileage - a worn carbon track and a faulty air-temperature sensor.

Saturday 23 October 2021

E46 318i Touring: New front drop-link for MOT

The 318i Touring was up for MOT this week and failed only on the O/S front anti roll-bar link. Normally I would replace these as a pair, which would have been more cost effective as you can get a set of two from eBay for under £15. Time was an issue and I wanted to get it back for a re-test so had to buy one from Euro Car Parts for the same price, around £15. Annoyingly, the eBay pair were Lemforder and the single piece from ECP is Starline, but needs must.

The car has only just passed 104k miles, so this could well have been the original anti-roll bar linkage and boy was it seized on. I only got a couple of turns on the top nut before the 5mm Allen-key in the stud stripped and rounded, so had to cut the rubber boot off to get a 17mm spanner on to the flats at the back. Even so, progress was painstakingly slow. Couldn’t even get a grinder in there as things are surprisingly tightly packed on E46. This made an otherwise quick and easy job last a bit longer, but it is nearly 20 years old.

Tuesday 5 October 2021

E30/E28: Adjusting AFM (Air-Flow Meter) - change air/fuel rich/lean mixture


This is for BOSCH AFM units, fitted to most E30 and other BMWs fitted with Bosch Motronic or Jetronic injection systems.

The AFM, or Air Flow Meter, is a metal flap that is drawn open by air entering the engine and the position of the flap tells the ECU how much air is coming in so it can inject the right amount of fuel. The stock parameters for the AFM are set at the factory and unique to each car and BMW recommend that these settings should NEVER be adjusted... so do it at your own risk!!

Why would the AFM need adjusting??

  • You have done a ‘gas-test’ and the results show your car is running rich (too much fuel for amount of air) or lean (too much air for the fuel being supplied) and wish to adjust for emissions / fine-tuning purposes.
  • You have an air leak after the AFM, so more air is getting in than the ECU is supplying fuel for and the engine won’t run, especially when cold.
  • You have an over-fuelling problem where too much fuel is being supplied for the amount of air and flooding the engine.

Adjusting the AFM in the second two instances is a quick and dirty way to get your car running well enough to drive it, but is not a long-term fix for an underlying problem, so bear this in mind before messing with the AFM.

Wednesday 29 September 2021

BMW E21 323i Baur wins HERO-ERA Summer Trial

I've been interested in HERO (The Historic Endurance Rallying Organisation) since owning my red E21 and had intended to enter that car in one of the smaller events, as they host a few throughout the year. The big one is the Summer Trial in June and it was nice to see another E21 taking first place this year. A Baur cabriolet no less. Better late than never to throw up a pic of Angus McQueen and Mike Cochrane's HERO winning 323i...

Pic: Classic & Sports Car Magazine, Aug 2021

HERO EVENTS & ERA EVENTS - The Original Classic Rally -

Sunday 26 September 2021

E30 318i: Replacement Speedometer/ Odometer

Had to bite the bullet and buy a replacement speedo / odometer for project E30 this week as after many different attempts to fix the original one [THIS POST], I had to declare it totally junked. These are not cheap and sit around the £65-70 region, but I got a deal on one for £59... still an unwanted cost but at least I no longer have to tape an old iPhone to the dash with a speedo app!

Now the question is, do I swap in the number row from my old odometer or leave the ones in from this one, some 100k miles less.... Hmmm.

As per the pics, the areas of concern on my old speedo are not problem on the replacement, with resistors, capacitors and other components all looking mint. There is also no charring to the back of the PCB, so no sign of this unit overheating in the past and the odometer gearing is perfect. This unit has still covered 154k miles over the last 35 years, but has clearly had an easier life than the one from my E30!

Showing the healthy resistor on the newer speedo on the left and the burnt out one to the right.

E30 318i: Speedometer / Odometer faults + check list

If your E30 speedometer is broken, your odometer isn't turning or both, then here is a troubleshoot check list to find and fix the fault. Doing the work yourself is a bit fiddly, but totally doable if you are handy with a soldering-iron.

