TheBeast's 1993 750il Thread

[theBMWbeast]

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Waterpump is in, praying for no leaks now. Everything is reassembled and looking good. Still getting a check engine light at idle, goes away if you give it some gas. C9 Lambda control. Cleaned the MAFS with some cleaner, and the MAF specific code seems to be gone. Going to look at the fuel lines, return has a kink in it . Then going to perform a smoke test.

Also, the AC compressor is covered in fresh oil. Any hints as to where this could be leaking from? Tired of leaving spots on the street.

[balidawg]

Is the C9 code for bank 1 or 2? I would probe sensor voltages (MAF, O2, etc.) on both banks and compare them. Makes it easier to identify a problem when you effectively have two 6 cylinder engine systems in there. If you can get the pinout for the DMEs and access their connectors while still installed, should be easy to probe the same signal on both banks and compare. Would also be good to get the EML module pinout and probe his voltages.

Not sure where the oil leak is coming from. I usually get a diagram or photo of the motor, identify all the possible oil leak sources on that, then methodically check each one on the engine itself. Clean an area well, run the engine a bit, look for leaks with bright lights and a mirror.

If I lived near the valley, I’d come over and help you. That car has some good memories for me!

[theBMWbeast]

I’m unsure which bank it was for, I didn’t know how to get it to specify. I will try your suggestions though, I’m thinking it’s probably something simple. As far as the oil leak is concerned, I’m going to do just that and look at a diagram. My first thought was timing chain tensioner, as it is on that side for the m30, but I’ve got no clue for the m70!

We’ll have to get together once I get the car back on the road, I wouldn’t mind taking a drive

[theBMWbeast]

Got the car wrapped up and out of the driveway. Coolant finished bleeding, blew through the expansion tank line, seemed to be a little blockage. Redid my work with the fuel lines, no more kink in the return. Put hubcentric rings on the style 32s. Changed the oil/filter/ oil sensor oring. All seems to be okay, for now. I did get some smoke, I’m hoping spilled fluids. Doesn’t smell like coolant, maybe oil or atf...
No more check engine light (currently), so I believe the kink was messing with the mixture (when I moved the return line to be straight, the engine sound changed). We will see.

Want to get rid of the rough idle once and for all, I’ve read posts of people with 750s, that say sometimes they wonder if their car is even running when it is on. Unfortunately you can’t mistake when my 750 is on, sitting inside it. Plan to check distributor cap and rotor, maybe clean them up if needed. Have a smoke tester that I can pull out as well. Then I’m headed to the DMV, to get temp registration hopefully, so I can drive the car to get smogged.

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[Cactuar]

That's a lot of work, good job!

I'm in the same boat when it comes to the rough idle, still got some roughness in my car. When I changed the motor mounts on my car it made a big difference though, maybe yours are also bad.

[theBMWbeast]

That's a lot of work, good job!

I'm in the same boat when it comes to the rough idle, still got some roughness in my car. When I changed the motor mounts on my car it made a big difference though, maybe yours are also bad.

Thank you! I’m trying my best to get it back to the level it was before the 4 or 5 year hibernation.
Funny you mention the motor mounts, there’s a spare set in the trunk. Problem is I don’t know if they are the replacements or the originals lol. I’ll have to consult with Bali.

[theBMWbeast]

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Other side was just as bad. New ones on order

[theBMWbeast]

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New cap and rotor

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Failed smog... I’m not afraid of maintence costs, as I knew what I was getting into; but I really did expect the car to pass, and to be able to drive it. Now it’s a proposition of whether it is really worth it or not to continue working...

I failed because of high hydrocarbons, I’m going to look into alternative causes besides the cat, see what can be addressed cheaply or tested cheaply, and make my decision from there. I’ve had a sneaking suspicion of a vacuum leak somewhere, so I’ll start there. Hopefully it’s something simple!

[Sansouci]

Here in NY the cars over 25 no longer have a smog test but a check engine light will fail the inspection. Although they go hand in hand, removing the dash light solves the regulatory problem

[shogun]

I once copied this from the Bosch website: Three Reasons for Gas Analysis
5 Gas Analysis - Bosch Technologies Group
Three Reasons for Gas Analysis
* Identify engine performance and mechanical problems
* Test the running efficiency of the engine
* Test for exhaust emissions against state and federal standards

Combustion Chemistry and Gas Analysis.

* The combustion process releases the energy stored in the fuel
* Fuels consist basically of carbon(C) and hydrogen(H) referred to as hydrocarbons (HC).
* Under ideal conditions all of the HCs would be converted to H2O, CO2 and heat.

Combustion Chemistry and Gas Analysis.

