E36 325i problems

[riksey90]

Hi guys,

I've owned my first BMW for 3 months now and am more than happy with it apart from a niggling problem I'm experiencing.

I have a 1994 E36 318is with an M50B25 non VANOS swap, the vehicle still has the 318is diff. I did not do the swap myself however I have just rebuilt the engine top to toe after a valve drop by the previous owner. I obviously have not driven the vehicle before the rebuild and have nothing to compare current fuel consumption figures to. On average through town I get between 15 and 17l/100km with about 12l/100km on the freeway. Along with hesitations, a few pops and farts from the exhaust and terrible hunting at idle.

Now, to the list of things I've done to remedy this problem;
Took my car through to a mechanic friend and hooked it up to his diagnostics. Diagnostics showed a dead MAF (My car utilizes the six pin hot wire type) so I managed to source a second hand Bosch unit in good working order, diagnostics test assured it was indeed in good working order. My car did not hunt at idle and accelerated smoothly without hesitation the moment I plugged the new MAF in. During the second diagnostics test the real time graphing showed an intermittent flat line from the TPS, a few jiggles of the plug and a stern talking to remedied this issue. After we were satisfied that the TPS was in good working order (tested resistance with multimeter) and wiring was in good shape I was more than excited to travel at least a little further on my hard earned cash that seemed to be disappearing into the petrol tank.
To my surprise my car was still consuming fuel at the same rate it was with a dead MAF and intermittent TPS fault which leads me to believe there is someone else hiding in the wood pile. Yesterday morning I pulled my MAF, throttle body, TPS and intake boot off. I inspected the boot for cracks, cleaned out the throttle body, tested the TPS again and cleaned out my MAF using a little paraffin, electrical spray and a lot of patience. I put it all back together and took my car for a spin. I could not believe how smoothly and hard it pulled all the way up the rev range, it honestly felt like a different car, not its usual gas guzzling, lethargic self. The fuel consumption indicator sat considerably lower down the scale while traveling my usual route (I tend to study it a lot so as to compare current fuel consumption while driving other vehicles along the same route) It really was a treat to drive and continued to reward me until I put it to bed last night.

This morning was an entirely different story. Started it up and tried to reverse out the carport and found I had to rev the nuts off of it to get it to attempt even the slightest incline across my garden. I know you have to be a little more understanding before the old girl reaches operating temp. but I've never experienced anything with this little enthusiasm to move, not even my hateful, carb'd Golf was this bad. The drive to Pick n' Pay was a confirmation of how terrible the power delivery actually was. Once back home I dried my eyes and set about this issue again. I replaced the main DME relay, studied all the ground straps, unplugged MAF and TPS sensors separately to listen for the dip in idle and got the multimeter out to confirm I hadn't damaged anything and yet my car is still a dog.

I have been fed many stories about it being the shorter ratio diff or even my freeflow exhaust system. No one can really answer me and when they do I get the usual, "Oh but backpressure" nonsense. Just for interest's sake I have the standard headers, two 50mm pipes all the way to the rear with two '2 in 2 out' resonators built by Powerflow as far as I know.

All sensors showed to be in good working condition when last on diagnostics (about a month ago) and the drivability of my car seems to be getting worse and worse and heavier on fuel. The car has covered about 2000km since full rebuild and oil changes have been done. I know a fresh engine would be slightly less efficient due to increased friction on new bearings and blow by until rings bed in properly but 17l/100km is ridiculous. Tight engines, diff ratios and exhausts can't explain the car driving beautifully yesterday and like a dog today.

I realize this is quite a lengthily post but I would really appreciate if it was read through and if anyone could help me.
Thanks in advance.

 

[Maljan]

At one stage we had two E36's in the home - a 328i for me and a 318is for the wife. The difference in engine revs at was quite noticeable. The 318is revved a lot higher than the 328i at any speed. That might explain your high fuel consumption. My 328i gave about 9 to 10 l/100km on the highway, if I remember correctly.

With the shorter ration, your car would be a lot faster off the line. I have heard of guys swopping the diff from a four-cylinder into a six-cylinder car for this very reason. If fuel consumption is more important than quarter mile times, a diff swop is worth looking at. There might even be a drag racer who would be happy to trade.

I hope you get your engine running the way it should. :=):

 

[danieljames]

What's the diff ratio on that car currently? I have the standard diff in my 325 which is a 3.15. And it'll have to be much shorter to give such bad consumption figures. Although that still doesn't explain the pms symptoms of the car.

---

2c....

Check crank position sensor and cam position sensor. There might be faulty connections. Also engine temp sensors. I can't tell u their locations in the engine bay...