** A more detailed guide / thread all about E30 speedometer / odometer faults by 03IRM3 on is here -, which was a great help. **

NOTE: If your speedometer is not reading, before starting to diagnose the instrument the first thing to check should be if there is a pulse being generated by the speed-sensor in the differential, see E30Zone Wiki here.

Broken Odometer drive gear.
This is the most common problem when the odometer has stopped turning. The drive gear from the stepper motor that turns the larger cogs tends to split on higher mileage cars causing it to skip teeth and not turn the odometer gearing. Replacement gear sets can be bought from eBay for a few quid.

Burnt out resistor.
This is the main power resistor on the 12v + input to the PCB and it's never usually failure of this component that causes it to burn out. Instead, failure of a component further upstream is usually the culprit by drawing way too much current, causing the resistor to work double-time and overheat. This one was still working amazingly, given the heat it had been producing that charred everything around it, but I threw a new one in anyway. The value was about 150 ohms, so that's what I went with.

Blown capacitor.
Sudden failure of both speedo and odometer can often be down to the main power capacitor blowing. This is visible in the above pic to the right of (and next in sequence to) the burnt out resistor. It's a basic 220uF electrolytic capacitor and is very simple to replace with only two pins needing de-soldering, so should be the first step in troubleshooting a dead unit, even if the cap itself doesn't appear blown. Mine had been scorched by the overheating resistor, but seemed ok. I replaced it anyway, but it did not help with mine.

Snapped wire on Odometer stepper-motor coil.
This is rare, but does happen as 03IRM3 has seen one and mine had this too so I guess it does happen, where one of the single strands of copper coil for the stepper-motor snaps off its pin on the PCB. It’s possible that this happens due to time/age and vibration in the vehicle, but could likely be due to manhandling the unit while it is out for other repair work. Either way, it’s an easy fix to just solder it back in place and will be stronger than it was before at least.

UAF chip blown.
If none of the above fixes have worked and both speedo and odo are still not working, the likely culprit is that the UAF I/C chip has malfunctioned and is not processing inputs and outputs correctly, which leads to the resistor burning out, caps blowing and the odometer coil overheating. These UAF2115 chips are common, used in many speedo/odo units, taxi-meters, tachographs etc., so replacements can be found on eBay or electronic component sites for a few £/$, but this is probably the most advanced fix needed for these units and the question at this point is whether it's worthwhile. 03IRM3 has replaced chips as a last resort only to find the unit still won't work, so I decided that with all other fixes not working and my odometer still needing new drive gears that it was time to junk it and seek a replacement unit... [THIS POST].

Wednesday 15 September 2021

E30 318i: Replaced AFM (Air-Flow Meter)

I’d been messing with my AFM in order to get the car running ok when cold and when I finally fixed the massive air leak on the inlet manifold I then struggled to reset the AFM back to standard. 
In order to get the M40 to idle ok while the engine was cold I adjusted the mixture setting to run richer. Obviously this was providing enough fuel to stop the engine cutting out while the plenum was filling with as much air as the cylinders could gulp through the gap in the manifold gasket. It runs and drives ok in this setting, but idles quite high (about 1100rpm) and you can smell the stink of neat petrol out of the exhaust. Ok for short trips shunting the project car around but will need addressing to enjoy it before summer ends!
The real problem began when I had repaired the gasket, got the engine running smoothly and then tried to reset the AFM back to a stock, or near stock value. To begin with I had been putting marks and taking photos to recall where the settings were before I started messing, but you know how it is, once you get immersed into a several day long tweaking session (take that as you will!) the tendency is to get lost along the way.
I gave up trying in the end and decided the only way to dial this engine in and be sure I was not fighting with a dodgy AFM was to buy one that had not been messed with. This is in my interests anyway, as I got one from a car with far lower miles on it so the carbon-track is less worn and I know the air-temp sensor is OK too, which was a doubt with the original one.

Sunday 5 September 2021

E46 318i Touring: Replacing leaky Oil Cooler gasket [N42]

After fixing the major oil leak from the rocker-cover gasket [THIS POST], I noticed there was still some oil pooling on the under-tray and a fews spots dripping onto the road. I traced the source up the right side of the engine (looking from the front) and could see oil filling up some cavities in the cylinder-head to the left of the oil-cooler / filter housing, so determined this to be the culprit... yes, another common one, especially if the filter-housing has been removed for previous engine work.

