BMW Bosch Fuel Injection System Trouble-Shooting Guide

SYMPTOM:	PROBABLE CAUSE:
No cold start	Fuel-pump fault or clogged fuel-filter
	Additional air-valve not opening correctly
	Start-valve not opening correctly
	Leak in fuel system
	Throttle-valve plate not opening correctly
	Temp.-sensor fault
	Diode-relay fault
Poor hot start	As above then:
	Leaking / faulty injector
	Heat/time switch fault
Poor idle	Baffle-plate stop wrongly adjusted
	Leak in Vacuum-system
	Fuel-filter clogged
	Mixture-adjustment incorrect
Backfire from engine	Weak fuel mixture
	Fuel pressure too low
	Starter-valve leaking
Engine runs on after shut-off	Leaking / faulty injector
	Stiff/stuck baffle-plate
	Stiff/stuck control-plunger
Excessive fuel consumption	Control pressure too low
	Starter-valve leaking
	Leak in fuel-system
	Fuel mixture too rich
	Heat/time switch fault
Idle-speed too high	Control pressure incorrect
	Additional air-valve stuck open
	Baffle-plate stop wrongly adjusted

Detailed maintenance guide / diagrams in this post [L-Jetronic] - https://www.beemerlab.org/2020/03/bmw-bosch-l-jetronic-fuel-injection.html

Bosch K-Jetronic injection-system overview / diagram here - https://www.beemerlab.org/2019/11/e21e12e28-bosch-k-jetronic-fuel.html

Bosch L-Jetronic injection-system overview / diagram here - https://www.beemerlab.org/2019/11/e30e28e34-bosch-l-jetronic-fuel.html

BMW M10 Engine Family Tree

Interesting press release from BMW showing some derivatives of the much-loved 4-cylinder M10 engine, which I have covered in much detail before.

"With half the cylinders and half the power of todays V8 M3, the original 1986 car remains one of our all-time favourites. Its seemingly indestructible four-cylinder iron block, however, goes back to 1962 and the BMW 1500. This was also the block that formed the basis of the 1.5-litre turbo F1 engines that powered Brabham to many a race victory. That's not just the block type -- BMW Motorsport used actual 1500 blocks sourced from scrapyards, because the older the block, the fewer stresses remaining in it. Never has a production engine family been more versatile."

BMW 1990cc [2L] Engines 4 and 6 Cylinder Comparison - M10b20 and M60/M20 [E21 320, 320i, E12]

Up to 1977 BMW used 4-cylinder engines for its original 320 and 520 models, evolving from the trusty M10 used in the 2002. After 1977 they began to use freer-revving 6-cylinder engines for all the 2 litre models, the M60 and after 1981 the M20, both still using the same 1990cc, the latter of which has evolved into all the modern BMW straight sixes we know today. The 2 litre four pot is still a very sought after power-plant though, with its light weight and torquey character making for a more responsive front-end, particularly in the smaller chassis models.

I have wanted to compare the specs of these two engines side by side for a while now to see how the bore/stroke and power outputs stack up, so here goes:

CARBURETTOR:

	M10 4-cyl.		M60/M20 6-cyl.
Bore	89.0mm (3.504")		80.0mm (3.15")
Stroke	80.0mm (3.15")		66.0mm (2.60")
Capacity	1990cc (121.4 cu in)		1990cc (121.4 cu in)
Comp. ratio	8.1 : 1		9.2 : 1
Power (BHP)	109 @ 5800rpm		120 @ 6000rpm
Power (PS)	110.5 @ 5800rpm		122.4 @ 6000rpm
Power (KW)	82.5 @ 5800rpm		90 @ 6000rpm
Torque (Lbs ft)	115.7 @ 3700rpm		118 @ 4000rpm
Torque (Nm)	157 @ 3700rpm		160 @ 4000rpm

The 6-cylinder looks to be the faster motor, making a good 10 bhp more, with the shorter stroke and higher compression ratio no doubt making for a peppier drive. However, with its longer stroke and bigger pistons, the 4-cylinder still makes very similar torque, so unless you are screaming it all the time, the lighter engine might still make a more balanced drive under normal use.