But my understanding is that they control when and how the engine fires. Are there O2 sensors on your car? If there are sensors are they compatible?

 

[GPGrobler]

"Yesterday morning I pulled my MAF, throttle body, TPS and intake boot off. I inspected the boot for cracks, cleaned out the throttle body, tested the TPS again and cleaned out my MAF using a little paraffin, electrical spray and a lot of patience. I put it all back together and took my car for a spin. I could not believe how smoothly and hard it pulled all the way up the rev range, it honestly felt like a different car, not its usual gas guzzling, lethargic self. The fuel consumption indicator sat considerably lower down the scale while traveling my usual route (I tend to study it a lot so as to compare current fuel consumption while driving other vehicles along the same route) It really was a treat to drive and continued to reward me until I put it to bed last night."

Judging from the above, if I were you I would look at the MAF TB TPS and intake boot and the connections to the MAF and TPS before I look at other issues. Sometimes the problem is hidden for example the wiring for the MAF and TB can be broken or corroded inside the insulation causing bad or intermittent connections. Also, does your car have an ICV and has it been properly cleaned?

Hope you come right and keep us posted :thumbs:

---

I know you are a bit annoyed with the car but please do an intro in the New Members Area and post some pics of your ride.

Thanks :thumbs:

 

[riksey90]

Hey guys,

Thanks for the replies.

Funnily enough after I wrote up my initial post I left my car in the 'corner of shame' section of the garden with it's bonnet up while my immediate family and myself passed judgment from afar while having some tea. It started to drizzle later that afternoon so I went to close up and pop her back under the carport. Two swings of the starter and the the thing fired into life, I managed to move around the garden by just slowly releasing the clutch (which has always been an issue since my entire garden is on quite an incline) It seems as if the corner of shame had done the trick. However later that night while coordinating parking arangements for my New Years guests I had to shuffle my car over a bit and it was back to it's old tricks again. I believe I have a wiring issue, corroded contacts or a sensor that needs a smack to get it working properly again.

From what I can understand from what I've read on forums and found in manuals my car has a 3.43:1 diff ratio, or around there at least. I haven't found the stamped tag on my diff yet so I'll shoot under the rear with a torch tomorrow. I understand the shorter diff will be nice between robots but have the opposite effect on my fuel consumption on the open road. I am interested in swapping the diff for a taller ratio sometime in the near future.

On to the oxygen sensors. I haven't actually seen it or them myself but I have seen the heater relay in the fusebox and while on diagnostics I did see the oxygen sensor giving a healthy 0-5V signal when we fingered the throttle linkage. As far as I'm aware that is all in good working order. Just out of curiosity how did the E36s without oxygen sensors ensure correct mixtures? I know VW's MP9 system has a temperature sensor in the engine coolant and it determines whether the car is running rich or lean depending on which side of operating temperature the engine is sitting at. Slightly off topic.

So now my plans for tomorrow are as follows. I'm going to pull the engine loom out and test everything for continuity. Any sensor that can be tested with a multimeter will get a good shake and then tested thoroughly. I'm not too sure on how to test the cam and crank sensors but if the Bentley doesn't help I'll work something out. Then I'll put some more petrol in my car and go for a drive.

I'll go through the newbie section, post up some pictures and write a little story when I get some free time. At the moment getting this car running sweet is top priority.

Again, thanks for the replies guys. I'll come back with results as soon as possible.

Cheers.

---

Some points I didn't address, sorry.

The two engine temperature sensors in the side of the head are looking a little worse for wear. I might just swap them both out for new ones just for piece of mind, easy and cheap enough. I know the DME relies on the one sensor to switch between open and closed loop managment.

I pulled my ICV out, cleaned it and tested it the day I got the car. While I had the intake boot off the other day I replaced hose clamps and tightened all hoses that join in between MAF and TB to eliminate any chance of air being sucked in without the MAF knowing about it.

Another thing that has been troubling me is that I cannot find an intake air temperature sensor anywhere. It isn't in any of the locations the Bentley manual shows. Now does the DME look at the ambient air temp sensor in the air duct (yellow plug) or is there an air temp sensor inside the MAF aswell? There aren't any holes in my intake manifold, intake boot or airbox that have been bunged up and there ar no loose wires in the engine bay that look like they need a home.

I look forward to your replies.

Cheers.

 

[Nikhil]

Howzit bud

welcome to the forum, I think what you also need to do is check for vacuum leaks and check your coils and plugs, have a look at your fuel system aswell I somehow suspect it is a fuel related issue relating to the fuel pump or fuel filter.