* Unfortunately this complete combustion is rarely if ever achieved
* Short burn times, continuously changing mixture ratios and air temperatures, and combustion chamber quenching produce conditions which give rise to the formation of pollutants

Pollutants
* Incomplete combustion produces carbon monoxide (CO)
* Unburned fuel produces hydrocarbons (HC)
* High combustion temperatures produce oxides of nitrogen (NOX)

Other Exhaust Gases
* Carbon dioxide (CO2) is a product of complete combustion. Therefore the higher the level of CO2 the more efficient the engine is running.
* Oxygen (O2) level in the exhaust indicates the fuel-air mixture.

High O2=lean
Low O2=Rich

Gas Analysis as a Diagnostic Tool

Gas analysis

* Is a quick and accurate way to determine the running conditions of an engine
* By observing the 5 gas readings and understanding their relationship to each other you can diagnose the 3 major engine areas:

Fuel delivery
Ignition
Engine Mechanics

High HC Only
Hydrocarbons are unburned fuel. This can be caused by:
Ignition Timing (base and advance)
Vacuum Leaks (hoses, brake booster, manifold, evap. etc.)
Ignition (misfires, coil breakdown, etc.)
Mechanical (low compression, bad cam, etc.)
Catalytic Converter Failures

High CO Only
* Carbon Monoxide is a result of incorrect fuel/air mixtures. Causes include:
* For Carburetors (float level, power circuit, choke circuit)
* For Injection (injectors, pressure regulator, temp sensor, MAP/MAF sensor)
* For Both Systems (air filter, PCV, Evap, O2 sensor, air injection

High Nox Only
* NOX is caused by high combustion chamber temperatures. Check:
* EGR (valve, controls, solenoids, passages, vacuum hoses)
* Ignition Timing ( base and advance)
* Engine Temperature (cooling system, fan restricted exhaust, Thermostat)
* Vacuum Leaks (hoses, booster, evap, etc)
* Mechanical (carbon deposits, converter, etc)

High CO and HC
* Normally, when HC and CO are high it is the result of a CO failure driving the HC high.
* Correct for high CO first (Excessive fuel, restricted air, Evap., etc.)
* If HC is still high, test as high HC (ignition, timing, mechanical, etc.)

High CO and Nox
* These problems are normally incompatible. If they occur on the same test they will most likely occur at different points on the drive cycle
* Correct CO failure first
* Retest and locate NOX failure in drive cycle and correct as NOX failure only

HC and NoX
* High HC and NOX normally occur as the result of a lean misfire. Check for:
* Lean run (vacuum leaks, mixture problems, fuel delivery, etc.)
* Mechanical (oil burning can cause high combustion chamber temperatures)

CO, HC and NOX
* This is a complete breakdown of the emission systems or multiple failures. Check:
* Catalytic Converter (missing, damaged)
* PCM (closed loop, wiring, etc.)
* Drive cycle ( if failures occur at different points diagnose each failure separately)

[Altair67]

Failed smog...
because of high hydrocarbons...Hopefully it’s something simple!

Hi!

Had that happen several years in a row when they started clean air in Ontario Canada (parked car during that time). One of the testers eventually shared what the problem was with my car (combination of ethanol in cold weather in very old car with short city trips) and the tricks to fix it:

Fresh oil (cold short trips add fuel to it)

Premium gas NO ETHANOL, here's shellVpower@91

Do an extended highway run (>30'), and pull it with hot engine into test bay directly ie. right away.

They even recommended new sparks plugs and injectors, cant remember about the sparkplugs but I am pretty sure passed with flying colours without replacing the injectors which I may still have to do.

Cleanair tests were eliminated in the recent past.

Thanks to Shogun, I even got a chip to use regular gasoline in the future, still have to install it.

Let us know outcome
Hth

[theBMWbeast]

California won’t let us get away that easy Sansouci. Kinda surprises me that New York would have any leniency, they seem pretty strict.

Thanks for the tips Shogun & Altair. I’m going to run a smoke test Monday, and then Im gonna take that recommendation and get the car and the cats nice and hot and pull right into the test station. I just need it to pass, nothing more nothing less. Wish me luck.

[Altair67]

...Wish me luck.

https://www.pure-gas.org/index.jsp?stateprov=CA

You already have fresh sp, oil, etc... so

Good luck!

[f00g0057]

Hi!

Fresh oil (cold short trips add fuel to it)

Hth

Please tell me he didn't mean to add gas to the oil like the engine is a two stroke.

[letank]

Please tell me he didn't mean to add gas to the oil like the engine is a two stroke.

not at all, on a cold starting engine the air/gas is so rich that residual unburn gas drips past the rings and dilute the oil.

then of course, one of the byproduct of combustion is water that can collect as well; on my latest project due to short engine run, the oil filler neck has rusted

[letank]

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Failed smog... I’m not afraid of maintence costs, as I knew what I was getting into; but I really did expect the car to pass, and to be able to drive it.

I failed because of high hydrocarbons, I’m going to look into alternative causes besides the cat, see what can be addressed cheaply or tested cheaply, and make my decision from there. I’ve had a sneaking suspicion of a vacuum leak somewhere, so I’ll start there. Hopefully it’s something simple!

Here is a link to calculate the lambda, as strange as can be the calculator does not indicate any weirdness

http://www.factorypro.com/tech/Brett...lculations.htm

or

http://smogstats.com/Lambda_CAT.aspx

but then found this analysis on lambda interpretation

https://www.austincc.edu/wkibbe/lambda.htm

[theBMWbeast]

Thanks for all the suggestions guys. I’ve ascertained that the cause of failure is probably a vacuum leak, and a smoke test today confirmed it.

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I sincerely doubt that you can see the smoke, but regardless you can see the location. It almost appeared to be leaking from the throttles themselves, but on the drivers side of the engine, I could see cracking on the VCV hose. I assume this is the problem, both sides. I’ll order the parts to redo the VCV, wondering however if the throttle can let in unmetered air? Want to get to the bottom of this ASAP, I signed up for the SoCal Vintage and want to show the car there on November 2nd!

[shogun]

change all this
11 15 1 720 392 vacuum hose left
11 15 1 720 393 vacuum hose right
11 15 1 720 131 non return valve 2
11 15 1 718 642 2 stage valve left
11 15 1 718 713 2 stage valve right
http://bmwe32.masscom.net/sean750/vc.../VCVvalves.htm
and also check the hoses and the 2 valves for fuel tank breather valves http://bmwfans.info/parts-catalog/E3...urb_air_valve/

[Rich in Boston]

In Massachusetts, smog tests are not required for OBD1 cars which is nice for my 30 year old beast, just a safety inspection!

[theBMWbeast]

Thanks Shogun. I also added the two grommets (11151715844) and the other two hoses (11151729390 & 1115172931). Prices seemed to have gone up since that post, $130 for everything!
I’ll check the hoses and valves as well, I am assuming anything before the charcoal canister could be an air leak, but not after correct?

Funny, no safety inspections here! How’s that for backwards priorities?

[shogun]

Leaks are mainly from the hoses between charcoal cannister and throttle valves, in between are the breather valves http://e32b12.blogspot.com/search?q=tick

[theBMWbeast]

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Installed the new VCV and all hoses and grommets (mine were torn up, recommend it if you do this). Idle was better, but marginally. I will smoke test again and see if I can find anything else. I’m running out of ideas here, now I’m thinking maybe the temperature sensor could have it stuck in rich mode? But then in the same breath, I passed in the low speed test for hydrocarbons, but failed in the high speed. I would think it would be rich constantly if the temp sensor was the issue. I’m going to try disconnecting the battery tonight, to reset the ecu. Tomorrow I’ll see if that helps.

[balidawg]

There are three different coolant temperature sensors on the M70, all on the rear coolant crossover manifold. See part numbers 5, 7, 8 on this diagram.
https://www.realoem.com/bmw/enUS/sho...diagId=11_0785
I would measure their resistant at the DME connectors since the sensor connectors are tough to reach.
While you’re in there check all the signals you can access. Need to find the source of the issue and checking signals a good way to uncover clues.

On a side note, I spent a lot of time trying to get DIS and INPA working with this car for collecting data and troubleshooting. Sadly, I failed.

Shogun, do you have a diagram of the DME and EML connectors for this 1993 750iL?

[theBMWbeast]

There are three different coolant temperature sensors on the M70, all on the rear coolant crossover manifold. See part numbers 5, 7, 8 on this diagram.
https://www.realoem.com/bmw/enUS/sho...diagId=11_0785
I would measure their resistant at the DME connectors since the sensor connectors are tough to reach.
While you’re in there check all the signals you can access. Need to find the source of the issue and checking signals a good way to uncover clues.

On a side note, I spent a lot of time trying to get DIS and INPA working with this car for collecting data and troubleshooting. Sadly, I failed.

Shogun, do you have a diagram of the DME and EML connectors for this 1993 750iL?

Yeah what a pain, hidden on the back of the head. I’ll check the resistance as you said. The more I can eliminate as the problem, the better.
By the way, are the engine mounts in the trunk new or old? Don’t want to be chasing my tail if the perceived rough idle is just some shakey engine mounts.

[balidawg]

are the engine mounts in the trunk new or old? Don’t want to be chasing my tail if the perceived rough idle is just some shakey engine mounts.

I bought two new mounts, but not sure if I replaced either. May have done just the right side. Sorry, cannot remember.