INJECTION:

	M10 4-cyl.		M60/M20 6-cyl.
Bore	89.0mm (3.504")		80.0mm (3.15")
Stroke	80.0mm (3.15")		66.0mm (2.60")
Capacity	1990cc (121.4 cu in)		1990cc (121.4 cu in)
Comp. ratio	9.3 : 1		9.8 : 1
Power (BHP)	125 @ 5700rpm		123 @ 5800rpm
Power (PS)	126.8 @ 5700rpm		125.1 @ 5800rpm
Power (KW)	94.6 @ 5700rpm		92 @ 5800rpm
Torque (Lbs ft)	126.6 @ 4350rpm		122 @ 4500rpm
Torque (Nm)	172 @ 4350rpm		165 @ 4500rpm

The injected engines are a different story, with the compression ratio of the M10 not too far behind the 6-cylinder and both making the same power, though I would say the M20 is going to pull harder and smoother as you get up the revs and, ultimately have a higher redline. On the other hand, the 4-cylinder actually seems to be giving a bit more torque this time, obviously the higher compression and bigger bore contribute to this and it is all produced lower down the rev range. This could be why I have heard M10 enthusiasts saying it is more torquey, but either way it stands to reason that the lighter, more responsive handling and low-end grunt makes the 4-cylinder a better choice for round-town driving or even short-track racing.

I actually owned one of the rare 1990cc 4-cylinder M10 engines in 2012, having been given it with the '83 E21 316 I bought. The previous owner had intended to build it up and drop it into the E21, but never got round to the project and I decided not to pursue it given that the M10b18 1.8 litre unit was plenty quick enough for the car fitted with a twin-choke Weber carb, so I sold the 2 litre lump in bits, missing suitable con-rods, for £350!

More 1977 engine changes included the 1.6 litre engine used in the E21 316 now badged as the 315. The 316 now received a restricted-power version of the 1.8 litre M10 engine and a new model, the 318, was given a hotter version of the same engine. The 316 dropped back to 1.6 litres for economies sake with the newer M4x series of engines in the late E30 and E36.

BMW Tightening Torques [PDF]

Superb 136-page document from BMW showing the tightening torque for every different bolt / screw on your car. It covers generic torques for all BMWs, as well as model specific ones for petrol, diesel... even the V12.

https://drive.google.com/open?id=0B1JGYWCqjPsqSTBWRGZYdFBLS3c

CONTENTS:

• General Instructions
• Engine
• Engine Electrical
• Fuel System
• Radiator
• Exhaust
• Clutch
• Transmissions and Drivetrain
• General Electrical
• Instruments
• Equipment Accessories

GENERAL TORQUES:

M4 8.8 - 2.9 Nm M4 10.9 - 4.1 Nm M4 12.9 - 4.9 Nm	M8x1 8.8 - 26 Nm M8x1 10.9 - 36 Nm M8x1 12.9 - 44 Nm	M14 8.8 - 130 Nm M14 10.9 - 180 Nm M14 12.9 - 220 Nm
M5 8.8 - 5.9 Nm M5 10.9 - 8.3 Nm M5 12.9 - 10.0 Nm	M10 8.8 - 47 Nm M10 10.9 - 66 Nm M10 12.9 - 79 Nm	M14x1.5 8.8 - 143 Nm M14x1.5 10.9 - 200 Nm M14x1.5 12.9 - 240 Nm
M6 8.8 - 9.9 Nm M6 10.9 - 14.0 Nm M6 12.9 - 16.5 Nm	M10x1 8.8 - 54 Nm M10x1 10.9 - 75 Nm M10x1 12.9 - 91 Nm	M16 8.8 - 200 Nm M16 10.9 - 280 Nm M16 12.9 - 340 Nm
M7 8.8 - 14.8 Nm M7 10.9 - 21.3 Nm M7 12.9 - 25.5 Nm	M12 8.8 - 82 Nm M12 10.9 - 115 Nm M12 12.9 - 140 Nm	M16x1.5 8.8 - 216 Nm M16x1.5 10.9 - 303 Nm M16x1.5 12.9 - 364 Nm
M8 8.8 - 24 Nm M8 10.9 - 34 Nm M8 12.9 - 40 Nm	M12x1.5 8.8 - 87 Nm M12x1.5 10.9 - 123 Nm M12x1.5 12.9 - 147 Nm	M18 8.8 - 280 Nm M18 10.9 - 390 Nm M18 12.9 - 470 Nm
		M18x1.5 8.8 - 313 Nm M18x1.5 10.9 - 440 Nm M18x1.5 12.9 - 527 Nm

E21 316: Stance looking rather complete...