A replacement gasket was just £6.59 from eBay and comes as a two piece set including the main gasket that sits between the housing and the cylinder-head, as well as a smaller gasket that sits between the oil-filter housing and the coolant fed heat-exchanger. This latter one hardly ever leaks, as it's very rare to find a filter-housing that has been split apart during engine work, but it's nice to have one anyway and you may find it worth the time to replace this one while the housing is removed, though I could not see any signs of leakage so didn't bother.


1. Remove the lid to the air-con ducting that sits atop the firewall at the back of the engine by undoing the clips a quarter-turn, take out the pollen-filter and remove the weather-strip seal from the firewall.

2. Remove the air-con ducting itself by undoing the four screws using a T30-Torx socket and lifting it out.

3. Remove the rear right-side engine cover by undoing the two stud-nuts using a 10mm wrench.\

** Make sure you have a cloth / plenty of tissue to catch any oil that runs from the housing. **

4. Remove the three screws holding the oil-filter / cooler housing to the cylinder-head using a 10mm socket with a long extension bar. One is clearly visible in front of the housing, the other two being hidden down the back.

5. Lift the oil-filter / cooler housing upwards out of the head, catching any wayward oil and lift the housing clear, rotating it so as not to put too much strain on the coolant-hoses. The hoses do not need removing or any coolant draining for this job.

6. Remove the old gasket and clean both mating surfaces with a cloth and I find it always worth scraping any crud off with a razor-blade.

7. Insert the new gasket to the housing. A lug on one side sits in a notch in the housing so the gasket can only fit in one way. [If it's an older engine or the housing has been removed a few times before, it might be worth taking a belts-and-braces approach by applying some gasket sealant to the mating surface on the head, as I did with some white Corteco.]

8. Carefully place the filter/cooler housing back onto the cylinder-head, trying to spill as little oil as possible on the mating surface and reverse steps 4-1 to refit.

Monday 30 August 2021

E46 318i Touring: Handbrake / parking-brake repair + adjustment

The handbrake (e-brake) wasn't working properly on the left side of the E46 Touring, which I assumed would either just need adjusting or at worst the spring mechanism had failed. BMWs of this era have a drum-brake mounted inside the hub of the disc-brake that is used only for the parking-brake. It turned out that the sprung stud that holds the lower brake-shoe in place had come loose, worked its way round the drum and partially jammed the mechanism, as in top picture.

The slot that the stud locks in to is part of the backing plate for the disc and it had bent outward and rounded off over time, no longer giving enough metal for the stud to hold on to. I managed to build the slot back up using a cole-chisel and there is just about enough metal left to hold the stud firmly. If it happens again in the near future then a new backing plate may be required, but this is a hub off job and a whole load more work, so lets hope it doesn't. 

Annoyingly, I had to crack open a new £13 handbrake spring assembly kit just to use the one sprung retaining stud, guess I have some spares at least. With the left side now working correctly, I gave both sides of the handbrake a quick tighten up using the rotating adjuster inside the drum.

BMW E30 - LED instrument lights flicker with rheostat switch

Work fine wired straight to power, but flicker and come on and off when run through the dimmable rheostat switch. Switching back to 5w bulbs may be the only cure.

Sunday 29 August 2021

E30 318i M40b18: High / erratic idle issues NOW FIXED, stable at 800rpm + good throttle-response finally

After my cutting out when cold problem and no low-end throttle response from a busted lower inlet-manifold gasket (THIS POST) and high / pulsing idle issue from a poorly set throttle-stop screw (THIS POST), I have finally got the old E30 ticking over properly. It now sits at about 800rpm on idle and throttle response is smooth across the range. Pleasant.