 

[danieljames]

Just as an example a member not to long ago had starter issues and it turned out to be a loose battery cable......so I think a lot of patience is what will sort this car out. WRT testing the sensors I suggest a bit of googling as I know bentleys has some mistakes. Eg...crank sensor should read around 550 ohm instead of the 1.2k ohm stated in bentleys.

WRT the 02 sensors....i have no idea....i haven't seen any on my exhaust system yet lol.

You seem to know your way around an engine bay so im sure you'll get this sorted soon enough. Hopefully someone has had similar problems and will eventually pop a reply.

Good luck mate

 

[riksey90]

Hi guys,

I should've mentioned that it does have new plugs and all six of them are burning a lovely chocolate colour. I cleaned out all the coil boots with carb cleaner and inspected the terminals on all plugs and all seemed fine. I assumed that the plugs being chocolate coloured and all the same shade of chocolate indicated everything being alright on the firing side of things. I know you can test the coils but I understand that only one coil inside each coil pack is capable of being tested due to it being connected to the terminals on the outside of the coil pack while current in the other coil is induced (please correct me if I'm wrong)

Ha ha! Thanks danieljames. My previous car was a 1991 VW Caddy 1.8 Sport. I spent my life visiting Goldwagen in one of my parent's cars while the Caddy sat on axle stands with it's innards sprawled across the workshop floor. That vehicle tested my patients and grew my knowledge tenfold.

As to my escapades for today. I ended up at the beach for the day with girlfriend's family so was unable to get any work done on my car. I'm still in two minds about whether I had a better time at the beach than I would've laying under my car. I'll set about it tomorrow and see what I find. I'll definitely test the crank and cam sensors.

Thanks guys

 

[riksey90]

Howzit guys,

I ended up pulling the intake manifold to get to the harness that leads to the engine sensors. I tested the harness for continuity between the plugs for various sensors and the DME plug. All the wires are in good nic and I wiggled the wires while testing to make sure there wasn't a break in them. I tested all the sensors and they all returned results within spec according to the Bentley. The cam sensor gave me 1290 ohms and the crank sensor gave me around 700 ohms. Just wondering if that is within spec regarding to what danieljames posted.

Thanks

 

[a.hinge]

The O2 Sensors are in the headers directly by no 3 & no 6 exhaust outlets,
Difficult to get to .. if your looking to change them, generally better to do this when the engine is out. However its possible change them if you drop the headers, but still a pain.
regards

 

[riksey90]

Howzit man

Much time has gone by since this thread was last posted in and I believe I have found my problem, which I will get to in a moment.

Re oxygen sensors, my car has none. Turns out after lots of digging through old literature (One of my good friends was a mechanic at SMG in Maritzburg and had kept all his training material for me) and countless hours searching the web, from what I could gather it appears that early E36s came without oxygen sensors as we were still running leaded fuel here in SA. Leaded fuel attacks oxy sensors therefore it was better to do away with them. Closed loop control from the oxy sensor only really works at partial throttle at cruising speeds to optimize fuel consumption otherwise the DME runs it's factory set fuel and timing map when accelerating or generally arsing around in your own tyre smoke. Our early E36s ran quite happily without oxy sensors but just didn't get as good fuel economy as their overseas cousins.

On to my car. I definitely do not have any oxygen sensors. My fuel pump relay is in the socket that should house the oxygen sensor heater relay, whatever the relay in the fuel pump socket does is yet to be discovered. The two bungs in my headers have been closed as from the manufacturers and the exhaust system has no signs of a bung ever being present near the merge pipe. I even pulled a standard exhaust system from a 1992 325i and it did not have any oxy sensors either.

On to what I am 99% sure is my problem, the cause for a gargantuan appetite for fuel (17L/100km on a good day) my meagre Citi Golf/Opel Corsa (insert horrid grocery getter here) 0-100 times and my cylinder compression test figures of 6bar in each cylinder rather than 10bar, needs an introduction.

I purchased the vehicle after I had helped a friend strip down the engine for a rebuild. All engine work and spares were at the expense of my friend, the previous owner, so I was more then delighted with the situation. I attacked the rebuild with enthusiasm. During the rebuild and after noticing the new pistons had a slightly shorter deck height then the old ones I was told that those are the pistons with the correct part numbers that the engineers specified and that a lot of meat was skimmed off of the head. After much frowning I decided that the engineers surely know what they are talking about and continued to piece my new pride and joy back together with a huge grin on my face. Anyway, long story short I found out via the grape vine I have pistons for a 328i in my 325i. 325i and 328i motors both having the same bore and conrod length it is just the stroke that differs, 75mm and 84mm respectively, and the 2.8 pistons are 4.5mm odd shorter than 2.5 to compensate for the extra throw on the crank. I rolled the end of a length of solder into a ball, dropped it down the plug hole and turned the motor over by hand to confirm that there is a 7mm gap between the top of the outer extreme of the pistons and the lowest part of the head.