Squat, slammed, stanced, hellaflush, scrapin' and eating the modern metal for brekkies!

E21 316: More manifold gaskets for M10...

Stuck the new and much better quality exhaust-manifold gaskets on today from Euro Car Parts. They're thicker than the eBay ones and have steel rings round the inner rim like a head-gasket, should make a better seal. It's got rid of the cracking noise from that dodgy one on cyl. 4 [this post] and the engine sounds sweeter than ever.

Surprisingly the manifold nuts all came off as they should this time and left all eight studs in the head... weird, but it certainly made fitting the gaskets a lot easier.

E21 316: M10 Engine cured! - Culprit: manifold gasket...

After repeatedly timing the ignition perfectly to Z on the flywheel, [see this post], we decided there had to be something deftly wrong to be causing the loud noise and backfiring [in the vid below], rather than just the distributor being out of line.

The first hunch was the exhaust had broken while being twisted to get the cylinder-head out and was blowing like mad, but my initial inspections revealed no damage to the down-pipe or manifold and the four manifold gaskets looked all to be in position.

That is to say they LOOKED in position... Today, in the pouring rain, I got the car up on ramps to see what it was I'd missed and as soon as the torch flicked on I could see the answer at last - one of the exhaust-manifold gaskets had slipped off the stud and was only covering half the hole! Nightmare... Right at the back of the engine where we couldn't see and, ironically, the one for cylinder 4 that started all the trouble.

As you can see the gasket has been totally blown apart by the hot exhaust and has separated quite badly in the middle leaving only the metal. I checked the rest of the gaskets in my set for a spare, but can only find the same shape gasket with an oblong hole, perhaps for the E28, so tentatively decided to re-use the blasted one, correctly seated this time and caked in Holt's FireGum.

As soon as the engine fired up again it sounded like it used to. It's amazing the difference that gap in one single exhaust port made to the noise level. It was still idling low though and revving badly, so I grabbed the timing-light again to have another go, turning the distributor to line up Z on the flywheel - 25 degrees before TDC. Now the 30 year old M10 has really begun to purr once more. Awesome! Still some fettling to do on the carb. tuning, throttle/choke cables and checking to see if my damaged manifold-gasket is holding up, but at least she's back on the road after a tense month!

E21 316: M10 Distributor/Ignition Timing: Strobe Light Ahoy!

So my adventures into re-timing the spark-plugs continue with the purchase of a Gunson Xenon timing strobe-light! I went for the cheapest kit in Halfords, but it was still a slight pain at £45, considering it's in addition to a new dizzy-cap and rotor-arm, set of spark-plugs, compression-test kit, gasket-set, oil, coolant and a 30mm socket to turn the engine from the crank, but as I just can't seem to get the old M10 engine running happily I guess it's just as vital and at least we can use it to time in our old MGA engine this summer (hopefully).

Before I start to moan again about the intricacies of re-timing the distributor I should say that I know there is no need to remove it in order to get the cylinder-head off and the dizzy should really be left in place to save all this trouble, but the diaphragm on mine was blocking one of the head-bolts so that wasn't an option for me.

The timing light works by flashing every time your 1st-cylinder spark-plug fires. There is a timing-mark on the spinning crank-pulley or flywheel that passes a stationary mark on the block at the exact point the 1st spark-plug should be firing. When the flashing light from plug 1 is aimed at the spinning pulley it shows the timing-mark in a fixed position in relation to the stationary mark and allows you to gauge how how many degrees before or after the correct point the spark is. Clever stuff.

On the BMW M10 engine, there are two timing-marks on the flywheel, one for top dead-centre [TDC] and another, called Z, that corresponds to the right point before TDC that the 1st spark-plug should be firing. The marks are visible with the flashing light through a small oblong hole at the back of the crankcase. It's easy enough to find the hole, but seeing into it with the timing-light is a challenge in itself, let alone trying to adjust it or move the dizzy-cap and I ended up having to stand over it with my feet on the strut-tops to steady myself enough without leaning in from the side and crushing the wheel arches. There is another TDC timing-mark on the rearmost rim of the front crank-pulley, which is a lot easier to see with the timing-strobe from the n/s of the engine-bay, but the mark is tiny so when you do find it it's best to file a larger notch across the whole pulley - mine had this done already and it makes things a lot clearer.

It's best to first time your engine to Z on the flywheel, at 2200rpm, using 0 degrees of advance on the timing-light gun - just shine it into the oblong hole and rotate the distributor-cap until the large pointer is lined up with the silver ball, not the TDC line. Now check the front crank-pulley for reference by shining the light at it with 0 degrees advance. The groove for TDC should appear around 25 degrees before the stud on the engine-block. Rotate the dial on the timing gun slowly to 25 degrees and the groove should move in line with the pin. Simples.

Ignition timing isn't too much of a fine art, so as long as the rotor-arm contact is roughly on point no.1 on the dizzy with the engine at top dead-centre then it should fire right up and not need much adjustment to find Z. Mine was still making the god awful noise after repeatedly timing to Z, but this turned out to be a badly positioned exhaust-manifold gasket [in this post] so, obviously, check everything else isn't amiss before starting to mess with ignition timing.

E21 316: M10 Misfire Woes:

Went on a Maccies run with some work colleagues on New Year's Eve and I may have been pushing the old girl a bit hard, when a horrible clanging noise began from the engine and got worse quickly. Some of the guys at work suggested the first stop should be the rotor-arm and dizzy-cap so we managed to get some delivered through the parts dept. that afternoon, but it was still chugging on a mixture of cylinders and it limped home for me then refused to start again. When it eventually did the old M10 barely managed to fire 3 cylinders.

My list of diagnostic checks was:

Replaced distributor-cap and rotor-arm.

Tested all 4 plug-leads.

Replaced all 4 spark-plugs.

Removed, cleaned and rebuilt Weber carb.

Checked valve-clearances and confirmed all valves appear to be moving correctly, turning the engine by hand.

Finally diagnosed cylinder 4 as no firing.

Plug and lead tested again, this time sparking against the suspension turret.

Compression test revealed Cyl. 1 and 2 @ 150psi, 3 @ 45psi and 4 @ 25psi.


This all seems to point to a bust head-gasket between the 3 and 4 cylinders. It is unlikely the valves for 2 cylinders would have bent or suddenly need adjusting at the same time, so off with its head and lets look at that gasket.

*UPDATE: The head came off pretty quickly and revealed one seriously blown head-gasket right between the 3rd and 4th cylinders [detailed pics in this post]. Diagnosis spot on, but the culprit may be a slight warping at that end of the alloy-head - not very much at all, but still a worry considering it looks to have been skimmed before. Either way, the new head-gasket is on [I went for a full head set off eBay for £27.99, which includes the manifold gaskets etc.] and the car is running on all four cylinders again, though not as happily as it could be. I was forced to remove the distributor and seem to be having some issues with ignition timing since putting it back [in this post], and the carb. still hasn't been tuned properly since the rebuild, so a range of fettling awaits before I can drive it for the first time in 2013.

E21 316: Head Gasket - well and truly blown!

Here are some pics of the blown head-gasket that turned out to be the misfire culprit [from this post: ] and it turned out my forum-eductaed guess was right and it had failed right between the 3rd and 4th cylinders. Kaboom!

No damage to the water/oil galleries thankfully, but still a catastrophic way for the gasket to fail so quickly under a bit of load. You can see best in the bottom pic of the head where the gasket has begun to fail at the left side of cylinder 4, taking that down and then blowing through to cyl. 3. Not good. An examination of the cylinder-head when removed showed that it is warped a tiny bit, so it looks like the engine has been overheated at some point before I got the car and this is probably going to happen again. Oh well, priest-like driving will be the order of the day unless I just go seat-of-the-pants until it goes again, but in the long-term, an M44 engine-swap from a more modern 318is is looking like a must!

M10 Engine: Weber Carb. Rebuild [Twin DMTL]

As mentioned in this post [], rebuilding my Weber DMTL carburettor was one of the first things on my list of curing my misfire problems, which turned out to be a more serious blown head-gasket. Still, restoring the carb. is one of the first things the previous owner told me I should do and gave me a brand new Weber rebuild-kit with the car, so I guess it can't hurt the old girl.

This job isn't for the faint hearted though, so if you have a disposition towards botching fiddly things as I generally do, then it's probably best left to a pro - I messed up my throttle-cable and had to replace it, and fettling the throttle-spring arrangement was all but impossible to get back to how it was. It's still not right, throttle springs etc. a bit loose, but at least its running ok again.

Here's a great guide for tuning the carb. once it's rebuilt: http://www.carburetion.com/Weber/adjust.htm

**CAUTION: If you're running a Weber on an E21 then your 'Bowden' throttle-cable will likely have been cut to fit through the cable-eye on the throttle linkage. Cutting the metal end off the cable causes it to lose its tension and the strands begin to unravel immediately so be very careful when removing and fitting the cable to the carb. [especially if you need to do it more than once which broke mine], as once the cable has begun to expand inside the sheath it binds very easily and you will need a new one. These aren't in production anymore either and I got the last one from BMW Classic in Park Lane, though I'm sure plenty are still out there, but still save yourself the worry!

E21 316: M10 Coolant/Radiator Troubleshooting

The car has no overheating issues, it's running like a dream, but the temp. gauge does have a habit of wandering between slightly over normal during slow driving or standing at idle. With cool air blowing into the cabin the needle goes slightly higher again, but never goes above about half way between normal and 3/4, even going uphill or driven hard. On a clear motorway run with lots of cool air the needle drops and sits about the same distance below centre, reaching as low as half way between 1/4 and normal. I'm thinking either a clogged radiator or a stuck thermostat and everyone has backed me up, but I thought I'd take a hard look at it this weekend and try to diagnose the problem in clarity before swapping anything.

Symptoms:

Needle fluctuates between slightly cold and slightly too hot in mixed driving conditions. With heater controls set to hot and the fans turned off temperature fluctuates least, but any attempt to blow air into the cabin, hot or cold, causes the temperature to vary more and only cold air blows regardless of heater setting. 

The radiator is plenty full of coolant, but there doesn't appear to be a lot of circulation. The return pipe from the engine to the radiator is red hot, while the send pipe from the radiator to the engine is cool. This pipe should be cooler than the other, but not this cool, so it looks like the radiator valve is not releasing cooled water once the engine has warmed up. Hot water also flows through the heater-core to warm the air, which would explain why I'm not getting any. 

Diagnosis:

It's definitely looking like a thermostat stuck in the closed position and not releasing water from the radiator, but the pipe to the thermostat, even where it exits the radiator is also cool to the touch. My temp. gauge also doesn't just go up and up, it fluctuates to cool as well, so it could still just be a case of a clogged radiator. Let's hope it's the latter, because the first thing I'll be doing is a full radiator-flush to see if there's an improvement, then changing the thermostat if the problem persists. If this fails, then it could be a new, and expensive, radiator or one of the harder to source temp. sensors or even the water-pump. Hmm.

Flushing:

Went to Halford's this morning and bought a pack of Holt's 2-part RAD-Flush [£6.99] and 2 litres of engine-coolant [£15.98]. Drained the system and found plenty of blue coolant in there and no oil, but quite a bit of rusty sludge. The car holds 7 litres of coolant, but I only got about 5 out of it. I removed the radiator [the hoses are off anyway as there's no drain plug] and gave it a good flush with the hose. A lot of rusty sludge and orange water poured out and the water appeared to contain no coolant at all, but once the water had run clear there was no sign of a blockage. I re-fitted and filled the radiator, it took about 5L of water, and poured in the first stage of RAD-Flush, though I'm not sure how it will flush the system if the thermostat won't release coolant. 

The instructions say to run the car at fast-idle for 30 minutes, but without knowing if there's water pumping round the block I decided to abort if the engine went hotter than normal. I stopped running the engine at 13.5 minutes as the needle started to reach 3/4 on the gauge. A quick check of the radiator hoses revealed the same story - in-hose red hot and out-hose now freezing, so I'm guessing there's no coolant in the engine itself at all now. This means I can no longer drive the car as I have been until the problem is fixed, unless I back-fill the engine with water through some other hose, but it will require draining again anyway when the new thermostat arrives.

Thermostat:
All signs now point to the thermostat. Here's a couple of good checklists posted on eHow to help diagnose a broken thermostat, or other possible causes with similar symptoms - http://www.ehow.com/list_6018650_signs-car-thermostat-broken.html / http://www.ehow.co.uk/list_6018650_signs-car-thermostat-broken.html.
I re-drained the radiator and it ran almost as clear and cold as it went in. A little hot water came from the thermostat side of the hose, but it seemed to be more of the blue coolant mixture. I removed the top hose to the thermostat and about a litre of the warm blue coolant mixture gushed out, another litre coming as I removed the hose in the thermostat's side. It would seem that the radiator hasn't been part of the cooling-system since I've owned the car!
I got the thermostat completely out and immediately I could see it's stuck completely closed to the radiator hose, and only partially open to the bypass valve. Water is being pumped through the thermostat and straight back to the engine and this, along with the non-viscous fan, is the only thing cooling the engine. Quite frankly, I'm amazed the overheating problem hasn't been more severe! I guess with it being summer I never noticed the lack of hot air and not using the cold-air blower kept it close to normal. I could live without the cold-air during a British summer, but as winter rolls around I've noticed that the side-windows are impossible to de-mist. Warmth from the engine itself does de-mist the screen, but as the weather grows colder I can't be sure - best to fix this problem sooner rather than later.
Just bought a new budget thermostat from GSF car-parts on eBay. It's not OEM quality, but it is guaranteed and is much, much cheaper @ £12.50 with free postage, although I paid £20.40 for included next-day delivery, which is still good. I really hope this proves to be the only problem with the cooling!

Does an early '80s E21 316 with an M10 run on unleaded fuel?

The answers before I bought the car pointed to yes but it turns out that the four-cylinders might not after all. Ignition timing is fine, apparently, down to as little as 92-octane unleaded fuel, but valve wearing is still a problem and an additive is recommended. It's about £8 a per tank so could be expensive over time. I don't reckon the previous owner had been putting any in regularly or they would have given me half a bottle with the car, so I think I'll be taking my chances.

The other thing is regular 95-octane unleaded or 98-octane super. The engines are designed for 100-octane leaded petrol so regular unleaded might be a fair drop performance wise, but does it make a difference to the valve wear?

As we parted company the previous owner said to fill it with super to get the best out of the engine, but said it would run fine on regular and that was all that was available to me at the filling station so it had to do. The car charged home without a grumble from the engine and feels very lively indeed, though I'll be filling it with super next and see if it makes any difference.

UPDATE: It turns out my engine has had the hardened valve treatment so it can run any unleaded without excessive top-end wear, so I haven't needed any costly, annoying additives and that's a relief. The engine seems happier starting up and a bit livelier running on 97/98-octane petrol, which is what I've been using for the infrequent use the car gets. Obviously the power gain isn't vast on a 100bhp engine and super-unleaded is dear stuff, so now I'm starting to use the car a lot more I'll be switching back to 95 RON for the sake of economy.

Fuel Consumption:

I've worked out from averages that my late 316 M10 1.8L engine, running a Weber DMTL carb. and the 5-speed 'sport' gearbox is giving me ~26mpg, which isn't bad at all really. Using the lower octane 95 RON fuel may give better mileage, or may make it worse, either way I would imagine the difference will be negligible given the amount I drive the car.