Wednesday 28 July 2021

E30 318i: Leaking clutch slave-cylinder... fluid low

Now the E30 is running well I took it out for a test run and noticed that all of a sudden the gears were grinding a little bit. Checked the fluid reservoir and the level had dropped to about 10mm, not good. Looked under the car and saw a spot of fluid on the drive right under the slave-cylinder. My guess, and no prizes for guessing right here, it was a leaking slave-cylinder and, hey presto... sure looks like one to me.

Replacement is ordered. I went for a cheap and cheerful one off eBay for just £16.50, though £25-40 seems to be the going rate. Be fitting this when I have chance. Looking forward to the bodywork, but mechanical jobs just keep popping up... that be old BMWs!

Monday 26 July 2021

E30 M40 316i / 318i: Adjusting Throttle-Body and Idle Stop-Screw

Yes, this is set at the factory and they say it should never be messed with, but as the youngest M40 engined BMWs are approaching 30 years old now, chances are the stop-screw and throttle-plate will have been adjusted at some point in its life. 

Here I will explain what happens when it is adjusted, the problems it may cause if it has been and how to reset it back to stock. 


The stop-screw should have a paint mark on it from the factory to show if it has been messed with, but after so many years the mark may no longer be visible. If you feel yours has been adjusted in the past, the main reason this has been done is likely to falsely raise a low idle caused by another issue, say an induction air leak. If an over lean mixture is causing a low idle, the tendency is to tweak the idle stop-screw to get the car to tick over at higher revs and stop the engine stalling out or running lumpy. This is a great short-term workaround, but will cause other issues with the AFM / DME and fuel delivery further down the line, particularly when the underlying issue is worked out.


The issues you will get with a poorly adjusted throttle stop-screw are:

High idle.

Hunting / pulsing revs. 

Poor or no low-end throttle response.

Erratic idle (if throttle position switch TPS is not engaged).

Bogging at high revs (where wide-open throttle WOT switch is not engaged).


There is only one way the throttle can be adjusted, via the stop-screw, though the throttle-cable itself can be adjusted to change throttle response somewhat, mainly with how the pedal / cable reacts to driver input and will not affect the fuel/air ratio and the engine idle.

** The intended job of the idle stop-screw is simply to stop the throttle-plate from jamming in the throttle-body and being difficult to open when the pedal is pressed and not to change the car’s idle characteristics. BMW recommend that this is never played with, so do so at your own risk. **

1. Back off the lock-but using an 8mm wrench.

2. Use a small flat screwdriver to wind the idle stop-screw in and out. 

* Clockwise will push the throttle-linkage further from its rest position, holding the throttle-plate open slightly and allowing more air to bypass it while the pedal is not pressed.

*Anti-clockwise will allow the throttle-linkage to close further and will reduce bypass air and choke the engine while the pedal is not pressed. 


You will need a set of A/F / imperial feeler-gauges as this is how the stock throttle-plate aperture is measured. 

** If you are only adjusting the throttle-plate and do not need to adjust the throttle position switch (TPS) then the throttle-body itself does not need removing and you can skip to step 7.**

Removing the Trottle-Body:

1. Remove the main air-inlet hose from the AFM to the throttle-body by loosening the jubilee-clip and easing it off.

2. Unclip the throttle-cable from the throttle-linkage and remove the two screws holding the throttle-cable mount from the top of the throttle-body housing using a 10mm wrench. Move the cable assembly to one side.

3. Remove the two water hoses and air vacuum-hose from either side of the throttle-body by undoing the jubilee clips and teasing the hoses off with a screwdriver.

4. Remove the six nuts from the upper inlet-manifold using an 11mm wrench and the two locating screws from the manifold using a 10mm wrench. Lift the upper inlet-manifold so that the throttle body can be fully accessed. 

5. Remove the throttle-body from the inlet manifold by undoing the four nuts using a 10mm wrench.

6. Turn the throttle-body upside down and remove the throttle-position-switch (TPS) by removing the wiring connecter and undoing the two cross head screws.

7. Back off the lock-nut of the stop-screw using an 8mm wrench. 

8. Use a small flat screwdriver to adjust the throttle stop-screw by the notch in the end of it. Obviously, clockwise will move the screw further out and make the throttle-butterfly rest in a more open position. Anticlockwise will allow the butterfly to close more.