In conclusion I can either go find the right pistons or just replace my crank with one out of a 2.8 and gain a couple cc. Either way it is going to require stripping down the engine again and dipping into the piggy bank.

Again I welcome any knowledge that the BMW fanatics community would like to share regarding this matter. If my measurements are wrong and I'm talking gibberish I am up for correction.

I look forward to your replies,
Thanks

 

[Gizmo]

I have a 328i crank rods and pistons for you if you're interested, drop me a pm.

 

[riksey90]

PM'd

 

[Sankekur]

I have no doubt that a compression that low will cause massive issues, but it still begs the question why was the issue intermittent? Mechanical problems like this don't normally come and go....



Personally I am actually surprised the the motor even starts let alone runs with that compression.

 

[JayDrft]

Riksey,

Sound like you got given a problem, or is it?

If what you saying is what I understand, it means that you have a low compression motor - which is ideal for a bolt on turbo.

Another way, without having to stripp the whole motor - Remove the head - that is a much better way to measure the piston to deck height, as well as giving you an oppurtunity to cc the head. Then you can actually work out your comp ratio, and decide what you want to do there, anything below 8.5 : 1 would be good for a turbo, making good efficient power. (a low comp ratio, will mean that its lazy without a turbo, explains your issues navigating around the yard).

Another question on my mind - the extent of the M50B25 swap...Was a suitable engine managment setup coupled to it? Is it a stock 2.5 ecu, is it an after market setup or is it a frankenstien creation - cause that will also determine how smooth it pulls through.

I dont want to go off on a tangent, but how about the head - is everything in check there?

I wouldnt replace the crank and rods to compensate for a low comp ratio - i would seriously consider, just adding a turbo to the equation - boosting at 0.6 bar will give you smiles for miles, and may cost the same as what it will cost to acquire new components and to rebuild...I would assume you havent even put 2000km on the new motor, so why tear it apart if its still ticking sweet?

My 2 cents, hope it helps.

Just to add - the compression test you done - gives an idication of the pressure in the bore, not a true reflection of the compression ratio - it could also be low, if its got some valves that are sticking or leaking. So the only sure fire wat to check, is get calculating once you got the head off.

 

[riksey90]

The intermittent problem I was experiencing was from a dodgy connection between the DME and one of it's sensors. I knew there was a problem and therefore thought that was the reason for my terrible fuel consumption. Only later after I performed many tests I found the compression issue. I never actually found which sensor it was. I borrowed a DME, crank and cam sensor from a mate of mine, swapped them out and the car ran much better. I swapped my stuff back in and the car continued to run well. Me tugging on the harness and fighting with plugs in hard to reach places obviously rectified the problem.

The intermittent problem I was experiencing was happening on top of this low compression problem that had always been there from the start. The intermittent problem caused lower rpm hesitations and idle fluctuation. Fuel consumption and acceleration has not changed since fixing the intermittent electrical issues.

---

The engine note that comes out the exhaust has a very 'wooly' sound to it. It is not crisp and doesn't crack when the throttle is stabbed (I'm running an even freer flowing exhaust than before with only one long resonator) Friends of mine with similar vintage Beemers all sound extremely crisp while mine sounds like the low compression agricultural cousin.

---

Hey JayDrft

Thanks for that post.

With regards to the initial engine swap. The motor and all its control units were lifted from a working shell and dropped into the vehicle. The motor is from 1992 and runs the big ugly 6 pin hot wire MAF, no vanos and no oxygen sensors. I knew the car for a good 5 years before taking ownership. I knew the car pre and post engine swap. After the swap it pulled hard all the way to the red line in every gear and handed out a couple hidings to other 2.5l powered Beemers.

The turbo route did cross my mind a couple times. I do not use the car everyday, thankfully or I'd be broke, but fuel consumption is a deciding factor on what I end up doing with the car. I know a 2.5l in line 6 will never sip juice like a little hatchback but I would like to chuck the girlfriend in the passenger seat and take a spirited whack up the Midlands without having to check my bank balance first to see if I can afford the petrol. Or if it was to retain its current fuel consumption it needs to be as fast as all f@#k (A guy I know's V 10 M5 gets similar fuel economy and he doesn't know how to lift his foot off the throttle) I would like to keep the car naturally aspirated for the time being as a BMW has a very distinct exhaust note and I feel a turbo would do it an injustice.