9. For the OEM setting, the throttle-butterfly should be 0.377” from the housing, so use your feeler-gauge between the side of the tube and either side of the butterfly until you find a happy medium.

10. Tighten the lock-nut up again with an 8mm wrench.

11. Now take the throttle-position switch (TPS) and locate it back in the housing so that the switch is depressed while the throttle is in the fully closed position. With the two screws loosened, the TPS can be swivelled left and right as in pic below to adjust the point at which it engages. The ideal placement for the switch is to have it click closed while the throttle is open about 1mm. (You will hear the quiet click from the TPS as it opens and closes.) When you’re happy with the TPS placement tighten the screws to lock it in place.

12. Before refitting the throttle-body, check the operation of the butterfly and TPS and make sure the butterfly is not binding to the body while fully closed as this will ruin low-end throttle response.

13. Refitting is a reversal of steps 5-1.

Wednesday 9 June 2021

E30 318i M40: GUIDE - Replacing lower inlet-manifold gasket - rough idle and stalling fixed!

After all the diagnosis and testing from THIS POST, I found the cause of my rough idle and stalling out when cold was a damaged paper gasket on the lower inlet-manifold allowing unmetered air to be drawn in to the plenum at will and confusing the AFM and DME over how much fuel to deliver. 

The engine just about ticked over when warm, albeit with a slight misfire. On cold startups however, the misfire was a lot more severe and at low revs the engine just couldn’t hold on, stalling out due to a way over-lean mixture. It would drive though, but there was no throttle response until about halfway up the rev range and power would arrive with a bang. It is amazing how sensitive these older engines with analog electronics are to unmetered air leaks!


I ordered a new gasket from eBay, it was a snip at £6.88. Be careful when ordering, older M10 engine gaskets are far more plentiful, so ensure yours is the right one for the M40... they have a funny shape which is quite distinctive. Choice was limited, in fact I could find one more gasket for sale of the right type and that came with a full £30 set including a head gasket, so be sure to check out carpartsinmotion, they have rare-fit stuff.


1. Undo the jubilee-clip and disconnect the large rubber duct from the throttle-body using a flat screwdriver or 7mm socket.

2. Unclip the throttle-cable from the throttle-linkage and remove the two 10mm screws holding the metal plate to the throttle-body so the cable assembly can be moved clear.

3. Remove the wiring connectors from the throttle position sensor [TPS] and idle control valve [ICV].

4. Remove the rubber hose from the bottom of the ICV.

5. Remove the vacuum air hose from the front side of the throttle-body by undoing the jubilee-clip and teasing it off carefully with a flat screwdriver.

6. Remove the two coolant hoses from either side of the throttle-body by undoing the jubilee clips and teasing them off with a flat screwdriver. 

7. Remove the six nuts from the upper inlet-manifold using an 11mm wrench [9 in diagram] and two locating studs in the centre with a 10mm wrench [13 in diagram]. 

8. The upper inlet-manifold can now be lifted out of the engine bay.

9. Remove the wiring connector from the fuel-rail / injectors. 

10. Remove the metal fuel send and return pipes from each end of the fuel-rail by undoing the jubilee clips. (This is where it gets messy, you may wish to plug or clamp the ends of these hoses). The send pipe is attached to the fuel pressure regulator [FPR] at the front of the fuel-rail and the return pipe is at the back of the rail.

11. Remove the five nuts holding the ports of the lower inlet-manifold to the head using an 11mm socket [4 in diagram].

12. Remove the two bracing bolts from the lower inlet-manifold using a 13mm socket. (They point towards the right side of the car) [11 in diagram].

13. The lower inlet manifold is now free to be removed. This can be a bit tricky as the rigid fuel pipes are routed through one of the gaps in the manifold ports. Also make a note of how the hoses to the throttle-body are routed through around the lower manifold, as it can be confusing once the upper manifold is bolted back in.

14. Clean off the mating surfaces of the cylinder head and the inlet manifold.

15. Carefully fit the new gasket to the studs on the head. It only fits one way round.

16. To refit reverse the above steps.