The solder down the plug hole is an old two stroke trick for measuring the squish band. My father is proficient in the dark art of tuning two strokes. This along with listening to the exhaust note, tasting the engine coolant and asking my dog's opinion is by no means a definite means to understanding what is going on inside my motor without opening it up. It was merely a quick test to formulate an idea of what's going on inside that big motor.

I will be pulling the head off to have a look before buying any spares.

Jay I appreciate that post.
Thanks

 

[riksey90]

Alright, so, resurrection of the century.

I pulled the head off and the pistons sat exactly 5mm from the top the block at TDC. Measuring all 6 cylinders and from different positions around the bore all measurements came back to 5mm on the knob. There was the low compression problem. The tops of the pistons and the exposed section of the bore were covered in an extremely thick layer of carbon and the exhaust valves and ports were horrifically sooty. I guess the low compression ratio was causing an incomplete combustion. Once I had cleaned the carbon from the tops of the pistons and bores and had inspected the bore for a ridge worn in from the rings and found nothing, I was happy to continue with my plan.

I managed to source a M52B28 crank that had not been ground and all the journals were in good condition. I simply turned the engine upside down, pulled the main and big end bearings caps out, lifted the M50B25 crank out and just as easily placed the M52B28 crank in it's place. I roped in my brother to help align the conrods to the journals on the crank as I lowered it in. I replaced the caps and torqued them up. Turning the motor over by hand and seeing the pistons come up flush with the top of the block at TDC had the workshop full of high fives and howls of excitement. I calculated a 10.3:1 compression ratio. I put the engine back together and dropped it back in the car with more enthusiasm than ever.

I fired the car up and it burst into life. Once the lifters had shut up it settled into a nice purr. I was slightly worried about running an extra 300cc without doing anything to the engine management side of things. After driving about 600km with a mixture of highway and town driving the plugs are a beautiful chocolate brown and the car goes like a stabbed rat. A friend suggested I tried some pink top injectors out of a 328i, the engine revs out freely and feels good up top but it idles like kak and has no low down grunt. I put the green injectors back in and the car runs a treat.

I'm so happy my BMW now drives like a BMW. The fuel consumption has not changed at all but at least now my car is worthy of a big petrol bill.

I might look into reflashing the DME just to be sure all is well with fueling and ignition timing. If I do I'll upgrade the fuel pump and put the pink injectors back in before hand.

Thanks for all the interest and suggestions as to what the problem might be. I'm ecstatic with the outcome.

 

[GPGrobler]

Alright, so, resurrection of the century.

I pulled the head off and the pistons sat exactly 5mm from the top the block at TDC. Measuring all 6 cylinders and from different positions around the bore all measurements came back to 5mm on the knob. There was the low compression problem. The tops of the pistons and the exposed section of the bore were covered in an extremely thick layer of carbon and the exhaust valves and ports were horrifically sooty. I guess the low compression ratio was causing an incomplete combustion. Once I had cleaned the carbon from the tops of the pistons and bores and had inspected the bore for a ridge worn in from the rings and found nothing, I was happy to continue with my plan.

I managed to source a M52B28 crank that had not been ground and all the journals were in good condition. I simply turned the engine upside down, pulled the main and big end bearings caps out, lifted the M50B25 crank out and just as easily placed the M52B28 crank in it's place. I roped in my brother to help align the conrods to the journals on the crank as I lowered it in. I replaced the caps and torqued them up. Turning the motor over by hand and seeing the pistons come up flush with the top of the block at TDC had the workshop full of high fives and howls of excitement. I calculated a 10.3:1 compression ratio. I put the engine back together and dropped it back in the car with more enthusiasm than ever.

I fired the car up and it burst into life. Once the lifters had shut up it settled into a nice purr. I was slightly worried about running an extra 300cc without doing anything to the engine management side of things. After driving about 600km with a mixture of highway and town driving the plugs are a beautiful chocolate brown and the car goes like a stabbed rat. A friend suggested I tried some pink top injectors out of a 328i, the engine revs out freely and feels good up top but it idles like kak and has no low down grunt. I put the green injectors back in and the car runs a treat.

I'm so happy my BMW now drives like a BMW. The fuel consumption has not changed at all but at least now my car is worthy of a big petrol bill.

I might look into reflashing the DME just to be sure all is well with fueling and ignition timing. If I do I'll upgrade the fuel pump and put the pink injectors back in before hand.

Thanks for all the interest and suggestions as to what the problem might be. I'm ecstatic with the outcome.

:clapper::roflol: